energy and exergy improvements for vale manso condominium · energy and exergy improvements for...
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Energy and exergy improvements for Vale Mansocondominium
Diogo Vieira de Castro Simões
Thesis to obtain the Master of Science Degree in
Mechanical Engineering
Supervisor: Prof. Tânia Alexandra dos Santos Costa e SousaDr. André Alves Pina
Examination Committee
Chairperson: Prof. Mário Manuel Gonçalves da CostaSupervisor: Prof. Tânia Alexandra dos Santos Costa e SousaMember of the Committee: Prof. Luís Filipe Moreira Mendes
November 2016
ii
Acknowledgments
I would like to express my gratitude and thanks to all of those who made the realization of this thesis
possible. Particularly:
To my co-supervisor, Professor Andre Pina, for the patience, for the time lost even on holidays, feed-
back, ideas shared during all stages and also for the excellent availability shown.
To Professor Viriato Semiao for helping me with all the necessary data from the monthly climatologi-
cal newsletter for 2015.
To Luısa Dias, condominium’s secretary, for all the patience for scanning all the electric invoices from
the last 10 years and also for all the availability and support through all stages of the thesis.
To Carlos Horta, condominium manager, for all the the feedback, ideas shared and for providing me
all the plants needed and explained me all the condominium facilities.
To my parents for giving me this thesis study idea.
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iv
Resumo
Esta tese de mestrado apresenta uma analise exergetica e uma auditoria energetica para o Condomınio
Vale Manso, situado na albufeira de Castelo de Bode, com base nos dados de consumos e de producao
de energia para o perıodo de 2010 a 2015. A analise exergetica e efectuada a micro-geracao de energia
e a analise energetica incide principalmente na eficiencia energetica dos edifıcios e espacos exteriores,
assim como dos equipamentos instalados e sob a responsabilidade do condomınio, nomeadamente
a ETAR, as Estacoes Elevatorias, a rega e iluminacao exterior. Para realizar a seguinte analise en-
ergetica a metodologia utilizada baseou-se essencialmente em tres fases, recolha de informacao exis-
tente, realizacao de trabalho de campo nas instalacoes e elaboracao final do diagnostico energetico.
Atraves da recolha de informacao, foi possıvel definir economias numa perspectiva de Eficiencia En-
ergetica e de Utilizacao Racional de Energia. Atraves da realizacao de trabalho de campo foi possıvel
compreender a articulacao de custos energeticos das instalacoes estudadas. O diagonostico exer-
getico feito a micro-geracao de energia composto por paineis solares permitiu concluir que melhorias
ao nıvel da exergia podem ser aplicadas. A ETAR, a rega e a iluminacao exterior sao analisadas e sao
introduzidas ideias para melhorar o consumo energetico e a respectiva factura electrica.
Palavras-chave:• Analise Energetica
• Eficiencia Energetica
• Energia
• Exergia
v
vi
Abstract
This thesis presents an exergy analysis and an energy audit for the condominium Vale Manso, located
in the bay of Castelo de Bode, based on data of consumption and of energy production for the period of
2010 to 2015. The exergy analysis is carried out to the micro-power generation and energy analysis fo-
cuses mainly on the energy efficiency of buildings and outdoor spaces, as well as the equipment installed
and under the responsibility of the condominium, namely the waste water treatment plant (WWTP), wa-
tering and outdoor lighting. In order to carry out the following energy analysis, the methodology used
was essentially based on three phases, gathering of existing information, carrying out fieldwork in the
installations and final elaboration of the energy diagnosis.
Through the collection of information, it was possible to define economies in the perspective of En-
ergy Efficiency and Rational Use of Energy. Through the realization of fieldwork it was possible to
understand the articulation of energy costs of the studied facilities. The exergy diagnoses made to the
micro-generation of energy composed by solar panels allowed to conclude that exergy level improve-
ments can be applied. The WWTP, irrigation and outdoor lighting are analyzed and ideas are introduced
to improve energy consumption and its electricity bill.
Keywords:• Exergy Analysis
• Energy Audit
• Energy
• Exergy
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Contents
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Resumo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Aims for the Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Thesis Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Basic Concepts 5
2.1 Energy Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 Primary, Final and Useful Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Exergy Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3 Efficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3.1 First Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3.2 Second Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.4 Photovoltaic Panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.4.1 Photovoltaic Cells Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.5 Portuguese Legislation for Energy Producers . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.5.1 In 2010 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.5.2 Actual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.6 Electricity Costs in Portugal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.6.1 Active Energy Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.6.2 Power in Peak Hours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.6.3 Contracted Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.6.4 Reactive Energy Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.6.5 Power Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
ix
3 Case Study 21
3.1 PV Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2 WWTP Operation Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.3 Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4 Methodology 28
4.1 Analysis of PV Panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.1.1 Energy Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.1.2 Exergy Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.1.3 Associated Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.2 Analysis of Electricity Consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.2.1 Energy Audit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
5 Results and Discussion 39
5.1 PV Panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
5.1.1 Results of Energy and Exergy Analysis . . . . . . . . . . . . . . . . . . . . . . . . 39
5.1.2 Cost Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
5.2 WWTP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.2.1 Energy Consumption in Super Void Hours . . . . . . . . . . . . . . . . . . . . . . . 45
5.2.2 Transformation of Aeration Process . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.2.3 Total Elimination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
5.3 Other Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
6 Conclusions 53
6.1 PV Panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
6.1.1 Exergy and Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
6.1.2 Cost and Investment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
6.2 WWTP and other facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Bibliography 57
A Technical Datasheets 59
A.1 Photovoltaic Datasheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
x
List of Tables
2.1 Energy prices over the last 6 years. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.2 Other electrical characteristics and their price. . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3 Multiplicative factors for tg ϕ factor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.4 Reactive energy prices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.1 Solar PV module parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.2 Expected energy production. (Information provided by Conergy) . . . . . . . . . . . . . . 23
3.3 Population that use the WWTP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.4 Industrial air liquid prices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.5 Power factor average over the years. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.6 Energy costs breakdown. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.1 Parameters for calculation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.2 Inflation values over the last 6 years. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
5.1 Overall heat loss coefficient. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
5.2 Energy efficiencies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5.3 Exergy efficiencies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5.4 Comparison expected/read values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5.5 Price difference between energy used in void hours and super void hours. . . . . . . . . . 45
5.6 Annual costs for scenario 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
5.7 Price difference between energy used in all hours and super void hours. . . . . . . . . . . 46
5.8 Annual costs for scenario 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.9 Annual energy spent with and without WWTP. . . . . . . . . . . . . . . . . . . . . . . . . . 48
5.10 Annual energy spent with and without WWTP. . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.11 Emissions with and without WWTP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
5.12 Primary energy conversion efficiencies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
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xii
List of Figures
2.1 Sankey’s diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 Schematic Energy System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3 Sankey’s for exergy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4 Schematic PV System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.5 Evolution of PV cell materials over the years. . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.6 Timetable for three-hourly energy consumption over the winter. . . . . . . . . . . . . . . . 15
2.7 Timetable for three-hourly energy consumption over the summer. . . . . . . . . . . . . . . 15
2.8 Power triangle diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.1 Condominium location in Portugal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2 Characteristics of PV panels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.3 Location of the WWTP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.4 Energy consumption in the last six years. . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.1 Point of maximum current. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.1 Solar irradiance values of 2015. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5.2 Temperature values of 2015. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
5.3 Influence of ambient temperature in cell temperature. . . . . . . . . . . . . . . . . . . . . . 41
5.4 Influence of ambient temperature in exergy efficiency. . . . . . . . . . . . . . . . . . . . . 42
5.5 Efficiency values for 2015 for constant radiation. . . . . . . . . . . . . . . . . . . . . . . . 42
5.6 Comparison between monthly read and prediction. . . . . . . . . . . . . . . . . . . . . . . 43
5.7 Payback time for prediction values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.8 Payback time for real values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.9 Difference and accumulated values over the years with scenario 1. . . . . . . . . . . . . . 45
5.10 Difference and accumulated values over the years with scenario 2. . . . . . . . . . . . . . 46
5.11 Energy consumed over the years with and without WWTP. . . . . . . . . . . . . . . . . . . 48
5.12 Costs over the years with and without WWTP. . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.13 Emissions with and without WWTP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.14 Primary energy used over the years. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
5.15 Primary energy consumed over the years. . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
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xiv
Nomenclature
AC Alternate Current.
COP Coefficient of Performance.
EDP Energias de Portugal.
EIA Energy Information Administration.
EMS Energy Management System.
EU European Union.
FF Fill Factor.
IEA International Energy Agency.
ILO Industrial Liquid Oxygen.
IPMA Instituto Portugues do Mar e da Atmosfera.
NOCT Nominal Operating Cell Temperature.
PESN Public Electric Service Network.
PF Power Factor.
PV Photovoltaic.
SCP Self Consumption Production.
SP Self Production.
TOE Tone of Oil Equivalent.
UV Ultra Violet.
UW Useful Work.
VAT Value Added Tax.
WWTP Waste Water Treatment Plant.
Greek symbols
xv
α Current Temperature Coefficient. (mA/◦C)
β Voltage Temperature Coefficient. (V/◦C)
η Solar Panel Energy Efficiency.
ηenergy Energy Efficiency.
ηpce Power Conversion Efficiency.
ηproduction Production Efficiency.
γref Efficiency Correction Coefficient for Temperature. (K-1)
ψ Solar Panel Exergy Efficiency.
τα Effective Product of Transmittance-Absorptance.
ε Semi Conductor Band Gap Energy. (eV)
εg Photovoltaic array Emissivity.
Subscripts
Ex,physical Physical exergy of the PV panel. (W)
Ex,solar Solar exergy input. (W)
Ex Total exergy output of the PV panel. (W)
hconv Convective heat transfer coefficient. (W/m2K)
hconv Radiative heat transfer coefficient. (W/m2K)
PEG Ideal power output of the PV panel. (W)
PL Real power output of the PV panel. (W)
ST,ref Total solar irradiation at reference conditions. (W/m2)
ST Total solar irradiation. (W/m2)
Tamb,NOCT Ambient Temperature at NOCT conditions. (K)
Tamb,ref Ambient Temperature at reference conditions. (K)
Tamb Ambient Temperature. (K)
Tcell,NOCT Cell Temperature at NOCT conditions. (K)
Tcell,ref Cell Temperature at reference conditions. (K)
Tsun Sun Temperature. (K)
UL Overall heat loss coefficient. (W/m2K)
VW Wind Speed. (m/s)
xvi
Chapter 1
Introduction
1.1 Motivation
During the last three decades the energy consumption worldwide has increased significantly, with in-
crease of around 2.3% per year, according to the Energy Information Administration (EIA). To combat
this dramatic increase, governments and associations around the world have made huge investments in
renewable energy, but these sources alone cannot sustain human needs, being necessary to use fossil
fuels. Fossil fuels are a limited resource, they are running out quickly, as its consumption is far superior
to its production, and they raise countless questions in health and environmental terms. The CO2 that is
injected into the atmosphere by fossil fuels produce annually about 21 billion tons. Half of this production
is directly discharged in the atmosphere, since natural resources can only absorb half of the amount.
Due to these problems, the investments policy of the current governments worldwide has changed
substantially, focusing mainly on what is called the energy three-lemma:
• Meeting the requirements for reducing CO2 emissions;
• Competitive energy costs;
• Securing the energy supply.
These aspects combine together expertise on applied economics, innovation theory, energy system
organizations and institutions, and the wider policy and regulatory context for energy.
Therefore it is important to study the use of renewable energies and know how to use them the best
way possible based on studies on the evolution of energy.
There are countless energy transformation processes, sources and three forms of energy most
known as primary energy, final and useful energy. In terms of useful energy, it is necessary to real-
ize how well it is being used. It is possible to approach this issue in two different ways, the energy
and the exergy. In contrast to energy, the exergy is the energy that produce useful work, evaluating
their potential to produce work. Taking as example electricity, the exergy of 1 kWh of electricity is 1
kWh because electricity can be completely converted into work. Another simple example is to consider
the heat, wherein the exergy of 1kWh at 60◦C (the corresponding work done by the ideal Carnot cycle
1
between 60◦C and the environmental temperature) is significantly lower (Palma [1]). Through exergy it
is also possible to know the effectiveness of using this energy, or how far is the ideal process. Thus,
and according to second law of thermodynamics, the efficiency of the process has a maximum of 100%,
which does not happen with energy efficiency, due to the first law of thermodynamics. The exergy ap-
proach allows us to identify, locate and quantify the main causes of the thermodynamic irreversibility of
a process, representing a powerful tool for determining the improvement and optimization of processes
in environmental impacts.
1.2 Aims for the Work
Acting at the level of technological efficiencies, investing in research and development in order to improve
them is important, but not enough. It is crucial to understand and improve the use of renewable energies,
such as solar energy.
