biomass in the energy industry an introduction
TRANSCRIPT
Biomass in the energy industry An introduction
Bio
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Biomass in the energy industryAn introduction
Supported by BP, as part of the multi-partner Energy Sustainability Challenge, which explores the implications for the energy industry of competing demands for water, land and minerals.
Biomass in the energy industry – An introduction is a study that provides contextual knowledge required for assessing the potentials and issues of using biomass for energy. The book is based on literature research and review by colleagues at the Energy Biosciences Institute (www.energybiosciencesinstitute.org) and is part of the Energy Sustainability Challenge (www.bp.com/energysustainabilitychallenge) series of handbooks. This book addresses the need for having a holistic view of the benefits and risks associated with bioenergy by studying the subject from agricultural, energy, environmental, technological, socio-economic and political perspectives. The book emphasizes that realizing the potential of biomass energy as a major player in carbon emissions reduction needs careful consideration of environmental aspects and competing demands of food, water, energy and other resources. Clear and consistent supportive policies are also required to facilitate significant financial investments for developing biomass conversion technologies and improving performance of biomass crops.
The handbook also provides key data about crops species and biomass types that are already in production or are being researched for biomass. The data includes plant characteristics, suitable growth conditions, required inputs and agricultural practices, co-products and alternative markets, as well as yield and energy productivity indicators.
The handbook offers a valuable guide for policy makers, businesses and academics on the characteristics of major biomass crops and the issues related to sustainable and responsible use of biomass for energy.
Biomass in the energy industry – An introduction shows:
n What role biomass plays in the global energy context.
n What fundamental knowledge is required to understand bioenergy systems.
n How biomass is converted to energy and what technological developments are under way.
n Why it is vital to view use of biomass for energy from socio-economic, environmental and political perspectives.
n What is the potential for bioenergy and how this potential can be realized.
n Where can biomass feedstocks be grown and what are the key characteristics of biomass crops already in production or being researched for biomass.
Published by BP p.l.c.© 2014 BP p.l.c.
9 780992 838713
ISBN 978-0-9928387-1-3
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
Plant types
Plant characteristics – icons in chapter 6
Propagation method
Annual Perennial
Photosynthetic pathway
Plant life cycle
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
CAM
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
Primary energy use
� Table 3.1Bioenergy production routes
BP Biomass HandbookTable 3.1 (20 December 2013)Draft produced by ON Communication
(Wood, straw,energy crop, etc.)
(Rape, soy, palm, etc.)
Lignocellulosic biomass
Feedstock Conversion Energy
Sugar and starch crops
Oil crops
Chemical process
Thermochemical process
Fuel for heatand/or power
Liquid fuels,transport fuels
Bioethanol
Other liquids
Biodiesel
Gaseous fuel
Biogas
Syngas
Pre-p
rocess
Biochemical process
Hydrolysis and fermentation
Transesterification
Other catalysis
Hydrogenation
Pyrolysis
Combustion
Gasification
Anaerobic digestion
Schematic diagram of bioenergy production pathways. Feedstocks on the left of the diagram are converted via a range of processes to solid, liquid or gaseous fuels on the right. No attempt is made to show relative scales of each process
Icons shown in grey indicate pre-commercial stages of adoption.
Biomass in the energy industry An introduction
First published 2014
We make no representation, express or implied, with regard to the accuracy of the information contained in this handbook and cannot accept any legal responsibility for any errors or omissions that may have been made.
Copyright © 2014 BP p.l.c.
All rights reserved. No part of this handbook may be reproduced, stored in a retrieval system, transmitted or utilized in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without written permission from Cameron Rennie, BP International Ltd.
Printing: Pureprint Group Limited, UK, ISO 14001, FSC® certified and CarbonNeutral®.
Paper: This handbook is printed on FSC-certified Cocoon Silk. This paper has been independently certified according to the rules of the Forest Stewardship Council (FSC) and the inks used are all vegetable-oil based.
This handbook was written and edited based on literature review by Dr Sarah Davis, Ohio University; John Pierce, BP Chief Bioscientist; and John Simmons, ON Communication; analysis and research by Dr William Hay, Researcher for Global Change Solutions and Reza Haghpanah at SPENTA; and project management by Sharon Rynders, BP and Morag Ashfield, ON Communication.
Designed, illustrated and produced by ON Communication, www.oncommunication.com
For more information
BP contact: Sharon Rynderswww.bp.com/energysustainabilitychallenge
Published by BP p.l.c., London, United KingdomISBN 978-0-9928387-1-3
Reference citation
Davis, S.C., Hay, W. & Pierce, J. (2014), Biomass in the energy industry: an introduction.
The Biomass handbook is part of a series that reflects the work of the BP-sponsored Energy Sustainability Challenge.
The other titles are:
Water in the energy industry – An introductionMaterials critical to the energy industry – An introduction (2nd edition)
These books can be downloaded at: www.bp.com/energysustainabilitychallenge
Acknowledgements
The insights and technical information presented in this document were shaped by the research of many academic scientists associated with the Energy Sustainability Challenge (www.bp.com/energysustainabilitychallenge) and the Energy Biosciences Institute (www.energybiosciencesinstitute.org). In particular, Prof. Steven Long, Prof. Chris Somerville, Dr Heather Youngs and Dr Caroline Taylor of the Energy Biosciences Institute provided useful data, insights and perspectives throughout the drafting.
In addition, we would like to thank the following people for their guidance in the writing and structuring of the handbook and for their technical review: Dr GÖran Berndes, Chalmers University; Prof. Dr Marcos Buckeridge, University of Sao Paulo; Dr Steven L Fales, Iowa State University; Dr Angela Karp, Rothamsted Research; Prof. Dr Iris Lewandowski, Universitat Hohenheim; Dr William Parton, Colorado State University; Dr Jeremy Woods, Imperial College.
We thank Matthew Trainer, Data and GIS Specialist in the Voinovich School at Ohio University, for the creation of detailed biome maps.
We are also grateful for the analytical insights and valued contributions from many colleagues within BP.
In acknowledging our gratitude to these individuals and institutions, we do not imply that they either endorse or agree with any statements or views expressed in this handbook.
Contents About this book
Contents and About this book – 3
Foreword by John Pierce BP Chief Bioscientist – 4
Foreword by Stephen P Long FRS Gutgsell Endowed Professor of Plant Biology at the University of Illinois, and Chief and Founding Editor, Global Change Biology – 5
Units of area and Units of energy – 6–7
1 Setting the context – 8 Global energy use Biomass and bioenergy Overview of agroecosystems Water use in agriculture Agricultural production of energy crops
2 Important concepts – 22 Global ecosystems and land classifications Land types Plant functional features Metrics of biomass productivity Energy issues and greenhouse gas accounting
3 Bioenergy potential – 34 Current bioenergy production Global potential bioenergy production How might this global potential be realized?
Developments in biomass conversion technologies
4 Economics, the environment and politics – 48 The socio-economic drivers and impacts of bioenergy Environmental sustainability The politics of biomass
5 Where can biomass feedstocks be grown? – 58 Growing regions (biomes) Regional characteristics: comparison table
6 Biomass feedstock crops – 70 Introduction to the selected crops Biomass crops: comparison table Biomass feedstock crops: complete list of references
Glossary – 115
3
The intent of this book is to provide an introduction to the potentials and issues associated with utilizing biological materials (biomass) for energy. Detailed information is provided on various biological materials, including currently important crops and those thought to have future potential. Contextual information associated with agriculture, energy and environmental considerations is also provided.
4
Foreword by John PierceBP Chief Bioscientist
Energy is at the foundation of all economic activity. It heats us, it cools us and it lights our lives. It drives our transport, communication and computer systems, and provides the heat and mechanical work required to transform materials into a dazzling array of useful forms. Energy utilization is strongly correlated with economic well-being, and we have become adept at deriving energy from a wide range of sources. Energy is abundantly available – and we use it abundantly. The majority of our energy derives from fossil fuels, and their use results in increasing concentrations of carbon dioxide in the atmosphere with worrying consequences for our climate. While we are likely to find fossil resources to fulfil our energy needs for many years to come, the pressing need to understand the effects of our energy use on our finite atmosphere, land and water resources has resulted in a burgeoning effort to find alternative renewable forms of energy with lower environmental impacts. However, any activity as large in scale as energy production requires very careful assessment and understanding of likely impacts. Approaches that are renewable in one dimension may be less so in another.
Sunlight is earth’s primary source of energy. Indeed, our fossil sources of energy derive from plant photosynthesis that took place long ago. The difficulty with all contemporary solar energy conversion methods is the dispersed nature of sunlight and the need to concentrate it into energy vectors that are more readily useable. Geological processes did this for us in making fossil fuels in rich, concentrated deposits, but renewable energies dependent on the sun require us to gather the energy produced over large areas. As a result, the use of such renewable energies requires significant new approaches for collection and distribution, and a sophisticated approach to land utilization.
The use of renewable biological materials as energy sources is an area of increasing focus. Plants cover the earth profusely and, using energy provided by the sun, convert carbon dioxide and water into useful organic compounds on a truly massive scale. To take advantage of this fecundity to effectively and sustainably provide a significant source of our energy needs without degrading other aspects of our environment will require diligent work to understand the scale of effort involved, the nature of the plants themselves, and how to conduct large-scale agriculture and forestry in the most environmentally responsible manner.
The impact of biomass and land availability on energy production is one of many questions being addressed in BP’s Energy Sustainability Challenge programme. Researchers from a number of leading universities are collaborating in this programme to establish trusted data on the land, water, materials and ecosystems footprints of different energy pathways. BP is pleased to support this contribution concerning the role of biomass in energy production. We would like to thank all involved, and especially our colleagues at the Energy Biosciences Institute and the reviewers, who have together helped to ensure that this book is factual and well-founded.
In detailing attributes of crops and biological resources currently in use for energy production, as well as emergent energy crops and issues associated with large-scale energy production from agriculture, we hope this book will provide an accessible overview and contribute towards a more sound understanding of the use of biomass in energy.
5
The carbon dioxide (CO2) concentration of our atmosphere has been monitored at the Mauna Loa Observatory, high over the central Pacific, since 1959, when it was 316 parts per million (ppm) of air. Since then CO2 has risen at an ever-accelerating rate and on 13 May 2013 reached 400ppm – a 27% increase in just over half a century, and more than 50% higher than the global pre-industrial level. Because of the differences in isotopic composition of carbon in the biosphere and that in fossil fuels, it has been shown that most of this increase is due to our use of fossil fuels. We have sufficient known fossil-fuel reserves to continue to increase CO2 concentration in the atmosphere to two and three times current levels. The physical laws of thermodynamics and radiative exchange tell us that if we increase the concentrations of long-wave radiation trapping gases, such as CO2, the earth will warm. While the details of climate change are uncertain, that climate is changing, and will continue to change substantially, is a fact. If this is not addressed, then food supply, biodiversity and our most vital ecosystem services are threatened.
At first sight bioenergy derived from plants would seem an ideal solution. Plants use energy from the sun to assimilate CO2 and trap chemical energy in the form of plant biomass. When the biomass or fuels derived from the biomass are combusted, the same CO2 is returned to the atmosphere. Thus energy is obtained for heat and work, with no net effect on the CO2 level in the atmosphere. In practice, some energy input is required to grow the crops, transport biomass and produce fuels. But with the possible exception of early corn ethanol operations, these almost always produce considerably more energy than they consume. Brazil has shown, through learning by doing, a rapid pace of improvement of its sugarcane ethanol system. By 2010 this change resulted in the sale of more ethanol for its automobiles than gasoline, and the production of a large proportion of dry-season electricity via combustion of the sugarcane bagasse.
Despite the seeming value of bioenergy, progress has been dogged by opposition, some well-intentioned and some grossly over-exaggerated, based on single issues that fail to recognize the wider feedstock options. Headlines such as “Food versus fuel”, “Water versus biofuel”, “Dirtier than coal” and “The next kudzu” have contributed to the emergence of policies inhibitory to progress, particularly toward more sustainable biofuels from perennial feedstocks. Indeed, we now have laws aimed at lowering invasive risk that apply to a crop if it is grown for bioenergy, but exempt if used for food, despite the fact that biologically, invasive risk will be the same, whatever the end use.
Bioenergy could be a major part of reduction of net carbon dioxide emissions, especially given the huge potential to improve agricultural productivity and sustainability. Realizing this key goal requires policies based on a holistic view of risks and benefits, as well as recognition of the different bioenergy feedstock options. Until now there has been no such holistic overview so, for the first time, this book provides one, outlining in one place a contemporary and forward-looking view of the issues. In addition, each current and proposed major feedstock is objectively analysed for key properties, including yield, agronomy, pests and diseases, handling logistics, environmental benefits and invasiveness. Particularly important is its illustration of the opportunities presented by a wide range of perennials that could provide substantial environmental benefits, restore ecosystem services to degraded land and use land unsuited to major food crops.
Foreword by Stephen P Long FRS Gutgsell Endowed Professor of Plant Biology at the University of Illinois, and Chief and Founding Editor, Global Change Biology
6 | 1 Introduction
6
Units of area
� Figure X.XXArea comparisons
Note: all values approximated to two significant figures apart from unit conversions.
BP Biomass HandbookFigure X.XX (10 December 2013)Draft produced by ON Communication
squ
are
met
res
m2
1 10 102 103 104 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020
10,0
00
100,
000
1,00
0,00
0
10,0
00,0
00
1,00
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ion
bill
ion
tho
usa
nd
bill
ion
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bill
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bill
ion
bill
ion
100
101 etc.
510,000,000km2 Surface of earth
150,000,000km2 Global land area
5,500,000km2 Amazon rainforest
Global maize harvest1,800,000km2
Texas700,000km2
Cuba110,000km2
Hong Kong1,000km2
Paris100km2
Central Park, New York3.4km2
Vatican City44km2
1 square kilometre (1km2)100Ha
1 hectare (ha)10,000m2
Tiananmen Square, Beijing44Ha
Professional football playing area7,000m2
1 acre4,047m2
Basketball court420m2
Standard parking space10m2
Average bath towel1m2
Table tennis table4.2m2
Lebanon10,000km2
Hyde Park, London1.4km2
1 Introduction | 7
7
Units of energy
� Figure X.XXArea comparisons
Note: all values approximated to two significant figures apart from unit conversions.
BP Biomass HandbookFigure X.XX (10 December 2013)Draft produced by ON Communication
squ
are
met
res
m2
1 10 102 103 104 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020
10,0
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0,00
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101 etc.
510,000,000km2 Surface of earth
150,000,000km2 Global land area
5,500,000km2 Amazon rainforest
Global maize harvest1,800,000km2
Texas700,000km2
Cuba110,000km2
Hong Kong1,000km2
Paris100km2
Central Park, New York3.4km2
Vatican City44km2
1 square kilometre (1km2)100Ha
1 hectare (ha)10,000m2
Tiananmen Square, Beijing44Ha
Professional football playing area7,000m2
1 acre4,047m2
Basketball court420m2
Standard parking space10m2
Average bath towel1m2
Table tennis table4.2m2
Lebanon10,000km2
Hyde Park, London1.4km2
� Figure X.XXEnergy comparisons
BP Biomass HandbookFigure X.XX (10 December 2013)Draft produced by ON Communication
jou
les
1 10 102 103 104 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020
10,0
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kilo k
meg
aM tera T
pet
aP ex
a E
gig
aG
5 x 1020JWorld energy consumption in 2010
1.9 x 1020JGlobal annual oil production
Solar energy received on earth every minute 6 x 1018J
Average power plant annual output 3.2 x 1016J
Oil passing through the Strait of Hormuz each hour 4.6 x 1015J
Typical road tanker full of gasoline1 x 1012J
One tonne of bioethanol3 x 1010J
Energy in one barrel of oil5.7 x 109J
Energy content of 1kg of maize1.6 x 107J
One megawatt hour (MWh)3.6 x 109J
One kilowatt hour (kWh)3.6 x 106J
Running a large television for one hour1 x 106J
Dietary energy in 100g dark chocolate2.2 x 106J
Dietary energy in one large apple4.2 x 105J
One kilocalorie or dietary Calorie4.18 x 103J
One British thermal unit (btu) = 1,055J1.055 x 103J
One calorie4.18J
Heating one gram (nearly one litre) of air through one degree Celsius1J
Energy content of one hectare of miscanthus5 x 1011J
Recommended human daily calorific intake1 x 107J
World population is forecast to reach 8.3 billion by 2030, and societies are becoming more affluent. Global energy use is rising with population growth and increased consumer demand, and there are concerns about the resulting carbon dioxide emissions to the atmosphere. Renewable energy offers a mechanism to reduce carbon emissions, and its production is expected to grow faster than overall energy growth through to 2035.
Biomass – the solid matter in biological organisms – can be converted into biofuels, heat and power, and biogas. Global use of bioenergy is expected to more than double by 2035, with heat and power being the largest consumers. Liquid transport fuels currently account for less than 5% of current bioenergy, though production is rising fast. Most biofuels are currently derived from crops that are also food for humans and animals, but non-food plants are also being investigated for their potential as biomass crops.
Societies throughout the world have converted significant areas of forests, savannah and shrubland into crop and pasture lands, while advances in technology and plant breeding have led to prodigious yield increases in commercial food and fibre crops. Similar improvements are expected for dedicated ‘energy crops’; these could potentially be grown on land currently less suitable for food production.
While economic and practical realities will limit the rate and extent of change possible, there is substantial land and technology available for improving the overall output of both food and biomass.
8
1 Setting the context | 9
1 Setting the context
Global energy use
The world’s energy use is complex and changing. Total energy use rises with population and economic activity, and technological and commercial innovations affect the type of energy used. As a result, the amount and type of energy use varies throughout the world depending on both technology and available resources.
Figure 1.1 shows how sources of energy differ across regions and by level of economic development. Biomass currently provides a very small portion of energy use in developed countries, whereas biomass is a primary energy source for heating and cooking in many developing countries. The reliance on biomass in Africa relative to all other regions is clearly shown, as is the relatively small contribution from renewable sources worldwide.
Population and income growth are the key drivers of the growing demand for energy. These factors and the development of energy-hungry technologies from the time of the Industrial Revolution to the present day are reflected in the energy demand curves shown in Figure 1.2. By 2030 the world population is projected to reach 8.3 billion, which means an extra 1.3 billion people will need energy; and world income in 2030 is expected to be roughly double the 2011 level in real terms[1].
Biomass
MiddleEast
LatinAmerica
Africa
Non-OECDAsia
EasternEurope/Eurasia
OECD AsiaOceania
OECDEurope
OECDAmericas
World
Per cent energy use by source tCO2/person
Hydro Other renewables
Nuclear Gas Oil Coal
4.7
17.1
7.2
9.0
5.1
4.6
5.9
0.9
2.8
� Figure 1.1
BP Biomass HandbookFigure 1.1 (10 February 2014)Draft produced by ON Communication
Figure 1.1
World energy use in percentage terms by region and by source in 2010. Each square in the regional stripe represents 1%. The major fossil and renewable fuels are shown in different colours. Circles show tonnes of CO2 emissions per capita in 2009[2, 3].
This chapter provides an introduction to the use of biomass for energy in the context of global energy use, the evolution of agriculture and projections for future uses of biomass.
10 | 1 Setting the context
Figure 1.2
Global use in exajoules (EJ) of the six most important energy sources since 1850. Historically, biomass use is mainly the traditional use of fuelwood; the renewable curve includes all modern renewable sources except biomass. Major technology advances are shown and also significant changes in energy source: coal replacing biomass in the Industrial Revolution; the increase in oil with the rise of the internal combustion engine; and gas for heating and power generation[4].
Figure 1.3
The increase in energy demand in billion tonnes of oil equivalent (toe), excluding biomass used for heat and cooking from 1990 to the present day, and projections until 2035. The effect of the global economic crisis from 2008 can be seen clearly[5].
Prim
ary
ener
gy
(EJ)
500
400
300
200
100
0
1850 1900 1950 2000
Vacuumtube
Television
Microchip
Nuclearenergy
Commercialaviation
Gasolineengine
ElectricmotorSteam
engine
Biomass Coal Oil Gas Nuclear Other renewables
� Figure 1.2
BP Biomass HandbookFigure 1.2 (20 Decmber 2013)Draft produced by ON Communication
Despite increasing energy efficiency, energy consumption is on the rise globally as shown in Figure 1.3. World primary energy consumption is projected to grow by 1.5% per year from 2012 to 2035, adding 41% to global consumption by 2035. The fastest-growing fuels are renewables (including biofuels), with growth averaging 6.4% per year from 2012 to 2035. Nuclear (2.6% per year) and hydro (2.0% per year) are both projected to grow faster than total energy consumption.
Among fossil fuels, natural gas use has grown the fastest (1.9% per year), followed by coal (1.1% per year) and oil (0.8% per year)[5]. The lower relative growth rates of fossil fuels, however, apply to a very large base of use. On an absolute energy basis, for example, coal use grew the most in the period 2000 –10 and the additional use of coal constituted almost 50% of the total increase in energy use.
Oil CoalGas
Figure 1.3
Nuclear Other renewables(includes biofuels)
Hydro
BP Biomass HandbookFigure 1.3 (11 June 2014)Draft produced by ON Communication
1990 2005 2020 2035
Billi
on to
e
EJ
100
200
300
400
500
600
700
00
18
15
12
9
6
3
Note: 1toe equals approximately 42 gigajoules.
1 Setting the context | 11
Biomass and bioenergy
Biomass refers to the matter in all biological organisms, but in the context of energy it is most commonly used to mean the solid material that can be harvested or collected from biological organisms – primarily from plants. This meaning is used throughout this handbook (definitions for terms used in this book that are unfamiliar or that have various meanings in common usage may be found in the Glossary at the end of this handbook). Major components of biomass include sugars, starches and oils produced from plants. These are extracted in great abundance today for energy production. The term biomass also includes the heterogeneous material found in even greater abundance in materials such as wood, plant stems and husks. All these materials can be converted into an energy form useful for heat, power and transport fuel.
Bioenergy is a general term referring to energy derived from any renewable biological material from plant matter, animals or organic wastes derived from plant and animal matter. In this handbook we focus primarily on the conversion of materials from plants (biomass) into bioenergy.
Bioenergy is produced from biomass in a number of ways, including:
●● Biofuels: liquid fuels mainly used for transport, produced by a variety of thermochemical and biochemical processes. These fuels can come from a wide range of plant and animal materials. The predominant forms today are bioethanol (derived from fermentation of sugars) and biodiesel (from esterification of plant and animal oils) with increasing amounts of the oils being treated with hydrogen to create hydro-treated vegetable oils (HVO) suitable for diesel use. A variety of new fuel
molecules are also at the research and early commercial demonstration phases. For instance, liquid biofuels derived from lignocellulosic biomass that has undergone thermochemical or biochemical processes are just beginning to appear in commercial quantities.
●● Heat and power: this includes the traditional form of bioenergy in which plant materials (such as wood or grasses) are collected and burned for heat. This heat can be used to generate electrical power as well. Early, large-scale adoption has often involved a mixture with coal for the generation of power as shown in Figure 1.4.
●● Biogas: a combustible gas produced by the anaerobic digestion of biological material. Biogas consists of a number of different compounds and hydrocarbons, the main ones being methane and carbon dioxide. It is produced from a wide range of materials, particularly wastes (especially those with relatively high water content), and from landfill. It is used primarily for electricity and heat generation. Biogas from anaerobic digestion should not be confused with syngas, which can be derived from both fossil and renewable sources of carbon (biomass). Syngas has a very different chemical composition (being composed of carbon monoxide and hydrogen) and is both made and used in a very different manner. Biogas itself can be converted to syngas for use in the production of fuels, but this is not a significant current practice.
Production routes of biomass to various fuels are discussed in greater detail in Chapter 3 with a summary provided in Table 3.5 and a schematic outline on the inside front cover of this book.
Figure 1.4
Woody biomass being blended with coal at a Colorado electricity generating plant to provide a mixed feedstock boiler fuel[6].
12 | 1 Setting the context
Biomass can also be used on a large scale in the production of industrial chemicals. Current processes primarily focus on converting starch and sugar into the desired chemical products, using microorganisms modified to produce the chemical of interest. In many ways these processes resemble those used to produce biofuels such as ethanol. This is an area of much research and commercial interest, and new processes and facilities continue to appear. Given the volumes of materials needed for the chemical sector, the overall use and demand for biomass for chemicals is much lower than that for energy.
Globally and traditionally, the largest use of bioenergy is for so-called ‘direct use’. This traditional use of bioenergy is mainly for heating and cooking, using biomass sources such as wood, charcoal, crop residues and animal dung. Much of it is used in small domestic stoves and open fires, and statistical data are therefore limited. Even in OECD countries, two-thirds of total bioenergy use is for heating, much of it sourced through forestry management. Figure 1.5 is a chart originally published by the International Energy Agency (IEA) depicting the use of bioenergy by sector in 2010 along with the potential use in 2035. The future estimates are based on the IEA’s New Policies Scenario, which takes into account broad policy commitments and plans to address energy-related challenges, even if the specific measures to implement these commitments are yet to be defined.
In this assessment, the total amount of traditional biomass consumed is expected to decline slightly over time, as access to modern fuels increases around the world. Excluding the traditional use of biomass, global primary use of bioenergy is expected to more than double from 22 exajoules (EJ) in 2010 to nearly 50EJ by 2035, growing at an average rate of 3.3% per year. Provision of heat and power are projected to be the largest consumers of non-traditional bioenergy, potentially growing from nearly 17EJ in 2010 to more than 37EJ by 2035. Together, these two sectors account for about two-thirds of the additional consumption of bioenergy in the IEA scenario.
A little more than 10% of current non-traditional bioenergy is in the form of liquid fuels for transport (i.e. biofuels). Brazil and the US are the largest producers of bioethanol, and Germany is the largest producer of biodiesel. The use of biomass for electricity generation (such as bagasse in Brazil and woodchip- and pellet-fuelled power generators in the UK) accounts for just over 20% of current non-traditional bioenergy.
Bioelectricity continues to grow in both OECD and non-OECD nations. In 2011 more than 35 countries had bioelectricity capacities exceeding 100 megawatts (MW). Total generation has increased by more than 170 terawatt-hours (TWh) (0.6EJ) from 2000, reflecting an 8% annual growth rate over the past decade[7]. With more than 100 countries enacting renewable electricity targets, bioelectricity is expected to grow. The IEA estimates that electricity generated from biomass could grow to 530TWh (1.9EJ) in 2017 and possibly to more than 1,470TWh (5.3EJ) in 2035, depending on the cost and availability of biomass.
While much work has been done to map the potential for global biogas production, there is little reliable data about current biogas production levels in many countries. While the contribution (in energy terms) is relatively small, biogas was used to produce roughly 3% of electricity use in Germany[8], provided heating and cooking fuel to nearly 40 million Chinese households[9], and made up 64% of the gas use for transportation in Sweden in 2010[10]. There is increasing production and local use of biogas from landfills, and growing interest in utilizing anaerobic digestion of biomass for biogas and production of electricity.
Heat and power production are, and are expected to continue to be, the largest uses of biomass, enabled by well-known and widely practised combustion technology. However, biofuels for transport are also expected to more than double by 2035, and significant research is under way to provide more cost-effective conversion technologies to enable more penetration into the transport sector with fewer environmental impacts than are currently associated with liquid fuels.
Figure 1.5
Use of bioenergy by sector in 2010 and 2035 (projected by the IEA for conditions where new policies are implemented). Use is estimated to rise from 53EJ in 2010 to 79EJ in 2035. The proportion used for heat by traditional methods (heating and cooking) is projected to fall considerably; the proportion used for heat via modern methods of production remains almost unchanged; while proportions used for power and transport by modern methods make significant increases[2].
� Figure 2.6aUse of bioenergy by sector in 2010 and 20351
Total 53EJ
BP Biomass HandbookFigure 3 (10 February 2014)Draft produced by ON Communication
Traditional58.8%
2010 2035
Other5.7% Heat
22.4%
Power8.5%
Transport4.6%
Total (projected) 79EJ
Traditional36.5%
Other5.5% Heat
24.6%
Power22.5%
Transport10.9%
BP Biomass HandbookFigure 1.6 (20 December 2013)Draft produced by ON Communication
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1 Setting the context | 13
Although biofuels currently supply only a small fraction of liquid transport fuels, production has been rapidly rising. Crops used to produce both food and fuel dominate today, though crops grown specifically for energy use are expected to increase in the future. While future projections of biofuels production are notoriously difficult to quantify, and the types of crops used and fuels made are subject to numerous technical, economic and political considerations, recent analyses suggest that biofuels could constitute approximately 6% of liquid transport fuels by 2035[2], with around three-quarters of the production continuing to come from North and South America[1]. Figures 1.6 and 1.7 provide example perspectives on the current and future mix of feedstocks for the supply of
biofuels to 2020. This projection, from the UN FAO, shows negligible growth of ethanol based on grains such as corn, the most significant source today, with growing volumes from sugarcane and, later in the projection, cellulosic biomass crops. Biodiesel is produced, and is expected to be produced, at much lower volumes (note different scales used in the graphs). Vegetable oil is projected to remain the most widely used source of biodiesel by volume. Waste oils, fats and tallows, as well as new crops with high oil yields and an ability to grow in diverse habitats (as exemplified by Jatropha in Figure 1.7), are anticipated to become a richer part of the mix.
Figure 1.6
Current and future mix of volumes of bioethanol supplied for fuel use projected annually to 2020[11].
Figure 1.7
Current and future mix of volumes of biodiesel supply projected annually to 2020[11].
BP Biomass HandbookFigure 1.6 (20 December 2013)Draft produced by ON Communication
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14 | 1 Setting the context
The bioenergy production chain consists of four main stages as shown in Figure 1.8. Biomass is grown, collected and often treated or densified into transportable forms such as bales, chips, billets or pellets to allow economical movement to the conversion facility. Following conversion to an alternate energy carrier such as electricity, heat, steam, liquid fuel or gas, the bioenergy can be distributed for end use in homes, vehicles and industry.
Biomass cultivation can encompass a wide variety of practices used in conventional agriculture and forestry. Where residues or wastes are the biomass source for energy, the production chain may begin with collection
and treatment, since primary cultivation is for other purposes including food, feed or timber production.
There are many ways to convert raw biomaterials into fuels. Active development worldwide is improving the various process efficiencies and widening their utility for different feedstocks (see Chapter 3 for more details on conversion processes).
As the use of bioenergy grows, there is increasing interest in developing new types of crops that produce a large amount of biomass per hectare and are grown specifically to supply energy. These plants are known as energy crops, examples of which are detailed in Chapter 6.
Figure 1.8
The four main stages of bioenergy production.
Biomasscultivation
Collection,densification,
transport and storage
Conversion toenergy carrier
Distributionand end use
� Figure 1.8
BP Biomass HandbookFigure 1.8 (18 November 2013)Draft produced by ON Communication
What makes an energy crop?
The first criterion for any energy crop is that it should be productive in terms of biomass yield per hectare to minimize the land area required. Second, the physical and chemical characteristics of the crop must be suitable for the conversion technology that will convert it into biofuel, biogas or power. For energy crops to make significant impacts on energy use, they must be grown on a large scale, so questions of sustainability (economic, environmental and social) must also be considered. The following characteristics are key traits that facilitate environmental sustainability:
Characteristics of an ideal bioenergy crop [12–14]
●● High-energy yield per unit growing area.●● Low-input, low-cost processing requirements. ●● Low greenhouse gas (GHG) emissions and energy
requirements.●● Easy to establish.●● Tolerant to extreme and/or variable environments.●● High efficiency of nutrient use.●● High efficiency of water use.●● Provide additional ecosystem services
and/or co-products.●● Suitable for a range of conversion processes into
various forms of bioenergy.●● Productive on soils and topographies less suited to
food crops.●● Low- or zero-invasive potential.●● Unrelated to native or major weed species to avoid
spread of genes and potential disruption of native ecosystems.
Inevitably, no single crop will meet all of these requirements, and the importance of a particular requirement depends on location. Chapter 6 of this handbook lays out the extent to which alternative energy crops address these requirements in different locations.
As a general rule, perennial crops meet many of these requirements: they do not require annual tillage and planting, and they often recycle nutrients and add carbon to the soil. As explained in Chapter 3, most
advanced biomass crops (both current and potential) are perennials, either trees or perennial grasses. Complex choices between maximizing yield and maximizing sustainability, however, have to be made. For example perennial grasses such as switchgrass and miscanthus can be highly productive in temperate environments. In the autumn these grasses transfer their nutrients to the root system so they can be retained over winter, even if the plant is harvested. Production in temperate environments is limited to the warm period of the year, and is therefore less productive than in moist subtropical and tropical environments where production is possible throughout the year. On the other hand, in environments with no dormant season, material must be harvested green. This gives higher yields but there are costs associated with drying fresh grass, and in this scenario there is less recycling of nutrients to the root system.
Geographical, topographical and social factors can also affect the choice of bioenergy cropping systems. As a crop, oil palm, for example, is not inherently less sustainable than other plantation crops. But many areas suitable for oil palm are naturally forested, so the conversion of carbon-rich peat-swamp forests in parts of South-East Asia can have environmental impacts that outweigh any benefit from producing renewable biofuel. Conversely, the introduction of perennial grass feedstocks on intensively managed land can create net carbon and GHG benefits through restoration of soil carbon and interception and reuse of nutrients. Indeed, the use of perennials as bioenergy sources can broaden opportunities for sustainable agricultural production: some grasses can stabilize eroding slopes, others tolerate saline soils, while succulent plants thrive in semi-arid areas.
Trade-offs between different crops are inherent in all forms of agriculture. As large new areas of bioenergy crops are contemplated, it is essential to minimize environmental impacts. Land resources are not infinite, so production of bioenergy crops must be carefully balanced with other uses for land, such as food, animal feed and material production.
1 Setting the context | 15
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World average maize grain yield increase
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1961 yieldsMaize grain: 1.65 dry tonne/haSugarcane: 15.08 dry tonne/ha
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BP Biomass HandbookFigure 1.9 (18 November 2013)Draft produced by ON Communication
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� Figure 1.9
BP Biomass HandbookFigure 1.9 (18 November 2013)Draft produced by ON Communication
Overview of agroecosystems
After the emergence of agriculture about 10,000–12,000 years ago, agricultural productivity increased slowly until the advent of mechanization in the 18th century, when horse-drawn drills, reapers and threshing machines allowed more land to be cultivated and also brought greater yields. The invention of the steam engine and steam plough increased productivity further and allowed previously unproductive land to be tilled. These gains were enhanced when tractors driven by internal combustion engines came to the market in the early 1900s. A modern tractor and plough can till many times more land in a day than a person with a horse, and combine harvesters reap in an hour what teams of people could only achieve in days.
Other agricultural practices have also improved dramatically. Crop rotation began in the 18th century. In the 19th century, more sophisticated fertilizer treatments emerged, along with increasing numbers of research organizations that advised farmers on best practice and introduced new strains of plants. The 20th century saw genetics and chemistry playing an increasing part in agriculture. The introduction of hybrid maize and dwarf wheat allowed dramatically improved yields; the Haber–Bosch process for fixing nitrogen allowed ammonia-based fertilizers to become cheaply available; and organic chemists developed a wide range of effective pesticides and herbicides. In the late 20th century and through to today, genetic marker-assisted plant breeding and genetic engineering (also known as genetic modification or genetic manipulation) have become hallmarks of the next revolution in agriculture in many parts of the world, spearheaded by large research organizations.
The application of all these technologies has driven prodigious improvements in the yields of many crops. Since 1961, for example, average yields of sugarcane and corn have increased by 41% and 166% respectively, as shown in Figure 1.9. The most favoured growing locations have seen even more dramatic yield improvements. These improvements have occurred steadily over decades while, at the same time, different crops have been developed to
respond to the changing demands for food, feed, fuel and materials. Future energy crops, such as those discussed in this handbook, would be expected to benefit from the same types of investment.
In addition to the changing nature of agriculture, the amount of land devoted to it has expanded significantly. Across the globe, cropland and pasture has expanded at the expense of primary forest, savannah and shrublands, as shown in Figure 1.10. Growth has been driven primarily by a rise in population and by the changing dietary intake of more affluent consumers.
Figure 1.10 Change in land use during various periods since 1765[16]. The figures on top of each category show the land-use change between 1765 and 2005, in million km3.
Figure 1.9
Increasing yields of sugarcane and maize grain over 50 years compared with yields in 1961. Moisture contents of 70% for sugarcane and 15% for maize grain were assumed[15].
–23.7 +8.3 +0.4 –5.4 –6.8 –1.7 +0.5 +9.4 +19.3
16 | 1 Setting the context
Increasing demand for meat proteins, as shown in Figure 1.11, driven by population growth, economic growth and changing dietary habits, is directing more and more resources into meat production. From an energy perspective, livestock production is quite inefficient. Intensive beef production, for example, commonly utilizes grains for feed, and can require 6–20kg grain/kg beef produced[17]. While there is continuous development in methods to improve the efficiency of meat production, it is estimated that 70% of all agricultural land is used in pastoral, mixed-system and intensive livestock production. Food, feed and energy uses will all compete for available land.
Despite the overall increase in land area devoted to agriculture, there are areas where farming has been abandoned across large regions. Some of this abandoned agricultural land has become reforested and is now valued for recreation, biodiversity and important carbon stocks (growing forests remove substantial amounts of carbon dioxide from the atmosphere). Many re-established forests, such as large areas of the eastern US, are actively managed for wood resources. Residual wastes from timber extraction and saw milling have increasingly been used for energy in the wood-products industry and can potentially provide bioenergy feedstock to other sectors (see Forest biomass box below).
Abandoned agricultural land that has not returned to forest or native ecosystems has, in many places, been developed for urban and residential use. Recently abandoned land, however, may also be shifting in and
Figure 1.11
The growth in demand for meat proteins for developed and developing countries[17, 18].
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BP Biomass HandbookFigure 1.10 (10 December 2013)Draft produced by ON Communication
out of agricultural production due to changing land ownership or altered economic incentives. Developing recently abandoned land for bioenergy production would have less environmental impact than developing land on which indigenous ecosystems have regenerated. It would also help maintain food production capacity that might be required in the future.
Forest biomass
Woody biomass is used for 80% of traditional primary energy use, totalling nearly 32EJ per year and supplying nearly 2 billion people with heat and cooking fuel. In developed nations, wood typically supplies less than 5% of primary energy. In the US, for example, wood is used to supply 1% of the electricity supply and 2% of primary energy, mainly to industrial users. Finland and Sweden are exceptions with nearly 19% of primary energy generated as heat and power from woody biomass[19,20].
The total potential for woody biomass could be as high as 110EJ per year (EJ/yr), according to the Intergovernmental Panel on Climate Change; however, the sustainable and acceptable limits of forest biomass use are still under debate and the use of forest biomass for energy is controversial. Historic depletion of forest resources in many parts of the world has instilled caution in communities considering re-expanding use of wood biomass for energy. In parts of the US, Canada, the EU and China, forest biomass is actually accumulating. Growing stock in the EU has increased nearly half a per cent per year for the past 23 years and US forest biomass has increased by 10% in a 10-year period. In the US and Canada, less than 1% of available forest biomass is currently harvested for all uses. The increase in tree stand density, increased dead woody biomass, and increasing climate stress have been implicated in more frequent and more severe forest
fires. Whether increased forest management will result in a sustainable and acceptable supply of biomass for bioenergy is not yet clear.
The situation for tropical forests is still worrisome. Forests in South America and Africa are still experiencing net losses, although deforestation has slowed in many regions including the Brazilian Amazon. Although an increase in tropical forest plantations for fruit, oil seed and timber production may eventually be a source of residual biomass for energy in some regions, such biomass may not be considered acceptable by some stakeholders. See Chapter 4 in this handbook for a discussion of sustainability criteria in policy.
Forest ecosystems can be very productive and offer some advantages to herbaceous energy crops. Trees store carbon, both above ground and in the soil, over a very long time period and so can be left as standing stocks. Herbaceous crops must be harvested before or soon after senescence or they will degrade and release their carbon. Trees can be grown on steeply sloping land and tolerate a wide range of soils and hydrologies. Finally, forests can provide a more diverse set of ecosystem services, but because forests are more complex and require longer rotations to accumulate biomass, a careful and detailed understanding of each forest system is required to assess long-term sustainability.
1 Setting the context | 17
Figure 1.12
Global Sankey diagram for annual fresh water withdrawn for human use [25]. From left to right, the diagram illustrates the continental distribution of withdrawals, the sectors (agriculture, industry, domestic) in which the water is used, the services provided by the water, and finally the return of the water to the hydrological cycle. Share of agriculture in total withdrawals is shown in yellow. In the final (right-hand) segments, changes in water quality during its use are indicated in different colours. The red segment indicates where energy is used in treating wastewater. The vertical width of each bar in the diagram is proportional to the volume of fresh water involved, measured in cubic kilometres (km3), and numerical amounts are provided with labels, also in km3.
Africa
Asia
Oceania
Europe
Recycled water
Hydropower
Agriculture~ 2700
Food~ 2700
Biofuels
Energy~ 470Industry
~ 775
Domestic~ 380
Domesticand industry~ 790
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Untreatedwastewater
Recycled water(direct to supply)
Return flows intosurface water and percolationinto groundwater
Atmosphere
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Pollutant parametersof return flow
Organic and inorganic compounds;nitrogen and phosphorous.
High temperature(effect on ecosystems).
Industrial effluent (silt and rock particlesand sufactants, heavy metals, high biological oxygen demand, blood contaminants).
Domestic effluent (excreta, urineand faecal sludge) together with grey water (kitchen and bathingwastewater).
DestinationPost-usetreatment
ServicesRegions Total applied water
Latin America
North America
Water use in agriculture
All biomass requires water to grow. The intensity of water use is determined by the volume of water withdrawn from local freshwater sources and subsequently consumed in their growth. Worldwide, about 80% of cropland is rainfed (not irrigated[21]) and provides about 60% of global crop production [22]. The remaining 20% of cropland, about 250 Mha[23, 24], is irrigated during at least part of the growing season and yields about 40% of all production. Freshwater withdrawals for agricultural irrigation constitute some 2,700km3 of water (or about 70% of world withdrawals) as shown in Figure 1.12, a Sankey diagram that illustrates the fate of water withdrawn for human use[25]. While many factors impact crop yield, the dominant factor in determining where irrigation is needed is the amount of rainfall. This varies dramatically: from desert regions where precipitation is rare to regions with more than a thousand millimetres of precipitation per year. As with food crops, the amount of water used for irrigation of biomass crops will be highly dependent on local conditions and the type of plant used. Common practice to date for the production of liquid biofuels has been to grow crops where little or no irrigation is needed. As a result, the intensity of water use for growing these crops is much lower than for agriculture on average, with estimates of about 0.5% of world freshwater withdrawals for 2010 biofuels production[26].
The water cycle (in which plants participate) involves the set of processes by which water circulates between the earth’s oceans, atmosphere and land. It involves precipitation as rain and snow, drainage in streams and rivers, and return to the atmosphere by evaporation
and transpiration. This water cycle provides essential ecosystem services. Regardless of whether vegetation is native or non-native, evaporation and transpiration affect the water flows into local streams and rivers. Vegetation thus plays a part in flood control.
Plants obtain the water they need from the soil via their roots. Soil water comes from precipitation, groundwater and from irrigation. Water is lost from the soil by evaporation, drainage and uptake by plants, with different types of plant cover withdrawing water at different rates. Plants take up far more water than they ultimately use in photosynthesis or store within their structure.
The remainder is released into the atmosphere (in a process called transpiration) to be recycled as rain. Plant canopies intercept some rainfall before it reaches the soil; this water is then lost through direct evaporation from the leaves. This loss can be particularly important in densely planted agricultural crops with complete canopy closure. Because the periods of highest rainfall in the year may be out of phase with crop demand for water, storage of water in the soil plays an important role in supporting crops. The capacity of the soil to store water that is accessible to plants depends on the soil texture. Sands absorb water rapidly, but can store little and drain quickly. Clay soils will not absorb water rapidly, making run-off and erosion more likely. Once they do absorb water, clay particles bind water molecules, so some of the water is not available to the crop. Soil organic matter is critical in increasing the water-holding capacity of soils.
18 | 1 Setting the context
Evaporation and transpiration provide another essential ecosystem service by cooling continental surfaces that could otherwise be much warmer at the height of summer. At the same time these processes provide water to the air, which in turn falls as rain elsewhere. Indeed a major concern of Amazon deforestation is that it could cause
increased regional droughts because less water will be evaporated. Other types of ecosystem services provided by plants include reduced loss of nitrate and other elements due to changes in peak flow drainage, and reduced soil erosion.
Agricultural production of energy crops
A primary driver for promoting energy crops is the desire to lower the amount of GHG associated with energy production and to find cheaper and more sustainable ways to produce biomass. It can be hard, however, to quantify the issues: economic data are difficult to pin down, with yields and prices for crops varying dramatically over time and regionally. There is also an imbalance in the amount of data available: we have plenty of information about traditional crops used in our food systems, whereas large-scale production of energy crops is still in its infancy. As a result, much of the information on energy crops is based on extrapolation from small datasets and emerging research findings. Chapter 3 of this handbook provides more details on the energy potential from biomass and issues associated with its large-scale production.
Although food production is the main purpose of agriculture, our farming systems also produce a wide range of non-food goods and services. As the world’s population grows and demands more resources from a finite amount of land, there is a need to prioritize these items. Goods and services arising from agriculture include food crops and
livestock, energy, organic materials (such as wood and cotton), specialist materials (such as bioplastics and other large-volume chemicals), carbon sinks, biodiversity and other ecosystem services. Ultimately, land will be used in a way that gives the highest economic return, and this will differ by location and by prevailing policy and regulation.
Our need for food remains paramount. To feed our growing population, we will need higher yields of existing crops, as well as new crops that can be grown on land currently less suitable for agriculture. Figure 1.13 provides a view of the distribution of land areas around the world with differing suitabilities for agriculture. Productivity of crops grown in different regions can vary manyfold with crop genetics and agricultural practice significantly impacting output. Major land areas, for example in Africa and the Ukraine, are currently producing substantially suboptimal yields.
One way to achieve significant increases in biomass production without compromising food resources is by converting marginal and abandoned land to bioenergy production. This could be done by replacing poorly
Agricultural suitability across the globe
n Closed forest
n Inland water bodies
n Irrigated area
n Land prime or well suited for agriculture
n Land suited for agriculture
n Land unsuited to poorly suited for agriculture
n Protected area
n Urban area
Figure 1.13
Suitability of land with appropriate levels of inputs for pasture and rainfed crops[27].
1 Setting the context | 19
performing crops with better alternatives as they become available and developing crops that can be grown on saline, water-logged or arid lands that cannot (economically speaking) support food production. Investments in bioenergy systems might even rehabilitate such land so that it could be used for future food production.
Many agricultural systems already yield more than one type of product simultaneously. For instance, when cereal crops are used to produce bioethanol, between a quarter and a third of the total weight of the grain is available after processing as a high-protein feed (known as distillers’ grains). Cotton produces cotton oil and cottonseed meal as well as fibre (cellulosic cotton lint). Excess straw can
be used for heat and power production or as feedstock for lignocellulosic biofuels. Similarly, the use of wood harvested from rubber and palm-oil plantations at the end of a plantation’s economic life does not displace the production of rubber or palm oil, but facilitates the replanting of such crops.
All of these approaches and more (increasing productivity and yield, diversifying crop patterns, bringing marginal land into cultivation and developing multi-use crops) will be needed to achieve significant expansion of agricultural output while minimizing environmental damage.
Chapter references[1] BP (2013), BP energy outlook 2030. BP, London, UK.
Available from: http://www.bp.com/content/dam/bp/pdf/statistical-review/BP_World_Energy_Outlook_booklet_2013.pdf [accessed July 2013].
[2] IEA (2012), World Energy Outlook 2012. International Energy Agency (IEA), Paris.
[3] The World Bank, Data Indicators Databank – CO2 Emissions. Available from: http://data.worldbank.org/indicator/EN.ATM.CO2E.PCcountries/1W?display =graph [accessed February 2014].
[4] Adapted from Nakicenovic, N. (2009), Supportive policies for developing countries: a paradigm shift. Background paper prepared for World Economic and Social Survey 2009.
[5] BP (2014), BP energy outlook 2035. BP, London, UK. Available from: http://www.bp.com/content/dam/bp/pdf/Energy-economics/Energy-Outlook/Energy_Outlook_2035_booklet.pdf [accessed February 2014].
[6] Kryzanowski, T. (2009), Big energy win with biomass, enrG Magazine. Available from: http://www.altenerg.com/back_issues/index.php-content_id=231.htm [accessed July 2013].
[7] International Energy Agency (2013), Tracking clean energy progress 2013: IEA input to the clean energy ministerial. OECD/IEA, Paris. Available from: http://www.iea.org/publications/TCEP_web.pdf [accessed February 2014].
[8] German Biogas Association (2013), Entwicklung des jährlichen Zubaus von neuen Biogasanlagen in Deutschland (Stand 11/2013). Available from: http://www.biogas.org/edcom/webfvb.nsf/id/DE_Branchenzahlen/$file/14-07-01_Biogas%20Branchenzahlen_2013-Prognose_2014.pdf [accessed February 2014].
[9] Global Methane Initiative, Country profile: China. Available from: https://www.globalmethane.org/documents/ag_cap_china.pdf [accessed February 2014].
[10] Swedish Energy Agency (2011), Biogas in Sweden factsheet. Available from: http://www.energimyndigheten.se/Global/Internationellt/Exportfr%C3%A4mjande%20o%20Bilateralt/Biogas_Sweden_Faktablad_HR.pdf [accessed February 2014].
[11] OECD–FAO (2011), OECD–FAO agricultural outlook 2011–2020. Available from: http://www.oecd.org/site/oecd-faoagriculturaloutlook/48178823.pdf [accessed February 2014].
[12] Dale,V. H., Kline, K. L., Wright, L. L., Perlack, R. D., Downing, M. & Graham, R. L. (2011), Interactions among bioenergy feedstock choices, landscape dynamics, and land use, Ecological Applications, vol. 21, pp. 1039–1054.
[13] Davis, S. C., Boddey, R. M., Alves, B. J., Cowie, A. L., George, B. H., Ogle, S. M., Smith, P., van Noordwijk, M. & van Wijk, M. T. (2013), Management swing potential for bioenergy crops, GCB Bioenergy, vol. 5, pp. 623–638.
[14] US Department of Energy (2006), Breaking the biological barriers to cellulosic ethanol: a joint research agenda. Report from the December 2005 workshop, DOE/SC-0095. Department of Energy Office of Science. Available from: http://genomicscience.energy.gov/biofuels/2005workshop/2005low_feedstocks.pdf [accessed February 2014].
[15] Food and Agricultural Organization of the United Nations. FAOSTAT database. Available from: http://faostat3.fao.org/home/index.html#HOME [accessed February 2014].
[16] Adapted from Meiyappan, P. & Jain, A.K. (2012), Three distinct global estimates of historical land-cover change and land-use conversions for over 200 years, Frontiers of Earth Science, vol. 6, no. 2, pp. 122–139.
[17] Giovannucci, D., Scherr, S., Nierenberg, D., Hebebrand, C., Shapiro, J., Milder, J. & Wheeler, K. (2012), Food and agriculture: the future of sustainability. United Nations Department of Economic and Social Affairs, Division for Sustainable Development, New York. Available from: http://www.un.org/esa/dsd/dsd_sd21st/21_pdf/agriculture_and_food_the_future_of_sustainability_web.pdf [accessed October 2013].
[18] Kanaly, R., Manzanero, L., Foley, G., Panneerselvam, S. & Macer, D. (2010), Energy flow, environment and ethical implications for meat production. UNESCO, Bangkok. Available from: http://unesdoc.unesco.org/images/0018/001897/189774e.pdf [accessed October 2013].
20 | 1 Setting the context
[19] Pelkonen, P., Hakkila, P., Karjalainen, T. & Schlamadinger, B. (2000), Woody biomass as an energy source – challenges in Europe, European Forest Institute, pp. 73–78.
[20] White, E. M. (2010), Woody biomass for bioenergy and biofuels in the United States – a briefing paper, General Technical Report PNW-GTR-825. US Department of Agriculture, Forest Service, Pacific Northwest Research Station, Portland, US.
[21] International Institute for Applied Systems Analysis (IIASA)/Food and Agriculture Organization of the United Nations (FAO) (2010), Global agro-ecological zones (GAEZ v3.0). IIASA, Laxenburg and FAO, Rome. Available from: http://www.fao.org/nr/gaez/en/# [accessed February 2014].
[22] WorldBank.org, Water resource management. Available from: http://water.worldbank.org/topics/agricultural-water-management [accessed July 2013].
[23] Siebert, S. et al. (2010), Groundwater use for irrigation – a global inventory, Hydrology and Earth System Sciences, vol. 14, no. 10, pp. 1863–80.
[24] Portmann, F.T., Siebert, S. & Döll, P. (2010), MIRCA2000—Global monthly irrigated and rainfed crop areas around the year 2000: a new high-resolution data set for agricultural and hydrological modeling, Global Biogeochemical Cycles, vol. 24, no. 1.
[25] Curmi, E., Richards, K., Fenner, R., Allwood, J.A., Kopec, G. & Bajzelj, B. (2013), An integrated representation of the services provided by global water resources, Journal of Environmental Management, vol. 129, pp. 456–462.
[26] Williams, E.D. & Simmons, J.E. (2013), Water in the energy industry: an introduction. BP, London, UK.
[27] van Velthuizen, H. et al. (2006), Mapping biophysical factors that influence agricultural production and rural vulnerability, Environmental and Natural Resources, series 11. FAO & IIASA, Rome.
Land is often classified according to potential use for agriculture. Broader climatic and ecosystem classifications are also used. Both systems are useful in considering which crops to grow and where to grow them.
Agriculture involves a series of operations to produce crops, and modern techniques are highly mechanized. Understanding the energy needs and GHG emissions of these processes is important for understanding whether growing biomass crops will be economic and energy efficient at a particular site.
Different plants employ different methods for utilizing carbon dioxide and water, allowing for plant growth under a wide range of conditions. The way in which each type of plant grows and develops affects its productivity and its potential yield.
Various raw materials derived from plants – including sugars, starch, cellulose, lignin and oils – are used in energy production. The physical properties and chemical complexity of these materials affect the ease and energy efficiency of processing them into biofuels.
22
2 Important concepts | 23
2 Important concepts
Global ecosystems and land classifications Land is commonly classified according to its actual or potential use for agriculture, and this is sometimes described as land capability classes. In the context of this handbook, however, where we review wide-ranging biomass crops (both potential and realized), we look at land more holistically because land not normally prioritized for agricultural use can sometimes support carefully selected biomass crops. Traditional land classification takes into account soil type, previous land use, fertility, water availability, potential for erosion and accessibility for agriculture. These remain important indicators of land that might support bioenergy production. Productivity
and sustainability of production will depend on these land characteristics, together with management and crop choice.
Land areas can be categorized by grouping ecosystems that have similar climatic, biotic and abiotic conditions. Each such group constitutes a biome, and different biomes give rise to different types of use – biomes are described more fully in Chapter 5. Figure 2.1 summarizes the global areas of different biomes, the types of feedstock or existing vegetation, and their carbon productivity and end uses. In short, the diagram connects biomes to the various services they provide [1].
Understanding bioenergy production systems requires background knowledge in many diverse fields. This chapter sets out some of the fundamental concepts. There is also a comprehensive glossary at the end of this handbook.
Tropical forests
Temperate forests
Boreal forestsCropland residual
Grasslands
Shrublands
Losses
Livestock respiration
Food waste
Potential natural vegetation [M km2 ]
Slice 1Land productivity[Pg C/y]
Final services[Pg C/y]
Slice 2 Slice 4Slice 3 Slice 5Actual land use [M km2 ]
Slice 6Harvesting[Pg C/y]
Modifications[Pg C/y]
Fire
[3.7]Livestock feed
Food [0.8]
Fuel [1.2]
Fibre [0.6]
[4.5]
[47.0]
ECOSYSTEM
SERVICES
Heterotrophicrespiration
Unit conversionarea to carbon
NPP0 loss
Pasture [28.1]
Cropland[15.0]
Unmanageddryland [14.8]
Forest[42.4]
Built-up [0.7]
Tundra and desert[28.9]
Tropical forests
Temperate forests
Boreal forests
Savanna
Grassland/steppe
Dense shrubland
Open shrubland
Tundra
Desert, polar desertRock/ice
[22.6]
[24.5]
[8.2]
[19.2]
[14.3]
[6.0]
[11.9]
[15.3]
[8.2]
NPP0 loss
NPP0 loss
[12.2Pg C/y]
[6.0Pg C/y]
[7.2Pg C/y]
[30.5Pg C/y]
[1.4Pg C/y ]
Crop harvest
[2.2]Wood harvest
[1.8]Grazed biomass
Meat
Fire
Waste assim.
Pollination
Pest control
Air quality
Water cycling
Water quality
Flood control
Erosion control
Soil formation
Nutrient cycling
Recreation
Scientific value
[0.84]
[1.8]
Carbon sink [2.6]
NPP0 loss
Losses
[1.1]
[1.8]
720 gC/m2
400gC/m
430gC/m
490gC/m
50gC/m
2
2
2
2
stock1530Pg C
stock80Pg C
stock310Pg C
stock220Pg C
Figure 2.1
Sankey diagram showing global biomes, vegetation, carbon productivity and end uses[2]. There are a number of nomenclatures currently used for biomes and those listed on the left represent a slightly modified classification by Ramankutty and Foley[1]. The left-hand column, slice 1, shows areas of potential natural vegetation, while slice 2 shows actual land use after appropriation for human use. Slice 3 shows land productivity in Petagrams or Pg (billion tonnes) of carbon per year and also the amount of carbon stored in these lands in Pg. The final three slices show how this carbon moves through harvesting and processing to final services. Also shown are losses to net primary productivity (NPP0) attributed to lower productivity on conversion from natural vegetation. Food, fibre and fuel account for only a small amount of final use. The majority of fixed carbon is available for use by other species, is ultimately respired (heterotrophic respiration) and contributes to a variety of services, collectively called ecosystem services. The vertical width of each bar in the diagram is proportional to the area of land use or the amount of carbon per annum associated with a particular segment[3].
24 | 2 Important concepts
One can see that more than a third of land has been actively transformed from its natural state to cropland, pasture and built-up areas. Cropland and pasture are found in several biomes, and most crop production is harvested every year. While crop productivity can be quite high, there are numerous routes for losses in productivity due to disease, fire, nutrient and climatic variability during harvest and even waste after harvest. These losses, and the relatively high fraction of harvest that goes to the relatively energy-inefficient production of livestock, results in only a very small fraction of the total productivity providing food, fuel and fibre. Otherwise unattributed production is allocated to various worldwide ecosystems.
There are disagreements in the literature as to how land types should be classified. Nomenclature varies by country and according to intended purpose. As a result, there are no internationally standardized definitions of land types and the quality of land-use data varies between countries. Land considered by some to be abandoned may actually be used informally for fuel and grazing. Some even conclude that no land is really ‘available’, as any choice in using land for a different purpose will ultimately affect the current use and output of that land, regardless of whether that use is deliberate. Despite these caveats, it is nevertheless useful to have a sense of the different land types and the terminology used to describe their potential productivity.
Land types
The US Department of Agriculture (USDA) describes eight land classes, based on soil types rated according to their relative ability to support common agricultural crops[4]. These are tempered by four sub-categories that recognize topographic problems that may limit production, including waterlogging, shallowness of the soil, erodibility and climatic limitation (such as extreme cold). The following categories condense these classes (and similar classifications by other national agricultural services) into five categories. These are not mutually exclusive: specific sites may fit one or more of these five categories.
Prime
Prime land can produce the highest yields of major commodity crops with proper agronomic management. It is easily accessed and cultivated, and is well suited to a range of crops, including food, feed, forage, fibre and oilseed. Despite its great potential, incorrect management (using techniques that reduce soil organic content or allow wind or water erosion) of prime land can degrade productivity. Prime agricultural land is usually rainfed, rather than irrigated, but irrigation can allow access to good soils climatically limited by inadequate rainfall. In this case, careful management is necessary to avoid excess salt deposition or exhaustion of water sources.
Marginal
Marginal land gives lower yields of annual grain crops than prime land, or has only limited potential for agricultural production. It may also be fertile land that is susceptible to erosion. Even though soil quality may be high, for example, cultivation of such soil on steep slopes can cause rapid soil loss unless terraces are economically feasible. Land that is marginal for conventional row-crop agriculture might support high yields of biomass crops: sloping land may support perennial bioenergy feedstocks (given sufficient water) while minimizing the risk of erosion relative to other land uses. Low productivity pasture, supporting one to two head of cattle per hectare, may also be in this category. In Brazil, with appropriate amelioration of soil nutrient deficiencies, such land supports significant yields of sugarcane.
Degraded
Degraded land can support only low productivity of conventional commodity crops. Degradation is usually the consequence of intensive management, usually associated with agricultural or forestry practices that result in the loss of organic matter, the production of laterites (hard, clay-like materials) in tropical soils, and actual loss of bulk soil by water or wind erosion. The dustbowl of the southern central US, where cultivation led to serious wind erosion, is a classic example. Such land, however, may provide viable yields of deep-rooted crops that bind the soil and have the potential to restore soil carbon. Land may also be degraded by excessive salt deposition through irrigation with low-quality water or pollution with industrial effluents or mining wastes. In some cases, land degradation is so severe that further agricultural use with traditional crops is not possible and the land is abandoned.
Abandoned
Land may be abandoned for various reasons, such as increasingly unreliable rainfall, competition from higher production elsewhere, or a collapse of local markets. In the eastern coastal states of the US, for example, much production became uneconomic following the Civil War, while the better soils of the mid-western US began to deliver grain at lower prices, making production progressively more uneconomic in the north. As a result much land in the eastern US has dropped out of cultivation in the past 150 years. This pattern of loss continues to this day. More recently, increasingly productive agriculture and the break-up of collective farms in Eastern Europe have resulted in abandonment.
Land previously used for crops or pasture is classified as abandoned if it is now unused and has not been converted to forest or urban use. If the period of abandonment has been short, such land may be converted back to agricultural use with relatively low economic and environmental cost. Long-abandoned land can, however, through the process of ecological succession, become host to diverse plant and animal communities. Re-established native communities often store large amounts of carbon (both in soils and above-ground biomass) and may also provide valuable ecosystem services such as protection of water catchment areas, wildlife conservation and recreation.
2 Important concepts | 25
Agricultural inputs and practices
Agriculture involves management that varies according to crop species, soil conditions, climate, topography and culture. Some of the most common practices for cultivating crops are explained below.
Tillage
Tillage is the preparation of land to receive crops, and is practised in many forms. For annual crops, it must be done every year (unless reduced or zero-tillage methods, as described below, are used). Traditionally, it involves turning the soil with a plough to bury weeds or crop residues, followed by harrowing to produce the fine tilth necessary for good seed germination. It is a major activity in agriculture, requiring either considerable labour or mechanization (with its concomitant cost in GHG emissions). Mechanized tillage has enabled huge increases in productivity by increasing the speed of ground preparation and by allowing more land to come under cultivation.
Tillage improves the conditions of certain soils unfavourable for agricultural production and is effective in helping to control annual weeds, but if used improperly can cause serious land degradation (erosion). Reduced- or zero-tillage methods, where seed is sown (using direct-drilling equipment) into unploughed land that has been cleared (by hand or using herbicides), are widely used to reduce cost, maintain soil carbon levels and reduce erosion. Many perennial bioenergy crops (such as sugarcane and miscanthus) are not sown as seeds, but the soil must still be prepared to accept the cuttings or propagules (see below) that are used to establish new plantings. Once perennial crops are established, no yearly tilling is required.
Propagation
Crops can be established by various means. Annual crops (see below) are typically grown from seed, while many perennial crops are grown from stem cuttings (e.g. poplar and sugarcane); by dividing roots or rhizomes (e.g. miscanthus); or from vegetatively produced plantlets (e.g. agave). Propagation can require significant labour. Mechanization can improve efficiency and potential yield, and reduce the amount of labour required; however, mechanization has a cost in terms of increased GHG emissions and soil compaction. Tissue culture provides a means for standardized propagation of plants with uniform genetic material, but this technique requires significant investments of time and specialized labour.
Fertilizer
Fertilizers provide nutrients needed by plants, and farmers apply them to maximize crop productivity. The three major plant nutrients are nitrogen (N), phosphorus (P) and potassium (K). Nitrogen is the primary nutrient limiting crop production, and the use of synthetic fertilizers providing nitrogen has been necessary to support the great increase in crop production enabled by improved genetics and mechanization. However, the manufacture and application of synthetic fertilizers cause significant GHG emissions, partly as a result of the energy required to produce them and partly because soil emissions of nitrous oxide (N2O) – a potent GHG – and other nitrogen oxides (NOx) are higher after application. In addition, nitrogen that is not taken up by the crop can be leached as nitrate into waterways, which can reduce water quality and cause eutrophication (a decrease in dissolved oxygen caused by algal blooms that are detrimental to oxygen-requiring organisms). The amount of leaching depends on the crop, soil and climate, and the fertilizer application rate and method.
Irrigation
Irrigation is the application of water to growing plants to eliminate water deficits. Without sufficient water, photosynthesis slows down, secondary physiological effects impede growth, and crop yields can be dramatically reduced. There are many ways of providing extra water, but the most efficient methods supply water very close to plant roots by using buried drip tubes, thus reducing water loss by evaporation. Well-designed irrigation systems provide water at the optimum times during crop growth, and avoid both under- and over-irrigation. Agriculture accounts for 70% of water withdrawals worldwide and water can, in some areas, be the major limitation to productivity.
It should be noted that there is no widely agreed definition of what constitutes abandoned land; indeed many can see social or environmental benefits in land that others would deem abandoned. Generally, abandoned agricultural lands acquire more value as native ecosystems as time since abandonment goes on. Thus, the most available lands for agricultural development are those that have been recently abandoned.
Reclaimed
Reclaimed land includes previously abandoned or degraded land that is brought back into agricultural use. It includes large spoil heaps (refuse materials from mining), which can be contoured and planted with appropriate pioneer species. In some cases, land can be reclaimed from the sea, as in the Netherlands.
26 | 2 Important concepts
Pesticides and herbicides
Pesticides are chemical compounds used to protect crops from weeds and pests, including insects and other herbivorous organisms, microbial diseases and viral infections. Herbicides are pesticides used to control weeds that compete with a crop for light, water and nutrients.
Although producing and applying these chemicals requires energy, these energy costs are much lower than for tillage and fertilizer application. Also, protecting crop yields by using these chemicals avoids the need to plant additional acreage. Some pesticides and herbicides can be toxic to humans and other organisms, so they must be used with care. Attempting to control the growth of pest organisms at a large scale invariably gives rise to the selection of variants that are resistant to the control method. As a result, continuing innovation and improved pest control management schemes are required to provide effective pest control. Many of the more modern pesticides and herbicides have much lower usage rates and much lower toxicity than earlier chemicals. The advent of genetically modified (GM) crops that enable the use of modern herbicides or that mitigate the use of some of the older, more persistent pesticides, have also contributed to more effective pest management.
Crop rotation
The practice of periodically alternating the type of crop grown on a field is known as crop rotation. Farmers have long known that land maintains its fertility better if crops are alternated, as plants have different nutrient requirements and some (such as legumes) can increase soil nitrogen levels and reduce the need for synthetic fertilizer. Alternating crops with different root systems can improve soil structure and tilth. Crop rotation can also help prevent the build-up of pests and pathogens that can occur with continuous planting of a single crop. The annual rotation of maize and soybeans, for example, has been practised extensively and helps to control corn rootworm, though it has been replaced in some areas by the advent of rootworm-resistant corn varieties. Soil nitrogen and soil organic matter can be enhanced by planting crops such as clover, and incorporating them into the soil prior to planting follow-up crops such as wheat. Traditional crop rotations can be complex, involving numerous crops and periods of fallow (idle, non-planted fields) over several years, but high-intensity agriculture has tended to replace these extensive rotation systems with new agricultural practices, fertilizers and improved crop varieties.
Intercropping
Intercropping is the practice of growing two or more crops together. It may be used, for example, to provide protection for a crop that takes time to establish. Crops must be chosen carefully to reduce competition and minimize management costs. Owing to the complexity and costs involved, intercropping has had only limited application in modern agriculture.
Harvesting
To accomodate the multi-year growth period required in plantation crops such as trees, harvesting can be staggered by location so that any given plot of land might not be harvested for many years. When crop rotation is practised, differential timing of harvesting will take place depending on the rotation scheme, e.g. one season may be fallow with no crops harvested. Otherwise, harvesting takes place one or more times per year, depending on growth cycle and environment. Some crops, such as sugarcane, are harvested ‘fresh’ and processed immediately. More typically, crops are allowed to senesce, cease production and dry (partially or almost completely) in the field prior to harvesting. This minimizes the energy costs of harvest by reducing the weight of water transported from the fields while maintaining the solid contents of the plants. A number of plants considered for energy production are perennial grasses with rhizomes (subterranean plant stems). For these plants, field-drying also allows nutrients such as nitrogen to be translocated into the rhizomes where they will be stored over the dormant season and used again in subsequent growing seasons. This reduces the need for fertilizers.
Coppicing
Coppicing is a method of producing many stems from a single tree, by cutting young trees repeatedly to near ground level every three to eight years. A coppiced tree produces numerous stems that can be harvested repeatedly without replanting. Numerous variants exist that allow for differing intensities of harvest.
Machinery
Modern, high-yield agriculture is highly automated and requires expensive machinery for tilling, planting, irrigating, fertilizing, applying pesticide and harvesting. Increasingly, so-called precision agricultural practices are being used. These involve global positioning devices and sensors to guide machinery able to apply fertilizer and pesticides in amounts tailored to each crop and soil, at resolutions of a few meters. Machinery allows significant labour productivity: a large, modern combine harvester can harvest maize at the rate of almost 10 hectares per hour. Co-evolution of genetics, agricultural practices and machinery have driven agricultural productivity to its current state of development, and there is still scope for improvement.
2 Important concepts | 27
Plant functional features
Plants can be grouped in various ways, including by morphology and physiology. Some useful groupings are discussed below. They are not mutually exclusive, but characterize different aspects of a plant’s growth, metabolism or constitution. For instance, soybean is an annual, herbaceous, nitrogen-fixing plant that uses the C3 metabolic pathway for photosynthesis; switchgrass is a perennial, herbaceous, non-nitrogen-fixing plant that uses the C4 metabolic pathway.
Life cycle
AnnualAnnual plants complete their life cycle within a single 12-month period. They are therefore sown, and later harvested, every year. This requires recurrent ground preparation, fertilizer application, and weed and pest management. With some annual crops, more than one cycle of growth can be accomplished within a year in suitable climates. ●● Examples – maize, rice, wheat●● Input levels – high
Biennial
The least frequent type of crop, biennial plants normally take two years to complete their life cycle. The first year is devoted to growing leaves, roots and stems. When colder months arrive, the plant becomes dormant. Some biennials require this period of cold before they can flower. During the following spring and summer, the biennial plant grows rapidly, ultimately producing flowers and seeds before dying off.
●● Examples – sugarbeet, onion●● Input levels – high
Perennial
Perennial crops live for a number of years – even for centuries (many tree species) or occasionally millennia (bristlecone pine). In moist tropical environments, growth is possible throughout the year but in colder or drier places perennial plants use various strategies to survive winter or the dry season. Trees have woody aerial parts (buds on branches and stems) from which growth continues when conditions are suitable. Other plants die back to underground organs (roots or underground stems) during the off-season. As perennial crops are only replanted after a number of years (the exact time varies widely between species), the cost and overall environmental impact of tillage and planting are lower than for annual crops.
●● Examples – sugarcane, oil palm, jatropha, willow, miscanthus, switchgrass
●● Input levels – generally lower than for annual crops
Not all plants can be exclusively categorized as annual, biennial or perennial, as the life cycle of some species is dependent on climatic conditions. Breeding strategies have also been employed to alter the life cycle of some species. There are wild soybean lines that are perennial, for example, but soybean is grown as an annual in commercial agriculture.
Photosynthetic carbon fixation pathways
All plants grow by capturing atmospheric carbon dioxide. Energy from sunlight is harnessed to convert carbon dioxide and water into carbohydrates (a store of chemical energy) and structural components. The annual cycles of carbon dioxide exchange into and out of the oceans and land are enormous: approximately 770Pg (billion tonnes) of CO2 are released to the atmosphere from the land and oceans, and an additional 29Pg of CO2 from fossil-fuel burning and man-made land-use changes. These releases are not quite compensated by the approximate 790Pg of CO2 that are absorbed by vegetation and the oceans[5] (see Figure 2.2). The yearly excess of CO2 introduced into the atmosphere has given rise to increases in atmospheric CO2 concentrations from about 315 parts per million (ppm) in 1960 to almost 400ppm today, with worrying implications for global warming. The importance of photosynthesis can be readily seen in the atmospheric record as yearly oscillations of the CO2 concentration. It reaches a minimum in the northern spring and summer and a maximum in northern fall and winter: as vegetation, which is predominantly located in the northern hemisphere, starts growing and fixing CO2 in the spring, and then annual vegetation dies back and releases CO2 via decomposition in the fall and winter [6]. Agriculture contributes a noticeable (Figure 2.1) and growing (Figure 1.10) proportion to CO2 exchange dynamics.
There are three metabolic pathways for carbon fixation that provide different responses to the environment (solar radiation, moisture, temperature, atmospheric CO2 concentrations). As a result, plants can adapt to a wide range of growing conditions throughout the world.