The case study used to conduct this project was Vale Manso condominium’s, placed on Aldeia do
Mato, in the municipality of Abrantes, on the banks of bayou of Castelo de Bode dam, occupying an area
around nine hectares consisting of 95 houses/villas.
The main objective of this thesis are related with improvements of useful energy and reduce energy
consumption:
1. Realize if the micro generation efficiency composed by photovoltaic panels is working at the optimal
point;
2. Reduce energy consumption, the respective invoice and environmental impacts of the condo;
The procedure for these studies demanded the gathering of all data for each case over the last five
years. All the monthly electric invoices and energy production data were essential for the study.
To accomplish these objectives an extensive bibliographic review was made in order to obtain all
the information about methods, efficiencies and assumptions made in other exergy studies applied to
photovoltaic panels. The results of this study were divided and organized according to the methodology
that was used.
2
1.3 Thesis Structure
The document structure presented is the following:
1. Introduction and motivation for the work.
2. Basic concepts, in which the general concepts necessary to the understanding of the thesis are
described, such as the concepts of energy, exergy, power factor and contracted power.
3. Methodology for the present work, where the mains steps taken to accomplish the objectives are
presented. All the equations used for the energy and exergy analysis are presented.
4. Case study of the work, where a description of the electric system and the photovoltaic panels is
present.
5. Results and discussion. A comparison between energy and exergy at the level of the photovoltaic
panels is made and reference values are compared with real ones. Improvements at overall level
of energy use and specially the water treatment plant are suggested in order to save energy and
costs. The chapter concludes with the impacts of removing the treatment plant and also with the
impacts of the proposed measures for lighting and irrigation.
3
4
Chapter 2
Basic Concepts
This chapter describes the basic concepts necessary for understanding the work. Initially concepts
as primary, final, useful, equivalent energy and their process of transformation are explained. A brief
explanation of the operation of the photovoltaic (PV) panels and their material is made. Global concepts
for efficiencies classification of energy flows in the economy are presented as well as the associated
laws of thermodynamics with efficiency. The chapter concludes with an explanation and prices for terms
such as Power Factor, Contracted Power and Reactive Energy.
2.1 Energy Analysis
There are important aspects that should be clarified about an energy analysis as well as the various
stages of energy. These various stages are called primary, final and useful energy. These phases of
energy and other concepts related to exergy flow will be explained in this section.
2.1.1 Primary, Final and Useful Energy
Nowadays the energy that is used at home has already suffered several processes of transformation
from its initial form of energy. There are three forms of energy that are going be explained: primary
energy, final and useful energy. All these energy stages have suffered different types of energy conver-
sions.
Primary energy is the true energy source, without any conversion or transformations, provided by
nature in a direct way, such as oil, natural gas, mineral coal and others (Boyle, Everett, and Ramage
[2]). Usually they are classified and measured in terms of calorific value of fuel or combustible renewable
sources. There is also the case where the energy carrier is neither a fossil fuel nor a renewable fuel,
such as a renewable energy. In this type of energy the evaluation and classification as primary energy
depends on the data source. In Equation 2.1 it is shown how primary energy can be calculated from all
stages ahead of it:
Primary Energy = Final Energy + Energy Losses (2.1)
5
Final energy is the second stage of the energy flow. It is the commercial form of energy, the one
that appears in meters, whether in factories or in domestic dwellings. Primary energy transition to final
energy is done through energy transformations, which takes into account all the losses of energy related
to transport, distribution, or even in thermoelectric plants.
The final stage of energy is the useful energy which is provided to the consumer through an end-use
device that consumes final energy. The useful energy is the energy that the consumer actually is using.
It can be used in heat processes, direct heating, and lighting, among others. Again, this final stage of
energy suffered a conversion process from the final energy, which involved energy losses. This transition
depends mostly on the efficiency of the end-use device.
All these energy components and how they are articulated are explained in Sankey’s diagram, which
is shown in Figure 2.1. This diagram basically demonstrates the relationship between the forms of
energy and their transformation stages.
Figure 2.1: Sankey’s diagram for energy. (adapted from Aguas [3])
From Figure 2.1, the production efficiency can be calculated from Equation 2.2 (Aguas [3]):
ηproduction =EfinalEprimary
(2.2)
And energy efficiency is defined in Equation 2.3 (Aguas [3]):
ηenergy =EusefulEfinal
(2.3)
Naturally all these energy conversion processes have wastes and waste production associated. All
energy forms are not only connected to the environment but also to waste produced through energy
transformations or energy use as shown in Figure 2.2:
6
Figure 2.2: Schematic Energy System (Orecchini [4]).
2.2 Exergy Analysis
The exergy term was defined by Zoran Rant in 1956 (from the Greek ex and ergon, meaning ‘’from
work”), having previously been investigated by other thermodynamics researchers, as J. Willard Gibbs
in 1873, however defining this part of the energy by other terms.
Exergy is a characteristic/property of a thermodynamic system that defines the available energy to
produce useful work (Moran, Shapiro, Boettner, and Bailey [5]). Can also be defined as the maximum
working potential of a substance (Wall [6], Cengel and Boles [7]). Exergy is always calculated through a
reference environment.
Contrary to energy, exergy is not conserved because it is destroyed by irreversible processes due
to the increase of entropy. Exergy is always measured against a reference, called dead state. This
dead state is usually characterized by reference values for ambient properties. In order to make this
clearer, take for example a source of heat and the work that can be produced through it. If the heat
source temperature is the same than the environment, then it is not possible to get work from it, and
the exergy of the system is zero. In contrast, if there is temperature difference between the system
and the atmosphere, no matter how small it may be, then there is the possibility of producing work and
consequently the existence of exergy (Wall [8]).
The exergy flow is defined essentially by four terms (Moran and Shapiro [9]):
• Physical;
7
• Kinetic (or mechanical);
• Potential;
• Chemical;
The sum of all these four components defines the specific exergy flow in Equation 2.4, which happens
when there is exergy transfer accompanied by mass flow (when a mass flow crosses the boundary of a
control volume)(Moran and Shapiro [9]).
Θf = (u+ pv) − (u0 + p0v0) − T0(s− s0) +V 2
2+ gz + ech (2.4)
Where u, p, v, h and s represent the specif internal energy, pressure, specific volume, specific enthalpy
and specific entropy, respectively. The u0, p0, v0, h0 and s0 represent the respective values of these
properties at the dead state.
With h = u+ pv and h0 = u0 + p0v0, Equation 2.4 becomes Equation 2.5 (Moran and Shapiro [9]):
Θf = h− h0 − T0(s− s0) +V 2
2+ gz + ech (2.5)
Where V , g, z, ech are velocity, gravitational acceleration, altitude and chemical composition of the
system, respectively. The physical exergy in Equation 2.5 deals with the internal energy, entropy and
pressure of the system (h, s, p), which only happens when there is a gradient of temperature or pressure
between the system and the environment. The kinetic exergy results from the velocity of the system
(V ), which only occurs if there is a velocity difference between the system and the environment. The
potential exergy deals with the altitude difference (z) between the system and the environment. The
chemical exergy results from differences between the chemical composition of the system (ech) and the
environment and the environment that have the potential to interact.
Exergy is then a much more appropriate way to analyze and study energy use processes (Ayres and
Warr [10], Serrenho, Sousa, Warr, Ayres, and Domingos [11], Guevara, Serrenho, Sousa, and Domingos
[12]). This part of energy is a much simpler way to approach different systems and the useful work that
can be taken from each of them if the reference temperature for all systems is the same. It is thus an
important and easy system comparison tool. Energy and exergy are similarly related in terms of energy
stages, as both are characterized by the same terms: primary, final and useful exergy (usually referred
as useful work).
Figure 2.3 represents Grassmann’s diagram applied to exergy of PV panels. The way to calculate
the losses or irreversibility is present in Chapter 4 (from Equation ?? to Equation 4.12), which lists all
necessary calculations to obtain useful exergy.
As mentioned, an exergy analysis has advantages over an energy analysis. Since exergy is the part
of energy that has potential to produce work, it is possible to realize which parts of the primary energy
sources were really productive from an economic standpoint. Furthermore it evaluates the thermody-
namic potential with the same references, regardless of the end-use or the device used, with a limit of
efficiency of 100% (Moran, Shapiro, Boettner, and Bailey [5]) as defined in 4.12.
8
Figure 2.3: Grassmann’s diagram for exergy.
Taking into account all these points presented, an exergy analysis is preferable to analyze an energy
system.
2.3 Efficiencies
The transformations of several energy stages are made through conversion processes. Yet, all these
processes have an efficiency associated, and as is obvious, the higher the efficiency of the process the
lower energy losses from process to process. It is possible to calculate the efficiency of each transfor-
mation from primary to final to useful. Still, for the present study the efficiencies of each stage are not
going to be analyzed.
2.3.1 First Law
In the literal sense of engineering, the efficiency of a solar panel is the relationship between the power
supplied to a system, solar energy, and energy produced by the system, electrical energy (Moran,
Shapiro, Boettner, and Bailey [5]). The energy efficiency of a solar panel is the ratio between the power
output and the energy originally delivered to the solar panel. In this definition only the PV array electricity
produced is considered as it can be seen in Equation 2.6.
η =Energy Output(electrical energy)
Energy Input(solar energy)(2.6)
Energy analysis is only concerned with the quantity of energy use and efficiency of energy processes.
It is not sensitive with the direction of the process, as an example, it does not object if the heat is con-
sidered to be transferred spontaneously in the direction of increasing temperature (Sarhaddi, Farahat,
Ajam, and Behzadmehr [13]). Another issue associated with this type of analysis is that it also ignores
9
reductions of potential energy, which could be used productively in other physical and/or chemical pro-
cess. However, this analysis can provide sound management guidance in those applications in which
usage effectiveness depends solely on energy quantities.
2.3.2 Second Law
Through the second law of thermodynamics, also known as exergy efficiency or rational efficiency, it is
possible to prove that no system can have efficiency higher than 100% (Cullen and Allwood [14]). With
this law it is possible not only to compare different devices with each other, but also to know the quality
of the energy that is being used and how close it is to the ideal state. The exergy balance of a certain
system can be calculated through Equation 2.7 (Sarhaddi, Farahat, Ajam, and Behzadmehr [15]).
Ein = Euseful + Elost + Edestroyed (2.7)
Also this Equation 2.7 is illustrated in the previous Figure 2.3 where it is possible to see all four
stages that exergy suffers, from its primary stage until useful exergy. The exergy loss, or availability loss,
is the degradation in the quality of energy. One part of the exergy loss is called irreversibility (Larson
and Cortez [16]).
One way to calculate the exergy efficiency can be through Equation 2.8 (Cullen and Allwood [14]).
ψ =Work Output
Maximum Possible Work Output(2.8)
Exergy analysis is, thus, the best way to understand and get a realistic view of the process. Exergy is
the maximum work that can be obtained from energy, and it is considered by many engineers a powerful
tool for the evaluation of the thermodynamic and economic performance of thermodynamic systems
in general (Sudhakar and Srivastava [17]). The energy utilization efficiency of an energy conversion
system can be calculated through this type of analysis. It deals with maximum exergy delivery or with
the minimization of irreversibility associated with the process. Unlike the energy analysis, as it was
referred before, exergy takes into account the climatic, geometric, and operating parameters of a PV
array and involves the thermal properties and chemical potential components of it directly. To perform
both analysis of the solar PV system, the quantities of input and output of energy and exergy must be
evaluated.
2.4 Photovoltaic Panels
The equations that govern the electrical system of the PV panel are quite complex so only a brief
summary about it is presented to get a general idea.
There are several mathematical models that describe the current-voltage of the PV nonlinear device.
10
One model that describes it can be Equation 2.9 (Soto [18]).
I = I1 − I0 ∗ [exp
(V + IRs
a
)− 1] − V + IRs
Rsh(2.9)
Where I, V , a, I1, I0, Rs and Rsh represents the current, voltage, ideal factor, light current, diode reverse
saturation current, series resistance, and shunt resistance, respectively. In order to be able to calculate
it, and especially to understand the characteristics associated to each phase of the PV panel (short
circuit, open circuit and maximum power point), five parameters are needed at reference conditions.
These are defined in Equations 2.10, 2.11, 2.12, 2.13, and 2.14 (Soto [18]).
At short circuit current through Equation 2.10.
I = Isc,ref , V = 0 (2.10)
At open circuit voltage through Equation 2.11.
I = 0, V = Voc,ref (2.11)
At the maximum power point through Equation 2.12.
I = Imp,ref , V = Vmp,ref (2.12)
At the maximum power point through Equation 2.13.
[d(IV )
dV
]mp
= 0 (2.13)
At short circuit through Equation 2.14.
[dI
dV
]sc
= − 1
Rsh,ref(2.14)
Where Isc, Voc, Imp and Vmp are short circuit current, open circuit voltage, maximum power point current
and maximum power point voltage, respectively. The subscript ”ref” indicates the value of parameters at
the reference conditions. A typical PV system is schematically represented in Figure 2.4 (Soto [18]).
Figure 2.4: Schematic PV System.
11
2.4.1 Photovoltaic Cells Material
There are several materials for photovoltaic cells and their efficiency will depend on the type of ma-
terial used. With the evolution over the years with the same material it is possible to obtain better
efficiency of the photovoltaic cell. The photovoltaic cells are divided into five groups: multijunction cells,
single-junction gaAs, crystalline silicon cells, thin-film technologies and emerging PV. All these types of
photovoltaic cells have been improving their efficiency over the years. For the year of installation of the
panels (2010), the use of polycrystalline cells had an efficiency approximately 20%, as can be seen in
Figure 2.5. The evolution of efficiency for each photovoltaic cell material can be seen also in Figure 2.5.
Figure 2.5: Evolution of PV cell materials over the years. (source: NREL)
2.5 Portuguese Legislation for Energy Producers
This section explains the differences between the laws applied at the time when the photovoltaic panels
were installed in the condominium and the current legislation.
2.5.1 In 2010
• Decree - Law No. 363/2007, November 2 (Ministry of Economy and Innovation)
Simplified the arrangements for electricity producers of renewable energies for micro genera-
tion through small power plants provided in the Administrative and Legislative Simplification Pro-
gramme SIMPLEX 2007. This decree law simplified significantly the licensing regime established
by Decree-Law No. 68/2002. It was created the Micro Production Registration System which in-
tegrates an electronic platform for interaction between producers and two compensation schemes
12
(general or subsidized).
• Decree - Law No. 118-A / 2010, 25 October (Ministry of Economy, Innovation and Development)
Simplifies the legal regime for the production of electricity through small power plants, called micro
production, by having new goals for encouragement of decentralized generation in low voltage
individuals. Proceeds to the second amendment to Decree-Law No. 363/2007, of 2 November,
and the second amendment to Decree-Law No. 312/2001, of 10 December.
The price agreed for the condominium was 586e/MWh (0.587e/kWh) for the first subsidized period
of six years, where the first one is the year of installation. The second period of the subsidized regime
(with no end predicted) set the price of electricity sold for 286e/MWh (0.287e/kWh).
2.5.2 Actual
• Decree - Law No. 153/2014, 20 October
This decree creates the legal regimes applicable to the production of electricity destined to self-
consumption and for sale to the public service, from renewable resources, through small produc-
tion. The Resolution of Council Ministers No. 20/2013 in 10 of April reformulated the present law
for current mini production and micro production schemes, revoking the Decree law No. 34/2011.
Thus, the new distributed generation system is set into two strands, the Self-Consumption Produc-
tion (SCP) and Small Production (SP).
The major differences between SCP and SP are: in small production all the energy produced is
injected into the Public Electric Service Network (PESN) while in self-consumption the energy produced
is delivered, preferably on the consumption location. The surplus of this production can be injected into
the network. Relatively to remuneration, the small production rate are maintained via auction, while the
energy injected into the network due to production surplus in self-consumption is paid based on Equation
2.15.
R = Eprovided ∗ IEMO ∗ 0.9 (2.15)
Where R, Eprovided, IEMO are electricity compensation provided to PESN per month (e), the electricity
provided (kWh) and value resulting from the simple arithmetic average of the closing prices for the
Iberian Energy Market Operator (IEMO) to Portugal.
The licensing process, either in SCP or SP, is a process managed by Electronic System for Pro-
duction Registration (ESPR). In the case of SP it is always necessary registration and certificate of
operation. For the SCP, these are divided into different levels and different licensing process for each of
these levels:
• Pinstalled <200 W - free of prior control.
• 200 W < Pinstalled <1.5 kW - prior notification of exploitation.
• 1.5 kW < Pinstalled < 1 MW - registration and certificate of operation.
13
• Pinstalled > 1 MW - production and exploration license.
Regardless the year and the legislation involved there are requirements needed for the condominium
to be an energy producer:
• An energy audit of the common parts must be done, with implementation of all the measures
identified that have a return smaller than two years;
• The installation requires authorization by the condominium assembly, which needs to have repre-
sentative majority of the votes corresponding to at least two thirds of the total joint owners. In the
meeting the description of the installation and place of implementation must be established;
2.6 Electricity Costs in Portugal
This section describes all the concepts present on the energy bill for Portugal, since the condominium
is located in Portugal. Each of the concepts explained have a different way of influencing the electricity
that will be invoiced monthly. The terms explained that can influence the energy consumed are:
• Active Energy;
• Power in Peak hours;
• Contracted Power;
• Reactive Energy;
• Power Factor.
2.6.1 Active Energy Costs
In order to have electricity consumption in a residence, it is needed to install an hourly rate for regulating
the energy prices to be charged depending on the time that it is being used. For such Energias de
Portugal (EDP) affords three different types of rates: simple, bi-hourly and three-hourly. The customer
can choose whichever best suits their use of electricity and, obviously, the most economical. The three-
hourly rate sets the price of electricity per kWh according to three time periods: void hours, full hours
and peak hours. The void hours can be divided into normal void and super void hours for some voltage
levels and they are, fundamentally, night period hours and weekends. The out of the void hours are
divided into full and peak. The price per kWh in full hours is slightly reduced compared to the simple and
bi-hourly fare. On the other hand, the price per kWh at peak hours is higher, so the three-hourly rate is
advantageous for very low consumption at this time.
The times for the three-hourly rate can be seen in Figures 2.6 and 2.7, which represent the winter
and summer schedule for special low voltage for the weekly cycle.
The energy prices over the last six years are presented in Table 2.1.
The electricity supply can be made under four voltage levels:
14
(a) Week days (b) Saturday (c) Sunday
Figure 2.6: Timetable for three-hourly energy consumption over the winter.
(a) Week days (b) Saturday (c) Sunday
Figure 2.7: Timetable for three-hourly energy consumption over the summer.
Table 2.1: Energy prices over the last 6 years.
YearThree-Hourly Fare
Void Hours (e/kWh) Super Void Hours(e/kWh) Peak Hours (e/kWh) Full Hours (e/kWh)
2010 0.0565 0.0527 0.1238 0.0902
2011 0.0588 0.0548 0.1287 0.0938
2012 0.0616 0.0570 0.1392 0.1015
2013 0.0832 0.0801 0.1170 0.1094
2014 0.0858 0.0823 0.1357 0.1245
2015 0.0916 0.0878 0.1483 0.1355
• Super high voltage: the tension between phases has an effective value higher than 110kV;
• High voltage: the tension between phases has an effective value between 45 kV and 110 kV;
• Normal voltage: the tension between phases has an effective value between 1 kV and 45 kV;
• Low voltage: the tension between phases has an effective value lower than 1kV:
– Special low voltage: contracted power higher than 41.4 kVA;
– Normal low voltage: contracted power lower or equal than 41.4 kVA.
The voltage drop is made through transformers, which causes losses in the order of 1% to 2%.
These losses, added to transmission losses (caused by transformation of energy and transportation)
15
make electricity prices increase with the decrease of the supply voltage.
2.6.2 Power in Peak Hours
The power in peak hours is the average active power in peak hours during the respective interval of time
of the invoice. This power aims to achieve customer to change energy consumption to more favourable
hours.
During the day are considered, on average, 4 peak hours, in periods where the energy consumption
is higher. For a daily cycle, the time table is:
• Winter period (October to March): from 9h30 to 10h30 and 18h00 to 20h30;
• Summer period (April to September): from 10h30 to 13h00 and 19h30 to 21h00.
The determination of the average power of peak hours is calculated using Equation 2.16.
Power =Energy in Peak Hours
Number of Days ∗ 4 Hours(2.16)
2.6.3 Contracted Power
Contracted power establishes the maximum power demand that can occur in a house, which limits the
instantaneous power consumption by cutting off the energy supply when the power being used by the
electrical equipment exceeds the contracted power. If there is a power cut it means that the contracted
power is not sufficient for energy needs and therefore it should be increased. The quality of the energy
supplied is limited by the power distribution in the country, which is controlled by EDP Distribution. The
contracted power can be checked in the electricity bill, which is expressed in kVA. The contracted power
can be increased at any time.
In Table 2.2 are presented the prices of some characteristics explained.
Table 2.2: Other electrical characteristics and their price.Year Power in Peak Hours (e/kW*day) Power in Peak Hours (e/kW*month) Contracted Power (e/kW*day) Contracted Power (e/kW*month)2010 0.545 - 0.0394 -2011 0.567 - 0.041 -2012 0.6115 - 0.0442 -2013 - 19.789 - 1.4972014 - 19.874 - 1.1182015 - 17.289 - 1.088
Between 2010 and 2012 the power in peak hours and the contracted power were calculated multi-
plying the respective contracted power with the days that it was used times the price. From 2013 the
calculation for these powers changed and it started to be multiplied by a factor. This factor divides the
total number of days of the month by the number of days of the invoice. The multiplicative factor for the
contracted power is always the same as the one applied for the power in peak hours.
16
2.6.4 Reactive Energy Costs
As the active energy is required to produce work, for example, rotation of the motor shaft, the reactive
energy is required to produce the necessary magnetic flux to operate motors, as transformers, etc.
However, the reactive energy ”takes up space” in the electric system that could be used for more active
energy, and increases the losses in distribution networks and the use in facilities, so their consumption
should be controlled.
For customers that use special low voltage level (with a contracted power greater than 41.4 kVA),
the reactive energy needs to be measured and has a cost value that increases with the consumption of
the client. In these situations the customer can only consume a volume of reactive energy (inductive),
without costs, during the period from 8h00 to 22h00, which cannot exceed 30% of the active energy that
is consumed in the same period. In order to have no penalization, no reactive energy can be injected
into the network (capacitive) in the period from 22h00 to 8h00.
The power factor reflects the degree of efficiency of electrical systems. High power factor values
(near 1.0) indicate efficient use of electricity, while low values indicate not only poor performance but
also represent an overload for the entire electrical system.
The reactive energy charged is estimated using tg ϕ factor, which is defined as the coefficient of the
reactive energy and active energy measured in the same period. A higher value of tg ϕ means a lower
power factor and a greater reactive energy being carried over the network.
The multiplicative factors to be applied to reference price of reactive energy, published by the Regu-
latory Authority for Energy Services, by level of inductive reactive energy billing are presented in Table
2.3.
Table 2.3: Multiplicative factors.
Description Multiplicative factorEchelon 1 For 0.3≤ tg θ <0.4 0.33Echelon 2 For 0.4≤ tg θ <0.5 1.00Echelon 3 For tg θ ≥ 0.5 3.00
Currently the inductive reactive energy consumed outside the void hours is charged to the customer
only if the tg ϕ factor is greater than 0.4. Reactive capacitive energy is the part of reactive energy that is
injected into the network in void hours, which is also charged to customers. The reactive energy prices
over the years, for special low voltage level, can be checked in Table 2.4.
Table 2.4: Reactive energy prices.
Year Reactive Energy (e/kWh)2010 0.02122011 0.22002012 0.23002013 0.00882014 0.02232015 0.0239
17
2.6.5 Power Factor
The power factor (PF) of any electrical system is defined as the ratio of real/active power, P, to the
total/apparent power, S, in the circuit. The power factor occurs only in AC electrical systems and is a
dimensionless number between -1 and 1. The real power is the capacity of the circuit to perform work
per unit of time while the apparent power is the product of the current and voltage of the circuit, which
due to the reactive elements in the load is always equal or bigger than the real power.
Most loads on the current power distribution system nowadays are inductive. In order to work, the
distribution system requires an electromagnetic field and a receiver from the network which are made
through real and reactive power. The reactive power, Q, is a measure of the stored energy that is
returned to the source during each cycle of alternating current. This power is also used to produce
the electromagnetic field necessary for the machine operation. The real power vector and the reactive
power vector added make the apparent power vector. This power triangle is shown in Figure 2.8.
Figure 2.8: Power triangle diagram.
So the AC power flow is composed by three components:
• Real power or active power, P, expressed in watts (W);
• Apparent power, S, expressed in volt-amperes (VA);
• Reactive power, Q, expressed in reactive volt-amperes (var).
A circuit with a low power factor needs to have higher electrical currents to perform the same work
than a circuit with a higher power factor.
In a case of an electrical installation, a low power factor considerably penalizes the energy con-
sumption and consequently the electric energy cost. To avoid a bigger energy consumption the cos θ
of the installation must be corrected. This correction allows a more rational use of energy, making sig-
nificant economic savings and important technical improvements. The economic advantages are more
important the higher the electricity energy consumption is.
For all these reasons it is important to be able to have the maximum power factor possible in an
electrical installation, which can be done through the help of capacitors that can be installed on an ap-
propriately weighted point of the electric network. The capacitors may be connected to the network in the
presence of inductive loads, which should not be adjusted beyond cos θ = 1 to avoid over-compensation,
which can lead to serious imbalances in the network, such as hazardous surges, overloads intensity on
18
the line and distribution devices. There are tables available that can calculate the power needed for the
capacitor to correct, depending on the installation power. Since this tables give no added value to the
perception and definition of the necessary terms they will not be shown.