C3
This is by far the most common carbon fixation pathway, found particularly (but not exclusively) in plants of temperate regions. It is called C3 because the initial molecule formed on capture of CO2 has three carbon atoms. During periods of light, plants absorb CO2 directly through open stomata (leaf pores); the open stomata also allow water loss. As a result, these plants can have lower water-use efficiencies compared with plants that use different photosynthetic mechanisms. ●● Examples – rice, wheat, potato, soybean, most trees
C4
The C4 pathway may have evolved as a mechanism to help plants survive in conditions of drought or high temperature. In these plants, the first product of CO2 fixation has four carbon atoms, and the mechanism of this fixation is more efficient than for C3 plants. In effect, C4 plants concentrate CO2 internally – using energy to do so – and then incorporate it into other products using mechanisms similar to C3 plants. As a result, C4 plants tend to have higher rates of photosynthesis and water-use efficiency than C3 plants in warm climates, and can assimilate CO2 at significant rates while losing less water than C3 plants. This group includes some of the most productive tropical crops. ●● Examples – maize, sugarcane, sorghum, miscanthus
28 | 2 Important concepts
CAM
Some plants living in arid environments have evolved a photosynthetic pathway called crassulacean acid metabolism (CAM). This metabolism operates in four stages and involves some enzymatic pathways that are similar to C4 metabolism. The difference is that, to conserve water, the stomata of CAM plants remain closed during the heat of the day. They open during the night, which allows carbon dioxide to diffuse into the leaves, to be converted into a four-carbon acid, and then stored until daybreak. Then, during the day, the four-carbon acid is broken down and CO2 is released internally to be converted to useful products while light energy is available. CAM plants can have greater water-use efficiency than either C3 or C4 plants.●● Examples – agave, cacti, pineapple
Nitrogen fixation
Some plants have a symbiotic relationship with bacteria that transform atmospheric nitrogen into a form that plants can use. Legumes (which include the bean family) are widely grown N-fixing agricultural crops, and are often used in crop rotations. Nitrogen fixation also occurs in free-living bacteria called diazotrophs that are most commonly found in soil, but are sometimes found in plant tissue. ●● Examples – soybeans, trees from the genera
Alnus and Acacia
Plant cell walls
Most of the bulk of biomass is actually plant cell walls, which serve as structural material. Other components of plant cells used for bioenergy, such as sugars, starch, oils and so on are storage reserves for the plant. Details vary by species, but in general, mature plant cell walls consist of
a middle lamella (the area between adjacent plant cells), a primary wall and a secondary wall. The major components of the cell walls, as shown in Figure 2.3, are carbohydrates (cellulosic microfibrils and hemicelluloses) and a matrix of cementing material – usually pectin in primary walls and lignin (a complex polymer that gives strength and rigidity) in secondary walls. (These compounds are described below.) The secondary cell walls only develop once the cells have stopped dividing and expanding, and are thus seen in non-growing tissues like the wood of trees. Secondary cell walls make up the majority of biomass, with cellulose, hemicellulose and lignin the predominant constituents.
Woody plants
Woody plants – trees and shrubs – are generally richer in lignin and hence lower in carbohydrate than other plants. At the end of the growing season the trunk (composed of cellulose, hemicellulose and lignin) persists. After winter, or at the end of the dry season, new growth is initiated from the over-wintering tissues (buds) within the persistent aerial stem and branches. Woody plants grow prolifically over large areas of the earth and have traditionally been – and continue to be – a significant source of biomass.●● Examples – poplar, willow
Herbaceous plants
Herbaceous plants are generally richer in cellulose than in lignin. At the end of the growing season, their aerial parts partially or completely decay. Herbaceous plants can be annual, biennial or perennial. In the case of biennials and perennials, the root system overwinters and produces new shoots when conditions are suitable for growth.●● Examples – switchgrass, maize
� Figure 9The Carbon Cycle
BP Biomass HandbookFigure 9 (5 September 2013)Draft produced by ON Communication
Photosynthesis
Sunlight
Organic carbon
Auto andfactory
emissions
OceanexchangePlant
respirationAnimal
respiration Soil
respiration
Dead organismsand waste products
Fossils and fossil fuels
Rootrespiration
Oceanuptake
Decayorganisms
Carbondioxide
Figure 2.2
Schematic diagram of the carbon cycle. Carbon dioxide in the atmosphere is taken up by plants and converted, using solar energy through the process of photosynthesis, into organic compounds. Some of these organic compounds are then used as food by herbivores and humans, whose respiration returns CO2 to the atmosphere. CO2 is also returned to the atmosphere when carbon compounds are burned as fuel. Fossil fuels were formed as a result of photosynthesis millions of years ago[7].
2 Important concepts | 29
Figure 2.3
Schematic diagram representing the main components of plant cell walls[8].
Bioenergy crop
Plant cells
Plant cell wall
Cellulosemicrofibril
LigninHemicelluloseCellulose
Sugar molecules
Glucose
Plant composition and products
The various biomass feedstock crops provide a range of raw materials from different parts of the plant. These materials may be used by the plant to store and transport energy internally, or as food stores (for seedling growth) in seeds, or as structural components (giving plants their stature, shape and resilience).
Starch from grain crops
Starch is a polymer of glucose, a six-carbon sugar, found in high abundance in grain crops. It has a wide variety of food and material uses, and is particularly important for fermentation into bioethanol. Starch is relatively easily converted to glucose in an enzymatic process, and the glucose is subsequently fermented by yeast into ethanol. Corn starch, for example, is the primary source of ethanol produced in the US.
Oil from seeds
Many crops have oil-rich seeds containing large quantities of oil in the form of triglycerides, which are glycerol molecules with three fatty acids (each typically having 16–18 carbon atoms) attached. These oils (also known as lipids or fats) are liberated by crushing the seeds, and their extraction is enhanced by the use of solvents. The triglycerides are very energy rich – approximating to the energy content found in fossil fuels – and can be converted into biodiesel molecules by reaction with alcohols or into renewable diesel (a form of biodiesel) by treatment with hydrogen.
Soluble carbohydrates
Soluble sugars are small, usually sweet, molecules found in plants. They include fructose, sucrose, glucose, mannose and a large variety of less abundant sugars. They have long been used in the production of alcoholic beverages and are readily fermented into bioethanol. Sucrose (a major component of sugarcane), for example, is obtained at a processing plant by crushing the sugarcane stem and washing it successively with hot water. The resulting sucrose solution is then fermented by yeast to produce an aqueous solution of ethanol that is in turn distilled to provide nearly pure ethanol. Sucrose is known as a disaccharide, because it is composed of two sugar molecules (one of glucose and one of fructose) linked together.
Structural polymers
The stems of herbaceous plants and the trunks of trees are strengthened by cellulose, hemicellulose and lignin. These large molecules interact and intertwine with each other to form lignocellulose. It is this lignocellulose that provides plants with their structural integrity, and which is the major source of carbon used for combustion (for example when burning wood). It is also a major target for technological approaches that seek to deconstruct lignin into its components for other uses in fuels and chemicals.
●● Cellulose Cellulose, found in the primary cell walls of all
green plants, is one of the most abundant organic compounds on earth. It is a large structural biopolymer composed of glucose molecules; it differs from starch in the way the molecules are linked. This configuration results in a tight crystalline structure (due to extensive hydrogen bonding), which makes it ideal for paper manufacture; vast quantities of it are used in the global pulp and paper industry.
30 | 2 Important concepts
It is also the primary constituent in cotton. However, because of its structure and close association with hemicellulose and lignin, it is more difficult to decompose into its constituent glucose molecules to facilitate fermentation than is starch. It can be decomposed by chemical treatment or by enzymatic action, usually using enzymes derived from fungi that live on cellulose in nature.
●● Hemicellulose Hemicellulose is another constituent of plant cell
walls. It is a cross-linked polymer made up of a variety of sugars, predominantly xylose, a five-carbon sugar. While cellulose is a complex of a single type of six-carbon sugar (glucose), hemicellulose consists of both five- and six-carbon sugars. The balance of these sugars varies with the particular species, and hemicellulose can contain a variety of different five- and six-carbon sugars. When rendered into its constituent sugars, the
resulting mixture of sugars is more difficult to ferment than the glucose derived from cellulose, and a number of thermochemical and enzymatic approaches are being tested to facilitate the process.
●● Lignin Lignin is a significant constituent of both woody
and herbaceous plants, conferring strength, water resistance and resistance to rot. Lignin’s properties are derived from its complex molecular structure (it is an amorphous, cross-linked, hydrophobic biopolymer). It is typically found with cellulose and hemicellulose in plant cell walls, where it helps to bind cellulosic fibres together and provides structure. It also defends the plant physically against microbial and fungal attack. It can be converted by thermochemical means to other compounds, or can be burned to generate heat and electricity.
Metrics of biomass productivity
There are various ways of measuring the productivity of crops and their impacts on ecosystems.
Net primary productivity, or NPP, is the projected total an-nual amount of plant growth. It is a net rather than a gross figure because plants use some of the captured energy for their own metabolism. NPP is measured in terms of mass per area per time unit, commonly grammes of carbon per square metre per year (gC/m2/yr). NPP can be used to esti-mate the potential biomass productivity of, for example, abandoned crop or pastureland. Estimated above-ground NPP for world ecosystems are useful in estimating overall biomass potential on a global scale. As such, NPP is often used by ecologists, and is inherent in the land productivity estimates in Figure 2.1
Yield is a term commonly used in agriculture. It is usually given as the amount of a crop end-product produced in a defined area, usually for a period of one year or one growing season. This is easily defined for an annual crop, but perennial crops can increase in yield to reach a stable plateau, often followed by gradual decline. In these cases, it is useful to consider an annualized yield based on production throughout the growing season(s).
Many units are used throughout the world for measuring yield: bushels (bu), tonnes, tons, kilograms and pounds for weight; hectares and acres for area. It is also common to report yields at particular levels of dryness. Fresh weight (as harvested), for example, is commonly used for sugarcane yields (reported in tonnes per hectare); maize yields are usually reported in bushels (56 pounds) of corn at 15.5% moisture content per acre; and biomass yields are commonly referenced as bone dry (or oven dry) tonnes per hectare. It is extremely important to be very clear regarding units of yield, as apparently similar units can give very misleading results. As the dry matter content is most useful for consideration of biomass potential and uses, tonnes per hectare (t/ha) of dry matter will be used in this handbook as the standard yield metric unless otherwise specified.
Some useful units and conversions for yield
1 hectare = 10,000m2 = 2.47 acres1 tonne = 1 metric ton = 1Mg = 1,000kg = 1.1023 tons = 2,205 pounds1 litre = 0.26 US gallons or 0.22 imperial (UK) gallons
Examples●● 1 bushel corn (15.5% moisture) = 21.5kg at 0% moisture●● 160bu/acre (15.5% moisture) = 8.5 tonne/ha (dry weight)
= 6.1 tonne starch/ha (at 72% starch content)
●● 1 tonne of sugarcane (70% moisture) = 300kg at 0% moisture●● 70 tonnes/ha (fresh weight) = 21 tonne/ha (dry weight)
= 10.5 tonne sucrose/ha (at 50% sucrose content)
2 Important concepts | 31
Energy issues and greenhouse gas accounting
A primary motivation for using biomass for energy is that plants ‘fix’ carbon dioxide from the air. Although this CO2 is subsequently returned to the atmosphere when the biomass is used as fuel, there is zero net GHG impact. This simple fact, however, is complicated by the many different energy requirements for agriculture, all of which can contribute to energy use and GHG emissions; it is therefore important to look at the broader picture.
Greenhouse gases*
The earth is covered with a blanket of atmospheric gases. Some of the gas molecules in the atmosphere absorb outgoing long-wave infrared radiation and re-radiate this heat back to the surface, like the glass panels of a greenhouse (hence the term greenhouse gases or GHGs). This keeps the earth’s surface warmer than it would be without such a protective layer. Important GHGs include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), water vapour and fluorinated gases (CFC, HFC, PFC and SF6). These gases – with the exception of fluorinated gases – exist naturally, but human activities (such as burning fossil fuels, deforestation, and large-scale agriculture and animal husbandry) have increased GHG emissions. As a result, the concentration of atmospheric GHGs is increasing at an unprecedented rate. In terms of bioenergy crop production, the crop plants take up atmospheric CO2 as they photosynthesize and grow. Some CO2 is released through plant and soil respiration, from the soil during tillage, and when energy is used for farming operations. In the case of perennial feedstocks, carbon removed from the atmosphere can be stored in the short and long term, because below-ground biomass is not disturbed by annual tillage and can instead be incorporated into soil carbon pools.
Energy requirements for crop production
Bioenergy crops capture solar energy that can be processed for use as fuel; however, producing such crops also
requires other energy inputs. Energy inputs for bioenergy production include the fuel needed for tillage, harvesting, processing and transporting the crop. The energy needed to manufacture fertilizer, herbicides and pesticides should also be taken into account, as should the energy needed to convert the harvest to biofuel or bioenergy. Energy inputs will vary depending on the crop. Representative energy needs for maize agricultural operations are shown as examples in Table 2.1.
Most harvesting operations consume significant amounts of energy; chipping wood is a particularly energy-intensive operation. Compared with the amount of carbon and energy harvested (e.g., the energy content of the maize harvested at an average yield of 5.2 tonnes/ha is greater than 90,000 MJ/ha), each operation has a relatively small impact, but taken together can aggregate to 10–15% of the total energy harvested. While the application of fertilizer does not require much energy, its production requires significant energy inputs.
Life cycle analysis*
This type of analysis was devised to assess holistically the impacts (often in terms of energy use and GHG emissions) associated with all stages of a product’s life. As applied to biofuel and bioenergy crops, this analysis helps to ensure that the total GHG emissions associated with the production and use of the bioenergy crop are lower than from an equivalent amount of energy derived from fossil sources.
Energy units
There are many units used to describe energy. These include calories, British thermal units, kilowatt-hours etc. The standard international unit for energy is the joule. This is a very small amount of energy, and so it is often useful to refer to large quantities, such as 1 million joules, or 1MJ. Some standard conversions and relative numbers are provided on pages 6 and 7.
Agricultural operation Energy(MJ/ha)
CO2 emissions(kg CO2eq/ha)
Tillage PloughingDisc harrowingSeedbed preparationCultivation
780210200200
62171616
Planting Corn plantingGrain drill planting
180140
1411
Chemical inputs Nitrogen fertilizer manufacturingFertilizer applicationPesticide applicationLime application
8,70060
10060
4804.88.14.8
Harvesting Corn grain SoybeanSwitchgrass (initial year)Switchgrass (after establishment)Trees (felling and skidding)Trees (chipping)
1,2801,210
260330
9,15016,700
100982126
7401,300
Post-harvest
Grain dryingStover mowingStover baling
2,810200140
1901711
Table 2.1
Representative energy needs in megajoule per hectare (MJ/ha) and CO2 emissions in kilograms of carbon dioxide equivalent per hectare (kg CO2eq/ha) for agricultural operations based on maize agriculture and for operations with other crops. Not all operations will be used for any given production strategy. CO2 equivalents represent all GHGs involved, taking into account their different global warming potential and different atmospheric residence times, and substituting the amount of CO2 that would correspond to the same impact [9, 10]. Nitrogen fertilizer energy need is based on 150kg/ha fertilizer application.
* For further reading, please see references on page 32: Greenhouses gases [11,12], Life cycle analysis [13,14].
32 | 2 Important concepts
Chapter references
[1] Ramankutty, N. & Foley J. A. (2010), ‘ISLSCP II historical croplands cover, 1700-1992’, in Hall, Forest G., G. Collatz, B. Meeson, S. Los, E. Brown de Colstoun & D. Landis (eds), ISLSCP initiative II collection. Data set. Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, TN, US. Available from: http://daac.ornl.gov//ISLSCP_II/guides/historic_cropland_xdeg.html [accessed February 2014].
[2] Haberl, H. et al. (2007), Quantifying and mapping the human appropriation of net primary production in earth’s terrestrial ecosystems, Proceedings of the National Academy of Sciences, vol. 104, no. 3, pp. 12942–12947.
[3] Bajzelj, B. (2013), University of Cambridge, Sankey diagram based on underlying data published by Haberl, H. et al. (2007), Quantifying and mapping the human appropriation of net primary production in earth’s terrestrial ecosystems, Proceedings of the National Academy of Sciences, vol. 104, no. 3, pp. 12942–12947; and by Ramankutty, N. et al. (2008), Farming the planet: 1. Geographic distribution of global agricultural lands in the year 2000, Global Biogeochemical Cycles, vol. 22, no. 1, pp.1–19.
[4] US Department of Agriculture, Natural Resources Conservation Service, National soil survey handbook, title 430-VI, Part 622 – Interpretative groups. Available from: http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/?cid=nrcs142p2_054242 [accessed July 2013].
[5] Denman, K. L., et al. (2007), ‘Couplings between changes in the climate system and biogeochemistry’, in Solomon, S. et al (eds.) Climate change 2007: the physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK and New York, US. Available from: http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch7.html [accessed July 2014].
[6] Tans, P., NOAA/ESRL ( www.esrl.noaa.gov/gmd/ccgg/trends ) and Keeling, R., Scripps Institution of Oceanography ( scrippsco2.ucsd.edu ).
[7] Adapted from the University Corporation for Atmospheric Research, Kid’s crossing, Cycles of the earth, Carbon cycle. Available from:
http://eo.ucar.edu/kids/green/cycles6.htm [accessed July 2013].
[8] US Department of Energy, Genomic Science Program. Available from: http://genomicscience.energy.gov [accessed February 2014].
[9] Adler, P. R., Del Grosso, S.J. & Parton, W.J. (2007), Life cycle assessment of net greenhouse gas flux for bioenergy cropping systems, Ecological Applications, vol. 17, no. 3, pp. 675–691. Available from: http://www.esajournals.org/doi/pdf/10.1890/05-2018 [accessed February 2014].
[10] West, T. O. & Marland, G. (2002), A synthesis of carbon sequestration, carbon emissions, and net carbon flux in agriculture: comparing tillage practices in the United States, Agriculture, Ecosystems & Environment, vol. 91, no. 1, pp. 217–232. Available from: http://web.ornl.gov/info/ornlreview/v40_3_07/documents/article17web_West_Marland_ag_net_flux.pdf [accessed February 2014].
[11] US Environmental Protection Agency, Overview of greenhouse gases. Available from: http://www.epa.gov/climatechange/ghgemissions/gases.html [accessed July 2014].
[12] Solomon, S. et al (eds.), Climate change 2007: the physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK and New York, US. Available from: http://www.ipcc.ch/publications_and_data/ar4/wg1/en/contents.html [accessed July 2014].
[13] US Environmental Protection Agency, Life cycle assessment (LCA). Available from: http://www.epa.gov/nrmrl/std/lca/lca.html [accessed July 2014].
[14] International Organization for Standardization (2006), ISO 14040:2006 – Environmental management – Life cycle assessment – Principles and framework. ISO, Geneva.
Bioenergy currently provides around 10% of the total global energy supply. Liquid biofuels account for less than 3% of transport fuel globally, but new technologies are being developed to convert more types of biomass to liquid fuels, driven partly by government policies to increase the use of renewable energy.
Estimates of potential annual bioenergy production range widely due to differing assumptions used in an inherently complex analysis. Carefully weighing the assumptions, estimates suggest that 150–200EJ/yr from biomass could be available by 2050 – which would represent a significant energy source and a significant increase from the current biomass utilization of about 50EJ/yr.
To realize the potential of bioenergy, the productivity of energy crops will have to increase. This will require improvements in both agricultural techniques and plant breeding. Given the great improvements that have been made to important food crops such as corn and soybean, it is reasonable to expect similar progress with biomass crops.
Improvements will also be needed in the processes used to convert biomass into fuel. Important current research is being conducted on a wide array of approaches for converting abundant but complex lignocellulosic materials from biomass into more useful fuels.
34
3 Bioenergy potential | 35
3 Bioenergy potential
Current bioenergy production
Bioenergy currently provides around 10% of the total global energy supply, equivalent to around 53EJ/yr as shown in Table 3.1. Oil provides almost a third of global energy, followed by coal and natural gas. Bioenergy supply is greater than the total of other non-fossil energy supplies and, as discussed earlier, is expected to grow at greater than 3% per year to 2035. Global estimates of final energy consumption are shown in Table 3.2. Almost half of the total consumption goes to heat. The significant differences between supply and consumption in Tables 3.1 and 3.2 are due to inefficiencies in converting the primary energy supplies into heat, transport fuels and, most particularly, electricity.
Table 3.1 Global energy supply in 2010 shown in EJ[1]
Primary energy supply 2010 532EJ Share of total supplyOil 172 32%Coal 146 27 %Natural gas 114 21%Bioenergy 53 10%Nuclear 30 6 %Other* 17 3 %
* Other includes hydro, geothermal, solar, wind and marine.
Table 3.2 Uses of energy supply in 2010 shown in EJ[1]
Total final consumption 363EJ Share of total final consumption
Heat 166 46%Transport 100 27%Electricity 64 18%Other* 33 9%
*Other covers those fuels that are used as raw materials and feedstocks in different sectors, and are not consumed as a fuel, or transformed into another fuel.
Table 3.3 shows a breakdown of bioenergy use by sector in 2010. Traditional use (open fires for cooking and heating in developing countries) accounts for almost 60% of bioenergy use, though there is a shortage of reliable statistics.
In Europe, where heat and power production constitute large uses of bioenergy feedstocks, biomass accounted for two thirds of primary renewable energy production in 2009. The bioenergy imported by Europe includes wood biomass sourced through forestry or dedicated woody crops, ethanol and biodiesel. Globally, biomass is the third largest contributor to renewable electricity after wind and hydro-electric power.
Transport accounts for around 100EJ of final energy consumption, most of it in liquid form, which constitutes the major fraction of overall liquid fuel use. There is a widely recognized need to develop low-carbon fuels (including biofuels) for transport. Biofuels currently account for less than 3% of transport fuel globally, but that percentage has grown over recent years.
Table 3.3 Bioenergy use by sector in 2010 shown in EJ [1, 2]
Bioenergy use by sector in 2010 (EJ)
Notes
Traditional 31.4 Small-scale use for heat and cookingHeat 12.0Transport 2.5 Approximately 100 billion litres of biofuels
were produced in 2010Power 4.6 331TWh (1.19EJ) of electricity was
produced from the 4.6EJ of bioenergy used in power generation
Other* 3.0 Total 53.5
*Other covers the energy used in production and processing industries, e.g. biomass farms, ethanol and biodiesel plants etc. and the losses in converting primary energy into final consumption form, e.g. gasification plants, ethanol and biodiesel plants etc.
There are several routes by which biomass can be converted into usable energy sources, as shown in the figure inside the front cover of this handbook. These routes have varying degrees of efficiency and are the subject of continuing research and development. Ethanol from sugar and starch, for instance, is produced at >90% of its theoretical efficiency, and esterification and hydrogenation of fats and oils are similarly efficient. Conversion of cellulosic materials to liquid fuels, however, is currently less efficient and has higher capital costs. Continued improvement in the efficiency and cost of alternative conversion methods will be required for these uses of biomass to be commercially relevant.
North America is currently the largest producer and user of biofuel. This development has been driven by the use of corn for ethanol production as a transport fuel and has allowed the US to overtake Brazil as the largest global producer of liquid biofuels. Still, in 2010, biofuels accounted for only 5% of the energy used for road transport in the US, while in Brazil this was closer to 23% [2].
This chapter discusses the current and possible future bioenergy production levels and provides information on the technological developments needed for realizing the potentials.
36 | 3 Bioenergy potential
Many of the developments in the use of bioenergy have been driven by government policies promoting renewable domestic energy for environmental and political reasons. In Europe, the use of bioenergy was driven by the European Commission’s Renewable Energy Directive (RED) until late 2012; in the US, government policy mandates the use of ethanol in gasoline under the Renewable Fuels Standard (RFS). A combination of subsidies for ethanol producers and tax incentives for flex-fuel vehicle purchases has encouraged bioethanol use in Brazil. China has also
recently mandated greater biofuel production, and the United Nations has recognized the economic and environmental potential of new biomass agriculture and bioenergy industries.
Multinational developments in bioenergy have led to expansion in international markets as shown in Figure 3.1. Solid biomass and vegetable oils are being shipped from North and South America, Africa and South-East Asia to Europe, which is currently the largest importer of bioenergy products (for use in many sectors).
Global potential bioenergy production
Biomass potential is defined as the energy available in harvested biomass. It therefore depends on both the level of biomass production (the gross yield of dry matter per unit area) and the amount of energy assimilated (the energy value of that dry matter) during plant growth. There is no single method or accepted approach for assessing biomass potential. Determining biomass potential depends on the level of environmental impact, land-use change, water availability, population and dietary changes assumed in an individual study. The more limitations accepted in a study, the lower the predicted biomass potential. A general hierarchy of biomass potential opportunity is often used: theoretical, technical, economic and realistic as illustrated in Figure 3.2.
The theoretical potential of bioenergy – whether used for heat, power or transportation – depends on just two fundamental factors: the primary energy production of the
biomass source and the efficiency of converting this into usable energy. Theoretical potential can therefore ignore competing land use and socioeconomic constraints, and gives estimates that are not particularly helpful for policy decisions. The technical potential is the harvestable biomass as limited by ecological, land area, topographic and agro-technological constraints. The economic potential is available biomass that meets the demand for biomass feedstock markets at a commercial price. Realistic potential is the amount of biomass that could be produced without negative social, environmental or economic impacts. Realistic potential also takes into account technological and market development issues. Figure 3.2, on the next page, depicts the effect of these increasing constraints when trying to calculate potential biomass production.
� Figure 3.2
BP Biomass HandbookFigure 3.2 (18 November 2013)Draft produced by ON Communication
Argentina
WesternEurope
Eastern Europeand Russia
Australia
JapanfromUS
fromSouthAmerica
Malaysia andIndonesia
South Africa
Middle East
Canada
United States
Brazil
Ethanol Vegetable oils and biodieselWood pellets
Figure 3.1
Map of world biomass shipping routes in 2011. Routes for ethanol, wood pellets and vegetable oils and biodiesel converge significantly on Western Europe [3].
3 Bioenergy potential | 37
Figure 3.2
Diagrammatic representation of the hierarchy of theoretical, technical, economic and realistic potential of biomass. The large theoretical potential shown at the base of the pyramid reduces as more constraints are included in calculations. Realistic potential is many times smaller than theoretical potential, and is difficult to quantify because many of the constraints are either abstract or hard to measure.
The IEA predicts that the world’s total energy demand will reach somewhere between 600 and 1,000EJ by 2050. Different scenarios for bioenergy availability predict that biomass could supply none of this energy, or all of this energy, depending on assumptions relating to regional diets, agricultural management, the type of land used for energy crops, land conservation policies and more. Examples of estimated land areas that could be used for biomass production are shown in Table 3.4, below.
A recent report from the UK Energy Research Centre [4] classified these varying estimates according to the following groups:
Low band (0–100EJ/yr by 2050)
These studies assume little or no availability of land for energy crop production (less than 400 million ha globally), together with a large population eating a meat-rich diet. Environmental protection measures are seen to limit the growth of cropland, and in some cases biomass residues are not considered. Agricultural systems are assumed to be generally low-input and extensive, with little or no increase in yields.
It is important to note that current bioenergy production, which includes wastes and residues, is in the middle of this range. Therefore, even the higher level of availability suggested by the scenarios in this band are likely to be achievable in practice with modest increase in agricultural yields in areas with the greatest potential.
Mid (low) band (100–300EJ/yr by 2050)
These studies generally assume that increases in agricultural yields keep pace with population growth and increasing demand for meat (although there are various ways of combining these factors to achieve the same overall result). Some studies assume conversion of grassland areas to bioenergy plantations. Biomass residues are also included.
Mid (high) band (300–600EJ/yr by 2050)
These studies generally make similar assumptions to those described in the mid (low) band description, but also assume that increasing yields can free up areas previously used for food production for bioenergy crops, with ~500–1,500 million ha used for bioenergy production.
High band (>600EJ/yr by 2050)
These are typically based on theoretical potentials and are only achieved with relatively low food demands (e.g. dietary shifts, increased agricultural production and/or low population growth). These estimates are also characterized by high levels of agricultural inputs (fertilizer, irrigation, energy) and the use of native and previously uncultivated areas for bioenergy production. Residues suitable for bioenergy production are also included. These studies assume that more than 2,500 million ha are used for bioenergy production globally. High-band estimates are also associated with the largest negative impacts on ecosystem services (such as biodiversity and soil and water quality) and are generally not considered the best path to sustainable energy. High-band estimates provide upper bounds for estimates of bioenergy potentials, but mid- and low-band estimates are more widely viewed as reasonable ranges for bioenergy production.
� Figure 11Hierarchy of theoretical, technical, economic and realistic potential of biomass
BP Biomass HandbookFigure 11 (5 September 2013)Draft produced by ON Communication
Social impactsAvailable technology
Market developmentsEnvironmental impacts
Economic impacts Realistic potentialMinimizes impacts.
Economic potentialAvailable biomass that meets market demands at the intersection of supply
and demand.
Technical potentialHarvestable biomass limited by ecological, land-area,
agro-technological and topographical constraints.
Theoretical potentialIgnores competing land use and socioeconomic or political constraints.
Can result in large potential values that are not helpful for policy decisions.
Band Example study Estimated land use(million ha)
Band estimate (EJ)
Low Hoogwijk et al. 2003 [5] 390 – abandoned crop land 0 –100
Mid (low) Beringer et al. 2011 [6] 140–450 – from new plantations 100 – 300
Mid (high) Hoogwijk et al. 2005 [7] 1,300 – abandoned agricultural land 300 –600
High Smeets et al. 2007 [8] 4,000 – converted from pasture >600
Table 3.4
Estimates of the amount of land that could be used for biomass in the future. Low estimates (0 –100EJ/yr) envisage less than 400 million ha under biomass crops; mid-estimates (100–600EJ/yr) envisage new plantations or the use of abandoned agricultural land; high estimates (>600EJ/yr) envisage 4,000 million ha converted from pasture used for growing biomass crops.
38 | 3 Bioenergy potential
As illustrated in Figure 3.3, there is a wide range of estimates for the potential of bioenergy, depending on many different factors including crop yields, management, diet, population growth and conversion efficiencies. All of these factors will affect the amount of land available for biomass for energy production. In addition, the impacts of climate change on overall plant yields and the amount of land required for food are complex, poorly understood and are the subject of numerous investigations. A recent assessment of numerous global agro-economic models showed that there were large uncertainties in estimates and large differences between models and between different geographies. However, in general, these studies tend to indicate a negative impact on crop production and an increase in land use required for food crops under conditions of increased climate change. At the same time, proper choices of where and how to grow bioenergy crops produced model results indicating that impacts on food prices were much smaller for scenarios that included up to 100EJ of production from lignocellulosic biomass than for those scenarios where this energy was derived from high carbon fossil fuels [9–11].
It is clear that biomass offers an opportunity for energy production but there are many social, political, economic and environmental conditions that affect the scale of this production. Because none of these conditions are static, there is unlikely to be a definitive calculation for the amount that can be produced. Still, the international consensus summarized in the IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation (SRREN [12]) was that 100–300EJ/yr could be achieved from
biomass by 2050. This takes into account factors such as population, economic, technology, food, fodder and fibre demand, climate change, and nature preservation requirements. The 164 scenarios reviewed in SRREN point to the most likely range of 80–190EJ/yr in 2050.
An analysis completed as part of the Global Energy Assessment (GEA [13]) (conducted by the International Institute for Applied Systems Analysis) reports global technical resource potential in 2050 (160–270EJ/yr) stressing stricter constraints related to possible competing land demands, problems posed by possible deforestation, and water availability. Deployment levels for year 2050 were 145–170EJ/yr in the GEA.
Taken together, these estimates of approximately 150–200EJ/yr from biomass by 2050 would represent a significant fraction of the total projected energy usage of 600–1,000EJ/yr and a significant increase in current biomass utilization of approximately 50EJ/yr.
There is a wide range of dispersion and uncertainty in the complex analyses undertaken to date regarding global potential of biomass. Uncertain and variable impacts of climate change on weather patterns make any projections additionally uncertain and subject to controversy. As a result, while the total amount of energy that may be ultimately derivable from biomass remains difficult to estimate, the estimates that we do have suggest significant potential. This provides an incentive to develop additional bioenergy crops and, while expanding their use, to further develop the precision of our outlooks with empirical evidence to help better understand their ultimate potential[14].
Figure 3.3
Total technical bioenergy production potential in 2050 in EJ/yr, by Smeets et al. (2007) . Four different scenarios are modelled and represent the following assumptions (from left to right): rainfed mixed agricultural systems (including pastoral practice) with modern technological production, irrigated mixed agricultural systems with modern technological production, irrigated cropland with only confined livestock and modern technological production, and irrigated cropland with only confined livestock and newly innovated technology for crop production. All scenarios assume high feed conversion efficiency[8].
� Figure 3.4
BP Biomass HandbookFigure 3.4 (18 November 2013)Draft produced by ON Communication
World
North America
Caribbean andLatin America
1,548
1,273
610
367
89
162
234281
49
117
282
347
2
5
231 39
3975
168204
13
13 24
22
23 26 31 37
40 5593
114
28
15819429
83111
223269
19 25 30
2 2 2 2
WesternEurope
EasternEurope
Middle East andNorth Africa
Sub-SaharanAfrica
CIS andBaltic States
South Asia
East Asia
Oceania
Japan
Dedicated woody bioenergy crops on surplus agricultural land
Surplus forest growthAgricultural and forestry wastes and residues
3 Bioenergy potential | 39
How might this global potential be realized?
Figure 3.4
Land use in Brazil, in 2013. Sugarcane utilized approximately 9Mha of the 60Mha devoted to agriculture, or about 1% of the total land area[15].
� Figure 3.5
BP Biomass HandbookFigure 3.5 (21 November 2013)Draft produced by ON Communication
Sugarcane9Mha1%
Non-cane agriculture
51Mha 6%
Urban areasand other uses
38Mha 4%
Pastures198Mha23%
Cerrado and other non-forest vegetation200Mha24%
Forests354Mha42%
Because of the large number of potential species, adapted to a wide range of different conditions, bioenergy crops can be grown across most areas of the globe that are capable of supporting plant life. Details of which crops are suitable for production in different regions can be found in Chapter 6.
Ultimately, land is used for a variety of purposes and bioenergy crops will need to compete and coexist with these multiple uses. Brazil is a country that produces a large fraction of its liquid fuels from sugarcane, and demonstrates the types of choices that need to be made. Brazilian land use in 2013 is shown in Figure 3.4. It has grown its sugarcane crop from a small base to 9Mha today. In doing so, choices have been made to intensify cattle production on pasture, to modify requirements for growing sugarcane to be more environmentally sound, to require setting aside additional land whenever sugarcane acreage is increased, and to take steps to preserve forested areas.
Sugarcane is an example of a crop that has use as both food and fuel. Approximately half the sugarcane that is harvested is used to produce sugar, the other half to produce ethanol. Countries with significant acreage in multiple-use crops such as corn, wheat and sugarcane have significant ability to respond to unforeseen problems with production by shifting the ultimate use of these commodities.
In many parts of the world, agricultural production does not meet its full potential as illustrated in Figure 3.5, which shows estimated yield gaps throughout the world for maize, wheat and rice. Yield gaps can be quite extensive over large areas of the world; often less than 20% of the potential yield is produced due to local conditions. Constraints include access to technology, the most suitable cultivars or best practice; the cost of inputs; suboptimal growing conditions; lack of transportation infrastructure; and, in many cases, a lack of established markets to drive demand.
By growing a wider range of improved food crops with improved management, yields could be boosted substantially and the land area required for food production reduced. This approach, implemented by region according to the climate, soil and local economies, would also help address the inequity of global food distribution. Figure 3.5 provides a view of the substantial gains that could be derived from improved practices. Those areas with the lowest achieved yields could benefit most from adoption of modern agricultural techniques and strict attention to optimum nutrient and water utilization. The large areas associated with large yield gaps suggest that significant improvements in overall production can be obtained.
Different crops in different parts of the world will have different potentials for yield increases. For example high-yielding crops such as sugarcane, grown in optimal conditions in parts of the southern hemisphere, are already producing significantly higher yields than before; further yield increases are likely to be gradual. In contrast, the production of biomass and grain crops in the subtropics has greater potential, as production is generally still far below any theoretical maximum production or productivity thresholds.
In 2010, for example, average corn (maize) yields were 9.6t/ha in North America and 6.0t/ha in Europe; while Africa produced only 2.6t/ha[16]. Additionally, many of the crops most suitable for energy production have had scant attention paid to them, so there is every reason to expect significant improvements in yields with diligent application of modern practices.
While it is difficult to predict future crop productivity with any certainly, predictions can be made using a variety of approaches. As with potential land areas, yields can be theoretically, technically, economically or practically feasible. Unlike land, however, which is clearly limited and whose area cannot be significantly increased, the limits of crop productivity are far higher than current yields and are amenable to technological innovation. Intensive agriculture, focused on a few important crops, has seen dramatic improvements through combinations of agricultural practices, genetic advances and modern technology. An example of such improvement is shown in Figure 3.6, which plots US corn yields through time.