The power factor of an installation, which is defined in Equation 2.17, is an important parameter for
calculating the power correction equipment that must be installed.
PF =Real Energy√
(Real Energy)2 + (Reactive Energy)2(2.17)
The active energy is defined as the sum of the energy used in full hours and in peak hours, which
are defined in kWh. The reactive energy consumption is defined in Kvarh. These values are always
available in the monthly bill of the electricity distributor but it is also possible to calculate them through
the electricity meters, although it is necessary to know the multiplication factors of the readings.
19
20
Chapter 3
Case Study
The condominium is placed on Aldeia do Mato in the municipality of Abrantes on the banks of Castelo
de Bode dam (see Figure 3.1). It occupies an area around nine hectares with 95 houses and it was built
in 1995. Since its construction there is a WWTP operating which is a fundamental facility for this study.
Halfway through 2010, 18 photovoltaic panels were installed in order to sell the electricity produced and
subsequently slaughtered on the electric invoice of the condominium.
Figure 3.1: Condominium location in Portugal. (source: Google Maps)
3.1 PV Description
The energy produced is sold to EDP with a previously established amount, providing an excellent re-
turn to the micro-generation installation owner. For this purpose, the micro-producer establishes a sale
contract of that energy with the public energy distribution network, ensuring the return on their invest-
ment. The energy produced by the PV panels is transformed into compatible public energy through an
21
inverter, which is explained next as well as other important devices in its construction. This energy is
then accounted through a meter that measures all energy produced injected into the network. This me-
ter transmits the produced energy, in kWh, that is going to be credited into the condominium’s account.
This way the energy produced can be sold to the electricity distributor, in this case EDP.
In order to further encourage the production of energy, EDP was committed to evaluate the sold
energy for a higher price in the year zero (the year in which construction is made) and the next five
years. After all bureaucracies have been made, the PV panels chosen for installation were provided by
Conergy, a company based in Frankfurt, in Germany.
As characteristics the panels have 230 Wp (230 W at the maximum power), and are composed of
polycrystalline modules, which is the most prevalent bulk material for solar cells. The micro generation
consists of 18 panels of these.
To the construction of the PV panels four essential devices are needed:
1. Cell - composed by 3 busbar cells, which helps getting the best out of the silicon material;
2. Frame and glass - composed by 4 mm thick solar glass and warp resistant frame can withstand
the most extreme of conditions;
3. Connection sockect - composed by 3 passively cooled bypass diodes guarantees maximum yields
even in unfavourable environmental;
4. Inverter - converts the electricity produced into accountable electricity into public network;
Figure 3.2: Characteristics of PV panels. (source: Conergy)
The characteristics of the panels are presented in the Table 3.1.
The PV panels had an initial investment of 19500e(counting with all costs, from the panels them-
selves to converters and with all necessary electrical cables and electrical installation), which according
to forecasts of Conergy would be returned in about six years, i.e. in 2016 the condominium would have
paid all of the initial investment and would already be in a position to start take advantage of energy
production.
However, all these calculations were based on predictions and all predictions have errors associated.
The expected data were provided by Conergy based on the energy that would be produced monthly. The
22
Table 3.1: Solar PV module parameters.
Solar PV module parameters Value for calculationPV module type Conergy 230
polycristaline siliconNumber of cells in series per string, Nm 6Number of strings, Ns 10Cell dimensions, Amod 0.024 m2
The short-circuit current at the reference conditions, Isc,ref Ns*8.34 A(for total array)
The open-circuit voltage at the reference conditions, Voc,ref Nm*36.66 V(for total array)
Maximum power point current at the reference conditions, Imp,ref Ns*7.82 A(for total array)
Maximum power point voltage at the reference conditions, Vmp,ref Nm*29.54 V(for total array)
The current temperature coefficient, α 4 mA/◦CThe voltage temperature coefficient, β -0.123 V/◦CThe efficiency correction coefficient for temperature, γref 0.004◦C-1
The semiconductor band gap energy, ε 1.12 eVThe effective product of transmittance–absorptance, (τα) 0.9The PV array emissivity, εg 0.88The specific heat capacity of silicon solar cell, Cp 0.721 J/(kg*K)The PV total array mass, m 22 kgThe length of solar module, L1 1.651 mThe width of solar module, L2 0.986 mThe depth of the solar module, L3 0.046 m
expected values are presented in Table 3.2. The values of energy production forecast were calculated
based on other energy production of solar panels with a similar location in Portugal.
Table 3.2: Expected energy production.(Information provided by Conergy)
Month Energy (kWh)
January 342February 338 Autumn/WinterMarch 535
April 490May 564June 573 Spring/SummerJuly 610August 619September 545
October 467November 328 Autumn/WinterDecember 314
Year 5725
23
3.2 WWTP Operation Characteristics
When the set of houses and the hotel were built the parish where the tourist complex is set had no
station for the treatment of waste water so the only two solutions available at the time were to connect
the pipes to the nearest station in Abrantes or to build their own WWTP. The responsible engineers for
building decided to create their own WWTP, so that the dwellings would become self-sustainable in this
aspect.
The type of WWTP chose was selected mainly for the following reasons:
• The occupation of the hotel and dwellings varies widely due to it being mainly used for holidays
and weekends. This variation originates waste water volumes for WWTP quite variable throughout
the year, in addition to significant variations throughout the day;
• The treated effluent cannot be discharged on the surface of Castelo de Bode dam requiring the
design of a zero discharge system;
• The permeability tests carried out have revealed very modest infiltration rates. The treated effluent
is applied over the soil and vegetation - a small fraction infiltrates and the rest changes phase to
vapour through the processes of evapo-transpiration;
• The need to apply superficially the treated effluent over the soil and vegetation, forces the produc-
tion of a final effluent with high quality;
• Limited land surface with good topographic conditions;
• The need to operate with a low noise level and no smell due to the proximity of habitations;
• The need to have a reliably WWTP, with the greatest possible degree of automation.
Based on the above circumstances and the announced restrictions, the selected WWTP has the
following treatment characteristics:
• Pumping stations at the bottom of the condominium;
• Organic matter stabilization, nitrification, denitrification and phosphorus removal sludge reactor
activated with discontinuous type;
• Chemical coagulation of biological treatment of waste water;
• Filtration system, consisting of two stages of operation and fully automatic cleaning;
• Disinfection by ultra violet (UV);
• Aeration system;
• Application system of treated effluent with sprinklers to the overgrown patch of land in the sur-
roundings of the WWTP;
• Collection of occasionally existing runoff;
24
• Pumping station of the previous drained of the treatment plant.
The plant in question serves the private apartments, which consists in a group of houses, and the
hotel. For such it was considered for the project a population of 441 people as it can be seen in Table
3.3. In Figure 3.3 it is possible to see the location of the referred WWTP.
Table 3.3: Population that use the WWTP.
Type PopulationHotel 425 Houses w/ 5 rooms 3011 Houses w/ 4 rooms 5510 Houses w/ 3 rooms 6015 Houses w/ 2 rooms 6042 Houses w/ 1 rooms 16812 Studios 24Gatehouse 2Total 441
Figure 3.3: Location of the WWTP.
The aeration system mentioned above in the characteristics of the treatment plant deserves special
attention since it will be one of the processes that will be addressed in order to assess energy and
money savings. The chosen system to aerate the WWTP was conditioned by its location as it is close to
houses and therefore should have a ventilation system that produces the least noise possible. Since the
treatment plant has been built almost 20 years ago, this aeration system was the most suitable process
for that time so it can be out of date nowadays. The aeration process is done through hydro-ejectors with
oxygen, or through an oxygenator, where it performs a biphasic mixture of liquid and gaseous oxygen.
25
The oxygen consumed by the WWTP is stored in its own reservoir that will be provided by a specialized
firm. The prices related to industrial liquid oxygen are shown in Table 3.4.
Table 3.4: Total costs related to industrial liquid oxygen.Month Rental Reservoir (e) ILO (e) Quantity (x103m3) H.H.M *(e) Liquid Value (e) Total** (e)January 343.13 674.46 2.10 32.47 1050.06 1291.57February 343.13 347.82 2.05 32.92 723.87 890.36March 343.13 649.74 2.02 32.47 1025.34 1261.17April 343.13 559.22 1.74 32.47 934.82 1149.83May 343.13 674.46 2.10 32.47 1050.06 1291.57June 343.13 600.31 1.87 32.47 975.91 1200.37July 343.13 644.37 1.88 32.92 1020.42 1255.12August 343.13 575.59 1.79 32.47 951.190 1169.96September 343.13 756.64 2.36 32.47 1132.24 1392.66October 343.13 347.82 1.98 32.92 728.56 896.13November 343.13 642.03 1.97 32.92 1022.77 1258.01December 343.13 608.52 1.87 32.92 989.26 1216.79Total (per year) 4131.63 7080.98 23.74 391.89 11604.50 14273.54
*H.H.M - Handling Hazardous Material. **The value presented in Total already takes into account
VAT (23%).
3.3 Electrical Characteristics
The electrical circuit of the condo was composed by three electricity meters, two associated with the
pumping stations located on the lower points of river bank, one on each side, and a main meter. The two
meters responsible for the pumping stations represented an electric power consumption of about 5%
of total consumption, which are not significant. Nowadays these two points are no longer in operation
in order to reduce the costs associated with each meter. The pumping stations consumed on average
3kWh while the fixed monthly costs related with contracted power and other charges were quite signifi-
cant. The elimination of these two delivery points meant that the power supply had to be delivered from
the main one. This elimination has saved about 400e/year, but led to a cost around 3000e, which has
a payback period of 8 years. The integration of these points into the main meter kept the consumption
virtually unchanged.
The main meter is now responsible for all electricity consumption, since it is responsible for all elec-
tricity of the condominium, the WWTP, the water reservoir and the gatehouse. In a global view the
consumption is distributed as follows: 29% for outdoor lighting, irrigation, pool pumps etc; 43% for the
WWTP; 22% for water reservoir; 6% for pump stations and the gatehouse. The water reservoir is a
reservoir for water that is extracted from the river and is stored for irrigation and pools when needed.
The electricity consumption over the past six years can be seen in Figure 3.4.
It should also be noted that the percentages reported for each type of installation were defined
through energy audits previously performed, so the author had no way to confirm these values.
The WWTP is the facility that requires more attention regarding energy and cost saving measures
because almost half of the electric consumption goes directly to it.
26
Figure 3.4: Energy consumption in the last six years.
The power factor has an important role in the electrical system of the condominium because it in-
fluences the energy consumption and consequently in the electric energy cost. A higher power factor
means that the electricity consumed is almost the same that is being charged. Table 3.5 shows the
average power factor for each year, in all six years.
Table 3.5: Power factor average over the years.
Year Power Factor (%)2010 90.332011 87.922012 94.252013 92.252014 94.822015 93.38
The price of energy consumed over the last years is presented in Table 3.6. The values in Table 3.6
represent the monthly sum of the referred energy over a year.
Table 3.6: Energy costs breakdown.Year Power in Peak Hours (e) Active Energy (e) Reactive Energy (e) Contracted Power (e) Total (e)2010 1806.88 5807.83 150.77 554.73 10233.862011 2363.59 6934.54 87.47 607.82 12291.912012 2655.39 8517.31 139.27 668.07 14735.272013 2357.21 7402.69 23.26 881.25 13117.372014 1040.60 5095.99 62.70 807.24 8618.122015 975.16 5409.57 11.85 495.65 8477.45
The value presented in Total already takes into account the VAT (1.23%).
Initially the contracted power of the condominium was 41.41 kVA but when the houses began to
be inhabited the contracted power was increased to 63 kVA since the previous power could not be
sufficient. Afterwards the condominium understood that 63 kVA was excessive and the contracted power
was reduced to 41.41 kVA, which is in operation for over 15 years. Since the data used for the analysis
were the last 6 years, this temporary change in the contracted power had no influence on the results.
27
Chapter 4
Methodology
This chapter describes the two different methodologies applied in the study. First, the methodology
used for the PV panels analyses are explained, as well as all equations used in this case. Next the
methodology used for the WWTP (and all its electrical components), outdoor lightning and irrigation is
explained.
4.1 Analysis of PV Panels
4.1.1 Energy Analysis
The amount of solar energy that reaches the earth’s surface depends on the season, local weather
conditions, location and orientation of the surface, but normally the standard test conditions is for 1000
W/m2. This value is based on the conditions that the absorbing surface is perpendicular to the sun’s
rays and with clear sky. Fortunately, Portugal is in a perfect position with abundant solar radiation. In
most parts of Portugal, clear sunny weather is experienced, on average, for 240-280 days per year. The
solar radiation, which comes from all these sunny days, is then perfect to provide adequate energy solar
for electricity and thermal applications. Despite this high potential, solar energy technologies are now
starting to be used, but not as widely as they should. Renewable energies are known for their clean
and renewable nature, and they are the main substitutes for fossil fuels in the incoming years. There
are perfect climatic conditions in Portugal to harness enormous energy for solar applications. Solar cell
or PV cells are one of the most significant and rapidly developing renewable-energy technologies, and
their potential future uses are notable.