40 | 3 Bioenergy potential
Figure 3.6
Graph showing average US corn grain yields from 1866 in bushels/acre and kg/ha. Important developments in plant breeding provided improved yield potential, by allowing the switch from open pollinated varieties to hybrids with increasing sophistication. These improvements allowed increased planting densities, which, coupled with the use of nitrogen fertilizer, crop protection chemicals and mechanization, drove large yield improvements. More recently, genetic modification has continued to extend the yield limits. N.B. 1bu/acre (15.5% moisture) = 53kg (dry-weight)/ha[18].
Gra
in y
ield
(kg
/ha)
Gra
in y
ield
(bu
/ac)
5,000
3,000
4,000
2,000
1,000
01860 1880 1900 1920 2000
10,000
8,000
9,000
7,000
6,000
11,000
1940 1960 1980 2020
180
160
140
120
100
80
60
40
20
0
Open pollinated Second generationhybrids
First generationhybrids
Biotech (GM)
� Figure 3.6
BP Biomass HandbookFigure 3.6 (21 November 2013)Draft produced by ON Communication
Incr
easin
g us
e of
nitr
ogen
ferti
lizer
,
mec
hani
zatio
n an
d cr
op p
rote
ctio
n ch
emica
ls
Figure 3.5
Estimates of yield gaps in terms of percentage of attainable yield achieved throughout the world for maize, wheat and rice. Gaps were estimated by comparing observed yields to those from areas with high yields within zones of similar climate using data from around the year 2000[17].
Major cereals: attainable yields achieved (%)
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
3 Bioenergy potential | 41
A summary of crop production technologies
Land use can be minimized by growing the crop with the highest economic yield for a particular location. Some of the ways in which crop yields can be increased are explained briefly below.
Irrigation
With competition for water resources set to increase, particularly because of population growth and climate change, irrigation of substantial areas devoted to energy crops poses additional risk. Prudent measures to avoid such risk restrict energy crop production to areas of high water availability or where precipitation provides the large majority of needed water.
As mentioned previously, although overall agriculture accounts for almost 70% of total worldwide water with-drawals, the amounts withdrawn for liquid biofuels pro-duction accounts for about 0.5% owing to choices made regarding crop types and growing locations that do not tend to use significant irrigation. Significant expansion of crops for bioenergy production will be most sustainable in locations that do not require significant irrigation.
Nutrition
Plants need adequate nutrition to achieve their full yield potential. Both the manufacturing and application of fertilizer use significant amounts of energy and produce GHG emissions, which must be factored into the life cycle analyses of bioenergy production. Some energy crops, particularly perennials, are highly efficient at recycling nutrients and have low input requirements but, in other cases, there are large numbers of nutrient inputs required. The net benefit of these inputs for increasing energy yield and displacing fossil fuel emissions can be greatly reduced by the energy and GHG costs of manufacturing and applying large numbers of nutrients. There are also issues surrounding the short- to medium-term availability of potash (potassium carbonate) and phosphate due to political factors in areas with key reserves, such as parts of North Africa [19].
It is perhaps more important that any expansion in energy-crop production is carried out in a way that protects nutrients in the soil by reducing erosion during establishment and cultivation. Returning nutrients to the crop from processing waste (for example using bottom ash from biomass combustion as a fertilizer or applying the digestate from anaerobic digestion) can reduce the inputs needed.
Crop protection (pesticides and herbicides)
Weeds, pests and diseases are estimated to reduce global crop yields by as much as a third. The use of pesticides and herbicides is currently estimated to account for some 21–53% of theoretical crop yield and be some 52% efficient at increasing actual crop yields on food and fibre crops. Work is now beginning to investigate potential issues with dedicated bioenergy crops, such as rust caused by Melampsora in willow, for which many resistance genes have been identified and used in breeding. In fact, the introduction of resistant willow varieties has led to an almost doubling of yields, illustrating the importance of effective crop protection, whether by chemical or genetical means.
The use of pesticides and herbicides can be expensive and have unwelcome environmental costs. As a result, crop management is generally focused on maximizing value and minimizing use. There are currently large differences in the use of chemical protection between bioenergy crops: crops such as corn and soybean have relatively high rates of use, while biomass crops such as miscanthus and willow have relatively low usage rates, although the latter require greater inputs for weed control at establishment. An advantage of many energy crops, however, is that they are relatively undomesticated. Great potential therefore exists to breed in resistances to pest and diseases from the wide germplasm available.
Tillage
For annual energy crops, such as cereals and many oilseed crops, moving from conventional to minimum- or zero-tillage systems can reduce energy inputs and increase soil carbon levels. However, establishment requirements differ between crops, and best practice must be decided on a case-by-case basis.
Perennial and woody crops in temperate areas are often used to increase soil carbon stocks. This is in part because these cropping systems do not require annual tillage and the crops turnover roots during the growing season, adding to the organic carbon in the soil. Provided that high-carbon-stock land is not converted to plantations (for example the conversion of tropical peatland for oil palm production in parts of South-East Asia) and cultivation methods are carefully chosen, perennial crops could present a significant opportunity to ‘re-carbonize’ agricultural soils in some areas.
Mechanization
Improving the efficiency of planting, nutrient, pest management and harvesting operations can increase the harvested yields of biomass and reduce overall cost. Mechanization may also allow potential sources of biomass, which would otherwise simply be disposed of (such as exhausted oil and rubber plantations in West Africa), to be used for bioenergy.
In general, the large areas of land that will be required for significant production of bioenergy crops will require extensive mechanization to be effective and economical.
Genetic improvement
There is considerable scope to increase biomass yields through the use of plant breeding and genetic modification (GM). The potential for such increases depends both on the techniques used and the level of domestication of the crop species. The practice of selection and breeding for the most favourable traits in plants has been used since the beginning of agriculture. GM is a more recent development for crop improvement, and essentially allows one to accelerate the process of selection and breeding by directly increasing the number of gene copies that are responsible for desirable traits and reducing or eliminating genes that code for undesirable traits.
42 | 3 Bioenergy potential
Many breeding programmes for bioenergy crops are in their infancy, so there is the potential for large increases in yield from conventional breeding and genetic modification. Established agricultural crops such as maize and wheat are expected to have a lower (though still significant) potential for yield increases, as they have already been subject to intensive genetic improvement. Nevertheless, further improvements could be expected in crops currently used to produce food by focusing on attributes that are important for conversion to bioenergy.
GM has been proposed as a key method of improving bioenergy crop yields and enabling species to withstand stresses such as drought, salinity, extreme temperatures or attack by pests and diseases. There is also the possibility that GM could allow more efficient and cost-effective biofuel production, for example by increasing photosynthetic efficiency or improving the breakdown of lignin during processing.
The use of GM crops has already been widely adopted around the world but there is strong resistance to GM organisms in some markets. The use of the technology in non-food crops may be less of an issue in certain circumstances, but costs for developing GM crops and gaining regulatory approval are high and can prohibit their widespread use. As previously indicated, many of the potential bioenergy crops have not been widely used in agriculture, so there is expected to be broad scope for their agronomic improvement through both improved management and conventional breeding strategies.
Potential from ‘new’ crops
Estimated yields for bioenergy can also be expected to increase with the introduction of new bioenergy crops. As conversion technologies mature, there will be greater flexibility for accommodating different feedstock compositions. As a result, biomass sources can be diversified temporally (different harvest dates) and across local landscapes, regions and the world. There is the potential to develop new sources of bioenergy both from species of plants that are not currently commercial crops and from crops that are currently grown for other purposes.
There are many proven and potential bioenergy crop species, ranging from widely grown agricultural crops to niche species promoted as being academically interesting but that have not been proven in agronomic practice or commercially. By matching potential biomass crops with optimum locations, biomass yields could be improved, the landscape could be diversified, and ecosystem services might in turn also be improved.
While achieving a diversified landscape of bioenergy crops is a potential benefit of developing new biomass crops, it will not be without challenges. There are many difficulties in taking a wild or semi-wild species and trying to adapt it rapidly for commercial production, as has been proved in recent years with numerous attempts to commercialize Jatropha curcas (jatropha) as an oilseed feedstock for biodiesel. While companies continue to investigate the potential of jatropha, early efforts revealed that, while the shrub would grow in semi-arid areas with little or no agronomic input, it would not produce commercially viable yields of oil under these conditions.
Another consideration is the risk of introducing highly invasive non-native species to an ecosystem. In the past, such introductions have often ‘escaped’ from ornamental horticulture; some species (such as kudzu) now proposed as potential feedstocks for bioenergy production, are themselves prolific weeds. In many respects, the properties of an ‘ideal’ biomass crop – vigorous, perennial, fast growing and an efficient user of nutrients – mirror those of weedy plants, and care will be needed to ensure that risks to native communities are minimized. With an awareness of this risk, diversified novel biomass crops should include more native species, selected by regional biome types.
The literature describes almost 200 plant species currently used in some form for the production of bioenergy, or which have the potential to do so in the future. We provide an abbreviated list at the end of the Chapter 6 (see Additional species on page 100) to illustrate the variety of species currently being considered for bioenergy. These examples of novel bioenergy crops species have acquired different levels of scientific interest and are at varied stages of commercial development. It is far from being a definitive list of candidate varieties for bioenergy production.
With the diversity of potential biomass crops, it is difficult to project the potential production of bioenergy in the future. This is in part because yields will no doubt be improved as agricultural practices are tested and developed for each new crop. We need only look to the history of current commodity crops. Soybean, for example, is now grown across both temperate and tropical regions all over the world. Yet the modern varieties are derived from a wild plant that was selected for cultivation (see The soybean story on the next page).
Data and research needs
In order to facilitate the development of bioenergy and feedstock crops, further research and data are needed.
Genetics
There is a need for better understanding of the genetics and traits of improved varieties, particularly for new crops that have not been fully commercialized.
Agronomy
An understanding of the best ways to sustainably produce economic yields from many of these potential crops is required. There is also a need to find out how best management practices can be integrated with existing agricultural systems and other land uses.
Below-ground biomass and soils
There is currently limited knowledge on the below-ground biomass (roots and rhizomes) of different cropping systems and of how soil carbon levels change under different land-cover types. These data are key to identifying where best to grow different bioenergy crops, to understanding land use, and to evaluating their potential impacts for sustainability and climate-change mitigation.
3 Bioenergy potential | 43
The soybean story: an example of crop development
As agricultural systems develop and crop science improves, so crops can be adapted from their original use to meet a number of different market requirements. This can be illustrated by the example of soybean, which was originally identified as a source of protein for human food, and is now used for a wide variety of products, including as a bioenergy feedstock.
Soybean (Glycine max (L.) Merrill) is currently grown on around 90 million hectares globally, having been successively improved and distributed from the wild relative G. soja in China some 4,500 years ago.For the first half of the 20th century China was still the leading global producer of soy, used as a food and animal feed crop. Although the crop was first introduced into the US in 1760, large-scale production only started in the 1950s but grew rapidly so that, today, the US is the world’s largest producer followed by another relative newcomer, Brazil, where farmers adopted the crop only in the 1970s.
From Brazil, soybean production spread south to Argentina (now the third largest producer globally) and back across the Pacific to India. There is also some production in Africa.
Crop development has mainly focused on the selection of plants with large seeds with the first formal breeding programme originating in China in 1913. In the late 1920s the US sent crop scientists to the country to learn about the crop and collect germplasm. The breeding programme in Brazil was particularly successful, adapting the crop and its associated nitrogen-fixing bacteria to new soils and different photoperiods.
In line with many other crops, the majority of soybeans are now a product of targeted breeding, including genetic engineering. Genetic modification to date has sought to improve yields primarily through herbicide tolerance and insect-resistance traits. Though mainly grown for its protein content, new soybean varieties are also being developed with modified oils, suitable for different food and bioenergy uses.
As the crop has expanded, global markets have developed. High-income countries account for almost half the total consumption. Soy is traded on futures and options markets around the world, with the main use as animal feed and cooking oil. Worldwide roughly 20% of soybean oil is used for biodiesel production despite the low yield relative to other bioenergy crops. However, illustrating the flexibility of the crop, a wide range of products are produced around the world: these include fermented products, juice and fresh beans. There is no sign that soybean yields are about to plateau, suggesting it will have a key role to play as a major crop for some time.
Many bioenergy crops that are already established in agronomic practice, or that are close to becoming so, require developed markets in order to drive the necessary technical development and investment. In most situations where the widespread production of crops for bioenergy has been undertaken by farmers, government initiatives have boosted demand through programmes such as those that support the use of ethanol in Brazil and the US. Debates around the benefits of bioenergy and changes in government policy can act as a strong disincentive to such developments at all levels of the supply chain.
Life cycle analysis
While guidelines for life cycle analysis (LCA) have been developed, there are still discrepancies between the way LCA is applied to different energy forms and land uses. There is a need to integrate data collection with life cycle impacts in a way that is comparable across energy sources and regions.
Land-use change
Understanding the impacts of land-use change is important. While complex, it is relatively straightforward to determine the direct effects caused by a change in land use from its previous (uncultivated, pasture etc.) condition to one of bioenergy crop cultivation (direct land-use change or DLUC). There is also interest, however, in determining the magnitude of any indirect effects of using land for a new purpose – such as growing bioenergy crops – and there is no scientific or political consensus on how to treat such indirect land-use change (ILUC).
44 | 3 Bioenergy potential
Developments in biomass conversion technologies
Biomass is often highly variable and diffuse when harvested, making it expensive to transport and less predictable as a feedstock than conventional fuels. There are several processes to prepare biomass into convenient and usable energy sources, including techniques that improve the handling and logistical properties of biomass feedstocks before conversion. Processes currently in use are outlined in Table 3.5.
This table provides a brief description and key characteristics of the major stages in processing biomass. In practice, these are stages that would be included in a bioenergy production chain, either in the same facility (such as during the production of biomass-to-liquid (BTL) fuels) or to facilitate logistics (such as pelletizing solid biomass fuels before transport). Many of these different technologies can be used together in different process variants. Additionally, these processes are at very different stages of their technological evolution, with combustion, for example, being very highly refined and extensively practised whereas others, such as lignocellulosic hydrolysis and fermentation, are just starting to appear commercially.
To achieve full commercial potential and continuing investment in the sector, current efficiencies and technologies will need to be improved.
The two most important trends in biomass utilization are greater electrical power production and initiatives to develop cellulosic and advanced biofuels. Both of these developments will increase demand for lignocellulosic feedstocks. At the same time, new technologies are likely to increase conversion efficiency, meaning that more energy can be produced from a given quantity of biomass. This will reduce the inputs and land requirements to produce a given amount of energy or fuel.
Currently, bioenergy is used to produce around 1.2EJ of electrical power. New installations and the conversion of coal-fired power stations to biomass fuel could increase this to 5.4EJ by 2035[2]. Much of this activity is expected to occur in the US and Germany, although other parts of the European Union (EU) and Asia are also developing projects to produce electricity from bioenergy.
By the end of 2013 there were numerous cellulosic biofuel production projects around the world, ranging from small demonstration projects to full-scale facilities just commencing commercial operations. Though technological difficulties in developing robust, economical processes have resulted in a slower-than-expected evolution, currently initiated commercial operations should substantially increase the production of cellulosic biofuels in the near future. Most of these plants are planned for the Americas, although Europe and Asia are also key locations for companies involved in the sector. These include oil producers, current biofuel producers, biotechnology companies, and dedicated lignocellulosic and advanced biofuel companies. Most are looking to produce bioethanol or other alcohol-based fuels from cellulosic materials, with diesel, intermediate feedstocks and other chemicals representing the other outputs.
3 Bioenergy potential | 45
Tab
le 3
.5
Tab
le s
um
mar
izin
g c
urr
ent b
iom
ass
conv
ersi
on
tech
no
log
ies.
Th
ese
ran
ge
fro
m p
re-p
roce
ssin
g th
rou
gh
co
nver
sio
n to
hea
t an
d p
ow
er, c
onv
ersi
on
of o
ils to
fuel
s, b
iolo
gic
al r
ou
tes,
ther
mo
chem
ical
ro
ute
s an
d th
e co
nver
sio
n o
f bio
mas
s to
gas
.
Tech
nolo
gy /
tech
niqu
eD
escr
iptio
nCu
rren
t sta
tus
Suita
ble
feed
stoc
ksEn
ergy
out
puts
Pre-
proc
essi
ngPe
lletiz
atio
nPh
ysic
al p
roce
ss.
Com
mer
cial
ly v
iabl
e an
d w
idel
y ca
rrie
d ou
t.An
y dr
y m
illab
le b
iom
ass,
incl
udin
g w
ood
(onc
e tu
rned
into
saw
dust
), ce
llulo
sic
biom
ass
and
cere
als.
Prod
uces
a s
olid
fuel
for f
urth
er p
roce
ssin
g (g
ener
ally
via
com
bust
ion
or o
ther
ther
mal
tre
atm
ent).
Torr
efac
tion
Ther
moc
hem
ical
pro
cess
whe
re w
ater
and
ot
her v
olat
ile c
ompo
unds
in th
e bi
omas
s ar
e re
mov
ed in
the
abse
nce
of o
xyge
n at
te
mpe
ratu
res
of 2
00–3
20o C
.
Tech
nica
lly p
rove
n an
d so
me
pilo
t-sca
le
plan
ts in
exi
sten
ce.
Gene
rally
woo
dy b
iom
ass
is u
sed,
but
cou
ld
be a
pplie
d to
oth
er c
ellu
losi
c bi
omas
s cr
ops.
Prod
uces
a ro
bust
den
sifie
d fu
el s
uita
ble
for l
ater
com
bust
ion.
Torr
efied
fuel
s ha
ve a
gr
eate
r ene
rgy
dens
ity th
an th
e m
ater
ials
fro
m w
hich
they
wer
e de
rived
and
are
hy
drop
hobi
c.
Conv
ersi
on to
hea
t an
d/or
pow
erCo
mbu
stio
n/co
-firin
gTh
erm
oche
mic
al p
roce
ss w
here
bio
mas
s is
bu
rnt i
n th
e pr
esen
ce o
f oxy
gen
to p
rodu
ce
heat
.
Fully
com
mer
cial
.M
ost d
ry b
iom
ass.
Can
be u
sed
to g
ener
ate
heat
or,
whe
n co
mbi
ned
with
ste
am o
r Org
anic
Ran
kine
Cy
cle
gene
rato
rs, c
an b
e us
ed to
pro
duce
el
ectri
city
.
Chem
ical
rout
es to
bi
odie
sel f
rom
oils
Tran
sest
erifi
catio
nA
chem
ical
pro
cess
whe
re a
n al
coho
l (su
ch
as m
etha
nol)
is c
ombi
ned
with
a v
eget
able
oi
l to
prod
uce
a fa
tty a
cid
alky
l est
er.
Fully
com
mer
cial
.Ve
geta
ble
oils
from
cro
ps s
uch
as
rape
seed
, soy
a an
d oi
l pal
m a
nd w
aste
oils
fro
m c
ooki
ng.
The
resu
lting
alk
yl e
ster
is s
uita
ble
for u
se
as a
tran
spor
t fue
l in
com
pres
sion
igni
tion
engi
nes.
Hydr
ogen
atio
nTh
e ch
emic
al p
roce
ss o
f add
ing
hydr
ogen
to
veg
etab
le o
ils to
cre
ate
hydr
ocar
bon
chai
ns.
Com
mer
cial
and
gro
win
g.Ve
geta
ble
oils
and
was
te o
ils fr
om c
ooki
ng.
The
resu
lting
hyd
roca
rbon
is s
uita
ble
for
use
as a
tran
spor
t fue
l in
com
pres
sion
ig
nitio
n en
gine
s.
Biol
ogic
al ro
utes
to
bio
etha
nol f
rom
ca
rboh
ydra
tes
Hydr
olys
is a
nd
ferm
enta
tion
A bi
o-ch
emic
al p
roce
ss (u
sual
ly a
ided
by
phy
sica
l/che
mic
al p
repa
ratio
n of
the
feed
stoc
k) w
here
sug
ars
are
ferm
ente
d in
to p
rodu
cts
(par
ticul
arly
eth
anol
). W
here
st
arch
-bas
ed fe
edst
ocks
are
use
d, a
n ad
ditio
nal s
tage
– s
acch
arifi
catio
n –
is
requ
ired
befo
re fe
rmen
tatio
n w
here
the
star
ches
are
con
verte
d in
to s
impl
er s
ugar
m
olec
ules
by
enzy
mat
ic h
ydro
lysi
s.
Fully
com
mer
cial
with
sig
nific
ant r
esea
rch
and
deve
lopm
ent a
ctiv
ities
und
er w
ay to
pr
oduc
e bi
ofue
ls o
ther
than
eth
anol
.
Usua
lly h
igh-
suga
r or h
igh-
star
ch
feed
stoc
ks s
uch
as s
ugar
cane
, mai
ze a
nd
whe
at.
Afte
r fer
men
tatio
n th
e et
hano
l is
gene
rally
di
still
ed to
rem
ove
surp
lus
wat
er b
efor
e it
can
be u
sed
as a
tran
spor
t fue
l. F
urth
er
mol
ecul
es fo
r gas
olin
e, d
iese
l and
indu
stria
l ch
emic
al u
ses
are
at th
e de
velo
pmen
t and
ea
rly c
omm
erci
aliza
tion
stag
es.
Lign
ocel
lulo
sic
hydr
olys
is
and
ferm
enta
tion
Afte
r var
ious
pre
treat
men
ts to
libe
rate
ca
rboh
ydra
tes,
num
erou
s or
gani
sm a
nd
proc
ess
varia
nts
are
bein
g in
vest
igat
ed fo
r th
eir a
bilit
y to
con
vert
cellu
losi
c fe
edst
ocks
in
to a
lcoh
ol-b
ased
fuel
s.
Som
e pi
lot p
lant
s ex
ist b
ut th
ere
is li
ttle
com
mer
cial
-sca
le a
ctiv
ity a
nd th
e fir
st
com
mer
cial
faci
litie
s ar
e ju
st b
egin
ning
to
oper
ate.
Cellu
losi
c bi
omas
s.M
ost o
f the
se p
roce
sses
are
des
igne
d to
pr
oduc
e al
coho
l-bas
ed fu
els.
Ther
moc
hem
ical
rout
es
to fu
els
or p
ower
Gasi
ficat
ion
Ther
moc
hem
ical
pro
cess
usi
ng h
igh
tem
pera
ture
s (6
00–1
,100
o C) t
o tu
rn b
iom
ass
into
a ‘s
ynga
s’ in
the
abse
nce
of o
xyge
n.
Som
e tri
al g
asifi
catio
n pl
ants
hav
e be
en
esta
blis
hed
to p
rodu
ce e
lect
ricity
or l
iqui
d bi
ofue
ls, a
lthou
gh th
ere
have
bee
n fe
w
larg
e-sc
ale
com
mer
cial
suc
cess
es.
Gene
rally
cel
lulo
sic
biom
ass.
Th
e re
sulti
ng s
ynga
s ca
n be
bur
nt to
pr
oduc
e he
at a
nd/o
r pow
er. A
ltern
ativ
ely
it ca
n be
turn
ed in
to a
liqu
id fu
el (o
r oth
er
rene
wab
le c
hem
ical
s) u
sing
the
Fi
sche
r–Tr
opsc
h ca
taly
sis
met
hods
.
Pyro
lysi
sA
ther
moc
hem
ical
pro
cess
whe
re th
e fe
edst
ock
is s
ubje
cted
to h
igh
tem
pera
ture
s (~
475–
490o C
) in
the
abse
nce
of o
xyge
n to
pr
oduc
e a
liqui
d ‘b
io-o
il’, a
ligh
t syn
gas
or a
so
lid b
ioch
arco
al (b
ioch
ar).
Pyro
lysi
s of
indu
stria
l was
te h
as b
een
prac
tised
com
mer
cial
ly b
ut p
yrol
ysis
us
ing
biom
ass
is ju
st b
egin
ning
to b
e co
mm
erci
alize
d.
Any
biom
ass,
incl
udin
g w
aste
s.Py
roly
sis
oils
and
oth
er p
rodu
cts
may
be
turn
ed in
to li
quid
tran
spor
t fue
ls v
ia fu
rther
pr
oces
sing
or m
ay b
e bu
rnt t
o pr
oduc
e he
at
and/
or e
lect
rical
pow
er.
Bioc
har m
ay b
e bu
rnt o
r, in
som
e pr
oces
s va
riant
s, u
sed
as a
n am
endm
ent t
o
impr
ove
soil.
Biol
ogic
al ro
ute
to b
ioga
sAn
aero
bic
dige
stio
nA
biol
ogic
al p
roce
ss w
here
con
sorti
a of
m
icro
bes
brea
k do
wn
solid
bio
mas
s in
to
met
hane
and
CO 2
via
suc
cess
ive
proc
esse
s of
met
abol
ism
.
Fully
com
mer
cial
.M
ost e
ffect
ive
on w
et b
iom
ass
sour
ces
incl
udin
g gr
een
ener
gy c
rops
, man
ures
, se
wag
e an
d fo
od w
aste
s.
Biog
as m
ay b
e bu
rnt t
o ge
nera
te h
eat a
nd
pow
er.
It ca
n al
so b
e pr
oces
sed
for u
se a
s a
trans
port
fuel
(CN
G) o
r cle
aned
prio
r to
inje
ctin
g in
to g
as d
istri
butio
n ne
twor
ks.
46 | 3 Bioenergy potential
Chapter references
[1] International Energy Agency (2012), Key world energy statistics 2012. OECD/IEA, Paris.
[2] International Energy Agency (2012), World Energy Outlook 2012. International Energy Agency (IEA), Paris.
[3] International Energy Agency (2011), adapted from IEA technology roadmap: biofuels for transport, p. 30. OECD/IEA, Paris.
[4] Slade, R., Saunders, R., Gross, R. & Bauen, A. (2011), Energy from biomass: the size of the global resource.Imperial College Centre for Energy Policy and Technology and UK Energy Research Centre, London. Available from: http://www.ukerc.ac.uk/support/Energy+from+biomass%3A+the+size+of+the+global+resource [accessed February 2014].
[5] Hoogwijk, M., Faaij, A., van Den Broeka, R., Berndes, G., Gielen, D. & Andturkenburg, W. (2003), Exploration of the ranges of the global potential of biomass for energy, Biomass and Bioenergy, vol. 25, pp. 119–133.
[6] Beringer, T., Lucht, W. & Schaphoff, S. (2011), Bioenergy production potential of global biomass plantations under environmental and agricultural constraints, GCB Bioenergy, vol. 3, pp. 299–312.
[7] Hoogwijk, M., Faaij, A. & Eickhout, B. (2005), Potential of biomass energy out to 2100, for four IPCC SRES land-use scenarios, Biomass and Bioenergy, vol. 29, pp. 225–257.
[8] Smeets, E. M., Faaij, A. P., Lewandowski, I. M. & Turkenburg, W. C. (2007), A bottom-up assessment and review of global bio-energy potentials to 2050, Progress in Energy and Combustion Science, vol. 33, no. 1, pp. 56–106.
[9] Muller, C. & Robertson, R. D. (2014), Projecting future crop productivity for global economic modeling, Agricultural Economics, vol. 45, no. 1, pp. 37–50.
[10] Schmitz, C. et al. (2014), Land-use change trajectories up to 2050: insights from a global agro economic model comparison, Agricultural Economics, vol. 45, no. 1, pp. 69–84.
[11] Lotze Campen, H. et al. (2014), Impacts of increased bioenergy demand on global food markets: an AgMIP economic model intercomparison, Agricultural Economics, vol. 45, no. 1, pp. 3–116..
[12] Edenhofer, O., Pichs-Madruga, R., Sokona, Y. & Seyboth, K. (eds) (2011), Special report on renewable energy sources and climate change mitigation. IPCC, Cambridge University Press. Available from: http:// www.ipcc.ch/pdf/special-reports/srren/SRREN_Full_ Report.pdf [accessed October 2013].
[13] International Institute for Applied Systems Analysis (2012), Global energy assessment: toward a sustainable future. Cambridge University Press, Cambridge, UK and New York, US, and the IIASA, Laxenburg, Austria. Available from: http://www.iiasa.ac.at/web/home/research/Flagship-Projects/Global-Energy-Assessment/Home-GEA.en.html [accessed October 2013].
[14] Slade, R., Bauen, A., Gross, R. (2014), Global bioenergy resources, Nature Climate Change, vol. 4, pp. 99–105.
[15] Nassar, A. M., Moreira, M. (2013), Evidences on sugarcane expansion and agricultural land use changes in Brazil, ICONE (Institute for International Trade Negotiations). Available from: http://www.iconebrasil.com.br/publication/study/details/568 [accessed March 2014].
[16] Food and Agricultural Organization of the United Nations. FAOSTAT database. Available from: http://faostat3.fao.org/home/index.html#HOME [accessed February 2014].
[17] Mueller, N. et al (2012), Closing yield gaps through nutrient and water management, Nature, vol. 490, pp. 254–257.
[18] Nielsen, R.L. (2013), Historical corn grain yields for Indiana and the US, Crop Science, vol. 46, pp. 528–543. Available from: http://www.kingcorn.org/news/timeless/YieldTrends.html [accessed February 2014].
[19] Zepf V., Reller A., Achzet B., University of Augsburg, Rennie C., BP, Ashfield M. & Simmons J., ON Communication (2014), Materials critical to the energy industry – an introduction, 2nd edition. Available from: www.bp.com/energysustainabilitychallenge [accessed February 2014].
Significant expansion of bioenergy will require continuing improvement in the cost basis of biomass production and its conversion to fuel. Major financial investments are needed to develop new technology and to improve the variety and performance of biomass crops.
If biomass is to make a significant contribution to world energy needs, it will have to be produced on a large scale and without detriment to the environment. This will require reconciling competing demands for food, water, energy and other resources.
Management choices regarding which crops to grow in which locations can completely determine whether biomass production is beneficial or detrimental to GHG emissions.
Supportive and consistent government policies are needed to provide a degree of certainty for industry to undertake the serious financial investments required to further develop biomass potential.
48
4 Economics, the environment and politics | 49
4 Economics, the environment and politics
The socio-economic drivers and impacts of bioenergy
Biomass provides energy to millions of people in the form of cooking fuel, heating, electricity and transportation fuel. The potential benefits are many and varied as outlined in Table 4.1. Bioenergy contributes to individual households and communities as well as national and international energy portfolios.
There are several key factors critical to understanding the socio-economic impacts of bioenergy:
●● With the exception of municipal waste, biomass is largely a rural resource.
●● Land and water resources that are needed to support biomass production may be privately or publicly owned and may therefore be subject to different governance and governance related to other uses.
●● Biomass can be expensive to transport but bioenergy products such as fuel and electricity can be exported and traded regionally and internationally.
Because biomass is bulky and relatively expensive to transport, use for bioenergy tends to be a local activity (generally within 100km). This means that bioenergy opportunities are location dependent, as described in other chapters of this handbook. Because most biomass resources are in rural areas with lower economic opportunities on average, bioenergy systems can have large positive effects, including improved standard of living through access to energy and jobs.
In many areas, bioenergy systems contribute to maintaining or creating rural employment. New jobs may
arise directly in the production and processing of bioenergy crops, and also indirectly in crop research and development. Increased demand for agricultural and forestry residues can increase incomes in these industries, while bioenergy production can generate more employment and a wider range of jobs per unit of energy generated than other energy sources. Of course, the number and type of jobs, the skill level required, and the local economic impact will be different with different biomass sources and will vary by region.
The local nature of biomass also means that smaller sources of bioenergy can have very important impacts. This is especially true in communities that do not have access to conventional energy sources. These potential improvements in rural economies may also help to avoid the abandonment of land, while encouraging agricultural competitiveness and providing diversified income streams for farmers. Although inefficient compared with large-scale schemes, small-scale schemes can significantly benefit local populations.
Unlike biomass, biofuels can be transported with relatively low cost. There are, however, cases where densified or pretreated biomass may be exported from local sources for conversion elsewhere. One example is the shipment of wood pellets from North America to EU member states such as the UK, which has been incentivized by renewable energy policy, as mentioned in Chapter 3 of this handbook. Whether it is biomass or biofuels that are traded, the social acceptability of sourcing and production must be accounted for at both ends of the supply chain.
This chapter provides an overview of the main issues associated with large-scale use of biomass from socio-economic, environmental and political perspectives.
Table 4.1.
Some of the potential socio-economic benefits associated with bioenergy [1].
Social aspects
Increased standard of living● Environment.● Health.● Education.● Community wealth and infrastructure.
Social cohesion and stability● Mitigating rural depopulation.● Regional development.● Rural diversification.● Support of traditional agricultural or forestry culture.
Economic aspects
Macro-economics● Security of supply/risk diversification.● Economic growth through business expansion or employment.● Export potential.● Import substitution (effects on GDP).
Demand-side economics● Employment.● Income and wealth generation.● Induced investment.● Support of related industries.
Supply-side economics● Increased productivity.● Enhanced competitiveness.● Improved infrastructure.● Labour and population mobility.
50 | 4 Economics, the environment and politics
The demand for resources
With the global population predicted to grow to 9 billion by 2050 and large numbers of people becoming more affluent and demanding of consumer goods and services, the demand for energy, food, water and other resources is rising fast. Of all the competing demands for resources that overlap with bioenergy, the demand for food is both the most serious and the most visible. Current world food production is sufficient to meet global demand, but economic factors, distribution failures and waste prevent that demand from being met. So far, any impacts of biofuels and bioenergy on food prices or availability appear to be modest[2]; however, the effect of future expansion of bioenergy on food production remains a concern and is shaping bioenergy-related policies in many regions.
The social acceptability of biomass use, including modes and locations of biomass production and conversion technology choices, is complex and variable. Some groups oppose recovering energy from the organic material in municipal solid waste, contending that it will create a market for waste and interfere with waste reduction efforts. Others object unequivocally to using forest biomass (especially from publically owned lands) or food or feed products for bioenergy. Although proponents of bioenergy can supply good evidence for well-managed sustainable use of all of these biomass sources for bioenergy, these objections are important as they shape policy and have profound impacts on the availability and type of biomass and biofuels that will receive investment.
Economic challenges
Unleashing the full potential of bioenergy will depend largely on developing new conversion technologies that are cheaper, more efficient and use a wider range of feedstocks. The commercial development of such technology at a meaningful scale requires significant
capital investments, with the magnitude and risk varying according to the particular conversion pathway. Substantial investment is also required in feedstock (crop) improvement and cultivation methods. Adopting new crops is risky for farmers, especially when commercial biofuel plants, utilizing new crops, are not yet economically viable without subsidy. Without incentives to offset some or all of this risk, investors are unlikely to support the construction of commercial facilities lacking some level of guaranteed return, and farmers are unlikely to commit to planting a large acreage of energy crops when greater returns are available elsewhere in the marketplace. In any case, there will always be intrinsic competition for land use from a variety of economic sectors, depending heavily on location. Ultimately, the rate of economic return will determine land use.
As well as investment challenges, there are practical issues to overcome to commercialize large-scale bioenergy projects. These include building supply chains and logistical facilities capable of aggregating large quantities of feedstock while minimizing GHG emissions of the resulting energy product.
Once the initial hurdles of commercializing an integrated supply chain are overcome, investors also need to be aware of the volatility of natural commodity markets. Managing the risk associated with yield variability from year to year, caused by seasonal weather variations or commercial factors, is a key consideration. Climate variability can also lead to inconsistent feedstock quality (due to the physiological responses of the plants); this can affect the processing requirements and economic yield.
While the risks are significant, the rewards can be significant too: when appropriate technology, feedstock availability and policy are aligned, substantial investment is possible. Examples include the Brazilian sugarcane ethanol industry, the US corn ethanol industry, and the growing use of waste wood for electric power generation in the UK.
Environmental sustainability
If bioenergy is to be truly sustainable in economic, social and environmental terms, it will be important not to disrupt native ecosystems and world food resources; careful management will be required with regard to the production of feedstock and siting of conversion facilities.
Environmental sustainability requires attention to land, air, water and biodiversity. The state of resources before bioenergy development and the changes in those resources caused by bioenergy development are both key factors for understanding sustainability. Much of the information addressed in this handbook has been directly related to land-use issues, but embedded in every land-management decision is a potential impact on water, air and biodiversity.
Water availability (quality and quantity) is of increasing concern globally, not only in relation to agricultural use, but also in relation to the rising demands for industrial and domestic water. Because agriculture is responsible for 70% of worldwide freshwater withdrawal[3], expansion of agriculture for energy production warrants special attention. Different bioenergy crops have different water requirements, so choosing appropriate crops for each geographic location is critical. While rainfed cultivation
does not require water withdrawal from lakes, rivers and groundwater, it can still affect downstream users by redirecting precipitation and altering groundwater recharge and river flows when high yielding biomass crops utilize more of the available water than natural vegetation. There are clearly areas around the world where ample water availability can support very high-yielding energy crop production, but in other areas water-use efficiency and downstream consequences will prove to be more important selection criteria than yields.
Water quality is reduced in many regions by large-scale agriculture devoted to intensively managed annual crops (because of their high requirements for fertilizer and pesticides). Crops with lower input requirements (such as perennial crops) can lead to water-quality improvements if they replace these agricultural systems. Some of the plants considered for bioenergy, such as willows and switchgrass, have historically been used along waterways to help protect water resources from pollution, stabilize the waterway bank, and improve aquatic and wildlife habitat. In contrast, approaches that displace native wetlands, forests and grasslands could result in a degradation of water quality.