PV cells convert light, i.e. both direct and indirect sunlight, into direct current electricity in a solid-state
semiconductor device. Their performance depends, not only on the PV system characteristics (overall
heat loss coefficient, open circuit voltage, short-circuit current, maximum power point voltage, maximum
power point current and PV array area), but also on climacteric conditions (ambient temperature, solar
radiation intensity, clouds). Solar irradiance is made of diffuse irradiance and direct beam irradiance.
Diffuse irradiance is caused by scattering processes in the atmosphere. The beam radiation is contained
within the solar angle subtended by the solar disk. PV systems use both beam irradiance and few diffuse
28
component (Sudhakar and Srivastava [17]). The problem associated with this type of radiance is that,
even on a very clear day, the diffuse irradiance represents at least 20% of the total irradiance (Wyman,
Castle, and Kreith [19]).
The maximum amount of irradiance that is received by a surface is always normal to its direction.
Therefore, the design and position of a solar PV system are important and need information before its
construction.
Solar PV system can be evaluated in terms of energy efficiency and exergy efficiency, also known
as the first and second law of thermodynamics. Energy efficiency, for PV systems, measures the ratio
between the input solar energy and the output electrical energy. The electrical output power is the
product of voltage and current of the PV device. The main problem of the electrical output is that it is
not constant, even under constant solar irradiation. However, there is a point of maximum power (see
Figure 4.1) which is achieved when the voltage is Vmp (< Voc) and current is Imp (< Isc) (Joshi, Dincer,
and Reddy [20]).
Figure 4.1: Point of maximum current . (Adapted from Cengel and Boles [7])
In Figure 4.1, EGH (W) represents the highest energy level of electron at maximum solar irradiation
conditions, which is equivalent to the area under the I − V characteristic curve (∫ Voc
V=0I(V )dV ), which is
called PGH . In addition, EL (W) is the low-energy content of electron, which is the pratical case, called
PL. PL is thus equivalent to PL = Imp ∗ Vmp. The maximum power point for the PV system is restrained
by a term called ‘’Fill Factor” (FF ) which is defined as shown in Equation 4.1 (Joshi, Dincer, and Reddy
[21]).
FF =VmpImpVocIsc
(4.1)
The power conversion efficiency of a PV panel, ηpce, can be defined as a function of PL and ST in
Equation 4.2 (Dincer and Rosen [22]).
ηpce =VmpImpSTAarr
(4.2)
29
Where ST and Aarr represents hourly measured total solar radiance and PV array area, respectively.
The solar power conversion efficiency can also be defined in terms of the Fill Factor, FF . Based on
Equation 4.2 and Equation 4.1 it can be calculated through Equation 4.3 (Dincer and Rosen [22]).
ηpce =FFVocIscSTAarr
(4.3)
The input energy of the energy efficiency of the PV system has an important role for its efficiency
calculation, as it depends on the total solar irradiation, ST . However, the output power depends the
generated electricity of the PV cell, PL. Therefore, the energy efficiency is defined in Equation 4.4
(Dincer and Rosen [22]).
η =PGHSTAarr
(4.4)
4.1.2 Exergy Analysis
Cell Temperature
An exergy analysis takes into account the quality of the energy that is being used, which allows a better
use of the potential energy. This type of analysis combines the conservation of mass and conservation
of energy principles with the second law of thermodynamics.
Solar cells have losses both in convective and radiative losses. The electrical energy comes from the
electrical part of the solar radiation. The thermal part is considered as heat loss, once it is dissipated
to the ambient. Therefore, the temperature of the PV cell has an important role on the heat loss, and
consequently calculating the exergy efficiency of the panel. This temperature can be calculated by
Equation 4.5 (Skoplaki, Boudouvis, and Palyvos [23]):
Tcell =Tamb +
(ST
ST,ref
)(UL,NOCT
UL
)(Tcell,NOCT − Tamb,NOCT ) ∗ [1 − ηel,ref
τα (1 + γrefTcell,ref )]
1 − γrefηel,ref(τα)
(St
ST,ref
)(UL,NOCT
UL
)(Tcell,NOCT − Tamb,NOCT )
(4.5)
Where Tcell, Tcell,ref , Tcell,NOCT , Tamb, Tamb,NOCT and ST,ref are solar cell temperature, solar cell
temperature at reference conditions, nominal operating cell temperature (NOCT), ambient temperature,
ambient temperature at NOCT conditions and total solar radiance at the reference conditions, respec-
tively. Further, parameters UL, UL,NOCT , ηel,ref , (τα) and γref are overall heat loss coefficient, overall
heat loss coefficient at NOCT conditions, electrical efficiency at reference conditions, the effective prod-
uct of transmittance-absorptance and efficiency correction coefficient for temperature (0.004 ◦C-1 for
silicon solar cell), respectively.
A PV module is typically rated at 25oC under a radiation of 1 kW/m2. However, they usually work at
higher temperatures and different insolation conditions. In order to determine the power output of the
solar cell, it is important to determine the expected operating temperature of the PV module. The NOCT
is then defined as the temperature reached by the open circuit cells under the conditions listed (values
defined by the PV module manufacturer, Conergy):
• Solar radiation: 800 W/m2;
30
• Ambient temperature: 20◦C;
• Wind Speed: 1 m/s.
The PV array overall heat loss coefficient, UL is usually assumed as a fixed value or variable with little
effect in this type of analysis to simplify calculations. In order to make calculations as real as possible
it was not assumed constant in Equation 4.5, so the convection and radiative losses were included in
calculations by Equation 4.6 (Sarhaddi, Farahat, Ajam, and Behzadmehr [13]).
UL = hconv + hrad (4.6)
In which the convective heat transfer coefficient is calculated through Equation 4.7 (Watmuff, Char-
ters, and Proctor [24]).
hconv = 2.8 + 3VW (4.7)
Where VW is the wind speed. The losses between the PV array and the surroundings are included in
the radiative heat transfer coefficient, which is given by Equation 4.8 (Sukhatme [25]).
hrad = εgσ(Tsky + Tcell)(T2sky + T 2
cell) (4.8)
Where εg and σ are PV array emissivity and Stefan-Boltzmann’s constant, respectively. The effective
sky temperature, Tsky is equal to the Tamb.
Physical Exergy
The physical exergy depends only on the real electricity produced by the PV panel, PL. As such, it is
defined in Equation 4.9.
Ex,physical = PL (4.9)
Solar Exergy
In order to evaluate the exergy efficiency of the PV cell it is necessary to know the total exergy that can
be converted into electricity and the exergy from the total incident irradiation. As referred before, the PV
cells convert direct and indirect sunlight, which depend on atmospheric effects. The exergy provided by
solar irradiation can be calculated through Equation 4.10 (Dincer and Rosen [22]).
Ex,solar = ST
(1 − Tamb
Tsun
)Aarr (4.10)
31
Exergy Efficiency
The ratio of total output exergy and the total input exergy define the exergy efficiency. As a result the
exergy efficiency is expressed in Equation 4.11.
ψ =Ex
Ex,solar(4.11)
After substituting Equation 4.10 into Equation 4.11 the exergy efficiency is defined in Equation 4.12.
ψ =Ex,physical
ST
(1 − Tamb
Tsun
)Aarr
(4.12)
To perform all analyses previously referred there are a set of values needed to be defined. As such,
Table 4.1 was created, which shows all values assumed for calculations.
Table 4.1: Parameters for calculation.Parameters Value for calculationThe total solar irradiation at the reference conditions, ST,ref 1000 W/m2
The total solar irradiation, ST 520.833 W/m2
The ambient temperature, Tamb 290.92 KThe ambient temperature at the reference conditions, Tamb,ref 298.15 KThe ambient temperature at NOCT conditions, Tamb,NOCT 293.15 KThe cell temperature at the reference conditions, Tcell,ref 298.15 KThe nominal operating cell temperature, Tcell,NOCT 310.55 KThe PV array temperature, Tcell From iterationThe sun temperature, Tsun 5760 KWind speed, Vw 1 m/s
4.1.3 Associated Costs
For the installation of the micro-generation energy through solar panels it was necessary to collect sev-
eral proposals, evaluate them and choose the one that best suited to the case. After choosing which
ones to buy it was then necessary to make an investment to purchase them, a return of perspective
based on the expectations of the brand, and the costs associated with maintenance or any other un-
foreseen costs. In this chapter the costs involved in the process will be shown, from investment to
simple payback method and/or payback method taking into account inflation. All calculations were made
through the data provided by the condominium since the installation in mid-year of 2010 until the end of
2015.
Investment
In the definition of the term, investment is a money committed or property acquired for future income. In
a more popular way, it is an item or asset that is purchased with the hope that it will generate income
32
or appreciate in the future. In an economic sense, an investment is the purchase of goods that are not
consumed today but are used in the future to create wealth.
With this point in view the condominium decided to invest in the purchase of PV solar panels to have
a better use of solar energy and to reduce the monthly and/or annual costs.
Payback Period
Payback period in its definition is the length of time required to recover the cost of an investment. The
payback period of a given investment or project is a determining factor on whether to undertake the
project, since longer payback periods are typically not desirable for investment positions.
With all other external factors being equal (inflation, interest rate, etc.), the best investment is the one
with the shorter payback period, as expected. Investment implies immediate outflow of money, although,
it is expected to receive cash flows to reward for this output over time. The payback is the calculation
of this time (in number of periods are months or years) needed to recover the investment. The simple
payback method does not take into account the interest rate or inflation of the period or the opportunity
cost. Furthermore, not always the expected flows are constant.
There are two main problems with the payback period method:
• It ignores any benefits that occur after the payback period and, therefore, does not measure prof-
itability;
• It ignores the time value of money;
However, this method as some advantages, that should be considered as well:
• It is quite simple in its form of calculation and easy to understand;
• It provides an idea of risk of the project;
• It is a way to increase the security of the company’s/ buyer’s business;
• Suitable evaluation of projects in high-risk context;
Applying this definition to the study of PV panels, it is possible to make a prediction of what would
be the payback period taking into account the production forecasts provided by Conergy and compare it
with the payback that really happened.
In order to calculate the payback time, the profit that can be done during an year must be estimate
first based on Equation 4.13.
Profit = Price ∗ Production (in one year) (4.13)
Once that the value used for production was one year, the profit will be in a basis of a year, as well.
Using the simple payback time method, it would be the division between the investment and the
yearly profit as defined on Equation 4.14.
Payback T ime =Investmentsimple
Profit (in one year)(4.14)
33
If a more realistic analysis of what the payback time is, then inflation should be taken into account.
In a market economy, the prices of goods and services can change anytime. Some prices rise, others
fall. The inflation term is referred when there is a general increase in prices of goods and services and
not only when some specific item price rise.
The result is that one euro does not buy so many things as previously. In other words, a euro is worth
less than before. The inflation values have varied widely over the past five years so a simple average
was done, in order to use it in payback time calculations. All these values can be seen in Table 4.2
(source: Pordata).
Table 4.2: Inflation values.Year Inflation (%)2010 1.42011 3.72012 2.82013 0.32014 -0.32015 0.5Average 1.4
Equation 4.15 calculates the investment taking into account inflation.
Investmentinflation = Investmentsimple ∗ (1 + Inflation)n (4.15)
Where n is the number of years that was considered for the study.
Now the payback time can be calculated through Equation 4.16, but this time the investment that
goes in is from Equation 4.15.
Payback Period =Investmentinflation
Profit (in one year)(4.16)
In this equation should be remembered that the profit, which is in the denominator, is the profit taking
into account the value added tax (VAT) made on the produced energy price. The VAT is also previously
defined by EDP and agreed on 23%. The value used for the calculations was the sale profit (with tax)
and not the output produced price, once that the real value of sale is with the tax applied and not the
produced energy price.
4.2 Analysis of Electricity Consumption
4.2.1 Energy Audit
The diversity of forms of energy used in a consumer installation (industrial property, a set of buildings,
etc.) and the complexity of the different transformations that can intervene in the use of energy, justify
the need for strict measures in energy management. The method and level of management should be
34
able, always, to satisfy the fundamental questions:
• Know the energy consumption;
• Account energy consumption;
• Have data to decide;
• Act to optimize.
The method used for the study was:
• Measurement and evaluation of energy consumed, either globally or by the consumer’s productive
sector;
• Determining the proportion of energy in the total energy wasted;
• Analyzing the situation to determine possibilities for action and to set priorities and targets to be
achieved;
• Evaluating and monitoring the investments done.