4 Economics, the environment and politics | 51
Some crops currently used for bioenergy production, particularly arable crops such as maize, wheat, soybean and oilseed rape, have significant requirements for fertilizer and/or chemical crop protection. Not only does this counteract the reduction of GHG emissions, but poor nutrient management can also lead to lower soil quality. Where excess fertilizer is applied, there is a risk to water quality (as described above) and air quality as a result of nitrous oxide and other volatile emissions that can be produced. Crops should be carefully selected and appropriate management should include nutrient analysis, restricted timing of nutrient application, and the use of conservation drainage as required.
Annual bioenergy crops have the potential to degrade soils through poor cultivation practices, as has been demonstrated in some cases by the commercial agricultural management of many commodity crops. While all crops can be poorly managed, well-managed perennial and long-rotation crops have significant potential to increase soil carbon stocks and improve soil health, bringing previously degraded land back into economic production or managing the environmental impacts of intensified food-crop production. Introducing well-managed perennial systems to degraded soils can, over time, lead to more resilient agricultural landscapes capable of supporting both biomass and food crops with greater yields.
Biodiversity is most at risk if native ecosystems are displaced by cultivated systems. Biodiversity can also be affected by land-use change from one type of agriculture to another, but properly selected and managed bioenergy crops can enhance biodiversity in some cases. Diversified landscapes can host a wider range of insects, birds, small mammals, reptiles and amphibians than monocultures. On an overall acreage basis, deliberately selecting higher yielding crops can also limit the acreage under cultivation and improve habitat availability. It is important to note that in some areas (such as North America and Western Europe) the use of certain perennial energy crops (such as short rotation coppice or miscanthus) could actually provide greater biodiversity than typical annual crops such as wheat or maize.
Energy use, GHG emissions and the impact of land-use changes
Bioenergy projects today are increasingly motivated by demands for national energy security and decarbonization of energy. With respect to the latter, the choice of biomass source and type of processing will have a major impact. Overall emissions associated with biofuels production arise during production, distribution and processing of the feedstock, as well as the burning of the fuel by consumers.
Discounting the carbon dioxide released during bioenergy use (combustion), the agricultural production phase generally accounts for most of the total life cycle GHG emissions. These arise from the manufacturing of chemical inputs (such as fertilizer and pesticides), the use of energy in farming operations (including soil cultivation and harvest), and changes in the levels of carbon and nitrogen in the crop, soil and the atmosphere caused by cultivation. A major portion of the overall GHG emissions can be associated with fertilizer production (and use) alone. This varies, however, according to the crop: while maize may require 200kg N per hectare, miscanthus has been grown and harvested at some locations with no N input for 15 years with no loss of yield.
Extensive modelling and measurement is under way to understand factors influencing the GHG performance of bioenergy. Some legislation (such as the European Renewable Energy Directive) now requires clear limits on GHG emissions associated with the production of bioenergy, often together with additional sustainability criteria. While the techniques of life cycle analysis are well established, its use in complex emerging fields such as bioenergy is less well developed. It is therefore crucial that the scope and boundaries of the analysis are applied consistently and transparently to allow meaningful comparisons between alternative energy pathways. Data supporting the inclusion of GHG and other effects associated with land-use change is sparse and an important cause of diverging results from different studies. Especially when considering indirect land-use change, data are often entirely lacking.
From the perspective of the global carbon cycle, the ‘best’ bioenergy systems can be considered near-neutral in the sense that biomass carbon emitted during the biomass processing and final use was earlier sequestered during biomass growth. If bioenergy production causes (directly and/or indirectly) changes in land cover and use, there may be a net gain or net loss in terrestrial carbon stocks (i.e. net withdrawal or addition of atmospheric carbon). Some bioenergy systems (such as biomass extraction from forests managed with long rotation periods) are not carbon-neutral over shorter time scales, because carbon sequestration and emissions are temporally out of balance, though over longer time scales sequestration and emissions come into balance.
52 | 4 Economics, the environment and politics
While biofuels generally have lower GHG emissions than fossil fuels, careless choices regarding the production pathway, feedstocks used and additional fossil energy process inputs can actually result in increased emissions.
Table 4.2 outlines the ways in which factors in bioenergy production can influence emissions. Table 4.3 provides examples of how a single management decision can completely reverse the life cycle GHG emissions from a bioenergy production system.
As can be seen in Table 4.3, one of the most critical factors is land use and the increase or reduction of GHG emissions associated with land-use change. Converting carbon-rich wetlands into biofuel plantations, for example, can result in large GHG emissions, while planting perennial grasses on soils previously used for annual arable crops is likely to reduce GHG emissions.
Land-use change Direct land-use changes and associated GHG emissions (e.g. oxidation and volatilization of nitrogen and carbon) can entirely negate the GHG benefits of biofuel use. In other situations, for example a change from annual cropping to perennial crops for bioenergy, the GHG benefits may increase.
Feedstock type Some feedstocks (such as maize and soybean) have high nutrient- and crop-protection requirements. This may result in higher direct and indirect GHG emissions compared with low-input perennial crops (such as miscanthus or short-rotation coppice and co-products).
Agricultural practices
Energy is a key agricultural input, so any reduction in cultivation and other energy-intensive operations will reduce the GHG. Certain practices (such as minimum tillage cultivation) can also reduce GHG emissions that arise from soil disturbance.
Increasing yield also has a significant effect on reducing overall GHG emissions. GHG emissions associated with the production of nitrogen fertilizers generally dominate the GHG emissions from agricultural practices.
Manner of conversion
Like feedstock yield, the overall efficiency of the conversion process has a key role in reducing the overall GHG emissions.
Supply-chain logistics
Transporting biomass over long distances can place significant burdens on the economics of a bioenergy enterprise, and can also contribute to GHG emissions. Bioenergy producers will pay close attention to supply-chain logistics. Bulk ocean transport results in significantly fewer GHG emissions per unit of biomass or fuel than road transport, for example.
Type of energy replaced
Where bioenergy displaces fossil fuels (such as coal), the potential to deliver higher GHG savings is greater than where it displaces a lower GHG fuel (such as natural gas). In the process chain, GHG emissions are strongly determined by the fuel that is used for process energy generation.
End use of fuel The use of a unit of solid biomass for combined heat and power generation will have a greater efficiency (in strict energetic terms) than pure electrical generation, pure heating use or conversion to liquid fuels. The uses of bioenergy, however, are also dependent on energy demand, competition with other sources and the best energy carriers to fulfil this. In contrast with other renewable energy sources (such as solar or wind), biomass is well-suited for the production of liquid transport fuels.
Indirect land-use change (ILUC)*
The concept of ILUC posits that using land for one purpose (such as the production of bioenergy crops) renders that land unavailable for other uses (such as food production). Food production, for instance, will therefore be displaced to other areas, possibly causing the conversion of natural environments with high carbon stocks and biodiversity.
Because it is an indirect effect, there is much debate about how metrics can be designed to account for ILUC. To date, studies have assumed widely varying levels of emissions due to ILUC for the same fuel pathways. In general, since the first attempts to calculate ILUC impacts, estimates of emissions arising from ILUC have been substantially reduced. We now have a better understanding and can carry out more complex modelling, but there continues to be a significant lack of consensus about how to estimate ILUC and establish causality.
Table 4.2
Key factors determining bioenergy GHG emissions, with brief examples and explanations. In most cases there are many more examples for each factor.
Figure 4.1, on the next page, deconstructs the source of emissions that occur as a result of different land uses in a tropical forest or tropical grassland biome. The initial storage of carbon depends on the condition of the land. There is an ongoing exchange of GHG (including CO2, CH4 and N2O) between the terrestrial ecosystem and the atmosphere. The GHG flux, combined with physical characteristics of an ecosystem, determines the net radiative forcing, or potential to warm the atmosphere,
caused by that ecosystem. Negative radiative forcing, as indicated on the horizontal axis, are net emissions to the atmosphere and positive radiative forcing are net uptake by the ecosystem. The net GHG benefit of a tropical forest or grassland is the result of carbon storage in the plants and soil whereas the net GHG benefit of growing sugarcane for fuels largely results from displacing the emissions associated with fossil fuel use, shown with ‘max’ values in Figure 4.1.
* For further reading, please see reference on page 56: Indirect land-use change [4].
Table 4.3
Effects of a single management change on life cycle GHG emissions per unit of energy in biomass-based production systems[5]. Different management decisions are shown for different species. The assumptions used for each life cycle assessment vary across the species, e.g. palm and maize life cycles include co-products and end-use emissions whereas miscanthus and sugarcane life cycles include fossil-fuel displacement in their assessments. Therefore, comparisons should be made only within a species. Positive values indicate a net source (emission) of GHGs into the atmosphere and negative numbers indicate a net sink or reduction of atmospheric GHG. Note the large swings associated with land-use change in the palm and miscanthus life cycles. GHG emissions for comparative purposes: gasoline, 94g CO2eq/MJ and diesel, 85g CO2eq/MJ[6].
Crop Management decision Outcome GHG emissions g CO2eq/MJ energy produced
Palm (Indonesia)
Prior land use: rainforest 500
Prior land use: palm 28
Prior land use: palm – and best management practices adopted
-190
Miscanthus(UK)
Prior land use: forest 120
Prior land use: crop -45
Sugarcane (Brazil)
Traditional pre-harvest burning 32
No pre-harvest burning -13
Maize (US)
Traditional tillage 25
No-till practised -4
4 Economics, the environment and politics | 53
Figure 4.1
Graphical representation of the sources of GHG emissions occurring as a result of different land uses in a tropical forest and tropical grassland biome. The greenhouse gas value (GHGV) in the right panel is the sum of the GHG mitigation potential associated with the system prior to change (initial storage) and the change in GHG mitigation potential (ongoing exchange) of the terrestrial system over a 30-year period. Blue represents CO2, green represents CH4, red represents N2O, and black is the sum of all three gases in CO2 equivalents. Here, positive numbers indicate a net sink or retention of GHG, and negative numbers indicate emissions of GHG or increased radiative forcing that contribute to climate warming. The values shown as ‘max’ in the figure include an estimate of fossil-fuel displacement in the final GHGV value. The ones shown as ‘eco’ are just the soil/ecosystem biogeochemistry.The values for sugarcane are for crops in a variety of landscapes with varying amounts of forest cover [7,8].
0
Tropicalforest
Sugarcane(not burnt – eco)
Tropicalcropland
Sugarcane(not burnt – max)
Tropicalpeat forest
Initial storage Ongoing exchange Total GHGV
500 1000 1500 2000 2500 0 200 400 0 500
GHGV (Mg CO2-eq ha-1 30yr-1)
1000 1500 2000 2500
Much theoretical work has been carried out to assess the relative GHG emissions of different crop and energy pathways, as well as the impact of different agricultural management regimes (such as different tillage and seedbed preparation techniques, the use of cover crops, harvesting techniques etc.), but actual measurements of the GHG balance of different feedstock production systems – especially in commercially realistic settings – are rare. Post-harvest processing and transport also influence the total GHG emissions associated with any particular energy type.
The interactions of these various factors with local conditions mean that biofuels have differing energy efficiencies and climate, social and environmental impacts. The balance of beneficial GHG reductions with other considerations such as national security, and economic, environmental and social impacts that in combination are acceptable to societies around the world, will be a key determinant of the extent to which bioenergy is adopted.
54 | 4 Economics, the environment and politics
The politics of biomass
Policies designed to boost the development of renewable and low-carbon forms of energy need to be carefully designed. They must provide adequate support and certainty for the industry (actively encouraging the positive benefits) at the same time as addressing a number of potential challenges (preventing the development of unsustainable forms of energy). The intersection of biomass production with energy and agricultural sectors presents unique challenges for the early stages of this industry. This chapter provides an overview of some key issues.
Energy security
Bioenergy can potentially increase the energy security of a nation by using indigenous biomass grown within its borders. Such indigenous sources of bioenergy could provide other benefits to the national economy and reduce the risk of supply disruption.
The Global Bioenergy Partnership (GBEP) concluded in a 2008 study that, ‘Most of the bioenergy consumed in G8 +5 Countries is produced locally.’ Even as biomass becomes traded globally, there will be many more countries able to supply biomass energy than those with fossil fuel reserves. By not using energy resources (fossil fuels) that would otherwise be consumed, the development of a new energy resource (bioenergy) could improve energy resilience and security. Investment in local energy co-provision (such as electricity co-generated from a mix of fuels) can boost rural electrification programmes with all the concomitant development and health benefits.
Regulation for sustainability
As described above, not all forms of bioenergy perform equally in terms of their environmental footprint or social acceptability. Government policy and regulations are needed, but issues relevant to the efficacy of regulations are complex, so policies will need to be tailored both locally and nationally to protect human rights and promote other economic or social objectives.
Bioenergy production is an extension of several ongoing activities in other arenas including commercial agriculture, commercial forestry and waste management. All the activities have environmental regulations that vary regionally across the globe. Industry groups and third parties have developed a range of voluntary sustainability standards, some of which are relevant to bioenergy production. Examples include the Roundtable on Sustainable Soy, the Roundtable on Sustainable Palm, the Sustainable Forestry Initiative, the Forest Stewardship Council, the Sustainable Sugarcane Initiative, and Solidaridad. In addition, many countries and states are moving environmental regulation of agriculture, forestry and waste toward more inclusive sustainability standards to which biomass for energy will also be subject. Several key policies, however, have emerged in the past five years that include sustainability criteria specific to bioenergy production.
In Brazil, the expansion of sugarcane for ethanol has been subject to new policies that include agroecological zoning[9], a process that designates land appropriate for development without interfering with long-term sustainability goals. Amendments to the forest code now require 10% of land in sugarcane production to be set aside for native forests. In addition, special protections for riverbank areas are being codified.
In the US, biofuels must meet criteria regarding GHG emissions and land-use criteria to be considered as ‘renewable’ or ‘advanced’ and eligible to meet the Renewable Fuel Standard[10] mandates for 36 billion gallons of renewable fuel by 2022. To limit unsustainable land clearing for biofuels, for example, purpose-grown energy crops are only eligible for specific incentives when restricted to existing agricultural land that was cleared or cultivated prior to enactment of the Energy Independence and Security Act of 2007. Also, for wood residues to qualify they must be from planted trees derived from actively managed tree plantations on non-federal land cleared at any time prior to 19 December 2007.
The EU’s Renewable Energy Directive, which sets a goal for 10% renewable energy by 2020, also contains specific factors relating to the sustainability of biofuels. Criteria prohibiting use of lands with high carbon and/or high biodiversity and limiting GHG emissions were codified in 2010[11].
Indicators of sustainability for bioenergy have been outlined by the Global Bioenergy Partnership, a part of the Food and Agriculture Organization of the United Nations. Criteria for sustainable biofuels proposed by the Roundtable on Sustainable Biofuels, an independent multi-disciplinary organization, have also recently been approved as certification standards.
Commercialization of new technologies
It is generally acknowledged that the most efficient policies are technology-neutral and do not attempt to ‘pick winners’. The rapidly developing science around bioenergy is sometimes at odds with slower-moving political and economic landscapes. Recent bioenergy policies, however, appear to be ahead of the science and technology, particularly in the arenas of consequential life cycle analysis and next-generation biofuel conversions. In order to provide investor certainty, stable medium- and long-term policies to support markets for bioenergy are required.
Typically, government support for bioenergy takes the form of incentives or mandates, often linked to other energy or agricultural policies. Incentives can include feed-in tariffs, tax reductions or rebates, grants, loan guarantees, construction incentives or other supportive policies or fiscal instruments. Mandates may include obligations to use a percentage of bioenergy (or other renewables) in fuel or energy generation. These vary considerably from country to country, as Table 4.4 demonstrates, and are subject to politically imposed change.
4 Economics, the environment and politics | 55
Country Targets
Electricity Heat Transport fuels
Brazil Inclusion of 3.3GW of renewable energy (wind, biomass, small hydroelectric) into National Energy Grid by 2007. Once met, renewable sources to provide 10% of total energy consumption within 20 years[13]. MAnDATory
No targets. MAnDATory blend of 20–25% anhydrous ethanol with gasoline; minimum blending of 2% (B2) biodiesel to diesel by 2008 and 5% (B5) by 2013.
China China is finalizing a revised target for 16% of primary energy from renewables by 2020, including large hydro; plans include a target for 30GW of biomass power for 2020.
No targets. 15% of its transportation energy needs through use of biofuels in 2020.
India No targets. No targets. A 5% blending mandate for ethanol will be established before end of 2007, and Planning Commission has proposed to raise mandate to 10%. On biodiesel, the Committee for the Development of Biofuels has decided 20% of diesel consumption as blending target for 2011–12.
Mexico >1GW of Renewable Energy Sources (RES) by 2006. MAnDATory
No targets currently (targets under consideration).
No targets currently (targets under consideration).
South Africa 4% by 2013. No targets. Up to 8% by 2006 (10% target under consideration).
Canada No targets. No targets. 5% renewable content in gasoline by 2010 and 2% renewable content in diesel fuel by 2012.
France 21% RES by 2010. MAnDATory 50% increase from 2004 until 2010 in heat from RES. MAnDATory
5.75% by 2008, 7% by 2010, 10% by 2015, 10% by 2020. MAnDATory – EU target
Germany 12.5% by 2010, 20% by 2020. MAnDATory
No targets. 6.75% by 2010, which is set to rise to 8% by 2015; 10% by 2020. MAnDATory – EU target
Italy 25% by 2010. No targets currently (targets under consideration).
5.75% by 2010. MAnDATory 10% by 2020. MAnDATory – EU target
Japan Biomass power generation and waste power generation in the amount of 5.86 billion litres, as converted to crude oil, by 2010.
Biomass thermal utilization in the amount of 3.08 billion litres (this amount includes biomass-derived fuel, 0.5 billion litres, for transportation), as converted to crude oil, by 2010.
0.5 billion litres, as converted to crude oil, by 2010.
russia No targets in place, but considering a 7% RES target by 2020.
No targets. No targets.
UK 10% by 2010, 15.4% by 2016. MAnDATory
>1GWe of installed combined heat and power (CHP) capacity by 2010 with >15% of government buildings using CHP.
5% biofuels by 2010. MAnDATory
10% by 2020. MAnDATory – EU target
US No national targets but individual states are pursuing a variety of incentive programmes.
No targets. A MAnDATory Renewable Fuel Standard (RFS) of 34 billion litres of renewable fuel in 2008, progressively increasing to 136 billion litres in 2022 with 79 billion litres coming from advanced biofuels such as cellulosic ethanol. Non-renewable fuels are not considered in RFS.
EU 20% RES as overall target for all Member States by 2020. MAnDATory
No targets. 10% by 2020. MAnDATory – EU target
Table 4.4
Voluntary and mandatory bioenergy targets for electricity, heat and transport fuels (as stated in country summaries and key policy documents) in place in different countries in 2008. These policies change with time in terms of both the types of bioenergy being legislated and the absolute values of the various targets[12].
56 | 4 Economics, the environment and politics
Chapter references
[1] Domac, J., Richards, K., & Risovic, S. (2005), Socioeconomic drivers in implementing bioenergy, Biomass and Bioenergy, vol. 28, pp. 97–106.
[2] Baffes, J. & Dennis, A. (2013), Long-term drivers of food prices. The World Bank Development Prospects Group and Poverty Reduction and Economic Management Network Trade Department report.
[3] Williams, E.D. & Simmons, J.E. (2013), Water in the energy industry: an introduction. BP, London, UK. Available from: www.bp.com/energysustainabilitychallenge [accessed February 2014].
[4] Khanna M. & Crago C. L. (2012), Measuring indirect land use change with biofuels: implications for policy, Annual Review of Resource Economics, vol. 4, pp. 161–184.
[5] Davis, S.C., Boddey, R.M., Alves, B.J.R., Cowie, A.L., George, B.H., Ogle, S.M., Smith, P., van Noordwijk, M. & van Wijk, M.T. (2013), Management swing potential for bioenergy crops, GCB Bioenergy, vol. 5, pp. 623–638.
[6] US Energy Information Administration (2013), Levelized cost of new generation resources in the annual energy outlook 2013. Available from: http://www.eia.gov/forecasts/aeo/er/pdf/electricity_generation.pdf [accessed February 2014].
[7] Buckeridge, M.S., De Souza, A.P., Arundale, R.A., Anderson-Teixeira, K.J. & DeLucia, E.H. (2012), Ethanol from sugarcane in Brazil: a ‘midway’ strategy for increasing ethanol production while maximizing environmental benefits, GCB Bioenergy, vol. 4, pp. 119–126.
[8] Anderson-Teixeira, K. J. & DeLucia, E. H. (2011), The greenhouse gas value of ecosystems, Global Change Biology, vol. 17, pp. 425–438.
[9] Manzatto, C. V., Assad, E. D., Bacca, J. F. M., Zaroni, M. J. & Pereira, S. E. M. (2009), Zoneamento agroecológico da cana-de-açúcar: expandir a produção, preservar a vida, garantir o futuro. Documentos 110. Embrapa Solos, Rio de Janeiro.
[10] US Environmental Protection Agency (2012), Regulation of fuels and fuel additives: 2012 renewable fuel standards; Final rule (January 9), Federal Register, vol. 77, no. 5, pp.1320–1358.
[11] Directive 2009/28/EC of the European Parliament and of the Council, articles 17, 18 and 19. 2009. Official Journal of the European Union, L 140/16.
[12] Global Bioenergy Partnership (GBEP) (2007), A review of the current state of bioenergy development in G8 + 5 countries, GBEP, Rome. Available at: http://www.globalbioenergy.org/fileadmin/user_upload/gbep/docs/BIOENERGY_INFO/0805_GBEP_Report.pdf [accessed February 2014].
[13] World Resource Institute-SD-PAMs Database, Programme of Incentives for Alternative Electricity Sources (PROINFA), Available from http://projects.wri.org/sd-pams-database/brazil/programme-incentives-alternative-electricity-sources-proinfa [accessed August 2014].
The science, politics and economics of bioenergy are developing rapidly, as is our understanding of the requirements for producing bioenergy and the effects of expanding commercial implementation at local, national and global levels. It is now clear that there is no ‘one size fits all’ solution for bioenergy development. Different options will be appropriate at different scales and different locations, depending on available infrastructure as well as cultural and developmental contexts. Given this situation, precision and details matter when teasing out the benefits and potential advantages of biomass from the potential risks.
Overall, agriculture fixes a prodigious amount of carbon for use as food, feed, materials and energy. Given finite land resources, the most important lever for enhanced use of agriculturally derived materials is improved agricultural productivity – regardless of the ultimate use of the agricultural products. Finding mechanisms that
allow for improved productivity, while limiting negative impacts of highly productive agriculture, are important environmental, regulatory and policy considerations.
Increased production and use of biomass has the potential to reduce GHG emissions from energy production, reverse degradation caused by intensive agricultural systems, and create sustainable industries in rural areas. In order to contribute materially to global energy, food and climate security, bioenergy provision must expand only with careful and context-sensitive implementation. Otherwise, bioenergy developments may lead to unintended conflict and competition.
There is strong demand for bioenergy, and new technology is being developed to use biomass resources. Consistent policies that promote environmental, economic and social sustainability are essential to fulfil the potential of bioenergy development.
Domac, J., Richards, K., & Risovic, S. (2005).......
(ON - replace 10 with) Manzatto, C. V., Assad, E. D., BACA, J., Zaroni, M. J., & Pereira, S. E. M. (2009). Zoneamento agroecológico da cana-de-açúcar: expandir a produção, preservar a vida, garantir o futuro. Embrapa Solos. Documentos, 110.
Climate and soils determine which plants will grow in a particular place, so energy crops should be chosen for the growing region (biome) to which they are best suited.
One way of integrating biomass production into agriculture is to find areas that are marginal for food production but that will support the different needs of the most suitable energy crops.
Figures for rainfall, temperature and growing season – the main parameters for choosing crops – are given for the global biomes that will support significant plant life.
58
5 Where can biomass feedstocks be grown? | 59
5 Where can biomass feedstocks be grown?
Growing regions (biomes)
This chapter provides detail on the fundamental biophysical constraints imposed on agriculture. In order to understand the potential growing regions for biomass crops, we must consider the biophysical and climatic parameters such as temperature, precipitation, soils and land area that all vary across the globe. This chapter introduces regional categories (biomes) that are defined based on these ecological parameters. It provides the background and context for bioenergy crops in the global landscape. A summary table is provided at the end of the chapter as a quick guide to biomes that might host bioenergy crops.
Biomes are distinguished by climate, soil and vegetation in any classification scheme; they do not respect political borders. Here we present the biome categories recognized by the Food and Agriculture Organization of the United Nations (FAO) according to Udvardy’s Ecoregions[1], although they are named differently by various groups. Please note that we have included only the broad classification categories in the following pages, and not 100% of the land surface is depicted in the various biomes for this reason.
A biome covers a wide geographical area, so conditions within a biome can vary broadly. The rainfall and temperatures described in this chapter reflect annual average ranges. Within each biome, there will be variation and anomalies beyond the average figures. Temperature and rainfall patterns are affected by elevation, aspect, the prevailing wind direction and proximity to the sea or other large bodies of water.
Growing-season lengths, defined as the number of days from plant emergence or bud break until senescence (when leaves turn brown and dry down), are often determined by temperature and also vary widely across biomes. In warm climates, where plant growth may persist year-round, the growing season is sometimes defined by the occurrence of sufficient rainfall. It should be noted that rainfall distribution patterns are important – some climates have a single rainy season, others have a bimodal pattern – while tropical coastal climates are wet enough to allow growth throughout the year.
Soils are highly spatially variable, but the major soil classifications[2] in each biome are identified because these have an impact on vegetation and ecosystem productivity. Climate and soil, together, are key constraints on the growth of ecosystems (including agricultural ecosystems). Just as the flora and fauna of a biome are adapted to their native conditions, crop species can be more suited to particular locations, but growing-season length, soil quality and water availability place certain limits on productivity.
The potential for bioenergy production is also constrained by the conditions of a biome. Biomass crops are diverse, so optimal biomass production will be achieved by selecting regionally appropriate species and identifying land opportunities that will not displace native ecosystems or disrupt other agricultural commodities. This chapter provides context for the global landscape in which biomass production must fit.
Figure 5.1, on the next page, maps the general suitability of land globally for agriculture. The map shows suitability of currently available land for pasture and rain-fed crops based on the general requirements of conventional food-cropping systems as defined by the FAO[3]. Assumed environmental conditions and constraints include thermal climate, length of growing period, climate variability, soil types and qualities, and terrain slope classes. Based on these constraints, the suitability classes are mapped at a 5 arc-minute spatial resolution. Lands classified as well-suited for agriculture are dominated by prime agricultural lands, and lands classified as suitable can be considered marginal, both defined in Chapter 2. Lands classified as unsuitable or poorly suited for agriculture are less likely to support agricultural systems because of climate and/or soil conditions that are not tolerated by conventional food crops (e.g. low precipitation, extreme temperatures). Lands that are urban (>25% of resolved grid space in urban development), protected (according to the World Conservation Monitoring Centre), closed forest (>75% of resolved grid space in forest), or irrigated (>50% of resolved grid space irrigated) are classified separately, as these are lands that would be considered unavailable for agriculture[3]. Irrigated lands, which are used for growing food in some places of the world should generally be considered unsuitable because of the management intensity that would be required to maintain and expand bioenergy crops in these places.
Biomes described in the following pages are overlaid with areas of agricultural suitability. The ecological constraints on plant growth are also defined for each region to provide context for the specific crops detailed in Chapter 6.
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5 Where can biomass feedstocks be grown? | 61
These are potentially some of the most productive areas on earth because of the long growing season, moderate temperatures and abundant rainfall. South-east Brazil, southern China and New Zealand enjoy moderate temperatures, plentiful but not excessive rainfall and a growing season that lasts at least three-quarters of the year. Depending on the underlying geology, soils range from fertile volcanic and clay-based soils to weathered, infertile and acidic clay-rich soils. Globally abundant soils that have no distinct layers and soils that are only moderately developed also occur. The weathered soils need careful management to maintain their structure under cultivation. The US Department of Agriculture offers a useful guide to soil classification[2].
Current land use
As its name suggests, the natural vegetation of this biome is forest, both broadleaved and coniferous. But much of the forest has been replaced by smallholder cultivation and intensive mixed agriculture featuring both livestock and cereals. With correct fertilizer and liming where necessary to counteract soil acidity, a wide range of crops can be grown (including many forms of bioenergy crops).
Subtropical humid forest
n Closed forest
n Inland water bodies
n Irrigated area
n Land prime or well suited for agriculture
n Land suited for agriculture
n Land unsuited to poorly suited for agriculture
n Protected area
n Urban area
Agricultural suitability of land in subtropical humid forest
A B E
Useful numbersRainfall: 1,000 –2,500mm per yearTemperature: 10 – 30°CGrowing season: 270 – 365 days
C D
A
B
C
D
E
62 | 5 Where can biomass feedstocks be grown?
Heading
After tropical forests, the temperate hardwood forests are the most biodiverse forests of the world. This biome includes the eastern US, much of Western Europe and the eastern half of China. The natural vegetation of this biome has largely disappeared on some continents because of the natural productivity of these regions for agriculture, but on others this ecosystem has regenerated over the past century (such as the temperate forests of the eastern US). Winters can be moderately severe but summer temperatures are suitable for a wide range of crops. A range of soils is found, including those rich in organic material and having formed from limestone, wind-blown sediment or sand. Soils resulting from the weathering of clays, and partially developed soils, are also common in the eastern US.
Current land use
Large-scale commercial agriculture is well established. All major crop groups are grown, particularly cereals and vegetables. Livestock farming forms part of the land-use mosaic and a variety of forestry practices are used to manage the land that is still in forest, much of it secondary and having regenerated after previous logging events.
Temperate broadleaved forest
n Closed forest
n Inland water bodies
n Irrigated area
n Land prime or well suited for agriculture
n Land suited for agriculture
n Land unsuited to poorly suited for agriculture
n Protected area
n Urban area
Agricultural suitability of land in temperate broadleaved forest
B
C D
A
Useful numbersRainfall: 350 – 1,500mm per yearTemperature: -10 – 30°CGrowing season: 90 – 365 days
E
A
C
E
D
B
5 Where can biomass feedstocks be grown? | 63
Great swathes of the northern hemisphere, lying roughly between latitudes 50° and 70° North, are naturally covered by coniferous forest. This biome includes most of Canada and Russia, and the northern parts of Scandinavia. Conditions can be harsh in winter and the growing season is short, but coniferous trees are adapted to these conditions. In the coldest parts, soils overlay permanently frozen layers of ground (permafrost) so rooting depth is restricted. Typically soils under coniferous trees have been formed by weathering, which has stripped organic matter and aluminium from the surface and deposited them in the subsoil. The hard layer that results from such weathering and their free-draining nature render them poor for agriculture. Peaty soils have developed in poorly drained areas, where the lack of oxygen slows the decomposition of organic matter. These peat deposits are important global carbon sinks.
This is a very large biome (17% of global land area), a great deal of which is not easily cultivated for crops. With an average maximum temperature at the minimum required for growth of most crops, productivity is severely limited by the cold.
Current land use
Forestry still dominates the land use in the northern parts, which are inhospitable and sparsely populated. Some crops can be grown, including hardy cereals such as oats and barley, some tough vegetables and root crops such as beets and potatoes. Further south, on the better soils, large-scale growers produce cereals.
Temperate coniferous forest
n Closed forest
n Inland water bodies
n Irrigated area
n Land prime or well suited for agriculture
n Land suited for agriculture
n Land unsuited to poorly suited for agriculture
n Protected area
n Urban area
Agricultural suitability of land in temperate coniferous forest
Useful numbersRainfall: 100 – 1,500mm per yearTemperature: -30 – 5°CGrowing season: 30 – 180 days
The northwest coast of the US and Canada is a distinct area of coniferous forest that receives up to 5,000mm of annual rainfall, has an average annual temperature of 10°C, and a growing season that lasts up to 300 days in some places; this area is often classified as temperate rainforest.
64 | 5 Where can biomass feedstocks be grown?
Heading
Natural grassland is known variously as prairie (North America), steppe (Eurasia) and pampas (South America). Trees are scarce, restricted by the low rainfall or soil moisture and risk of fire. Historically, these areas were home to grazing animals, such as the North American bison, that moved freely in search of fresh grass following rain or fire. Some grassland soils are rich in organic matter, optimal for cultivation, and some are derived from weathered clay minerals but, in drier areas, they may be very low in organic matter with cemented subsoils or salty surface accumulations. Soils, based on shrinkable montmorillonite clays, have a heavy texture but, when irrigated, are suitable for arable crops.
In the prairie and steppe regions, winters are extremely cold, with freezing temperatures. The high altitudes of the great basin region of the US and China are arid as well as cold, and have little to no vegetative growth in some places.
Current land use
Large-scale commercial agriculture is successful in much of these areas, but erosion can be problematic. Irrigation extends the range of crops that can be grown, and no-tillage methods protect soil organic matter and reduce the risk of erosion. The vast majority of native temperate grassland has been displaced by agriculture that includes both crops and livestock.
Temperate grassland
n Closed forest
n Inland water bodies
n Irrigated area
n Land prime or well suited for agriculture
n Land suited for agriculture
n Land unsuited to poorly suited for agriculture
n Protected area
n Urban area
Agricultural suitability of land in temperate grassland
C D
Useful numbersRainfall: 50 – 1,000mm per yearTemperature: -10 – 30°CGrowing season: 0 – 320 days
B
A
E
A C
D
E
B
5 Where can biomass feedstocks be grown? | 65
Much of sub-Saharan Africa, apart from the tropical humid equatorial forest, is naturally covered with this type of vegetation. It is also found across much of India and highland South-East Asia, as well as in north-east Brazil. More sparse woodland than high forest, it differs from tropical grassland only in having slightly higher rainfall and having trees as the dominant vegetation. Soils vary widely in this biome from productive, moisture-retaining soils to highly weathered, nutrient-depleted soils, and others with heavy clay-rich sub-soils. Some clay soils have the capacity to shrink and expand, affecting water holding capacity and stability at the surface.
Current land use
Much of this area is cultivated by smallholders, but it also supports large commercial enterprises growing a wide range of crops. Total amounts and temporal distribution of rainfall limit what can be grown unless land can be irrigated. Highland Kenya, for instance, can expect two distinct rainy seasons per year, whereas further south, such as in Zambia and Malawi, rainfall is restricted to a single season. The weathered soils are often deficient in major and minor plant nutrients. Rice is widely grown in this biome, as found in India and Asia. In semi-arid parts of this biome, succulent crops such as sisal (Agave spp.) for fibre and jatropha for biodiesel can grow well.
Tropical dry forest
n Closed forest
n Inland water bodies
n Irrigated area
n Land prime or well suited for agriculture
n Land suited for agriculture
n Land unsuited to poorly suited for agriculture
n Protected area
n Urban area
Agricultural suitability of land in tropical dry forest
Useful numbersRainfall: 700 – 2,500mm per yearTemperature: 15 – 30°CGrowing season: 30 – 300 days
B
A
C
E
D
A
BC
E
D
66 | 5 Where can biomass feedstocks be grown?
Heading
66 | 5 Where can biomass feedstocks be grown?
Found in Colombia and Venezuela, central Brazil and northern Australia, tropical grassland is similar to tropical dry forest. It is the slightly lower rainfall that restricts the growth of trees in this biome. Soils range from dark clay soils to weathered, infertile and acidic soils.
Current land use
Land in this biome is often farmed by smallholders and large commercial enterprises. A wide range of crops can be grown, similar to those described in the tropical dry forest section, and these crops are restricted primarily by local rainfall patterns or the possibility of irrigation.
Tropical grassland
n Closed forest
n Inland water bodies
n Irrigated area
n Land prime or well suited for agriculture
n Land suited for agriculture
n Land unsuited to poorly suited for agriculture
n Protected area
n Urban area
Agricultural suitability of land in tropical grassland
Useful numbersRainfall: 500 – 2,500mm per yearTemperature: 15 – 30°CGrowing season: 30 – 300 days
A
B
C
B
A
C
5 Where can biomass feedstocks be grown? | 67
The most biologically diverse terrestrial ecosystem, harbouring vast carbon stocks, tropical rainforests are almost constantly in the news. More than 1,000 plant species can be found in a single square kilometre of many tropical rainforests, a quarter of which can be unique to a given area. Illegal logging and unregulated clearance for agriculture causes justified alarm in environmental circles. These forests occur fairly close to the equator, where day length varies only slightly, and temperature and humidity are constantly high. They include the Amazon and Congo basins, Indonesia, Bangladesh, Burma and coastal strips of western India, Thailand, Vietnam and north-eastern Australia. In many tropical rainforests, the nutrients are recycled so quickly that the soils are considered very poor despite the rich nutrients and biodiversity of the vegetation. Peat soils are, however, found in some tropical rainforests of the eastern hemisphere, with very rich organic material high in both carbon and nutrients. Both soil types are very sensitive to land-use change.
Current land use
Large areas of this biome are protected. The dense natural vegetation led to an early belief that rainforest soils would be very productive. Although the rainforest system is very efficient at recycling nutrients, cleared land quickly loses fertility as the high rainfall leaches minerals from the topsoil. The land needs careful management to conserve nutrients and minimize erosion. Smallholders cultivate plots, growing a range of crops, and commercial plantations, like oil palm, are also grown in this biome.
Tropical humid rainforest
n Closed forest
n Inland water bodies
n Irrigated area
n Land prime or well suited for agriculture
n Land suited for agriculture
n Land unsuited to poorly suited for agriculture
n Protected area
n Urban area
Agricultural suitability of land in tropical humid forest
Useful numbersRainfall: 1,500 – 5,000mm per yearIsland systems depicted on the map may have a mix of humid rainforest and dry tropical forest with rainfall as low as 700mm in some areas.
Temperature: 25 – 30°CGrowing season: 300 – 365 days
D
B CA E
A
B
C
D
E
68 | 5 Where can biomass feedstocks be grown?
Heading
68 | 5 Where can biomass feedstocks be grown?
True desert covers a significant land area equal to roughly 15% of the globe. Parts of the south-western US and Mexico, much of Northern Africa (and parts of south-western Africa), the Persian Gulf and most of Australia suffer from infrequent and unpredictable rainfall, and extremes of heat. Soils are poor, sometimes merely shifting sand. Some deserts actually have cold climates, and growth is restricted in these regions primarily by water availability.
Current land use
Desert areas are unproductive unless they can be irrigated, although some plants are adapted to these harsh conditions. Where irrigation is possible, the warm temperatures encourage productive crops – think of the strip of land bordering the Nile. Succulent crops such as sisal (Agave spp.) for fibre and jatropha for biodiesel
are suited to near-desert conditions. Semi-arid lands at the margin of true deserts are as large as the deserts themselves, totalling roughly 18% of the globe, and are considered more arable.
Desert
n Closed forest
n Inland water bodies
n Irrigated area
n Land prime or well suited for agriculture
n Land suited for agriculture
n Land unsuited to poorly suited for agriculture
n Protected area
n Urban area
Agricultural suitability of land in deserts
Useful numbersRainfall: Warm desert 0 – 350mm per yearCold desert 0 – 1,000mm per yearTemperature: Warm desert 10 – 30°CCold desert -14 – 18°CGrowing season: Warm desert 0 – 30 daysCold desert 0 – 210 daysAlthough some species may have evolved locally in order to survive the extremes of climate, most bioenergy crops will not tolerate these conditions, leading to zero growing days.
B
C E
A
A
C
D
EB
D
5 Where can biomass feedstocks be grown? | 69
Chapter references
[1] Food and Agriculture Organization of the United Nations, GeoNetwork (2001), Udvardy’s ecoregions.
[2] US Department of Agriculture, Natural Resources Conservation Service, National soil survey handbook, title 430-VI, Part 622 – Interpretative Groups. Available from: http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/?cid=nrcs142p2_054242 [accessed July 2013].
[3] van Velthuizen, H. et al. (2006), Mapping biophysical factors that influence agricultural production and rural vulnerability, Environmental and Natural Resources, series 11. FAO & IIASA, Rome.
Biome and type of agriculture Rainfall mm/yr
Temp*
oCGrowing
days**Crops Possible biofuel crops***
Subtropical/temperate humid forestLarge commercial and smallholder: intensive mixed agriculture, cereals and livestock, tree crops.
1,000 – 2,500 10 – 30 270 – 365 Cereals†, fibres, oil crops, pulses, roots/tubers, coffee, tea, sugar crops, fruit, vegetables, timber.
Maize, sugarcane, soybean, sorghum, pine, eucalyptus.
Temperate broadleaved forestLarge commercial and smallholder: tree crops, forest-based livestock, large-scale cereal and vegetables, cereal/livestock.
350 – 1,500 -10 – 30 90 – 365 Cereals†, fibres, oil crops, pulses, roots/tubers, coffee, tea, sugar crops, fruit, vegetables, timber.
Maize, switchgrass, miscanthus, soybean, wheat, cordgrass, oilseed rape, pine, willow/poplar, sorghum.
Temperate coniferous forestForestry, large commercial and smallholder: cereals/roots, forest-based livestock.
100 – 1,500 -30 – 5 30 – 180 Timber, cereals†, roots, tubers.
Willow/poplar, switchgrass, miscanthus, cordgrass.
Temperate grasslandLarge commercial and smallholder: irrigated mixed agriculture, small-scale cereal/livestock.
50 – 1,000 -10 – 30 0 – 320 Cereals†, fibres, oil crops, pulses, roots/tubers, sugar crops, fruit, vegetables, timber.
Maize, sugarcane, switchgrass, miscanthus, soybean, wheat, cordgrass, oilseed rape, sorghum.
Tropical dry forestLarge commercial and smallholder: tree crops, rice, cereals/roots.
700 – 2,500 15 – 30 30 – 300 Cereals†, fibres, oil crops, pulses, roots/tubers, tea, coffee, sugar crops, fruit, vegetables, timber.
Maize, sugarcane, soybean, sorghum, energy cane, jatropha.
Tropical grasslandLarge commercial and smallholder: extensive mixed cropping, cereal/livestock.
500 – 2,500 15 – 30 30 – 300 Cereals†, fibres, oil crops, pulses, roots/tubers, tea, coffee, sugar crops, fruit, vegetables, timber.
Maize, sugarcane, soybean, wheat, sorghum, energy cane, jatropha.
Tropical humid rainforestLarge commercial and smallholder: subsistence agriculture, livestock, tree crop, root crop, large proportions are protected land.
1,500 – 5,000 25 – 30 300 – 365 Cereals†, fibres, oil crops, pulses, roots/tubers, tea, coffee, sugar crops, fruit, vegetables, timber.
Oil palm, sugarcane, sorghum, energy cane.
DesertSubsistence pastoralism.
0 – 350 10 – 40 0 – 30 Succulents. Agave, jatropha.
Notes* Average annual temperature, based on FAO GeoNetwork[1]. Note regions, that would be distinct from
the ranges given in this table, are identified and described in the temperate coniferous forest, tropical humid rainforest and desert pages.
** In general, growth is limited by rainfall (or water availability) in tropical climates and by temperature in temperate climates. Although species might have evolved locally in order to survive the extremes of climate, some crops may not, leading to zero growing days. Crop selection and management can potentially extend the growing season in other cases.
*** Within a biome, the suitability of a site for a particular crop depends on a range of factors, including altitude, aspect, rainfall and soil type. Crops listed here are examples and are not intended to be a comprehensive list.
† Cereals are generally of the gramineous family and refer to crops harvested for dry grain only (specifically wheat, rice paddy, barley, maize, popcorn, rye, oats, millets, sorghum, buckwheat, quinoa, fonio, triticale, canary seed, mixed grain, cereals nes).
Regional characteristics: comparison table
Energy crop species have variable characteristics, making some more suited to certain conditions than others.
A range of examples of bioenergy crops, some already commercially produced, is provided here to illustrate the variation in crops grown across different geographic distributions and under different managements.
Current production levels of various crops provide perspective on the potential for biomass development.
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The statistics for the area of planting, producing countries and total production are based on FAOSTAT data for maize (corn), sugarcane, oil palm and soybean. For the other crops described in this chapter, data are not available from the FAO and specific reviews or meta analyses published in peer-reviewed literature have been used.
Yield and bioenergy deliverablesThe diagrams on the crop pages indicate worldwide average annual yield per hectare (ha) and the highest recorded yield per hectare (1ha = 100m × 100m or 2.47 acres) with equivalent fuel volumes and energy yields estimated. Yield data are based on commercial yields for widely grown crops, and on best available data for less widely grown crops. It should be cautioned that the yield of each crop varies dramatically across growing regions according to soil type, climate and management and, over time, in response to dynamic climate conditions. Ranges are included in the text, and are often very large because of these variables. Detailed information about yields in a specific area of interest are provided at the end of this chapter in the complete reference list on page 104. Symbols are used to represent the following values per hectare:
●● Dry crop mass in tonnes (t) – weight symbol.●● Liquid fuel derivable in litres (l) – barrel symbol. ●● Electricity that can be generated at 30% overall efficiency kilowatt hours (kWh) – light bulbs.
●● Practical energy use equivalent (per hectare) – car or house symbols.
Next to each car symbol is the estimated distance that can be travelled by an average family car using biomass from one hectare of land. This is estimated two ways: (1) based on the average annual yield of liquid fuel derived from one hectare; and (2) based on the greatest recorded yield per hectare. The family car category of vehicles does not assume the greatest achievable gas mileage (miles per gallon or litres per kilometre), but it does reflect modern vehicle efficiencies.
Parameters used in this calculation are:●● Consumption – gasoline 8 litres/100km and diesel 6 litres/100km.
●● Energy density of biofuels – bioethanol, 67% of gasoline; biodiesel, 91% of typical fossil-derived diesel blend.
●● Density of fuels – bioethanol 0.79kg/litre and biodiesel 0.87kg/litre.
●● Biodiesel conversion factor – 97% of crop oil (bioethanol yield varies per crop).
Next to each house symbol is the estimated number of months an average household energy budget could be supported using biomass from one hectare of land.
The household energy budget assumed is for a typical UK household with total of 20,000kWh/yr energy consumption. Normally, around 16,500kWh of the total is related to heating requirements, which is delivered by gas. In this calculation, the household uses electricity for all energy requirements including heating and cooking as well as lighting and cooling. The power generation efficiency assumed in the calculation is 30%.
The following pages provide key data about crop species and biomass types that are already in production or are being researched for biomass. This is not a comprehensive review of all species considered for bioenergy, as there are many others. Instead, this collection includes at least one representative of each major plant functional group or biomass type. For each crop page that highlights a species, there is a box that cites comparable plants or biomass sources that are also widely recognized.
Each ‘crop page’ contains the following sections.
Plant characteristics
IconsThese are pictorial guides to the type of plant, its photo-synthetic pathway and the current major energy use (more than one classification in each category sometimes applies).
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Icons shown in grey indicate pre-commercial stages of adoption. These icons are repeated on a fold out on the back cover.
Growth and production
Map Indicates latitude limits for commercial growth and the five countries with the greatest production of the crop. The political boundaries of large countries will cross the latitude limit in some cases whereas, in general, the growing zones do not.
Global production diagram Crop-specific data for global production of liquid fuels, heat or power are variable and difficult to substantiate. Where a crop is produced as a major product in a country, these data are routinely recorded at country level.
6 Biomass feedstock crops | 71
Introduction to the selected crops
72 | 6 Biomass feedstock crops
Maize (corn)
Zea mays L.
●● Type of fuel: ethanol (grain), biogas (whole plant).●● Stage of adoption: extensive commercial production of ethanol, leading source of biofuel in the world, commercial biogas production.
Maize, known as corn in the US, was first domesticated 10,000 years ago in Central America. Its distinctive lush foliage and tasseled flowers are now a common sight throughout the temperate and tropical world. With end products ranging from sweet corn to silage, maize is an important human and animal food, as well as providing biomaterials and fuel. Despite having been introduced to Africa only a few hundred years ago, it is now considered a vital staple there and in many areas has replaced traditional sources of starch such as cassava, sorghum and millet. The amount of maize consumed globally as food is dwarfed by the amount used to feed cattle.
In the US ~44% of maize was used for ethanol production in 2012, almost equivalent to the amount used for animal feed. In some European countries maize is the major biogas crop.
Plant characteristics
Maize is a tall, fast-growing annual grass reaching 2 or 3 metres at maturity in a single growing season. Using the highly productive C4 photosynthetic pathway, it produces corncobs that grow from nodes on the stem. The male flowers appear as tassels at the top of the plant.
Selective breeding of the original species focused on developing larger kernels and creating varieties with differing sugar levels. Thousands of maize varieties are now available, from sweet corn and ‘baby corn’ (eaten as vegetables) to starchier cultivars for various end uses. Green stems of maize are also used to make silage for cattle or biogas production. There are tens of GM hybrids, the first of which was created to give resistance to the
54˚N
36˚S
Top producing countries
Million tonnes*
USChinaBrazilMexicoArgentina
320180 55 23 22
*grainMexico
Argentina
Brazil
ChinaUS
World map with latitude limits for growth and five top producing countries
Global planting – 160 million hectares in 2010, with a 10-year average of 150 million hectares.
Global production of maize was 850 million tonnes grain (dry weight) in 2010. Worldwide average annual grain yield was 5.2 tonnes/ha from 2008 to 2010, but yields vary widely (with grain yields of up to 10 tonnes/ha in the US and total biomass ranging worldwide from less than a tonne to 28 tonnes/ha).
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6 Biomass feedstock crops | 73
potentially devastating European corn borer (Ostrinia nubilalis). Use of GM hybrids is linked to yield increases and reduced pesticide use. Additional transgenic hybrids have been developed for stress tolerance and resistance to certain pests and herbicides. Innovations in crop genetics, mechanization, fertilization, and pest and crop management have resulted in a fourfold increase in maize yields over the past 70 years in the US.
Where to grow it
Maize needs a frost-free growing season with optimal growing temperatures of 24 – 30°C. Plants grow best in warm climates but are damaged by temperatures above 45°C. It is grown successfully over a broad latitudinal range, from 54° North to 34° South. In temperate climates it is sown in spring and harvested in autumn; in climates with a pronounced wet season it is planted with the first rains and harvested as rainfall tails off. Maize is well adapted to medium-textured (0.25 – 0.5mm) soils. It can be grown in nearly every biome described in this handbook, but is most common in temperate grassland and temperate broadleaved forest biomes.
How to grow it
Large-scale mechanized production is the norm in commercial farms, although smallholders in developing countries grow and harvest maize entirely by hand. Reduced-tillage methods such as direct drilling protect the soil and improve soil organic carbon sequestration. Maize has higher yield when planted in a two-year rotation with a nitrogen-fixing crop such as soybeans. This is the most common rotation, but maize is also sometimes grown without rotation, in a three-year rotation with wheat and soybean, or in a three-year rotation that follows the sequence maize–maize–soybean. Intercropping is also practised over a small area in some places, with a variety of crops that can be planted between the rows of maize.
Inputs required
WaterThe crop needs adequate rainfall, in the range of 670 – 790mm during the growing season. Most maize agriculture in the US is rainfed, but the shallow-rooted crop is sensitive to water limitation in drier regions where rainfall is supplemented with irrigation.
FertilizerCommercial crops of maize are boosted by the application of nitrogen, phosphorus and potassium (N–P–K) fertilizer. Nitrogen is needed in relatively large quantities (140 – 200kg per hectare), especially on light sandy soils. This can lead to undesirable leaching of nitrates into groundwater if application rates are not carefully matched to soil type and rainfall or irrigation levels.
Pests and diseases
Maize is host to a range of diseases, including types of mildew (Peronoscleraspora sorghi – up to 80% yield loss), leaf spot (Cercospora zeamaydis – average 30% yield loss), and blight (Exserohilum turcicum – up to 70% yield loss). Fungal diseases sometimes gain entry to plants via holes made by maize borers, which are the most damaging insect pests wherever maize is grown, causing grain yield losses of 36%.
Globally, maize yields can be reduced by almost one-third due to weeds and pests: weeds (11%), herbivores (10%), pathogens (9%) and viruses (3%).
Defences
HerbicidesMany herbicides are used to control weeds on non-GM varieties. Glyphosate is widely used on GM maize bred for resistance to this herbicide. To help prevent infestation by Striga, a parasitic plant that causes extensive damage in Africa, seeds can be given a special chemical coating.
Top producing countries
Million tonnes*
USChinaBrazilMexicoArgentina
320180 55 23 22
*grain
World map with latitude limits for growth and five top producing countries
Dry weight in tonnes
2,000 litres
5.2 tonnes
Litres of bioethanol fuel
gasoline equivalent of 1,400 litres
Maize average annual yield per hectare
Maize yields – global average and top producing countries
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What distance could you drive?18,000km11,000 miles
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PesticidesMany different pesticides are used on maize, the type and amount depending on the region of the world. The use of GM maize resistant to European corn borer has reduced the need for pesticides against this pest. A range of pesticides is available for use against other pests such as armyworms. Non-chemical ‘push-pull’ strategies that used trap crops to attract pests to the outside of the field in addition to intercropping with plants that repel pests (and/or inhibit Striga) have also been very successful.
Harvesting
Mechanical harvesting is the norm in commercial production to ensure harvest at the optimal time. As with other grain crops, the seed must have dried sufficiently for efficient combine harvesting. For maize kernels, optimum moisture to avoid seed damage during harvest is usually 22%. Moisture above 30% will result in poor kernel separation, and below 15% will result in a large portion of the kernels being cracked and broken.
Labour-intensive manual weed control and harvesting are still widespread in much of Africa. This involves cutting each stem by hand and stacking the maize into large stacks to dry further, before the kernels are removed from the cobs. For biogas production, maize is harvested with a chopper when a dry matter content of 25 – 30% is reached. In a process called ensiling, the whole crop can also be cut and chopped when relatively fresh, optionally inoculated with acid-forming bacteria, and stored for later use as animal food (silage).
Yield
Worldwide average annual grain yield was just over 5 tonnes/ha, but yields vary hugely (from one-fifth of a tonne to 28 tonnes/ha if the whole plant is harvested). High yielding fields in the US can exceed 10 tonnes/ha of grain.
Ethanol yield from maize is ~390 litres per tonne of grain.
Alternative markets
Maize is grown for food and animal feed, with the proportion allocated to these markets heavily dependent on the region of the world. Turned into high-fructose corn syrup, it is an ingredient in many processed foods. It is also used to make starch and cereals, and fermented to make alcoholic drinks such as bourbon. Corn oil is another important foodstuff that is essentially a by-product of making animal feed. Maize is also used as a biomaterial for packaging and disposable cups.
Co-products
From the cropMaize stover and cobs (the crop residue after the kernels have been extracted) has potential use as bioenergy feedstock for cellulosic ethanol production.
From conversion to fuelThe main co-product of fermentation is sold as high-protein animal feed called dry distillers grains and solubles. This co-product is a major commodity that adds value to the corn grain ethanol supply chain. Carbon dioxide from fermentation is also often collected and used to make carbonated beverages.
Invasion risk
Maize is generally not considered an invasive species, but risk of invasion with or without transgene dispersal into the Mexican landraces (varieties) from where modern maize arose is cited as a potential risk associated with the large, nearby US corn crop. This risk is currently debated in the scientific literature.
Key references
●● Doebley, J. (2004), The genetics of maize evolution, Annual Review of Genetics, vol. 38, pp. 37 – 59.
●● Kim, S. & Dale, B. E. (2005), Environmental aspects of ethanol derived from no-tilled corn grain: non renewable energy consumption and greenhouse gas emissions, Biomass and Bioenergy, vol. 28, no.5, pp. 475 – 489.
●● Leakey, A. D. B. et al. (2004), Will photosynthesis of maize (Zea mays) in the US corn belt increase in future [CO2] rich atmospheres? An analysis of diurnal courses of CO2 uptake under free-air concentration enrichment (FACE), Global Change Biology, vol. 10, no. 6, pp. 951 – 962.
●● Oerke, E. C. (2005), Crop losses to pests, The Journal of Agricultural Science, vol. 144, no. 1, pp. 31 – 43.
●● US Department of Agriculture, Economic Research Service, corn background data.
This box highlights another international commodity crop that is harvested for grain.
Wheat (Triticum aestivum)
●● Photo in production: from Midwestern US.●● Why is it similar? Also one of the top grain commodities in the world; grain of plant harvested for food, feed and fuel; intensive inputs; often grown in rotation with other crops.
●● What makes it different? Uses C3 photosynthesis; can grow in colder climates than tolerated by corn; lower yielding than corn.
●● Growing regions: Top five producing countries are China, India, the US, the Russian Federation and France.
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74 | 6 Biomass feedstock crops
Sugarcane Saccharum officinarum L.
●● Type of fuel: solid combustion of residues (bagasse) for heat and electricity, ethanol.
●● Stage of adoption: extensive commercial production, leading source of biofuel in the world before the recent rise of corn ethanol.
Once the instant gratification of chewing sugarcane was discovered, the spread of the plant from its origins in the island of New Guinea and India was rapid. Carried by Arab traders, sugarcane surged across the Middle East and North Africa, reaching Spain by 715AD. Sugarcane crossed the Atlantic in 1493 with Columbus who introduced it to the Caribbean island of Hispanolia, and the Spanish carried it on to South America. The popularity of processed sugar in Europe, in the 18th century, led directly to the huge rise in plantations across European colonies in the Caribbean and in Brazil.
Plant characteristics
Sugarcane is a giant perennial grass, growing stems up to 4 metres high and 5 centimetres in diameter. It uses a C4 photosynthetic pathway that is particularly efficient in concentrating sucrose into multiple stems that grow from the plantbase.
At the end of the 19th century, breeders settled on S. officinarum as the variety of choice for yield and disease resistance. Today, there are around 70 cultivars of S. officinarium in commercial use, with 58 of them being hybrids, often crossed with S. spontaneum. At the time of writing, there are no commercial GM cultivars although field trials are ongoing.
Where to grow it
Sugarcane does not survive frosts and it grows best in areas with long, warm growing seasons followed by slightly cooler and drier but sunny ripening and harvesting season. This restricts the commercial raising of sugarcane to land below 1,500 metres from 36° North to 31° South,
36˚N
31˚S
Global planting – 24 million hectares Global production – 1,700 million tonnes (fresh weight)
Top producing countries
Million tonnes*
BrazilIndiaChinaThailandMexico
720290110 69 50
*fresh weightMexico
Brazil
China
IndiaThailand
World map with latitude limits for growth and five top producing countries
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6 Biomass feedstock crops | 75
primarily in the tropical and subtropical biomes but also in the southern edges of the temperate broadleaved forest biome. The plants are tolerant of a wide variety of soil types. The soils must be well drained, however, if planted on heavy clays.
How to grow it
Sugarcane is grown as a monoculture and, although it produces seeds, is harvested before seed production occurs to maximize sugar concentrations of the stems. Commercial cultivation is accomplished by planting sections of stems. These produce new stalks known as ratoons, which need between nine and 24 months to reach a harvestable state. Plants can last up to 10 years but productivity decreases after five to seven ratoon cycles, so they are normally re-planted then to maximize yield. Stems are now often machine planted and the soils are typically fully tilled, although minimum tillage is being practised in some regions of Brazil.
Inputs required
WaterSugarcane is sensitive to drought: 1,500 to 2,000mm of rain is required to avoid irrigation. In water-limiting conditions, research has shown that 10mm of water raises yields by 1 tonne of cane per hectare. Vinasse, an organic liquid containing high amounts of organic carbon (6,000–23,000mg C per litre) generated as a by-product of fermentation, is also sometimes recycled to the sugarcane fields to supplement water needs; 10 – 15 litres of vinasse is generated for every litre of ethanol.
FertilizerTo maximize yield, commercial growers use significant amounts of nitrogen, phosphorus and potassium (N–P–K) fertilizer as well as lime, with nitrogen application having the greatest environmental impact. The most effective method of delivering these elements is through
fertigation, where the nutrients are added to irrigation water and via application of vinasse. Reported rates for fertilizer application vary widely within a range of 45–300kg per hectare.
Although still debated in scientific literature, there is some evidence that biological nitrogen fixation (via nitrogen-fixing bacteria) supplements the nitrogen requirements of sugarcane in rare cases.
Pests and diseases
Sugarcane is affected by many diseases caused by fungal, bacterial and viral attacks with an estimate, in India, of 15% crop loss due to disease. The red rot fungal disease, which is common globally, severely damages yields and has wiped out one sugarcane variety in India, while another fungal disease, smut, can cause crop losses of 70%.
The plants are also commonly vulnerable to attack from insects that bore into roots and stalks, as well as nematodes in the soil that eat roots. The most serious pest group are white grubs of the beetle family Coleoptera, which can reduce sugar yield by up to 39%. Some mammals are also a threat, with rats known to cause crop loss, again of 39%, in many growing regions.
The effects of pests and diseases are always a risk, but can often be effectively controlled.
Defences
Herbicides A range of herbicides, including glyphosate, metalochlor, alachlor and paraquat, are commonly used prior to planting and to aid plant maturation. Use varies by region and by legislation, with some herbicides banned in certain legislations.
PesticidesA wide range of pesticides is used against threatening species, including root borers and white grubs. Pesticide application is widely variable and difficult to generalize.
Wet weight in tonnes (63–73% water)
5,800 litres
71 tonnes
Litres of bioethanol fuel
gasoline equivalent of 3,900 litres
Sugarcane average annual yield per hectare
Sugarcane yields – global average and top producing countries
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What distance could you drive?
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76 | 6 Biomass feedstock crops
Harvesting
The crop can be harvested by hand or mechanically. When harvested manually, two techniques can be employed depending on local practice and custom. Mature green canes can be cut on ripening or on the day after the fields have been burned. Burning removes poisonous snakes and non-useful plant material, and improves worker safety by removing sharp leaves, so the yield per worker is more than twice as high as for green cane: five tonnes per day compared with two. Mechanical harvesting is carried out on unburned crops and, although the productivity is much higher, it leaves long stumps and residual cane, which promote pests and disease as well as causing soil compaction and splitting of the cane stumps that inhibits ratoon growth. The practice of burning is being phased out of commercial operations in response to concerns over local air quality, the wasting of energy contained in the leaf material, and improvements in harvesting machinery.
Yield
Sugarcane worldwide yields average 71 tonnes fresh wet weight per hectare, with wide variation between countries (0.9–122 tonnes). In Brazil, converting sugarcane to ethanol produces on average 82 litres per tonne. Brazil produced 21 billion litres in 2011, some 25% of global bioethanol production.
Alternative markets
Although sugarcane has been used for large-scale bioethanol production since 1975, the primary market is sugar, and sugarcane provides 70% of the world’s sugar. Many sugarcane mills serve both markets simultaneously.
Co-products
Crop residueLeaves and other plant debris, often called ‘trash’ that is often left in the field, are sometimes collected for animal feed or composted and returned to the fields.
BagasseAfter the cane is crushed and the juice extracted, the resulting fibrous material, called bagasse, is used for a variety of purposes. Its original use to fuel the process continues, both for the extraction of juice and for the conversion to bioethanol, with the added benefit of lowering the overall carbon footprint of the resultant biofuel product. Some plants produce enough energy from burning bagasse to power the entire process, with surplus to export as electricity. This generation is rapidly increasing, enabling Brazil to meet 6% of its electricity demand in 2011, with the potential of generating far more from the bagasse available across the country. Bagasse is also used to make paper and board.
Vinasse A liquid rich in plant nutrients, vinasse is a significant by-product of the distillation process (10 litres of vinasse are produced for every litre of ethanol). If carelessly disposed of it can cause environmental pollution by lowering the pH value of the soil and water, but it is often amended and returned to sugarcane fields as a form of irrigation and fertilization.
Invasion risk
Modern cultivars of sugarcane are not considered invasive and typically fail to persist without human assistance. Most of the competitive and invasive traits found in the original species have been lost during plant breeding. Hybrid cultivars do not produce rhizomes or produce vigorous seedlings, although after a ratoon cycle some volunteer plants may appear in the next crop. There are certain sugarcane cultivars, in particular S. spontaneum, that are considered invasive due to rhizome production.
Key references
●● Hartemink, A. (2008), Sugarcane for bioethanol: soil and environmental issues, Advances in Agronomy, vol. 99, pp. 125 – 182.
●● James, G. (ed.) (2004), Sugarcane, 2nd edition, Blackwell Publishing Ltd, Oxford, UK.
●● Lisboa, C. C. et al. (2011), Bioethanol production from sugarcane and emissions of greenhouse gases – known and unknowns, GCB Bioenergy, vol. 3, pp. 277 – 292.
●● Renewable Fuels Association (2012), Accelerating industry innovation: 2012 ethanol industry outlook. RFA, Washington DC.
This box highlights another important crop that is also harvested for high soluble sugar concentrations.
Sweet sorghum (Sorghum bicolor)●● Photo in production: Brazilian cerrado.●● Why is it similar? Also uses C4 photosynthesis; high sugar concentration in stem.
●● What makes it different? Grows in colder climates; wide genetic variation; typically lower yielding than sugarcane; produces grain that is a primary product.
●● Growing region: Top 10 producing countries are the US, India, Mexico, China, Nigeria, Argentina, Sudan, Ethiopia, Australia, Burkina Faso.
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6 Biomass feedstock crops | 77
Switchgrass Panicum virgatum L
●● Type of fuel: solid combustion for heat and electricity, cellulosic ethanol.
●● Stage of adoption: early commercial stage for heat and electricity, pre-commercial stage for liquid ethanol.
Switchgrass is a native wild grass found in a range of habitats from eastern Canada to Central America. Its deep roots and tolerance of poor soils make it useful for preventing erosion, and its ornamental habit is valued by designers aiming to create ‘prairie-style’ naturalistic gardens. Low fertilizer requirements and resistance to insect attack give switchgrass as-yet-unfulfilled potential as a feedstock for bioenergy.
Plant characteristics
Switchgrass is a clump-forming C4 perennial that grows up to 1.5 metres tall. It spreads slightly by stout rhizomes, especially in wetter conditions, and the delicate flower heads and seeds are attractive in late summer. There are distinct ‘upland’ and ‘lowland’ varieties of switchgrass (about 25 cultivars in total), and several naturally occurring strains of the plant. These have been selected for improved yield or ornamental qualities. The lowland varieties have greater potential yields than upland varieties, but are more susceptible to cold damage and are thus less suited to higher latitudes.
In 1992 the US Department of Energy began a research programme to develop switchgrass as a bioenergy feedstock. Research is ongoing into GM varieties and there is now evidence that modifications to lignin content, for example, can reduce pretreatment costs and increase fermentation yields.
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78 | 6 Biomass feedstock crops
Where to grow it
The wide natural range of switchgrass reflects the genetic variability of the plant – useful to the grower in that there are varieties to suit different microclimates and soil conditions. The genetic variability also provides a useful starting place for plant breeders seeking to improve productivity. Switchgrass has in the past been grown in latitudes between 55° and 17° North, but could also be grown in the southern hemisphere. Switchgrass will not thrive in extremely acid or alkaline soils, or where the soil temperature reaches 40°C, and is most common in the temperate broadleaved and temperate grassland biomes.
How to grow it
Switchgrass is usually grown as a monoculture, but because it is an out-crossing species, the monocultures are genetically diverse populations. It is typically established by seed drilled (or spread and raked) directly into clean ground. Seed priming can sometimes improve germination rates. Prior tillage is not necessary, but a firm seedbed is required. Growth is initially slow and there is no harvest in the first year. But by the second year biomass production can reach 60% of a mature stand, and the crop remains productive for more than a decade.
Inputs required
WaterSwitchgrass is found in the wild in damp areas, but it is considered to be reasonably drought-tolerant under cultivation. The genetic variability mentioned above gives a wide range of average water use efficiencies, from 2 – 103kg/ha/mm. Irrigation is not normally used but can boost production in drought conditions.
FertilizerBecause switchgrass evolved under low-nutrient conditions, it grows well without additions of phosphate and potassium, although it may require supplements over the long term. Some additional nitrogen can be beneficial, although not in the first year, as this encourages weed growth. Too much nitrogen causes switchgrass to ‘lodge’ (grow luxuriantly and collapse particularly under heavy rain or strong winds), which hampers harvesting.
Pests and diseases
Insects that chew leaves and roots can be pests of both seedbeds and established stands. Insect damage is generally slight, however, and does not require pesticide use. Fungal diseases and the barley yellow dwarf virus have been reported. Yield losses greater than 50% were reported from smut disease.
Defences
HerbicidesVarious broad spectrum herbicides are widely used to clear the ground of broadleaved weeds before drilling seed.
Pesticides Not normally necessary.
Harvesting
Essentially a form of haymaking, harvesting switchgrass involved cutting the grass using a mechanical mower. The dry grass is then baled, or sometimes chopped and collected in a module building system that compresses the chopped material into a denser mass for transportation.
World map with latitude limits for growth
Dry weight in tonnes
2,900 litres
14 tonnes
Litres of bioethanol fuel
gasoline equivalent of 2,000 litres
Switchgrass average annual yield per hectare
How long could you supply energy for a house?World
12 moNtHS
Best recorded
20 moNtHS
Effective energy available
World
Best recorded
20,000kWh
33,000kWh
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What distance could you drive?25,000km15,000 miles
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6 Biomass feedstock crops | 79
Yield
Historically, switchgrass has been grown for forage but its potential as a source of liquid biofuels has reached an advanced stage of research. Because its potential as a lignocellulosic feedstock is still being investigated, there are no reported data on this crop from agencies such as the FAO. In North America and Europe, switchgrass yields range from 10 to 23 tonnes/ha (dry weight) and conversion efficiencies to ethanol range from 180 to 240 litres/tonne.
In terms of thermal energy, switchgrass has a calorific value of 17GJ/tonne.
Alternative markets
Switchgrass has traditionally been used as fodder for cattle, and it is often planted to stabilize soils at risk of erosion and to increase biodiversity as part of conservation projects. Like other lignocellulosic materials, it can be burned in power stations to produce electricity.
Co-products
From the crop Currently none.
From conversion to fuel Wastes after ethanol production could be burned as fuel.
Invasion risk
Switchgrass can easily become an invasive species and displace other native species if not properly managed. It can grow well on marginal lands, and interspecific competition can affect water and nitrogen availability.
This box highlights another temperate perennial grass species with wide tolerance ranges.
Cordgrass (Spartina spp.)●● Photo in production: Illinois, US.●● Why is it similar? Also has wide genetic variation; growing regions very large and diverse; C4 perennial; limited commercial production; potentially a dedicated energy crop.
●● What makes it different? Can grow in saturated and salty soils.
●● Growing region: Limited commercial production, but the native range spreads across all of North America, and parts of South America, Africa and Europe.
Key references
●● McLaughlin, S. & Kiniry, J. (2006), Projecting yield and utilization potential of switchgrass as an energy crop, Advances in Agronomy, vol. 90, pp. 267 – 297.
●● Monti, A. (ed.) (2012), Switchgrass. Springer, London.●● Vogel, K. P. (2004), ‘Switchgrass’, in Moser L.E. et al. (eds) Warm-season (C4) grasses. American Society of Agronomy, Crop Science Society of America and Soil Science Society of America, Madison, WI, US.
●● Lewandowski, I., Scurlock, J. M. O., Lindvall, E. & Christou, M. (2003), The development and current status of perennial rhizomatous grasses as energy crops in Europe and the US, Biomass and Bioenergy, vol. 25, no. 4, pp. 335 – 361.
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81
Miscanthus Miscanthus x giganteus Greef et Deuter
●● Type of fuel: solid combustion for heat and electricity, cellulosic ethanol.
●● Stage of adoption: commercial use for heat and electricity, developmental stage for liquid biofuel.
Originating in South-East Asia, varieties of miscanthus have long been valued in gardens for their tall, upright stature and elegant flowerheads. But in the past 30 years, as its potential to become a biomass crop was realized, breeding efforts have focused on productivity. Natural hybridization between two different species (M. sinensis and M. sacchariflorus) has created the giant miscanthus (Miscanthus x giganteus), a sterile hybrid that produces large quantities of biomass very efficiently. Giant miscanthus is the only genotype commercially grown for biomass.
With its healthy, vigorous growth and low management requirements, miscanthus is easy to grow. There are challenges, however, in producing the rhizomes required for establishment on a large commercial scale.
Plant characteristics
There are more than a dozen species of miscanthus, all of them perennial grasses with spreading rhizomes (an underground organ that produces both shoots and roots). Some grow as tall as 4 metres. Most of the leaves are firmly attached to the stems, although some fall as litter in autumn and winter. The tough woody stems persist through the winter. New shoots emerge from the rhizome as temperatures rise in the spring. Giant miscanthus is a sterile hybrid that does not produce seed, making it more useful than similarly productive non-hybrid cultivars that have invasive tendencies through seed dispersal. Like maize, sugarcane and switchgrass, it photosynthesizes using the C4 metabolic pathway.
World map with latitude limits for growth
It is estimated that 30,000ha is grown in Europe for co-firing in the UK and for heat in Austria, Switzerland and Germany.
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6 Biomass feedstock crops | 81
Where to grow it
Miscanthus is adaptable to a range of climates and trials have been successful in latitudes from 56° to 37° North. Its tolerance of cold is unusual in C4 plants and it can withstand freezing winter temperatures once established. The best yields are achieved in soils that do not dry out. Interestingly, miscanthus also does well on sandy soils as long as water supply is sufficient, because weed competition is less in such conditions.
How to grow it
As the crop will remain in the ground for two decades or more, good establishment is crucial, for which thorough ground preparation is vital. After removing weeds using a broad-spectrum herbicide, ground is ploughed and a good tilth created. If no herbicide is applied, other weed control methods are typically required. Miscanthus is usually established by planting small pieces of rhizomes, ideally using specialized machinery. It is important to use fresh, vigorous rhizomes. Planting is done in spring once the soil has warmed and there is still plenty of moisture available. A seeded variety has recently been developed for Miscanthus x giganteus but it has not yet been broadly tested.