An energy knowledge of all electric installation is the preliminary stage for energy management. This
first phase corresponds to the development of an energy audit which should provide a very important set
of information. An energy audit is no more than an examination of the energy units, it can also be seen
as an x-ray to all energy system and equipment in order to, not only reduce the wastes but also to reduce
the costs associated with energy consumption. Energy audit allows providing specific information and
identifying the real possibilities to save energy. From an energy point of view of a consumer installation,
this energy audit made aims to:
• Determine the forms of energy used;
• Examine how energy is used and the costs;
• Establish energy consumption structure;
• Identify opportunities for improving energy efficiencies;
• Analyze technical and economic solutions that were found;
• Set energy consumption targets without any change in the process;
• Propose a program for the actions and investments to be undertaken;
• Propose an organized system of energy management.
The methodology used in the implementation of the energy audit, consisted in four stages of inter-
vention:
• First phase - the preparation of the audit (collection of data corresponding to the historical records
of at least the last three years of activity);
35
• Second phase - intervention at the installation facilities to be audited (characterize the energy
equipment about their consumption and energy efficiency);
• Third phase - process the information collected in the first two phases (technological solutions
(energy and process) in order to be implemented and aiming to increase the energy efficiency and
decrease the costs of the system);
• Fourth phase - preparation of the report of the energy audit (all processes/measures or even
investments to be made are present).
All these four stages were applied to the waste water treatment plant, outdoor lightning and irrigation.
Ideas for WWTP
The WWTP is the facility that has bigger energy consumption for the condominium, so an energy audit
was made in order to reduce energy consumption and associated costs. As a matter of agreement, the
time-line considered for energy cost analysis was the same for PV panels (2010-2015).
As such, next are some ideas that will be analysed and check their impacts either in energy, costs
and carbon dioxide emissions.
1. Change the energy consumption from void hours to super void:
To analyze the effects of the first idea proposed, two possible scenarios were considered:
(a) The amount of energy that had been consumed by the treatment plant in the void hours will
now be consumed in the super void hours;
(b) The amount of energy that had been consumed by the treatment plant at any time will now
be consumed in the super void hours.
The first scenario proposed is the real case of operation of the WWTP, since the normal schedule
of operation is in void hours and super void hours. However, there are reservoirs connected
to pumping stations that have a waste water accumulation sensor which, if activated, starts the
process of the WWTP whatever the time of day, until the reservoirs are empty. To take into account
the case in which the accumulation sensor is activated the second scenario was created.
In both cases, it is considered that the use of electricity of the WWTP was about 42%-43% (varies
slightly) of the total electricity demand, as previously mentioned.
2. Transform the aeration process from industrial liquid oxygen to atmospheric oxygen:
This idea is relative to the transformation of the aeration process. The transformation process will
present savings because the purchase of industrial liquid oxygen (ILO) will no longer be required.
The energy needed to mix the atmospheric oxygen may increase the energy consumption slightly,
although Lena Ambiente e Energias guaranteed that it will be insignificant.
In order to use atmospheric oxygen it is necessary to make an investment in equipment so it can
support such transformation. The company hired to assess the facilities and submit a budget was
Lena Ambiente e Energias that proposed the following setup:
36
• Venturi aerator-jet, composed by:
– Electronic bomb group AFP 1041.4 M15 / 4D;
– Portable installation support PN 61350527;
– Venturi tube with outlet DN100 08,090,151;
∗ Price: 3882.75 e (without VAT);
• Electronic bomb, composed by:
– Group AFP 1041.4 M15 / 4D;
∗ Price: 1992.90 e (without VAT).
3. Total Elimination of WWTP:
The elimination of the WWTP is studied on this idea. The WWTP will be replaced by the WWTP
of the municipality of Martinchel.
This idea has to take into account two aspects:
(a) The total elimination of the WWTP which allows savings at the level of energy and associated
costs;
(b) The elimination of ILO supply because the WWTP will no longer be in operation.
In any of the ideas it is important to remember that when the total energy is being calculated it already
takes into account factors as the power contracted and reactive energy out of the void. The formula used
was Equation 4.17.
Total = Energy in V oid Hours× Price+ Energy in Super V oid Hours× Price
+ Energy in Peak Hours× Price+ Energy in Full Hours × Price
+ Power Peak Hours× Price× Factor + Contracted Power × Price× Factor
+Reactive Energy × Price× Factor
(4.17)
It should be noted that the total price based on the total energy is calculated taking into account the
VAT.
Ideas for Outdoor Lighting
In the previous section 3.3, reference is made to another set of facilities of the condominium that can be
also improved. The outdoor lighting of the condominium, despite not representing a significant expendi-
ture, is something that can be improved at any time.
The lighting has been greatly improved taking into account other energy audits already performed
along the years by various companies. Outdoor lighting is already working autonomously through a light
sensor so it depends if it is summer or winter. In the summer it turns on around 21h00 and turns off
around 6h00, as for example in December it turns on around 18h00 and off around 8h00.
37
One of the most basic measures to be taken today is the replacement of ordinary bulbs for low
consumption, a measure that has already been made. However there are still some ideas that can be
taken, such as:
1. Replacement of exterior lamps for LED lamps:
This idea would require an investment in lamps from the condo, since all the lamps have to be re-
placed. This idea has to take into account that there are 33 lampposts (19 single and 7 with double
lamps) scattered throughout the area inhabited with a power of 40 W each. The approximate cost
of a LED lamp with similar characteristics is 40 e.
2. Reduction of illumination to half:
This idea can be implemented in conjunction with the idea presented above or separately making
no investment as suggested. This idea is intended to reduce outdoor lighting to half if not detected
any movement outside, as such it is needed a motion sensor for each street lamp. The cost of
these sensors presents a range of values between 15-20 e.
Ideas for Irrigation
Watering of all condominium gardens also presents clear deficiencies that can be substantially improved.
Irrigation works through an automatic device that determines when it begins and when it ends, yet this
device does not take into account several atmospheric characteristics such as temperature or even to
humidity.
The water used for irrigation of the condominium is water that is drawn from the dam through a pump
which is then stored in the reservoir water. This reservoir is the one referred in Section 3.3 as one of the
big spenders of energy. However, this reservoir is also used by the hotel which pays the condominium
their share of energy used, so the percentage of that energy should take this into consideration.
The following are some ideas for implementation:
1. Humidity sensor:
Through this idea it is intended that irrigation is done when only low levels of moisture are expe-
rienced by a sensor. This avoids situations such as in rainy days, when the watering is working
while is raining which is an authentic waste of energy. Nevertheless, to implement this idea an
investment in humidity sensors has to be taken.
2. Watering at night:
Watering should be carried out at night since ambient temperature is lower and higher moisture
levels, which cause less absorption of irrigated water to the environment being better utilized by
the field.
38
Chapter 5
Results and Discussion
This chapter presents the main results obtained. Initially, a comparison of results between energy and
exergy analysis for PV panels is made, followed by a comparison with several reference values, pointing
out the effects of those differences in results. Then, a cost analysis is made comparing the real values
with expected values pointing out where these differences are more significant.
Afterwards, the proposals previously suggested for the WWTP and other facilities are analyzed and
the results are shown at the level of energy savings and associated savings in monetary terms.
5.1 PV Panels
5.1.1 Results of Energy and Exergy Analysis
In this study, an extensive energy and exergy analysis of the PV panels installed in the condominium
Vale Manso, in Abrantes, Portugal, was done. The first thing to estimate for both analyses was the cell
temperature. In order to do it, there were a set of values needed, which are shown in Table 3.1 and
Table 4.1.
Equation 4.8 was used with an initial value for the cell temperature to compute the radiative heat
transfer coefficient. Then Equation 4.6 was used to compute the overall heat loss coefficient, which can
be seen in Table 5.1, which was then used to obtained a new estimated values for the cell temperature
with Equation 4.5. The process was repeated until convergence was achieved. The value for the cell
temperature was found to be on average 301.033 K.
Table 5.1: Heat Losses.Heat Losses Calculated values (W/m2K) NOCT values (W/m2K)hconv 5.8 5.8hrad 5.025 5.082UL 10.825 10.882
All the necessary data to calculate the values of energy analysis are presented in Table 3.1 and Table
5.1. With Equation 4.2 and Equation 4.4 it was possible to obtain the values presented in Table 5.2. As
39
referred before, the energy efficiency can also be calculated through the Fill Factor (Equation 4.3) which
is why it is also presented in the Table 5.2.
Table 5.2: Efficiencies.Efficiencies Reference Values Real valuesηpce 0.142 0.143η 0.187 -FF 0.756 0.756
Through Equation 4.12 it was possible to obtain the exergy efficiency of the solar PV panels, consid-
ering the average values presented in Table 3.1 for solar radiation and ambient temperature. Again in
Table 5.3 the reference values are compared with real ones.
Table 5.3: Exergy efficiencies.
Efficiency Reference Values Real valuesψ 0.147 -
The difference between reference and real values is due to the value of the absorbed solar flux, ST ,
the cell temperature Tcell and ambient temperature Tamb. The value for the total solar irradiation and
the value for ambient temperature was calculated by an annual average of the values published in the
monthly climatological newsletter for 2015 by Instituto Portugues do Mar e da Atmosfera (IPMA) to the
place where the PV panels are geographically located in Portugal. The real values were obtained from
the production of electricity of the PV panels, considering the number of hours for sunlight, the PV area
and the number of PV panels.. The values for total solar radiance throughout the last year can be seen
in the Figure 5.1. The average value for ST was 521 W/m2, with a minimum of 235 W/m2 for December
and a maximum of 900 W/m2 for July.
Figure 5.1: Solar irradiance values of 2015.
Temperature effects are presented to see its effect on the various efficiencies. It is important to
remember that the solar radiance values only consider the sunlight hours, while the temperature values
consider all day hours including both sunlight and night hours.In this scenario the solar radiation was
kept constant, 521 W/m2. The average ambient temperature during the year was 291 K, registering a
40
minimum of 281 K for the month of January and a maximum of 304 K for July, which are shown in Figure
5.2.
Figure 5.2: Temperature values of 2015.
The ambient temperature has an effect on exergy efficiency not only through its direct influence,
but also through the cell temperature. The ambient temperature has a relationship of almost direct
proportionality since its increase is reflected directly from the cell temperature as can be seen in Equation
4.5. This effect can be seen in Figure 5.3.
Figure 5.3: Influence of ambient temperature in cell temperature.
Through the ambient temperature and cell temperature is possible to see these effects on the exergy
efficiency in Figure 5.4.
It can be seen in Equation 4.2 that the ambient temperature is not taken into account so the power
conversion efficiency will not change according to ambient temperature. The same applies for energy
efficiency, in Equation 4.4, that depends on the electricity generated and the incident solar radiation.
With Equation 4.12 it is possible to see that solar exergy relies on the ambient temperature, which takes
into consideration atmosphere radiation losses. Furthermore, it should be recalled that the physical
exergy also takes into account the ambient temperature directly and indirectly through the heat losses
from the PV cell. The variation of efficiency values can be seen in Figure 5.5.
The conversion power has an invariable efficiency value of 0.141 and the energy efficiency of 0.188.
The exergy efficiency has a minimum value for the month in which the ambient temperature is higher,
41
Figure 5.4: Influence of ambient temperature in exergy efficiency.
Figure 5.5: Efficiency values for 2015 for constant radiation.
in July, with a value of 0.145 and a maximum corresponding to minimum temperature in January with
an efficiency of 0.156. It is also possible to verify through Figure 5.5 that the highest values for exergy
efficiency correspond to months in where the ambient temperature is smaller and therefore the cell
temperature is lower. The efficiency is greater when the ambient temperature is lower due to heat
losses that exist in PV cells.
Exergy is the useful energy that is being actually used for converting solar energy into electricity that
will later be sold to the public network. The exergy efficiency of the panel can be increased even if the
radiation intensity is high. It can be done if the cell temperature of the PV array is reduced by a internal
cooling circuit, or more practical passing cold water on the PV surface. Beside irreversibility there are
PV cell losses which are mainly due to factors as thermalization, junction contact and recombination.
5.1.2 Cost Analysis
In this section all results related with the investment made will be evaluated. All the data provided by the
condominium was essential for this chapter. Therefore, after collecting all the necessary data of the past
five and a half years it was possible to compare results between reality and expectations of Conergy.
In Figure 5.6 it is possible to see the differences between expected values and actual read values
(both in kWh) and the aggregate of both lines over the years. The actual read values were taken from
the PV meter over the last six years.
42
Figure 5.6: Comparison between monthly read and prediction.
The measured energy production was found to be most of the times greater than the prediction
for each month, as can be seen in Figure 5.6. Through the same figure it can be seen that spring
and summer months were constantly more favorable compared to expectation, having produced more
electricity than expected. The months considered as spring and summer were from April to September,
with an average value of production of 567 kWh.
In contrast, the autumn and winter months were months where energy production was slightly lower
than expected or almost equal. The months considered as autumn and winter were from January to
March and from October to December, with a value of electricity production of 387 kWh.
A comparison between average values for spring/summer and autumn/winter for each year can be
seen in the next Table 5.4.
Table 5.4: Comparison between average read and expected average values.