Inputs required
WaterMiscanthus crops are drought-tolerant except in the early stages of crop establishment, when it may require irrigation to improve establishment rates. Miscanthus x giganteus requires a minimum of 450mm of water per year, but will attain greater yields with higher rainfall.
FertilizerRegarded as a low-input crop, miscanthus has in some sites been grown successfully for more than a decade with no nitrogen inputs. The autumn leaf-fall returns some nutrients to the soil but, more importantly, the perennial crop has an efficient nutrient cycle, where in autumn nutrients are relocated from the above-ground shoots to the underground rhizomes. Recent studies show little response to nitrogen application in the first five years and a small response in subsequent years (0.02 tonnes/ha increasing in yield for every kilogram of nitrogen applied per hectare) although this is likely to be site dependent. There are indications that there may be nitrogen-fixing bacteria associated with miscanthus in some places. Potassium and phosphorus fertilizer should be applied according to withdrawal, which is about 0.5kg P and 1kg K per tonne of dry biomass.
Pests and diseases
Miscanthus is regarded as a crop with few pests and diseases, but it is not immune to damage: the corn borer (Diatraea grandiosella) can reduce dry matter yield by up to 30%. Sixty-nine pathogens have been recorded that affect miscanthus, although no severe damage has been reported.
Defences
HerbicidesBroad-spectrum herbicides are needed to control weeds at intervals during the first two years. After that, the roots and canopy of the grass suppress weed growth.
PesticidesNot generally required.
5,600 litres Europe
12,000 litres Midwest winter US
Litres of bioethanol fuel
gasoline equivalent of 3,700 litres
gasoline equivalent of 7,900 litres
Dry weight in tonnes18 tonnesEurope
38 tonnesMidwest winter US
Miscanthus average annual yield per hectare
How long could you supply energy for a house?Europe
16 moNtHS
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34 moNtHS
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0 10 20 30 40 50 60 70 80 10090Thousand km
What distance could you drive?
47,000km29,000 miles
99,000km61,000 miles
Effective energy available
Europe
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27,000kWh
57,000kWh
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PerennialWoody Grain or seed
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82 | 6 Biomass feedstock crops
Harvesting
Annual harvesting starts in year two or three, with biomass increasing by 80% from the first to the second year after planting. The crop is usually harvested in late winter to early spring after the woody stems have dried and before new shoots appear. This maximizes the amount of nutrients returned to the soil but reduces the overall yield by 30 – 50%, as biomass is lost to litterfall during winter. The grass is cut and baled, or collected with a forage harvester.
Yield
As the potential of miscanthus as a lignocellulosic feedstock is still being investigated, there are no reported data on this crop from agencies such as the FAO. Most of the yield data are sourced from scientific investigations.
Yields per hectare are impressive, reaching well over 40 tonnes (dry weight) per hectare at best. Averages depend on time of harvest, as mentioned above. Autumn (fall) yields an average of 25 tonnes/ha in Europe and 47 tonnes/ha in the US Midwest. Winter yields are lower (18 in Europe and 38 in the Midwest).
In terms of thermal energy, miscanthus has a calorific value of 18GJ/tonne.
Research into the conversion of miscanthus to ethanol has a reported conversion efficiency of 310 litres/tonne.
Alternative markets
Miscanthus is becoming more widely used in Europe to augment coal in power stations and thus reduce GHG emissions. It can also be used for pressed particle board. In Asia it is a traditional roofing material, and in Europe is popular as horse bedding.
Co-products
From the cropCurrently none.
From conversion to fuelWastes from ethanol production could be burned as fuel for heat and/or power.
Invasion risk
Miscanthus x giganteus itself has a very low risk of invasion because it is a sterile hybrid that does not produce seed. This biomass variety is a relative of several species, such as Miscanthus sinensis, that are considered highly invasive.
Key references
●● Clifton-Brown, J. et al. (2001), Performance of 15 miscanthus genotypes at five sites in Europe, Agronomy Journal, vol. 93, pp. 1013 – 1019.
●● Davis, S. C. et al. (2012), Impact of second-generation biofuel agriculture on greenhouse-gas emissions in the corn-growing regions of the US, Frontiers in Ecology and the Environment, vol. 10, pp. 69 – 74.
●● Heaton, E. A. et al. (2008), Meeting US biofuel goals with less land: the potential of miscanthus, Global Change Biology, vol. 14, no. 9, pp. 2000 – 2014.
●● Lewandowski, I. & Clifton-Brown, J. (2000), Miscanthus: European experience with a novel energy crop, Biomass and Bioenergy, vol. 19, pp. 209 – 227.
●● FP7 OPTIMISC (2012), Uses of miscanthus.
This box highlights another high yielding perennial grass.
Energy cane (Saccharum officinarum variety bred for fibre instead of sugar)●● Photo in production: Florida, US.●● Why is it similar? Also a high yielding C4 grass with low nutrient requirements.
●● What makes it different? Grows in warmer, subtropical climates, south of the latitudes where Miscanthus is most productive.
●● Growing region: Currently there is very limited commercial production, but plantations are developing in the southern US.
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
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C4C3
Herbaceous
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Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
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Bioethanol Biodiesel BiogasHeat and power
Power usage
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C4C3
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Current dominant energy use
Other
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PerennialWoody Grain or seed
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Current dominant energy use
Other
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6 Biomass feedstock crops | 83
Oil palm Elaeis guineensis and E. oleifera
●● Type of fuel: biodiesel.●● Stage of adoption: extensive commercial production.
Although oil palm originated in West Africa and tropical parts of Central and South America, the biggest oil palm plantations are now in Indonesia and Malaysia. Palm oil was traditionally used for cooking and making soap, but it has become an important raw material in processed food. Biodiesel from palm oil has been in production for a quarter of a century.
Oil palm now produces 32% of world vegetable oil, despite covering only 4% of land area devoted to oil crops.
The crop has raised controversy for decades. Producers love its high yields but critics point to serious environmental damage caused by large-scale plantations that displace native rainforest. Changing land use from forest or peatland releases large amounts of carbon dioxide
and, even though the oil palm acts as a carbon sink, it can take 40 years or more to achieve carbon payback.
If oil palm does not displace native forests, plantations can result in a net carbon sink and efforts are under way to establish guidelines for more sustainable growing techniques. For example, there is a Roundtable on Sustainable Palm Oil that has developed a certification system for sustainable oil palm producers.
Plant characteristics
Oil palms have stout single trunks and leaves that can reach 5 metres in length. Bunches of fruit are formed at the top of the trunk and it is the fruit pulp that provides palm oil. Palm trees bear fruits starting in the fourth year. Selective breeding has created a hybrid (the Tenera variety) with a particularly high percentage of oil in the fruit for commercial production. A complete breeding programme using controlled pollination can take eight to 10 years.
15˚N
12˚S
Global planting – 15 million hectares.Global production – 220 million tonnes of palm fruit, 44 million tonnes of oil.
Top producing countries
Million tonnes*
IndonesiaMalaysiaNigeriaThailandColombia
9088 9 8 3
*fruitThailandMalaysia
Indonesia
World map with latitude limits for growth and five top producing countries
ColombiaNigeria
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84 | 6 Biomass feedstock crops
Where to grow it
Oil palm is a tropical crop that needs constant warmth and humidity. Optimum temperatures are in the range of 24 – 28°C and commercial production is not possible if seasonal mean temperatures vary by more than 6°C. It grows best in well-drained sandy soils and is limited to low altitudes and a fairly narrow equatorial belt (15° North to 12° South) that corresponds to the tropical humid rainforest biome.
How to grow it
Palm trees can be productive for many years, but they are typically replanted after about 20 years when they become too tall for efficient harvesting. Ground for planting may be cleared mechanically or by burning, followed by tillage or herbicide treatment. Leguminous ground cover is often established before the young palm trees are planted, with the aim of preventing erosion and increasing the nitrogen content of the soil. Palm leaves are also left between the rows of trees for the same reasons.
Inputs required
WaterOil palm needs a constant water supply and high humidity for optimum production with daily evapotranspiration rate of 5 – 6mm of water. While research shows that irrigation in dry climates can increase yields by approximately 36%, irrigation is unnecessary in the very wet climates where oil palm is often cultivated.
FertilizerHigh levels of fertilizer, particularly nitrogen and potassium, are required throughout the life of an oil palm. Plantations on peaty soil are especially prone to potassium deficiency.
Pests and diseases
The heat and humidity typically needed by oil palm are also ideal conditions for plant diseases to flourish. Decaying palm fronds left to protect the soil and replace some nutrients provide shelter to a range of pests. Not surprisingly therefore, oil palms are prey to a range of diseases including trunk rot (Ganoderma sp.) and dry basal rot (Ceratocystis sp.), which can reduce yields by 20 – 60%. Grasshoppers can defoliate young palms or severely depress yield by up to 40% in older plantations. Some of the worst pest attacks are thought to have been exacerbated by overuse of broad-spectrum pesticides that killed beneficial insects along with problematic species. In many plantations owls are kept to control mice that can damage the crop.
Defences
HerbicidesThe use of herbicides can be reduced by using leguminous ground cover to suppress weeds between young palm trees. Herbicides are still needed before planting, and paraquat is commonly used, despite its toxicity to humans.
PesticidesBroad range pesticides are not recommended because they can exacerbate a pest outbreak. A range of pesticides has been used, but some are very toxic.
Harvesting
The heavy bunches of fruit are cut by hand, sometimes using a chainsaw. This requires strength and dexterity, as the leaf fronds around the fruit are armed with tough spikes. Removed leaves are left on the ground. Bunches of fruit are then taken to a processing mill for stripping.
World map with latitude limits for growth and five top producing countries
Fruit yield in tonnes oil yield in tonnes
3,000 litres
14 tonnes 2.9 tonnes
Litres of biodiesel fuel
mineral diesel equivalent of 2,800 litres
Oil palm average annual yield per hectare
Oil palm yields – global average and top producing countries
25
20
15
10
5
0
1960 1970 1980 1990 2000 2010
Aver
age
yiel
d (to
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/ha
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l pal
m fr
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Global average yieldColumbiaIndonesia
MalaysiaNigeriaThailand
World
Best recorded
0 10 20 30 40 50 60 70 80 10090Thousand km
What distance could you drive?
46,000km29,000 miles
75,000km46,000 miles
6 Biomass feedstock crops | 85
Yield
The fresh-fruit yield from the palms average 14 tonnes/ha, with an average oil yield of 2.9 tonnes/ha per year. Maximum yields have been reported in Malaysia (with up to 23 tonnes fruit and 4.5 tonnes oil per hectare) and Colombia (with up to 19 tonnes fruit and 4.7 tonnes oil per hectare).
Alternative markets
Palm oil is processed and refined to produce a range of products, many of them used in food production and as cooking fats and cosmetics. Fruit bunches must be sterilized and then threshed to separate the palm fruit, which is then pressed to extract the crude oil. Several refining stages are then required to produce oil suitable for further processing. The kernels are separated from the fruit bunches, and are often processed separately in a mill with other oilseeds.
Co-products
From the cropPlant biomass remaining after oil extraction can be used to make paper, fibreboard or used as solid fuel.
From conversion to fuelResidues such as the sludge from milling (decanter cake) and empty fruit bunches have high nutrient content and make good fertilizer. Glycerol can be used in cosmetics. Palm oil mill effluents are often used for biogas production.
Invasion risk
Oil palm is generally not considered an invasive species and typically requires a large amount of plantation maintenance to prevent weed competition. Elaeis guineensis (African oil palm), however, has been observed to be potentially invasive in Micronesia.
Key references
●● Corley, R. H. V. & Tinker, P. B. (2003), The oil palm, 3rd edition, Blackwell Publishing Ltd, Oxford, UK.
●● Lim, S. & Teong, L. K. (2010), Recent trends, opportunities and challenges of biodiesel in Malaysia: an overview, Renewable and Sustainable Energy Reviews, vol. 14, pp. 938 – 954.
●● Yee, K. F. et al. (2009), Life cycle assessment of palm biodiesel: revealing facts and benefits for sustainability, Applied Energy, vol. 86, pp. S189 – S196.
This box highlights another woody plant that is grown for oil.
Jatropha (Jatropha curcas)
●● Photo in production: Indonesia.●● Why is it similar? Also a woody plant that grows as a shrub or tree with oil-rich seeded fruits (inedible in this case); grows in tropical regions of the world.
●● What makes it different? Not a food commodity because the products are toxic; grows in very dry tropical conditions as well as the moist tropics and is lower yielding than palm oil. Without irrigation, yields of the oil-rich seeds are little more than 2 tonnes/ha in well-established plantations. With irrigation and fertilizer, this figure increases to 12 tonnes/ha or more. Jatropha uses both the C3 and CAM photosynthetic pathways, depending on water availability.
●● Growing region: Although this plant grows throughout the tropical and subtropical regions of the world and is considered invasive in some regions, commercial production is very limited. Small-scale plantations have been developed in Africa and India. It has also been introduced in South-East Asia with differing levels of production efficiency, and work continues to improve the genetics and agronomy of the crop around the world.
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
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PerennialWoody Grain or seed
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E DC4C3
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PerennialWoody Grain or seed
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CAM
86 | 6 Biomass feedstock crops
87
Soybean (soyabean, Ta dou, daidzu)
Glycine max
●● Type of fuel: biodiesel.●● Stage of adoption: extensive commercial production.
Soybean was domesticated in China – references to ‘shu’ appear in ancient literature dating back 4,500 years – and its cultivation spread to Korea, Japan and other parts of South-East Asia roughly 3,000 years ago. The domesticated plant is shorter than its wild relatives and has much larger seed. More recently the plant has been grown for high-protein animal feed, with oil as a co-product. Seventy-five per cent of all cultivated soybean is GM, primarily to impart herbicide resistance.
There is broad global knowledge of soybean agriculture because of the long history in cultivation. It has a low yield per unit area, and requires a larger land footprint than many other bioenergy crops, but it produces high amounts of protein, significant amounts of oil, and the conversion of the oil to biodiesel produces little waste.
Plant characteristics
Soybean is an annual leguminous plant with clover-like leaves that uses the C3 photosynthetic pathway. The beans are produced in short, slightly furry pods. Its long domestication is reflected in the 45,000 Asian varieties (landraces) stored in international seedbanks – there are 23,000 varieties in the Chinese gene bank alone. Breeding now involves genetic modification, and glyphosate-resistant soybean is widely grown. Modifications have also been made to increase the production of particular fatty acids (e.g. the mono-unsaturated 18-carbon oleic acid) in the bean.
52˚N
39˚S
Global planting – 99 million hectares.Global production – 240 million tonnes seed.
Top producing countries
Million tonnes*
USBrazilArgentinaChinaIndia
9169531513
*seed
US
Brazil
China
India
Argentina
World map with latitude limits for growth and five top producing countries
C4C3
Herbaceous
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Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
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PerennialWoody Grain or seed
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Bioethanol Biodiesel BiogasHeat and power
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Current dominant energy use
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PerennialWoody Grain or seed
Seed Stemcutting
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6 Biomass feedstock crops | 87
Where to grow it
Considered a warm-season crop, soybean grows between 10°C and 40°C, at altitudes below 1,000 metres from 52° North to 39° South. It is widely planted across the subtropical humid forest, tropical humid rainforest and all temperate biomes. It needs a free-draining soil and is most productive on clay loam. Soybean is moderately salt-tolerant.
How to grow it
Soybean is an annual crop, grown from seed planted in early to late spring. Although it is often grown as a monoculture, yields are better when grown in a two-year rotation with maize. Zero-tillage (direct-drilled) systems also give better long-term results than traditional land preparation (ploughing and harrowing to make a seedbed).
Inputs required
Water Soybean has moderate water requirements – average irrigation of 140mm – (it loses roughly 600mm in evapotranspiration in a growing season) and increases in yield as a result of irrigation have been documented. Water requirements depend on soil, rainfall and temperature, and should be calculated for each site and meteorological conditions.
FertilizerBeing a legume, soybean has nitrogen-fixing bacteria in root nodules, although soybean uses more nitrogen than it can acquire through this symbiotic relationship. Nitrogen fixation is inhibited when nitrogen fertilizer is used, and early studies showed no increased yield from applying nitrogen. But more recent studies suggest that modest applications of nitrogen (less than 50kg per hectare) can increase yield by 0.6 tonnes/ha. Applications of phosphorus and potassium are also required. Matching fertilizer requirements to each specific site reduces GHG emissions.
Pests and diseases
Soybean is prey to a host of serious pests and diseases. They include a pod borer specific to soybean (Leguminivora glycinivorella – 20 – 50% yield losses), a late-season fungal disease (Macropomina phaseolina – up to 70% yield losses) that can destroy more than two-thirds of the crop, and soybean rust (Phakopsora meibomiae and P. pachyrhizi) able to cause up to 80% loss in yield. Soybean cyst nematode (Heterodera glycines) occurs widely in regions where the crop is grown and causes considerable losses.
Defences
Herbicides The advantage of glyphosate-resistant soybean is that glyphosate can be used to control weeds without damaging the crop. Because glyphosate is broken down on contact with soil, this makes it a better choice from an environmental perspective than more persistent or more toxic herbicides (also used in soybean cultivation). Choice of herbicide and concentration should be tailored to the type of soil, climatic conditions and developmental stage of the plants.
Pesticides Various pesticides are available, with control regimes varying regionally. Estimates of attainable yield protection range from 25% in Central Africa to 43% in southern Europe.
Harvesting
Most soybean is harvested with combines once the crop has reached a moisture content of 13 – 15%. Delaying the harvest after this time is detrimental, as overripe pods shed their beans and over-dried beans (less than 12% moisture) tend to shatter during harvest. Losses after the optimum date can amount to 11kg per hectare per day.
oil yield in tonnes
Grain yield in tonnes
480 litres
Litres of biodiesel fuel
mineral diesel equivalent of 430 litres
0.44 tonnes2.4 tonnes
Soybean average annual yield per hectare
Soybean yields – global average and top producing countries
3
2
1
0
1960 1970 1980 1990 2000 2010
Aver
age
yiel
d (to
nnes
/ha
– se
ed)
Global average yieldArgentinaBrazil
ChinaIndiaUS
0 10 20 30 40 50 60 70 80 10090Thousand km
What distance could you drive?World 7,200km 4,500 milesBest recorded 9.000km 5,600 miles
88 | 6 Biomass feedstock crops
Yield
The yield of seeds on average varies between 1.5 and 3 tonnes/ha with a worldwide average of 2.4 tonnes/ha. The oil yield represents between 17% and 20% of the seed mass, resulting in 0.41– 0.48 tonnes of oil per hectare per year.
Alternative markets
The main products from soybean are the whole beans, the protein-containing defatted soybean meal, and oil that are used for food and feed. Many processed foods include soya products, and soybean meal is vital feedstuff for meat production.
Co-products
From the cropDuring soybean processing, the defatted soybean meal, the major product (about two-thirds) from soybean processing, is primarily used as animal feed, with a small portion as protein ingredients for the food industry. The soybean oil can also be used in various other biomaterials, including printing ink, candles and waxes, low-temperature lubricants, industrial cleaners and metalworking fluids, lotions and paint additives.
From conversion to fuel The glycerol that is a co-product of biodiesel conversion can replace glycerol made from petroleum. Glycerol has many uses in cosmetics, food, oral care, tobacco, synthetic polymer production and synthetic resins.
Invasion risk
Soybean is typically considered non-invasive, but cultivated soybean can hybridize with wild strains. The use of specific no-planting zones is a simple and effective way to avoid transgene dispersal in the case of GM soybean.
Key references
●● Hymowitz, T. & Newell, C. (1981), Taxonomy of the genus glycine, domestication and uses of soybeans, Economic Botany, vol. 35, pp. 272–288.
●● Singh, G. (ed.) (2010), The soybean: botany, production and uses. CAB International, London, UK.
●● Kim, S. & Dale, B. E. (2009), Regional variations in greenhouse gas emissions of biobased products in the United States—corn-based ethanol and soybean oil, The International Journal of Life Cycle Assessment, vol. 14, pp. 540–546.
This box highlights another important oil crop that is produced commercially.
Oilseed rape or canola (Brassica napus)●● Photo in production: Canada.●● Why is it similar? Also an oil-rich C3 plant, grown for both food and biodiesel, and although the highest yielding oil crop in temperate regions, rapeseed is low yielding relative to other biomass feedstocks.
●● What makes it different? Much greater cold tolerance; salt tolerance; greater fertilization rates recommended; does not host symbiotic nitrogen-fixing bacteria like soybean.
●● Growing region: Canada is the largest producer, followed by China, India, Germany and France. Together, more than 15% of the world’s vegetable oil is supplied by canola.
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6 Biomass feedstock crops | 89
Willow and hybrid poplar (Short-rotation woody species)
Salix and Populus spp
●● Type of fuel: Solid combustion for heat and electricity, cellulosic biofuels.
●● Stage of adoption: developmental stage for liquid biofuel, extensive commercial use for heat and electricity.
The graceful form of weeping willow trees reflected in water and unmistakable exclamation marks of Lombardy poplars are familiar sights in many temperate landscapes. In fact, these trees have diverse forms, with the smallest willow being a creeping arctic species. But most share the useful attribute of growing readily from cuttings – which merely requires pushing a length of stem into the ground. This ease of propagation and fast growth make the trees invaluable producers of biomass, especially in soils that do not dry out. Moreover, they can be grown in rapid cycles in which they are cut back or coppiced roughly every three to five years (called short-rotation coppice or SRC) or seven
to 11 eleven years (called short-rotation forestry or SRF). Woody crops grown in this way are already widely used as fuels for heating and in thermal power stations.
Plant characteristics
There are 300 – 500 willow species that have a wide range of genetic variability. There are fewer poplar species but an estimated 125 elite poplar cultivars. Most species are trees or large shrubs with questing roots, although when grown as coppice most roots are found within the first 30cm of the soil profile. Willows show great diversity of form, but the shrub willows (roughly 2 – 3 metres tall) are most suitable for biomass.
Native poplar grows as a single-trunked deciduous tree with a wide variety of growth rates, heights and leaf structures among species. Some species of poplar, however, can also be grown as short-rotation coppice. Breeding has focused on crossing species to give hybrids of increased height and vigour, and there are many varieties available commercially.
75˚N
34˚S
Top producing countries
Thousand hectares
ChinaIndiaFranceTurkeyItaly
4,9001,000
240130120
Top producing countries
Thousand hectares
ArgentinaRomaniaNew ZealandSweden
46242015
Argentina
New Zealand
China
India
France
Sweden
Italy Turkey
Romania
World map with latitude limits for growth and five top producing countries
Keyn Poplarn Willow
Poplar
Willow
Willow Hybrid poplar
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90 | 6 Biomass feedstock crops
91
Where to grow it
Willow and poplar are native to temperate broadleaf and conifer biomes in the northern hemisphere. Poplar grows from 66° North to as far south as 30° North; willow can grow from 75° North to 34° South. They grow best where there is regular rainfall and in water-retentive soils; they are slow to establish on heavy clay. Some varieties can withstand extremes of heat and cold (40–50°C), and all are frost-hardy when dormant over winter.
How to grow it
Cultivation techniques exploit the ability of many broadleaved tree species to regrow (coppice) strongly when all their aerial growth is removed. The cut stumps quickly produce vigorous new shoots, nourished by the established root system, and multiple harvests can be taken from a single planting.
Poplar and willow can be established mechanically, by planting ‘rods’ cut from year-old shoots into clean ground in the spring. For good establishment, the soil should be ploughed and harrowed before planting. Plantations can remain productive for more than two decades. Crops are grown both as monocultures and in polycultures with multiple varieties. The benefits of mixed planting (reducing the spread of pests and diseases) are sometimes outweighed by increased costs of managing and harvesting a non-uniform crop.
Inputs required
WaterThe availability of water is more important than soil type when selecting growing sites. Willow and poplar are both thirsty crops, often needing more than 100kg of water per day during the growing season. Poplar water use ranges from 50 to 110kg per day; willow species use about 105kg per day, although wide genetic variation for water use is found in both trees. Generally, both species require a
minimum of 600mm rainfall annually. Although these crops are tolerant of wet sites, the ground must be firm enough at times to allow the use of planting and harvesting machinery.
FertilizerFertilizer use in commercial plantations is dictated by deficiencies noted in the leaves. The removal of large quantities of biomass over several years depletes the soil of nitrogen, so nitrogen is added as necessary, with a typical range of 20 – 80kg N per hectare added to willow (usually after harvest) and up to 200kg N per hectare to poplar annually when nutrient depletion is evident.
Pests and diseases
Various leaf and stem diseases, particularly rusts but also spots and cankers, can decrease growth rate and yield from 10% to 100% depending on the conditions. Stem borers and beetles are also prevalent, causing 50 – 100% damage to populations. Pests and diseases are generally more serious in young crops. Weeds compete with newly planted cuttings for light and nutrients so weed suppression is necessary. Control may also be needed after coppicing, when increased light levels lead to a spurt in weed growth.
Defences
HerbicidesWeed control in early establishment is essential: a range of herbicides is used to clear the ground during establishment in the first year and after coppicing. An alternative to initial herbicide use is to plant cuttings through weed-suppressant horticultural membrane.
PesticidesSome resistance has been bred into certain varieties of willow and poplar. There is no standard pesticide treatment, but a range of pesticides of varying environmental toxicity can be used to control insect damage when infestations arise.
World map with latitude limits for growth and five top producing countries
Global planting5.3 million hectares in plantations plus 3.9 million hectares in agroforestry and conservation (for soil and water protection). Global production38 million tonnes/yr.
Dry weight in tonnes
7.1 tonnes
Poplar average annual yield per hectare
How long could you supply energy for a house?World
7 moNtHS
Best recorded
33 moNtHS
Effective energy available
World
Best recorded
11,000kWh
55,000kWh
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Global planting90,000 hectares for wood production plus 86,000 hectares for land reclamation and conservation.Global production660,000 tonnes/yr.
Dry weight in tonnes
7.3 tonnes
Willow average annual yield per hectare
How long could you supply energy for a house?World
7 moNtHS
Best recorded
24 moNtHS
Effective energy available
World
Best recorded
12,000kWh
39,000kWh
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Harvesting
The plants are cut off close to the ground at harvest. The first year’s crop is small, but is removed to stimulate growth. Subsequent harvests are made after leaf-fall at intervals of three to 11 years, depending on variety, growing conditions and harvest technology available. Harvesting is highly mechanized and consists of either cutting and storing whole stems, or chipping the stems immediately after harvest. The latter approach requires drying equipment, as a mass of moist chips will rapidly heat up (as happens in a compost heap). The harvested wood has a moisture content of around 50%.
Yield
The yield for these trees has to be considered over a harvest cycle of three to five years for SRC (willow or poplar) or around seven to 11 years for SRF (poplar grown as single stems). Worldwide average annual yields of both willow and poplar are about 7 tonnes/ha, but there is huge variation between sites. Improved varieties produce higher yields, with many commercial growers now achieving 10–14 tonnes/ha.
Biofuel (liquid) yield is not yet known because the process is still under research. Thermochemical conversion pathways have been shown to successfully yield liquid fuels. In terms of thermal energy, willow has a calorific value of 20GJ/tonne and poplar 19GJ/tonne.
Alternative markets
Biomass from willow and poplar is already used as fuel in thermal power stations. Poplar grown in single stems (rather than coppiced) has various uses including plywood and pulp for paper. The trees’ hardiness and tolerance of waterlogging makes them useful as windbreaks and in bioengineering to stabilize soils. Some poplars and willows are also effective in phytoremediation of soils with heavy metals and have facilitated the reduction of nutrient run-off from agricultural landscapes.
Co-products
From the cropCurrently none but poplars and willows is rich in secondary metabolites (e.g. salicin, later developed as aspirin, was first identified in willow).
From conversion to fuelWhen burned as fuel for heating or in power stations, only ash residues remain. If used to make bioethanol, the wastes after hydrolysis and fermentation could be burned for heat.
Invasion risk
Some species naturally shed branches, which can then re-root, and both poplar and willow can be potentially invasive in some environments. This has been historically observed in Australia and New Zealand, where Salix fragilis L. and Salix cinerea L. were found to rapidly colonize along streams. Future improvements in genetic engineering may increase productivity but also plant invasiveness.
Key references
●● Karp, A., Hanley, S. J., Trybush, S. O., Macalpine, W., Pei, M. & Shield, I. (2011), Genetic improvement of willow for bioenergy and biofuels, Journal of Integrative Plant Biology, vol. 53, no. 2, pp. 151–165.
●● Fischer, G. et al. (2005), Biomass potentials of miscanthus, willow and poplar: results and policy implications for Eastern Europe, Northern and Central Asia, Biomass and Bioenergy, vol. 28, pp. 119 – 132.
●● Davis, S. C. et al. (2012), Harvesting carbon from eastern US forests: opportunities and impacts of an expanding bioenergy industry, Forests, vol. 3, pp. 370 – 397.
●● Jansson, S., Bhalerao, R. & Groover, A. (eds) (2010), Genetics and genomics of Populus. Springer, New York, NY, US.
●● Lantmannen Agroenergi (no date), Manual for SRC willow growers. York, UK and Orebro, Sweden.
This box highlights another group of woody plants that can be managed as short-rotation forestry systems.
Pine, eucalyptus (Pinus spp., Eucalyptus spp.)●● Photo in production: Australia and Brazil.●● Why is it similar? Softwood (e.g. pine) and hardwood (e.g. eucalyptus) plantations also comprise C3 trees that are intensively managed to produce wood biomass; harvest rotation lengths range from five to 25 years. Eucalyptus coppices regrow vigorously from cut stumps and are often managed like poplar and willow.
●● What makes it different? After harvest, pine trees must be reseeded (eucalyptus can also be grown from seed rather than relying on coppice regrowth); greater rates of soil degradation occur in this system relative to coppicing woody crops.
●● Growing region: Wood plantations exist all over the world, with the largest production currently in the US followed by Brazil, the Russian Federation, Canada, China and northern European nations. India produces the largest amount of wood that is intended exclusively for fuel.
Pine Eucalyptus
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92 | 6 Biomass feedstock crops
Wood residues
●● Type of fuel: Solid combustion for heat and electricity, cellulosic biofuel.
●● Stage of adoption: early commercial production.
The main use of wood is now industrial – sawn timber, poles, manufactured panels, plus pulp and paper. Although tree-breeding programmes aim to reduce waste at source by producing trees with minimally tapering trunks and few branches, residues arise at all stages of production, from harvesting though to the final product. The many by-products of timber production therefore represent a significant source of woody biomass, which can be burned for heat or used in thermal power stations.
As timber processing will be a major industry for the foreseeable future, wood wastes are a reliable source of biofuel feedstock. Improvements in timber harvesting techniques will reduce the amount of wastage during logging, but this represents only a small fraction of the whole.
Characteristics
Wood residues take many forms, including logging waste (tree tops and branches), sawdust and shavings from sawmills, pulping liquor from paper production, and waste wood from construction and demolition sites. The material is far from uniform. As well as the obvious physical difference between, say, sawdust and waste lumber, tree species differ in their carbon and lignin contents. Hardwoods tend to have a higher carbon content than softwoods (55% versus 46% on average).
The moisture content of woody waste depends on species, time of harvest and source. Poplar and willow can have moisture contents of more than 50% and primary mill residues less than 20%.
Accessibility
Logging, wood processing and production industries provide a ready supply of wood residues. The largest source of uniform-format material comes from forest product industry waste. But there is also a large amount of woody waste (termed ‘brash’) that is left on the ground after forestry operations because it is currently uneconomic to retrieve; it also supports recycling nutrients in some places (not all residues should be removed). Collecting timber waste from demolition and construction sites, and from urban tree management, would provide another source of woody residues.
Global planting – n/a. Global production – 240 million tonnes of wood chips and particles plus 31 million tonnes of mechanical wood pulp (dry weight).
Top producing countries
Million Tonnes
USCanadaRussia FederationBrazilChina
284139136128102
US
Brazil
Canada
China
Russia Federation
World map showing five top producing countries
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Alternative markets
Wood residues are used in pulp production, to make particle board for construction, as well as pellets for fuel.
Potential uses after conversion to fuel
Wastes after hydrolysis and fermentation can be burned for heat.
Key references
●● Food and Agriculture Organization of the United Nations, FAOSTAT Forestry database.
●● Haberl, H. et al. (2010), The global technical potential of bio-energy in 2050 considering sustainability constraints, Current Opinion in Environmental Sustainability, vol. 2, pp. 394 – 403.
●● Hoekman, S. K. (2009), Biofuels in the U.S. – challenges and opportunities, Renewable Energy, vol. 34, pp. 14 – 22.
●● US Department of Energy, (2011), U.S. billion-ton update: biomass supply for a bioenergy and bioproducts industry. Oak Ridge National Laboratory, Oak Ridge, TN, US.
94 | 6 Biomass feedstock crops
Herbaceous crop residues
●● Type of fuel: Cellulosic biofuel, solid combustion for heat and electricity, biogas production.
●● Stage of adoption: extensive commercial production for other uses, pre-commercial scale for biofuel.
Characteristics
Mostly bulky, with variable handling requirements, agricultural wastes have different carbon (50 – 70%) and lignin (7 – 19%) contents depending on the crop. Moisture contents usually vary between 10% and 30%. Most crop residues would be collected in the field, although residues are sometimes available at the site of pre-processing for fuel, as with sugarcane bagasse.
Accessibility
Crop wastes are usually cheap and widely available wherever there is large-scale commercial agriculture. Global availability mirrors crop production patterns – the largest source of uniform-format material is rice straw, followed by wheat straw, maize stover and sugarcane bagasse. These four feedstocks together have been estimated to have the potential to annually produce 418 billion litres of bioethanol. Estimates for the potential of all crop residues suggest that 1,200 billion litres of bioethanol could be produced annually.
While sugarcane bagasse is already collected and a readily available by-product of processing, the other agricultural residues are dispersed across fields and would
require additional collection and handling. The biggest risk of using this low-cost, lightweight and plentiful material is the depletion of soil organic matter and increased erosion of agricultural soils. To guard against this, soil organic matter must be regularly monitored and it is suggested that only a proportion of available residues are collected. Reduced or zero-tillage systems allow a greater proportion of crop waste to be removed without increasing erosion risk.
Alternative markets
Crop wastes have, for millennia, been used as soil conditioners, low-grade animal feed and animal bedding. Left on the soil they are particularly valued to prevent erosion, improve soil texture and provide some degree of nutrient recycling (although nitrogen losses can increase in the short term).
Potential uses after conversion to fuel
Wastes after hydrolysis and fermentation can be burned for heat.
Global planting – n/a.Global production – 1.6 billion tonnes (dry weight).
Top producing continents
Million tonnes*
AsiaNorth AmericaEuropeSouth AmericaAfrica
920220220110 38
*dry weight
AsiaNorthAmerica
SouthAmerica
Europe
Africa
World map showing five top producing continents
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Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
6 Biomass feedstock crops | 95
Key references
●● Cherubini, F. & Ulgiati, S. (2010), Crop residues as raw materials for biorefinery systems – a LCA case study. Applied Energy, vol. 87. pp. 47 – 57.
●● Kim, S. & Dale, B. E. (2004), Global potential bioethanol production from wasted crops and crop residues, Biomass and Bioenergy, vol. 26. pp. 361 – 375.
●● Lal, R. (2005), World crop residues production and implications of its use as a biofuel, Environment International, vol. 31, pp. 575 – 84.
Herbaceous crop residues average annual yield
Current fuel yields vary according to crop, as shown in the table below.
Residue/crop ratio Estimated ethanol yield (L kg-1 dry mass)
Energy yield (MJ kg-1 dry mass)
Maize stover 1.0 0.29 98
Barley straw 1.2 0.31 100
Oat straw 1.3 0.26 88
Rice straw 1.4 0.28 94
Wheat straw 1.3 0.29 98
Sorghum straw 1.3 0.27 91
Sugarcane bagasse 0.6 0.28 94
Mean 1.2 0.28 95
96 | 6 Biomass feedstock crops
97
Miscellaneous wastes
●● Type of fuel: methane gas for heat and electricity, ethanol, biodiesel.
●● Stage of adoption: early commercial production of methane, pre-commercial stage for ethanol, early commercial production of biodiesel from used cooking oil and animal fats.
Characteristics
Miscellaneous wastes include municipal organic waste, sewage and animal manure as well as fatty oil and cooking oil wastes. These wastes have different properties, although there are similarities between animal manure and sewage, and between fatty waste and waste cooking oil. Moisture content varies from 5% to 80%, and most wastes need to be dried before further processing can take place. Given the variation in source material in this broad category, it is not surprising that they give rise to a wide range of fermentation products, chemical extracts and processing residues.
Using waste materials to generate energy has great environmental benefits, can reduce methane emissions and avoid the need to expand the area of landfill sites (and dealing with the environmental issues that this practice raises). Special equipment is needed to prevent environmental contamination and minimize public nuisance in their processing.