YearAutumn/Winter Spring/Summer
Read (kWh) Expected (kWh) Read (kWh) Expected (kWh)
2011 443 387 632 567
2012 438 387 591 567
2013 337 387 587 567
2014 382 387 608 567
2015 383 387 628 567
Average 397 387 609 567
The first year of production, 2010, is not present in the Table 5.4 because the PV panels were
installed only in August of the same year.
As can be seen from Table 5.4, most of the average read values are above to what was expected,
which leads to an average difference between read and expected values positive with a value of 26 kWh,
in all five years. Figure 5.6 shows precisely this point where can be sees the difference between the
accumulated read values and the accumulated predicted values have a positive difference.
This positive value is the starting point for the next topic, the payback time. As mentioned previously
in Chapter 4, EDP provided a power sale price of electricity by the micro-generation at a higher price
43
to encourage the beginning of energy production. Therefore, the sale price agreed with the power
distribution network was 0.5866 e/kWh. Considering the forecasted values from Table 3.2, the prediction
of electricity production would be 5.725 MWh/Year, which multiplied by the selling price gives the profit.
Using Equation 4.13 the predicted produced profit is 3358.29 e/Year. Applying the tax of 23% on this
amount the selling price is 4130.69 e/Year.
Employing Equation 4.14 the return of the money would be 4.7 years, corresponding to 4 years and
8 months, i.e, in April of 2015 the condominium would have recovered their investment. If the inflation
is considered, then through Equation 4.15 the investment is now 21049.58 e. Using Equation 4.16 the
return of the money would be in 6.1 years, which represents more four months compared with the normal
investment (without inflation). This differences can be seen in Figure 5.7.
Figure 5.7: Payback time for prediction values.
Comparing these values with the read ones it is expected that the real payback time is shorter than
the expected, since the energy produced was higher than expected, and consequently the profit as well.
Figure 5.8: Payback time for real values.
Figure 5.8 shows precisely this point, in which is possible to see that the Sales line intercepts the
Investment line and the Investment with inflation line before than the previous Figure 5.7.
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5.2 WWTP
5.2.1 Energy Consumption in Super Void Hours
For the first scenario, Table 5.5 presents the price differences between void hours and the super void
hours. It can be seen that the biggest difference between the values was in 2012.
Table 5.5: Price difference between energy used in void hours and super void hours.
YearThree-Hourly Fare
Void Hours (e/kWh) Super Void Hours(e/kWh) Difference (e/kWh)
2010 0.0565 0.0527 0.0038
2011 0.0588 0.0548 0.0040
2012 0.0616 0.0570 0.0046
2013 0.0832 0.0801 0.0031
2014 0.0858 0.0823 0.0035
2015 0.0916 0.0878 0.0038
This difference is demonstrated in Figure 5.9, which shows the estimated monthly difference in costs
of the WWTP between the operating hours assumed in scenario 1 and the assumed current operating
hours.
Figure 5.9: Difference and accumulated values over the years with scenario 1.
In the same Figure 5.9 it can be seen that in the year in which the difference in the cost of energy
is higher, the slope of the accumulated line increases. It is also possible to verify that the monthly
difference is greater in summer months of every year (the difference is greater the higher the energy
consumption, which occurs in summer).
The monthly differences line is majorly between 1e and 6 e, so it can be expected that the accu-
mulated value at the end of the six years is not significant. This difference can be verified in the annual
costs with and without the measure designed in scenario 1, which are presented in Table 5.6. Using this
scenario, the accumulated value of savings would be 263.87 e, which in turn divided by 95 dwellings
would mean savings of 2.78 e per habitation, at the end of six years.
This idea to be implemented has to change the hours of operation of the WWTP. A mere idea like
this already brings savings to the condominium, despite being relatively small.
45
Table 5.6: Annual costs for scenario 1.Year Normal Costs (e) Costs in Scenario 1 (e) Difference (e)2010 10233.86 10202.71 31.152011 12291.91 12246.15 45.762012 14735.27 14664.43 70.842013 13117.97 13082.47 35.502014 8618.12 8581.08 37.032015 8477.45 8433.85 43.60
For the second scenario, the results presented follow the same line of thought than the first one.
Table 5.7 shows the electricity price differences for different time of the day per year (the difference
between void and super void hours is in Table 5.5). The biggest difference between the peak hours and
super void was again in 2012, while the difference between full and super void hours is growing over the
years.
Table 5.7: Price differences between energy used in all hours and super void hours.
YearThree-Hourly Fare
Diff. (Peak -Super Void) (e/kWh) Diff. (Full -Super Void) (e/kWh)
2010 0.0711 0.0375
2011 0.0739 0.0390
2012 0.0861 0.0390
2013 0.0369 0.0467
2014 0.0530 0.0422
2015 0.0605 0.0477
Through Figure 5.10 it can be verified that 2012 was the one with greatest difference between sce-
nario 2 and the current assumed operation. Due to this difference, the slope line of the accumulative
value increases according to it. Again, the greatest differences occur when the energy consumption is
higher, which occurs in summer months.
Figure 5.10: Difference and accumulated values over the years with scenario 2.
The cost differences are now much higher than in the previous scenario, whereby the expected
46
accumulated value is much higher. The annual costs in the assumed current operating hours and in
scenario 2 are presented in Table 5.8.
Table 5.8: Annual costs for scenario 2.Year Normal Costs (e) Costs in Scenario 2 (e) Difference (e)2010 10233.86 9006.49 1227.362011 12291.91 10738.83 1553.072012 14735.27 12904.74 1830.532013 13117.97 12208.44 909.522014 8618.12 8017.43 600.692015 8477.45 7717.61 759.84
In this scenario the accumulated value of the difference is 6881.01 e, which is a much higher value
and with greater impact than the last. This value divided by all joint owners represents a difference of
72.43 e, in the sum of six years.
This scenario is much harder to implement and it has a simplistic and perfectionist view of the operat-
ing hours of the WWTP. Since the house occupancy is very seasonal (occupation is up to 90% in summer
and 1% in winter and almost the same percentages for weekends and week days, respectively), this idea
without any adjustment to the size of the reservoirs connected to lifting pumps is extremely difficult to
perform. However, the condominium has already the weekly cycle for electricity tariffs instead of using
the daily cycle, which favors the cost of energy use for seasonal cases like this as this condominium is
used mostly for vacations.
5.2.2 Transformation of Aeration Process
To analyze the effects of this idea, first it must be taken into account the investment that has to be done,
referred in Section 4.2.1. The total investment is 7227.05e, which is divided in:
• Venturi aerator-jet = 3882.75e× 1.23%=4775.78 e;
• Electric bomb = 1992.90e× 1.23%=2451.27 e.
The implementation of this idea has to be taken into account the value of investment and the monthly
purchase price and with those values estimate how long it takes to return it. As can be seen in Table
3.4, the price of industrial oxygen is very high so the implementation of this idea is completely feasible.
The value of investment is 7227.05 e, which has a payback time of six months. The sum of months
cost, for example from March to August is 7328.02 e, which is already a higher value than the investment
that has to be done.
With this idea, after the investment, the annual savings will be about 7046.49 e in the first year and
in the following years 14273.54 e. This value has a huge impact on the annual accounts for the condo-
minium. For each house this idea has a financial impact around 150.25e per year, which summed in
all six years of data considered has a value of 901.49 e. This idea does not bring any savings in energy
consumption because the process involved in the aeration process will continue as before. The energy
consumption may increase slightly but it’s not significant in electricity consumption.
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5.2.3 Total Elimination
Once the WWTP is the largest consumer of energy in the electric system of the condominium, it is
expected that its removal has a major impact in terms of energy. Its elimination allows an average
energy saving of 28.383 MWh per year. The monthly energy differences can be seen in Figure 5.11.
Figure 5.11: Energy consumed over the years with and without WWTP.
The relationship between energy that is spent using the WWTP and the energy that is saved if it is
removed can be seen in the Table 5.9. Through the same Table it is possible to see that the energy
saved is 170.299 MWh in the sum of all years.
Table 5.9: Annual energy spent with and without WWTP.
Year Total Electricity (MWh) Electricity without WWTP (MWh) Saved (MWh)2010 65.123 37.771 27.3522011 75.340 41.437 33.9032012 88.707 50.563 38.1442013 71.673 40.296 31.3762014 47.085 28.251 18.8342015 45.977 25.287 20.690Total 393.905 223.606 170.299
With this energy saved there is an associated cost that is also spared. The prices for each type of
energy have been previously presented so using Equation 4.17 it is possible to calculate these costs.
Following the same type of presentation used for the energy, Figure 5.12 shows the monthly costs
considering the removal of the treatment plant.
A table similar to the one created for energy is present, Table 5.10, but this time applied to the costs.
As can be seen through Table 5.10, there is huge difference in values between applying this idea
and the previously suggested in Section 5.2.1. As such, the amount saved by applying this idea would
be 20826.98e over the six years, which gives 219.23e for each house. Still, there is the condition of
cancellation the ILO of the treatment plant that combines the idea referred before and this idea. Taking
into account the values presented in Section 5.2.2, the value to be added are the savings in the first
year, considering the investment done, plus the annual savings times the remaining five years, which
gives 78414.16e. If this value was added to the value that is saved by eliminating the WWTP the final
value is around 99241.14e. If an analysis is made individually it gives 1044.64e.
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Figure 5.12: Costs over the years with and without WWTP.
Table 5.10: Annual energy spent with and without WWTP.
Year Total Cost (e) Cost without WWTP (e) Saved (e) Removing ILO (e)2010 10233.86 7233.53 3000.32 7046.492011 12291.91 8453.64 3838.27 14273.542012 14735.27 10230.46 4504.80 14273.542013 13117.97 9135.82 3982.15 14273.542014 8618.12 6110.88 2507.23 14273.542015 8477.45 5483.26 2994.20 14273.54Total 67474.57 46647.59 20826.98 78414.19
Besides having positive impacts for the condominium in monetary terms, this idea will also have a
major impact in terms of emissions of CO2. Through the electricity bill is possible to consult the primary
energy sources that generated the electricity needed. Although much of the energy produced comes
from renewable sources (around 68% of the energy consumed comes from renewable energy) such as
hydro (10%), wind (39%), solar (from the micro generation, 16%) among others, there are also non-
renewable energy consumed (around 32%) which are quite harmful to the environment as coal (9%),
natural gas (13%), nuclear power (4%) among others. The CO2 emissions can be verified in Figure 5.13
which shows emissions over the years with and without WWTP.
Figure 5.13: Emissions with and without WWTP.
The CO2 emitted due to the consumption of the condominium and the estimated emissions without
the WWTP are presented in Table 5.11.
The quantity of CO2 emissions that have been released are not directly related with the amount of
49
Table 5.11: Emissions with and without WWTP.Year Emissions (Ton) Emissions without WWTP (Ton) Difference (Ton)2010 18.586 10.780 7.8062011 20.176 11.097 9.0792012 27.923 15.916 12.0072013 21.123 11.723 9.4002014 21.376 12.826 8.5512015 20.958 11.527 9.431
energy used. The energy used can have a maximum value in a certain year, yet in the same year the
sources used to generate that electricity could have come from renewable energies and therefore the
CO2 emissions are lower.
Another aspect related to pollution are the TOE consumed, which can be calculated knowing the
percentage of primary energy sources that provided the energy consumed. Knowing the conversion
efficiency of each primary energy it is possible to calculate the amount of primary energy used to produce
the energy consumed. The conversion efficiencies are not known, only range of plausible values. The
values used for calculations are in the middle of the range, which can be seen in Table 5.12.
Table 5.12: Primary energy conversion efficiencies.
Primary Energy Efficiency (%) Value used (%)Coal 35-45 40Natural Gas 50-55 53Oil 25-35 30Nuclear 33 33Renewable 100 100
Through the monthly bill for electricity it is possible to know what kind of primary energy produced
the energy consumed. As such, Figure 5.14 shows the percentage used of each type of primary energy
along the last years.
Figure 5.14: Primary energy used over the years.
As it can be seen in Figure 5.14 there are no data for the year 2012. This is due to the fact that the
condominium in that year decided to change the energy supply from EDP to Iberdrola, which did not
50
show the percentage or any indication about the primary energy which produced such energy. In 2013
the energy consumed was again provided by EDP so this information has returned to be present on
invoices and as such in Figure 5.14.
Given the data presented, the primary energy conversion efficiencies, the percentage of each pri-
mary energy used, and the total energy consumed is possible to calculate the primary energy consumed.
Figure 5.15 shows the primary energy consumed.
Figure 5.15: Primary energy consumed over the years.
The total energy consumed by the condominium is present only as a comparison.
The amount of primary energy used is directly related to energy consumption, which can also be
seen in Figure 5.15. Again the year 2012 is not present for the reasons explained previously.
Through a monthly analysis of the data used in the previous Figure 5.14 and Figure 5.15 it is possible
to conclude that the winter months are the ones that have lower values of primary energy consumed,
with much of the primary energy used based on renewable energies.
Either way, this idea is the one that deserves more attention from a financial, energy and emissions
point of view.
5.3 Other Facilities
The watering and exterior lighting do not have proper data that can be studied because the percentage
of energy used by these two components is not clearly defined. The energy percentages of these two
components are included in a range of values that includes other facilities such as the pool pumps
and others. As in all other points mentioned above, where an energy audit was practiced in order to
demonstrate that the hypothetical measures have energy improvements, the values that will be present
here are just an expectation.
However, if the same data was used, for example, for the WWTP, the error associated with these
expectations would be substantially higher, since the amount of power consumption for these portions
would be estimated and not precise. Despite this and applying the first idea proposed for the outdoor
lighting, it is known that the existing equivalent LED lamp can reach a percentage of 70% lower con-
sumption than lamps of low consumption, the ones that are being used. Although there is an investment
51
to be made, around 1320 e, the energy consumption is relatively lower and consequently the cost to
pay for the same electricity.
For the second idea proposed for outdoor lighting there is also an investment to be made, since there
are LED bulbs that have variable lighting, stronger or weaker depending on the sensor. In addition to the
investment of the lamps there are also the sensors, which increases the cost of the solution. However,
the investment to be made has an approximate value of 560 e (only for the sensors).
Taking as estimated that 80% of the exterior lighting remains at half the required illumination, i.e.,
motion sensors do not detect any movement and therefore the illumination keeps half, there are some
serious savings that can be taken. The energy estimation and the associated savings are extremely
difficult to calculate since the outer lighting consumes power in three types of different times, having three
different fares that are applied throughout the year. The percentage of the estimated illumination that
remains unalterable was chosen taking into account that the use of the condominium is very seasonal,
so in the winter it was assumed that the sensors would not sensor any kind of movement and in the
summer half of the sensors would feel motion.
For watering, the first idea proposed is the investment in moisture sensors that assumes that watering
is only activated when humidity levels are low. However, this idea works for rainy days which prevents
irrigation being activated when it rains which represents savings levels of water and energy that would
be totally wasted without any need. However, this idea has a disadvantage since the lower moisture
levels coincide with the hot peak hours during the day, which in turn causes an increased evaporation
of the irrigation water to the atmosphere instead of being utilized by the grass. As such, it is concluded
that the first idea proposed gives no advantage to the condominium, besides having to spend money to
pursue such an idea.
The second idea proposed is to water the grass at night, precisely when the humidity levels are
higher and so there are fewer losses of water irrigation to atmosphere, improving the percentage of
water received by watering. Besides this great advantage there is also the fact that the energy used
for irrigation coincides with the super void schedule, which allows watering that was previously turned
on between 11h00 and 12h00 will now run anytime between 02h00 and 06h00. With this idea it is also
possible to allow other systems to perform at the same time without existing any energy peaks and
therefore an increase in the contracted power without any need. Again, it is not possible to know for sure
within the electricity bill which percentage of energy that is being used for irrigation, so in this proposed
idea is not possible to calculate savings. However, despite the energy consumed remaining the same, it
would be used in a more rational way so it will allow the use of the same energy for a lower cost for the
condominium.
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Chapter 6
Conclusions
This chapter presents the conclusions regarding the analysis of the PV panels, the WWTP and other
facilities. The chapter ends with suggestions for future work.
6.1 PV Panels
6.1.1 Exergy and Energy
The experimental data that was used was essential for the study. Following are some conclusions of the
the study:
• The ambient temperature has influence in the exergy efficiency, through the cell temperature. A
higher ambient temperature will increase the cell temperature and therefore bigger heat losses will
occur.
• The exergy efficiency can then be improved if the PV array temperature is lower, even when the
solar radiation intensity is high. This can only be done if the PV array surface temperature is
reduced by an internal cooling circuit, or a more practical method as passing cold water by the PV
surface.
• In this analysis the wind speed was considered constant, which does not influence the results
accuracy as wind speed changes the cell temperature in the order of magnitude of hundredths of
degree being completely negligible its influence on the exergy efficiency. In other exergy analysis,
such as Sarhaddi, Farahat, Ajam, and Behzadmehr [13], the wind speed was also considered
constant, so it is not considered as an important influence parameter in the results.
• Although most people are not familiar with the exergy term, a reference and a brief explanation of
this type of analysis should be made (in catalogs, or when a buyer requests a budget), since it is
an important efficiency of the panel.
• Future studies should require more investigation in order to improve the solar PV efficiency, once
that the optimal efficiency is far from being achieved.
53
6.1.2 Cost and Investment
To frame the purchase of the panels today it is necessary to do a little research to find similar panels
in terms of features. When the condominium bought his small energy production, the competition be-
tween constructors of PV panels was still not high, so it payed off to purchase panels made in Europe,
specifically in Germany.
Today the competition by seeking the best compromise between price, quality and efficiency is quite
high and countries like China have led this competition. Companies such as Suntech, based in China,
with factories scattered around the world (London, Frankfurt, Johannesburg, Sidney and Tokyo), is today
one of the largest producers of PV panels worldwide. This company can commit a guarantee and
efficiency that competes with European brand panels or even American at a substantially lower price.
In order to get a better idea, the 18 panels that the condominium bought, nearly six years ago, cost
10387.29 e, 577.07 e for each panel (with other installation costs like cables, converters, counters,
etc. the price reaches up to 19,500 e). Today, panels with similar characteristics (polycrystalline cells,
60 cells per panel and 255 Wp) by Suntech would cost between 160-175 e per panel, which would give
a total between 2880-3150 e, corresponding approximately to one third of the investment done (only for
the PV panels). With this amount of investment, the payback time is substantially smaller, which further
encourages the purchase of PV panels for a better use of this renewable energy. However, nowadays
it should be noted that the rates that were provided for the price of electricity sold to condominium are
also substantially lower, so a more detailed investigation to the micro generations of today would have
to be made.
6.2 WWTP and other facilities
From the energy audit made should be noted that the associated savings for each idea suggested for
implementation represents only a forecast and may not be exactly correct. Any prediction has always
errors associated, which can be higher or lower. The suggested savings can also contain associated
errors, but it is expected that the calculated forecasts are as close to real values as possible, since it
was used a large time-frame to have a better sense of the energy consumption and of the costs.
The conclusions of the study are presented next:
• The first idea (change the operation hours to super void hours) can be easily applied. First the
condominium has to change the three-hourly fare (full, void and peak hours) to the three-hourly
fare that divides the void hours into super void hours. With this change only the operation hours
for WWTP must be adjusted.
The second scenario for this idea is much harder to implement because all energy used during the
day has to be changed to super void schedule. This is only possible if the accumulation sensors
are not activated, which in turn is only possible if the reservoirs are modified or increased. Once
the reservoirs are integrated in the condominium ends since its construction, the condominium
managers do not consider this a viable solution;
54
• The second idea (transform the aeration process) to be implemented requires Lena e Ambiente to
perform the change from ILO to atmospheric oxygen. Although there is an investment to do, it is
proven in the results that it is fully returned in six months.
• The third idea (eliminate the WWTP) is the boldest of them all. This is the idea that brings more
savings at all levels, both in cost and energy savings. Since this idea has the greatest impact is
normal that condominium managers are a little reluctant to take this step. The managers team
consists of five people and three of them think that this idea should advance. At the end of this
study it was given a budget of around 70000e that would be needed to take this measure. The
municipality would not bear any cost, yet it would provide all the equipment necessary to perform
such a measure. From Section 4.2.1 is possible to predict the payback time is around five and half
years;
The author believes this measure should be taken not only for savings in energy and costs but also
for the CO2 emissions saved.
• As to other facilities there are some ideas that can be taken, although there is no data for calcu-
lations. Regarding the exterior lighting the appropriate measure is to replace the bulbs by LED
lamps. As for watering the best action to take is to replace its operation to night hours due to low
humidity levels that are felt during the day and therefore a greater loss of water to the environment.
There are several other measures that can be taken in some condominium facilities:
• The installation of other PV panels for energy production. However, it is advisable to remember
that today there are no longer greater benefits for those who are producing energy because the
price of electricity sold is much lower for new contracts. Consequently, the payback time of the
investment to be made is higher, leaving the condominium managers not so comfortable with this
suggestions.
• The installation of solar thermal panels. This measure seems ideal for dwellings because the water
heating is done through boilers that use electricity.
However, the roof is shared by four houses being the roof of the upper house the same as that
of the lower. It is not difficult to understand that this suggestion causes big problems, if a house
desires to install it and one of the others does not, this will cause major conflicts. Besides this
issue, there is the aesthetic question, as the roof of the houses is visible even from the river level
of the dam, and aesthetically this solution may raise considerable problems.
• The integration of an energy management system to improve control of the energy spend on the
installations and more quickly realize where is possible to act to minimize costs. Energy manage-
ment systems (EMS) are intended to provide organizations elements of an effective management
model that can be integrated with other management requirements (source: PowerHouseDynam-
ics). This factor of integration is the key point in the organization’s management. The rules for
following the structure of the model based on the cycle (Hollifield and Habibi [26]):
55
– Plan - perform energy assessment and establish the baseline for energy performance indica-
tors (EPI), objectives, targets and action plans needed to produce results;
– Do - implement the energy management action plans including procedures and processes;
– Check - measure processes and products, the key characteristics of operations that deter-
mine energy performance against the energy policy and objectives, and report the results;
– Act - undertake actions aimed to continually improving performance of the EMS compared to
results achieved.
In a perspective of medium-long term, the major benefits for resulting from the implementation
of an EMS are related with reducing energy consumption and improvements in efficiency and
productivity of the processes, which consequently promotes the rationalization of energy costs.
Besides that, it also improves the environmental performance of the system.
56
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58
Appendix A
Technical Datasheets
In this appendix is attached a PDF file to the document, with a technical sheet of the equipment used in
the work (Provided by Conergy).
A.1 Photovoltaic Datasheet
59
Technical Data | Photovoltaic modules
Conergy PowerPlus 200P
Conergy PowerPlus 210P
Conergy PowerPlus 220P
Conergy PowerPlus 225P
Conergy PowerPlus 230P
Rated capacity (Pmpp) according to STC3 min. 200 Wp 210 Wp 220 Wp 225 Wp 230 Wp
Performance tolerance ±3 % ±3 % ±3 % +2.5 % +2.5 %
Module efficiency factor min. 12.29 % 12.90 % 13.51 % 13.82 % 14.13 %
Rated voltage (Umpp) 28.6 V 29.1 V 29.5 V 29.23 V 29.54 V
Rated current (Impp) 7.01 A 7.24 A 7.47 A 7.74 A 7.82 A
Off-load voltage (Uoc) 36.2 V 36.4 V 36.6 V 36.43 V 36.66 V
Short-circuit current (Isc) 7.86 A 7.93 A 8.00 A 8.24 A 8.34 A
Temperature coefficient (Pmpp) –0.45 %/°C –0.45 %/°C –0.45 %/°C –0.45 %/°C –0.45 %/°C
Temperature coefficient (Voc) absolute –0.127 V/°C –0.127 V/°C –0.130 V/°C –0.123 V/°C –0.123 V/°C
Temperature coefficient (Voc) procentual –0.35 %/°C –0.35 %/°C –0.35 %/°C –0.34 %/°C –0.34 %/°C
Temperature coefficient (Isc) absolute +2.1 mA/°C +2.1 mA/°C +2.1 mA/°C +4 mA/°C +4 mA/°C
Temperature coefficient (Isc) procentual +0.028 %/°C +0.027 %/°C +0.026 %/°C +0.05 %/°C +0.05 %/°C
Warranted power 1 12/90 years/% 12/90 years/% 12/90 years/% 12/92 years/% 12/92 years/%
Warranted power 2 25/80 years/% 25/80 years/% 25/80 years/% 25/80 years/% 25/80 years/%
Available from:
Pow
erP
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00
P–2
30P
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90
5
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200
9 ©
Co
nerg
y
1 Nominal operating temperature of the cell at 800 W/m² irradiation, 20° C ambient temperature, wind speed of 1 m/s
2 According to the manufacturer's current warranty conditions. The warranty extension is an after sales product of the respective sales organisation in your country.
3 Standard Test Conditions defined as follows: 1,000 W/m2 radiant power at a spectral density of AM 1.5 and a cell temperature of 25° C
Module dimensions (L x W x H): 1,651 × 986 × 46 mm Cell dimensions: 156 x 156 mmNumber of cells (polycrystalline): 60 NOCT:1 43.4° CMaximum permissible load: 5,400 PaGlass thickness: 4 mmCable: 2 x 1,000 mm length,
4 mm cross section
Plug type: Huber & Suhner: Plug connector with integrated twist lock
Module weight: 22 kgCertification: in accordance with IEC/EN 61215 Ed. 2,
IEC/EN 61730Product warranty:2 5 years, can be extended to
10 years on request
All figures are given in mm
www.conergy.com