Accessibility
Unlike wastes from crops, which have seasonal availability, miscellaneous wastes are produced throughout the year. This makes them reliable feedstocks for fuel production. The largest source of uniform-format material is animal manure, from which it is estimated that 9 – 25EJ/yr could be recovered globally.
Yield
Fuel yields depend on source material, with a range of 1–14 gigajoules per tonne. Municipal organic waste yields more than animal manure, on average.
Although an estimated 50EJ of energy is expected to be available from wastes by 2050, estimates of sustainably available energy from all waste residues, worldwide, range between 10 and 29EJ/yr.
Alternative markets
Organic waste is often incinerated to produce heat or co-generate electricity. Animal manures have long been used as fertilizer, sometimes after a period of composting. Animal manures, municipal waste and sewage can all be digested anaerobically to produce biogas, which has the added benefit of reducing carbon dioxide and methane emissions. Some of these waste materials can be processed into animal feed or biomaterials.
Potential uses after conversion to fuel
Wastes are highly variable and the by-products from conversion to fuel depend on the source material and fuel processing technology.
Key references
●● Cherubini, F. et al. (2009), Life cycle assessment (LCA) of waste management strategies: landfilling, sorting plant and incineration, Energy, vol. 34, pp. 2116 – 2123.
●● Hoogwijk, M. (2003), Exploration of the ranges of the global potential of biomass for energy, Biomass and Bioenergy, vol. 25, pp. 119 – 133.
●● Münster, M. & Lund, H. (2009), Use of waste for heat, electricity and transport—challenges when performing energy system analysis, Energy, vol. 34, pp. 636 – 644.
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
6 Biomass feedstock crops | 97
98
Photosynthetic algae
●● Type of fuel: biodiesel, ethanol.●● Stage of adoption: pre-commercial scale production.
Representatives of this vast group of organisms are found in almost all global habitats, reproducing rapidly to create oils, carbohydrates and proteins within their single cells. They do not ‘waste’ energy producing the infrastructure found in more complex organisms. Microalgae are already in commercial production for nutritional supplements but the promise of biofuel is as yet unfulfilled.
Despite a 20-year US–DOE-funded research programme into producing biodiesel from algae, the process is not yet commercially viable, with less than 76,000 litres being produced in 2010. Nevertheless, the fact that algal ponds can be established on otherwise unproductive land, plus the high potential yields, suggest that microalgae may become more important as production and harvesting techniques are further refined. Small-scale experimental results indicate a possible yield of 13,000 litres per hectare, with some suggesting that much higher yields may be achievable. It is also possible to ferment algae biomass to produce ethanol, although this has rarely been done.
Plant characteristics
There are somewhere between several hundred thousand and tens of millions of different algal species, all single-celled, although some form colonies. Research into biofuels has focused on the photosynthetic green algae and diatoms, because the lipids they manufacture can be converted to biofuels very efficiently.
Where to grow it
Microalgae grow spontaneously wherever there is water and sunlight. Commercial production (which is currently done to produce high-value products but not fuels) can therefore be done almost anywhere that water temperatures can be maintained between 16°C and 27°C. Optimum growth for many species is 20–24°C. High-volume production of low-cost biofuels requires access to moderate to high temperatures, sufficient sunlight and water and, in most cases, a source of CO2.
How to grow it
There are two methods in current use: open circulating ponds or enclosed photobioreactors that produce biomass of similar quality. Ponds are cheaper and simpler, relying on a paddlewheel to recirculate and mix the water. But they are open to the air, so there is the risk of contamination by dust, bacteria and other strains of algae. Photobioreactors maximize sunlight capture by containing the algal mix in small-diameter tubes and protect the algae from contamination. Closed systems present their own challenges, however, such as providing for sufficient CO2 transfer and making sure that heat and oxygen do not build up.
Inputs required
WaterMicroalgae can tolerate a wide range of salinity and have a large water requirement.
FertilizerFor optimum growth, algae need nitrogen, phosphorus and silicate (diatoms need this to produce their silicaceous coats) as well as a range of micronutrients. In closed systems, CO2 must also be supplied.
Contamination
Algal cultures are easily contaminated, so sterilization and hygiene techniques are important.
Harvesting
The removal and dewatering of the algae uses a great deal of energy. During the transesterification route of algae to biodiesel, the algae are first separated from the water by centrifuge or filtration and then dried, sometimes using solar energy. Algal lipids are then removed and transformed through reaction with an alcohol (such as ethanol or methanol) into biodiesel and glycerol.
Alternative markets
Pilot plants researching energy feedstock generate income by selling microalgae for animal feed or as specialist human nutritional supplements. Algae are also used in cosmetics and in the treatment of wastewater.
Co-products
From the crop Currently none, as production is still in the research stage.
From conversion to fuel Potential uses of microalgae residues after conversion to biodiesel are animal feed or to produce methane. Glycerol is a co-product of biodiesel conversion and can replace glycerol made from petroleum. Glycerol has many uses in cosmetics, food, oral care, tobacco, synthetic polymer production and synthetic resins.
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
98 | 6 Biomass feedstock crops
99
Key references
●● Brennan, L. & Owende, P. (2010), Biofuels from microalgae—a review of technologies for production, processing, and extractions of biofuels and co-products, Renewable and Sustainable Energy Reviews, vol. 14, pp. 557 – 577.
●● Chisti, Y. (2007), Biodiesel from microalgae, Biotechnology Advances, vol. 25, pp. 294 – 306.
●● Daroch, M. et al. (2013), Recent advances in liquid biofuel production from algal feedstocks, Applied Energy, vol. 102, pp. 1371 – 1381.
●● Schenk, P. M. et al. (2008), Second generation biofuels: high-efficiency microalgae for biodiesel production, BioEnergy Research, vol. 1, pp. 20 – 43.
Macroalgae are also researched for their bioenergy potential, but are very different from microalgae and require very different production pathways. Commonly known as kelp or seaweed, these organisms are grown today for food use, most commonly by tethering the strands of growing macroalgae in open seawater during their growing period and harvesting by collection. The macroalgae can be quite productive, but have a high content of water and salts, which degrade their fuel value. This research is in the early stages and the viability of macroalgae as a feedstock for fuel is uncertain.
6 Biomass feedstock crops | 99
Representative list of additional species of plants used (or with potential) for the production of bioenergy:
Agave (Agave spp.)Agave is a genus of succulent plants that grows in semi-arid and arid regions. These plants use the CAM photosynthetic pathway, fixing carbon during the night while closing their stomata (essentially pores in the leaves) to minimize water loss during the day, so have a much lower water requirement than many other crops. Yields vary according to species and location, but are reportedly between 1 and 34 tonnes/ha/yr. An additional potential advantage of agave is the availability of land formerly intended for agave fibre production, which is estimated to have been about 600,000 hectares worldwide. Agave species occur naturally in the south-western US, Central America and parts of South America. Varieties are commercially cultivated in Central and South America and Africa, and experimentally cultivated in Australia. Agave thus has the potential to be grown in many semi-arid regions of the world, specifically on land not otherwise used for food production.
BambooA family of perennial giant woody grasses of the subfamily Bambusoideae, these plants are native to equatorial and tropical regions around the globe. While bamboo is cultivated for a wide range of purposes, only small amounts are used for firewood. Annual yields of common native species range from 1.5 to 14 tonnes/ha. The stems have been found to have an energy content of ~17GJ/tonne dry matter and contain around 40% cellulose. Different species of bamboo mean that the potential crop species can be grown over a wide geographical area including southern Russia, Europe, North America and central Asia. Recent work in India has indicated that clear felling of the crop may open the potential for mechanization. A major concern with bamboo, however, is invasiveness and difficulties of removal once the plantation is no longer in use.
Black locust (Robinia pseudoacacia L.)A pioneer hardwood species found in North America, these trees displays rapid juvenile growth. Mature trees can reach a height of 15 – 35m and the plant has a high rate of photosynthesis. In trials, commercial stands have produced yields of 5 – 10 tonnes/ha/yr in three- or four-year-old stands; peak production is seen at seven years. It burns slowly and has very high energy content, making it an ideal feedstock. Because of the tree’s tendency to sprout from both the stem and roots, it may be suitable for both SRF and SRC. As a legume, its roots contain nitrogen-fixing bacteria, which can help improve soil fertility. A native of North America, the tree is also successfully grown in other areas including Europe; however, it has the potential to become invasive outside its native range.
Additional species
Camelina (Camelina sativa L.)Although promoted as a potential feedstock for biodiesel production, the unique properties and relatively low yields (1.5 – 3 tonnes of seed per hectare) mean that this plant, a member of the cabbage family, is likely to be confined to the specialist chemical market or jet fuels. Camelina can be widely grown in temperate agricultural systems.
Cassava (Manihot esculenta Crantz.)
There are many cultivars of cassava, a crop that has been domesticated for more than 2,000 years, some of which are grown as biofuel feedstock and others as food. It is one of the most drought-tolerant crops, can be successfully grown on marginal land, and has a great ability to produce more useable energy per unit of land than comparable crops. The cultivation of cassava as a feedstock for ethanol production is increasing rapidly with new plants in operation in South-East Asia, especially Thailand, China and Vietnam. Development is also under way in other parts of the world including Panama and Nigeria, where a Chinese energy company is planning a 110-million-litre-a-year plant. In addition to ethanol production, cassava residues are used to generate biogas.
Modern breeding efforts are focused on increasing the protein content to improve diets in Asia, South America and Africa, where it is already successfully grown. As well as having the potential to produce dedicated bioenergy crops based on the starchy tuber, ‘conventional’ cultivation already produces a large amount of vegetative material suitable for anaerobic digestion. Soil disturbance associated with harvesting below-ground biomass could, however, result in greater terrestrial carbon emissions than alternative crops.
100 | 6 Biomass feedstock crops
Diesel tree or Jesuit’s balm (Copaifera langsdorfii Desf.)Reaching up to 12m in height, this tropical rainforest tree produces hydrocarbon-rich oil, which is harvested by tapping. In tropical areas oil yields can reach 10,000l/ha/yr or more, although plantations can take 15 – 20 years to reach this level of production. Despite this slow attainment of full productivity, some farmers in Australia are investigating production of the tree as a crop following its introduction from Brazil.
Abyssinian mustard (Crambe abyssinica Hochst.)This herbaceous crop can be harvested after 100 days with an oilseed yield of 2.5 – 3 tonnes/ha, although it may be more suitable for high-value chemical production rather than bioenergy. It can be grown in areas with moderate rainfall such as central Asia and Western Europe.
Field pennycress (Thlaspi arvense L.)A naturally occurring small brassica, field pennycress is a low-growing annual weed often found in arable crops. It has attracted academic interest as a potential bioenergy feedstock due to its production of oil-rich seeds. It is widespread in areas of temperate agriculture.
Giant reed (Arundo donax L.)Found wild in parts of southern Europe, as well as the US and China, it is believed that this species could adapt to more temperate conditions. Producing yields of up to 40 tonnes/ha in the wild, it is regarded as the largest temperate grass after bamboo. The plant, however, is listed as an invasive species in the US and in the Global Invasive Species Database, and is considered a high risk for waterways.
Napiergrass (Pennisetum purpureum Schumach.)This is the true elephant grass (a term sometimes mistakenly used for miscanthus), a robust C4 grass that can grow to 6m in height. It requires nutrient-rich soils and yields under cultivated conditions are highly variable ranging from 2 to 85 tonnes/ha (dry mass). A native of the African grasslands, it is being investigated as a commercial species in many temperate and sub-tropical regions, with trials conducted in Central and South America, Africa and parts of Asia. It is considered a high-risk invasive species in the Pacific Islands, Australia and the US.
Prairie cordgrass (Spartina pectinata Bosc.)There are 16 species of Spartina, and they utilize the C4 photosynthetic pathway. Of the three species that have been seriously investigated for bioenergy use, S. pectinata is the most common, although yields in experimental trials have been variable (5–16 tonnes/ha), due to wide-ranging environmental stress factors. Despite this, prairie cordgrass can be more tolerant to salts and metals than other grass species. It is found throughout the US and Canada, and has potential for production in parts of northern Europe and Russia.
Reed canary grass (Phalaris arundinacea L.)A perennial C3 plant often found in cool damp climates, reed canary grass (unlike many other grasses promoted as bioenergy crops) can be grown from seed and harvested with existing equipment. There has already been some commercial breeding in Scandinavia; typical yields in the region are 10 tonnes/ha. It can be grown throughout North America and northern Europe and there are an estimated 10,000ha cultivated for pulp and paper and solid fuel production in Scandinavia. This plant is listed as an invasive species in the US and in the Global Invasive Species Database.
6 Biomass feedstock crops | 101
Biomass crops: comparison table
Sugarcane Corn Soybean Switchgrass Miscanthus Oil palm Poplar/willow Wood residue Crop residue Misc. waste Algae
Type of crop PerennialC4 Leaf/stem Sugar
Annual C4GrainStarch
AnnualC3Oil seed
PerennialC4Leaf/stemCellulose
PerennialC4StemCellulose
PerennialC3Oil seed
PerennialC3WoodyCellulose/lignin
Wastes from timber harvest and processing etc.
Straw from cereal crops etc.
Animal, municipal wastes etc.
Micro-cropAlgal lipids
Fuel type(commercial and pre-commercial)
Bioethanol,biopower, lignocellulosic ethanol
Bioethanol Biodiesel Biopower, lignocellulosic ethanol
Biopower, lignocellulosic ethanol
Biodiesel Biopower, lignocellulosic ethanol
Biopower, lignocellulosic ethanol
Biopower, lignocellulosic ethanol
Biopower, biogas Biodiesel
Latitude 37°N–31°S 54°N–34°S 52°N–39°S 55°N–17°N 56°N–37°N [2] 15°N–12°S Poplar: 66°N–30°N Willow: 75°N–34°S
[3]
Suitable soils Wide range, requires draining on heavy clay
Best on medium-textured soils
Best on clay loam; moderately salt-tolerant
Once established, tolerant of most soils
Dislikes heavy clay; best on water-retentive soils; also good on sand
Tolerates wide range of pH; best in sandy soils with good drainage
Wide range, but establish slowly on heavy clay
Water requirement [1]
(mm)
High1,500–2,500
Moderate670–800
Moderate600
Moderate520–750
Low-moderate450 minimum but will use more when available
High2,000–2,500
Low-moderate320–450 plus groundwater
High, esp. in raceway systems
Temp.(none grows well above 45°C)
Mean temperature at least 18°C
Optimum 24–30°C
10°–40°C Germinates above 8–10°C, optimum 25–30°C
Shoots grow above 7°C
Optimum 24–28°C [4]
Wide range: very tolerant of severe frost and heat
20–30°C
Fertilizer requirement(kg/ha/yr)
N: 45–300 P: 15–50 K: as required
N: 145–200 P: 26–110 K: 25–130
N: 0–70P: 32–155K: 30–320
N: 50–168 P: 0–35K: 0–45
N: 0–92P: 0–13K: 0–202
N: 114P: 14K: 149[5]
N: 20–210P: 13–93K: 25–174
Estimated from molecular formula of microalgal biomass: needs only N and P in ratio 4–45N:1P
Insect control Range of pesticides Range of pesticides
Range of pesticides Generally not needed
Generally not needed Range of pesticides Not commonly used
Global average yield(tonnes/ha/y)
71 wet 5.2 dry 2.9 (seed)0.44 (oil)
14 dry 18 (Europe) [6]
38 (North America) dry
14 (fruit)2.9 (oil)
Poplar: 7.1Willow: 7.3
270 million tonnes/y
1.6 billion tonnes/y Unknown Unknown
Area currently in cultivation (million ha)
24 160 99 Unknown Unknown 15 Poplar: 5.3Willow: 0.09
Energy equivalent of current biomass (EJ)
3.3 7.5 1.6 Unknown Unknown 1.6 Poplar: 0.69Willow: 0.013(biopower)
4.1EJ/y(biopower)
150EJ/y [7]
(biopower)11EJ/y (bioethanol)
10–29EJ/y [8]
Top three producing countries (or continents)
BrazilIndiaChina
USChinaBrazil
USBrazilArgentina
Unknown Unknown IndonesiaMalaysiaNigeria
ChinaIndiaFrance
USCanadaRussia
AsiaNorth AmericaEurope
Unknown Unknown
102 | 6 Biomass feedstock crops
Biomass crops: comparison table
Sugarcane Corn Soybean Switchgrass Miscanthus Oil palm Poplar/willow Wood residue Crop residue Misc. waste Algae
Type of crop PerennialC4 Leaf/stem Sugar
Annual C4GrainStarch
AnnualC3Oil seed
PerennialC4Leaf/stemCellulose
PerennialC4StemCellulose
PerennialC3Oil seed
PerennialC3WoodyCellulose/lignin
Wastes from timber harvest and processing etc.
Straw from cereal crops etc.
Animal, municipal wastes etc.
Micro-cropAlgal lipids
Fuel type(commercial and pre-commercial)
Bioethanol,biopower, lignocellulosic ethanol
Bioethanol Biodiesel Biopower, lignocellulosic ethanol
Biopower, lignocellulosic ethanol
Biodiesel Biopower, lignocellulosic ethanol
Biopower, lignocellulosic ethanol
Biopower, lignocellulosic ethanol
Biopower, biogas Biodiesel
Latitude 37°N–31°S 54°N–34°S 52°N–39°S 55°N–17°N 56°N–37°N [2] 15°N–12°S Poplar: 66°N–30°N Willow: 75°N–34°S
[3]
Suitable soils Wide range, requires draining on heavy clay
Best on medium-textured soils
Best on clay loam; moderately salt-tolerant
Once established, tolerant of most soils
Dislikes heavy clay; best on water-retentive soils; also good on sand
Tolerates wide range of pH; best in sandy soils with good drainage
Wide range, but establish slowly on heavy clay
Water requirement [1]
(mm)
High1,500–2,500
Moderate670–800
Moderate600
Moderate520–750
Low-moderate450 minimum but will use more when available
High2,000–2,500
Low-moderate320–450 plus groundwater
High, esp. in raceway systems
Temp.(none grows well above 45°C)
Mean temperature at least 18°C
Optimum 24–30°C
10°–40°C Germinates above 8–10°C, optimum 25–30°C
Shoots grow above 7°C
Optimum 24–28°C [4]
Wide range: very tolerant of severe frost and heat
20–30°C
Fertilizer requirement(kg/ha/yr)
N: 45–300 P: 15–50 K: as required
N: 145–200 P: 26–110 K: 25–130
N: 0–70P: 32–155K: 30–320
N: 50–168 P: 0–35K: 0–45
N: 0–92P: 0–13K: 0–202
N: 114P: 14K: 149[5]
N: 20–210P: 13–93K: 25–174
Estimated from molecular formula of microalgal biomass: needs only N and P in ratio 4–45N:1P
Insect control Range of pesticides Range of pesticides
Range of pesticides Generally not needed
Generally not needed Range of pesticides Not commonly used
Global average yield(tonnes/ha/y)
71 wet 5.2 dry 2.9 (seed)0.44 (oil)
14 dry 18 (Europe) [6]
38 (North America) dry
14 (fruit)2.9 (oil)
Poplar: 7.1Willow: 7.3
270 million tonnes/y
1.6 billion tonnes/y Unknown Unknown
Area currently in cultivation (million ha)
24 160 99 Unknown Unknown 15 Poplar: 5.3Willow: 0.09
Energy equivalent of current biomass (EJ)
3.3 7.5 1.6 Unknown Unknown 1.6 Poplar: 0.69Willow: 0.013(biopower)
4.1EJ/y(biopower)
150EJ/y [7]
(biopower)11EJ/y (bioethanol)
10–29EJ/y [8]
Top three producing countries (or continents)
BrazilIndiaChina
USChinaBrazil
USBrazilArgentina
Unknown Unknown IndonesiaMalaysiaNigeria
ChinaIndiaFrance
USCanadaRussia
AsiaNorth AmericaEurope
Unknown Unknown
Notes[1] Most water requirements are met by precipitation.[2] This range in successful trials; may well be wider.[3] The extreme southerly part of range being along water
courses in Argentina.[4] Commercial production limited to areas with only
a 6°C seasonal mean temperature variation.
[5] These figures for 10-year-old stands; 15-year-old stands have higher requirements for N, P and K (N: 162, P: 21, K: 279).
[6] Winter yields: harvest is usually done in winter, despite lower yields, to facilitate nutrient retention.
[7] Estimate of global availability of crop residues.[8] Estimate of current potential sustainably available bioenergy.
6 Biomass feedstock crops | 103
Maize (corn)
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Switchgrass
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Miscanthus
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Oil palm
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Soybean
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Glossary
Agroecosystem The organisms (crops, livestock, micro-flora and -fauna etc.) and environment (soils, water, climate etc.) of an agricultural area considered as an ecosystem.
Agroforestry A multi-use form of land management where trees are grown in association with arable crops or pasture.
Alcohols A class of organic compounds closely related to hydrocarbons. They are used in medicine, and in industry as fuels and solvents. Examples include methanol and ethanol, the substance that makes beer, wine and spirits.
Anaerobic fermentation A biological process taking place in the absence of oxygen, in which sugars are broken down into alcohols and carbon dioxide.
Annual crops Crops whose life cycle, from seed to harvest, is complete in less than 12 months.
Bagasse A term often used in relation to sugarcane production: bagasse is the fibrous residue left after the sugary juice has been extracted from the crushed cane.
Bioenergy Energy from any renewable biological material derived from plants or animals.
Biennial plants Plants that produce only vegetative growth (roots, shoots and leaves) during the first year; flowering and fruiting (followed by death) occur in the second year.
Biofuel Liquid fuels derived from biomass, used primarily for transport, including ethanol, biodiesel and other liquids.
Biogas A mixture of methane and CO2 produced by the bacterial decomposition (fermentation) of organic wastes and used as a fuel.
Biomass The solid matter in living or recently living organisms.
Biome A major ecological community (ecosystem) type (such as tropical rain forest, grassland or desert).
Bioplastic Plastics that are derived from biomass including oils, fats and starches.
C3, C4 and CAM photosynthetic pathways Green plants use energy from the sun to create
sugars from CO2 and water. This process is called photosynthesis and has three variants:
C3 The most common photosynthetic pathway, found particularly in temperate crops including rice and wheat. Such plants tend to have a lower water-use efficiency (WUE, see below) than plants with C4 and CAM metabolism, because the process of CO2 diffusion into leaf tissues through leaf pores also allows water to be lost through transpiration.
C4 The C4 pathway may have evolved as a mechanism to help plants survive drought or high temperatures, because C4 plants (including maize and sugarcane) are more common in tropical climates. They tend to have higher rates of photosynthesis and WUE than C3 plants, and the group includes some of the most productive tropical crops.
CAM Some plants, such as agave and pineapple, living in arid environments have a photosynthetic pathway called crassulacean acid metabolism (CAM). To conserve water during the heat of the day, their leaf pores remain closed. CO2 diffuses into the leaves while the leaf pores are open during the night and is used for photosynthesis during the day.
Carbon fixation The incorporation of carbon into organic compounds (such as simple sugars) by living organisms, chiefly by photosynthesis in green plants.
Carbon sequestration A process by which CO2 is removed from the atmosphere and held in solid or liquid form. It occurs naturally as limestones are produced in the oceans and peat and coals form. Large amounts of carbon are also trapped in biomass and in the soil. In recent years man-made systems have been sequestering CO2 by injecting the gas under pressure into deeply buried porous rock formations. It is an important process, given global concern about rising atmospheric CO2 levels.
Carbon sink A natural or man-made environmental, process or system that absorbs and stores carbon compounds. Often used to refer to the absorption and storage of CO2.
Cellulose A complex organic polymer (C6H10O5)n composed of glucose units, cellulose gives strength to the cell walls of green plants. Cellulose, extracted mainly from wood, is the basis of the world’s huge paper industry. The complexity of its molecular structure makes it difficult to deconstruct prior to fermentation for liquid fuel production.
Coniferous Mostly evergreen trees and shrubs, usually have needle-shaped or scale-like leaves. Not all conifers produce their seed within cones: the yew tree, for instance, produces berries. Conifers are generally adapted to withstand drought, and many of them can withstand very low winter temperatures.
Coppice Many broadleaved trees have the ability to coppice (to produce vigorous new shoots from the base) if they are cut down. This means that many crops of shoots or poles can be produced from each root, over many years. Few conifers are able to coppice.
Crop residue There are two types of agricultural crop residues: field residues are materials (including stalks and stubble (stems), leaves and seed pods) left on the ground after the crop has been harvested. Good management of field residues can increase efficiency of irrigation and help control erosion. Process residues are those materials (include husks, seeds, bagasse and roots) left after crop processing. They can be used as animal fodder, as soil improvers, and in manufacturing.
Cultivar (‘cultivated variety’) A variety or strain of plant that has been bred deliberately and whose characteristics persist under cultivation.
Direct land-use change (DLUC) Usually used to describe the direct and observable effects of change of land use from undisturbed habitat (such as rainforest) to agriculture or from one type of agriculture to another.
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116 | Glossary
Ecosystem A community of organisms and its environment functioning as an ecological unit.
Ecosystem services A wide range of services that together maintain the conditions for life on earth. The benefits/products of these services include food and water; nutrient cycling; flood and disease control; and spiritual, recreational and cultural benefits.
Esterification A reaction of an alcohol with an acid to produce an ester and water.
Ethanol A type of alcohol with the chemical formula C2H5OH. It is a volatile, flammable liquid used as a solvent and in fuel; it is also the intoxicating agent in alcoholic beverages. Bioethanol is ethanol produced from biomass.
Evapotranspiration The process of water loss from soil. This is a combination of evaporation from the soil surface and transpiration from the plants growing in it.
Fatty acids Organic acids containing a long chain of carbon atoms.
Feedstock A raw material, such as biomass or coal, used to supply energy or material to a commercial process.
Fertigation To fertilize and irrigate at the same time, by adding fertilizers to the water supply.
Genetically modified (GM, of an organism) Containing genetic material that has been artificially altered so as to produce a desired characteristic. The process of genetic modification attracts controversy.
Glycerol Also known as glycerin or glycerine, this is a sweet, water-absorbing sugar–alcohol compound. It is a by-product of biodiesel production and is widely used in the pharmaceutical industry.
Greenhouse gas (GHG) A gas that contributes to the greenhouse effect (by which the earth is kept warm by an atmospheric blanket) by absorbing infrared radiation. Carbon dioxide and methane are examples of greenhouse gases.
Haber–Bosch process An industrial process invented by Fritz Haber to react nitrogen and hydrogen, often used in the production of ammonia used in fertilizers.
Hemicellulose An organic polymer found in plant cell walls, as is cellulose (see above). Its structure is more complex than cellulose, though it is more easily broken down to single sugars (monosaccharides) and short-chain polymers with mild heat treatment.
Hydrolysis A process of decomposition involving the breaking of chemical bonds by the addition of water.
Hydro-treated vegetable oils (HVO) Diesel fuels produced by using hydrogen to remove oxygen from triglyceride components of vegetable oils and animal fats.
Indirect land-use change (ILUC) Used to describe ancillary or unintended and indirect effects resulting from changing the use of land for one purpose to another. If maize acreage in the US were used for fuel instead of animal feed, for example, and this created a market signal to plant more maize in Brazil using forest or pasture land, the impacts of the Brazilian conversion would constitute an indirect effect of the US action. The magnitude of any effects of ILUC is substantially more difficult to evaluate than DLUC.
Intercropping Growing two or more crops simultaneously (such as in alternate rows) on the same plot of land. An example would be growing beans between maize plants in smallholder farming systems in parts of Africa.
Life cycle analysis (LCA) Also known as life cycle assessment, it is a comprehensive interdisciplinary assessment that identifies and attempts to quantify the energy, material and waste flows of a product, and their impact on the environment.
Lignin A complex polymer related to cellulose that provides rigidity and forms the woody cell walls of plants and the cementing material between them. It confers strength and disease-resistance on woody plants, and is difficult to decompose to its constituent parts. The process by which plants deposit lignin in their cell walls is called lignification.
Lignocellulosic A word to describe various substances (consisting of cellulose intimately associated with lignin) found in the woody cell walls of plants. Woodchips would be an example of lignocellulosic biomass.
Lipid A group of naturally occurring molecules that include fats and waxes. Together with proteins and carbohydrates, lipids constitute the principal structural components of living cells.
Loam A soil consisting of a friable mixture of varying proportions of clay, silt and sand. Loams are productive agricultural soils.
Metabolic pathway A sequence of chemical reactions in a living organism.
Methane (CH4) A gaseous hydrocarbon fuel. It is lighter than air and forms explosive mixtures with air. It is produced by the decomposition of organic matter and is used as a fuel and raw material in chemical synthesis. It is a major greenhouse gas with a more powerful greenhouse effect than CO2.
Net primary productivity (NPP) The rate at which an ecosystem accumulates energy or biomass, excluding the energy it uses for the process of respiration.
Nitrous oxide (N2O) An atmospheric pollutant and greenhouse gas produced by combustion.
Peat Partially carbonized vegetable substance formed by incomplete decomposition of plant material in water. Peat is an important store of carbon, which is released into the atmosphere when peat is burned (for fuel) or when peat soils are brought under cultivation.
Perennial crop A crop from plants that live for more than one year. Examples include sugarcane, woody biomass and perennial grasses.
Photosynthesis See C3, C4 and CAM photosynthetic pathways above.
Polymer A substance whose molecular structure is built up of many similar units bonded together. Examples of plant polymers include cellulose (composed of glucose molecules) and starch (also composed of glucose, but bonded in a different way to give different physical properties).
Radiative forcing/exchange The difference between the amount of radiant energy received on earth from the sun and the amount radiated back into space. This is affected by, among other factors, the concentration of greenhouse gases in the atmosphere.
Respiration Energy yielding process found in living organisms involving the breakdown of nutrients, the use of oxygen and the production of carbon dioxide.
Rhizome A specialized underground plant stem that superficially resembles a root. It contains deposits of reserve food material, and produces both shoots and roots.
Semi-arid A climate type that has only light rainfall, often defined as having 25–50cm (10–20in) of annual precipitation.
Senescence The final growth phase in a plant or leaf, during which nutrients are taken back to the root system before leaf-fall or death.
Silage Fodder converted into succulent feed for livestock through anaerobic acid fermentation in a silage clamp.
Soil organic matter The organic component of soil, which includes the living biomass of microorganisms, and fresh and partially decomposed residues. It also includes well-decomposed, highly stable organic material. Surface litter is generally not included as part of soil organic matter but can become part of it if physically incorporated into the soil. Soil organic matter is of vital importance for nutrient cycling, erosion protection and for its water-holding capacity.
Short rotation coppice (SRC) A management regime that promotes the growth of multiple stems by cutting trees back quite close to the ground every two to four years. SRC is often used to produce woody biomass.
Short rotation forestry (SRF) A management regime under which trees are planted and then felled when they have reached a size of typically 10–20cm diameter at breast height. Depending on tree species and climate, this can take between three and 20 years, and is therefore intermediate in timescale between SRC and conventional forestry.
Starch A polymer of glucose that is the chief storage form of carbohydrate in plants. It is an important product for fermentation into bioethanol via its constituent glucose.
Stover A straw-like substance left over after grain crops like maize (corn) or sorghum have been harvested. It is used as feed for livestock and has potential for conversion to biofuel.
Subsoil The stratum of weathered material that underlies the surface soil. Subsoil lacks organic matter.
Tillage The preparation of land for growing crops.
Tilth The condition of soil after it has been ploughed and harrowed to create an even, lump-free surface. A tilth is required for consistent seed germination.
Topsoil Surface soil in which plants have most of their roots, and which is turned over during ploughing.
Traditional biomass Woodfuels, agricultural by-products and dung burned for cooking and heating purposes. Very widely used in developing countries.
Transpiration Loss of water from a plant, mainly through the leaf pores (stomata).
Tuber A short, fleshy, usually underground stem bearing minute-scale leaves each of which is potentially able to produce a new plant. A potato is a tuber.
Water-use efficiency (WUE) At a crop level, WUE is defined as the ratio of the crop mass yield to the water mass lost through evapotranspiration over the growing season. In practical terms, WUE can be thought of as crop yield per unit of water.
Image sources and credits
p. 72 Maize close-up from Shutterstock and harvesting from Tim Mies at the Energy Biosciences Institute.
p. 74 Wheat in production from Shutterstock.
p. 75 Sugarcane close-up and harvesting from Caio Fortes, BP.
p. 77 Sweet sorghum in production from Caio Fortes, BP.
p. 78 Switchgrass close-up from Tom Voigt and harvesting from Tim Mies, both at the Energy Biosciences Institute.
p. 80 Cordgrass in production from Tom Voigt at the Energy Biosciences Institute.
p. 81 Miscanthus close-up from Tom Voigt and harvesting from Tim Mies, both at the Energy Biosciences Institute.
p. 83 Energy cane in production from Joshua Drake, BP.
p. 84 Oil palm close-up and harvesting from Shutterstock.
p. 86 Jatropha in production from Shutterstock.
p. 87 Soybean close-up from Shutterstock and harvesting from Tim Mies at the Energy Biosciences Institute.
p. 89 Oilseed rape or canola in production from Shutterstock.
p. 90 Willow and hybrid poplar close-ups, as well as coppicing, from Tom Voigt at the Energy Biosciences Institute; short rotation harvest from Shutterstock.
p. 92 Pine and eucalyptus in production from Shutterstock.
p. 93 Forest waste being chipped from Nevada Division of Forestry.
p. 95 Corn stover residue collection from Tom Campbell at Purdue Agricultural Communication.
p. 97 Biodigester from Shutterstock.
p. 98 Algae pond © Cyanotech Corporation 2014 – Producers of Nutritional Supplements from Microalgae.
p. 99 Macro algae from Shutterstock.
p. 100 Cassava from Shutterstock.
Glossary | 117
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
Plant types
Plant characteristics – icons in chapter 6
Propagation method
Annual Perennial
Photosynthetic pathway
Plant life cycle
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
CAM
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
C4C3
Herbaceous
Plant types
Photosynthetic pathway
Propagation method
Current dominant energy use
Other
Annual
PerennialWoody Grain or seed
Seed Stemcutting
MicropropagationRhizome or root cuttings
Bioethanol Biodiesel BiogasHeat and power
Power usage
Car BarrelWeight
C3 C4
E D
Primary energy use
� Table 3.1Bioenergy production routes
BP Biomass HandbookTable 3.1 (20 December 2013)Draft produced by ON Communication
(Wood, straw,energy crop, etc.)
(Rape, soy, palm, etc.)
Lignocellulosic biomass
Feedstock Conversion Energy
Sugar and starch crops
Oil crops
Chemical process
Thermochemical process
Fuel for heatand/or power
Liquid fuels,transport fuels
Bioethanol
Other liquids
Biodiesel
Gaseous fuel
Biogas
Syngas
Pre-p
rocess
Biochemical process
Hydrolysis and fermentation
Transesterification
Other catalysis
Hydrogenation
Pyrolysis
Combustion
Gasification
Anaerobic digestion
Schematic diagram of bioenergy production pathways. Feedstocks on the left of the diagram are converted via a range of processes to solid, liquid or gaseous fuels on the right. No attempt is made to show relative scales of each process
Icons shown in grey indicate pre-commercial stages of adoption.
Biomass in the energy industry An introduction
Bio
mass in
the en
ergy in
du
stry An
intro
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ction
Biomass in the energy industryAn introduction
Supported by BP, as part of the multi-partner Energy Sustainability Challenge, which explores the implications for the energy industry of competing demands for water, land and minerals.
Biomass in the energy industry – An introduction is a study that provides contextual knowledge required for assessing the potentials and issues of using biomass for energy. The book is based on literature research and review by colleagues at the Energy Biosciences Institute (www.energybiosciencesinstitute.org) and is part of the Energy Sustainability Challenge (www.bp.com/energysustainabilitychallenge) series of handbooks. This book addresses the need for having a holistic view of the benefits and risks associated with bioenergy by studying the subject from agricultural, energy, environmental, technological, socio-economic and political perspectives. The book emphasizes that realizing the potential of biomass energy as a major player in carbon emissions reduction needs careful consideration of environmental aspects and competing demands of food, water, energy and other resources. Clear and consistent supportive policies are also required to facilitate significant financial investments for developing biomass conversion technologies and improving performance of biomass crops.
The handbook also provides key data about crops species and biomass types that are already in production or are being researched for biomass. The data includes plant characteristics, suitable growth conditions, required inputs and agricultural practices, co-products and alternative markets, as well as yield and energy productivity indicators.
The handbook offers a valuable guide for policy makers, businesses and academics on the characteristics of major biomass crops and the issues related to sustainable and responsible use of biomass for energy.
Biomass in the energy industry – An introduction shows:
n What role biomass plays in the global energy context.
n What fundamental knowledge is required to understand bioenergy systems.
n How biomass is converted to energy and what technological developments are under way.
n Why it is vital to view use of biomass for energy from socio-economic, environmental and political perspectives.
n What is the potential for bioenergy and how this potential can be realized.
n Where can biomass feedstocks be grown and what are the key characteristics of biomass crops already in production or being researched for biomass.
Published by BP p.l.c.© 2014 BP p.l.c.
9 780992 838713
ISBN 978-0-9928387-1-3