Utilization of geothermal energy with focus on Denmark

Department of Energy Sciences, Faculty of Engineering

Mechanical Engineering

Master Thesis 2010

Student: Hanna Elf

Supervisor: Svend Frederiksen, Professor at the Department of Energy Sciences

Examiner: Janusz Wollerstrand, Lecturer at the Department of Energy Sciences

Copyright Hanna Elf

Department of Energy Sciences, Faculty of EngineeringLunds Tekniska HögskolaBox 118SE-221 00 LundSweden

Institutionen för EnergivetenskaperLunds Tekniska HögskolaBox 118221 00 Lund

AbstractThis work will involve knowledge connected to geothermal sources, what they are and how they can be used for production of energy and electricity. Focus will be on the current situation in Denmark and to end by covering a possible Danish future development in geothermal.

Denmark is one of the countries most engaged in the development of district heating and currently more than half of the households are being heated through district heating. The capital region works on extending the existing network and converting a substantial amount of existing natural gas supply into district heating.

The utilization of geothermal energy varies greatly around the world and some countries have particularly favorable conditions, however Denmark has not yet been considered one of them. The heat in the Danish subsurface reaches a maximum of around 100 °C, which can be viewed as relatively modest but a sufficiently high temperature to be used in the district heating network. A collaboration between district heating companies in the metropolitan area has lead to a geothermal pilot plant where work is conducted on a possible expansion.

A recent survey1 from The Geological Survey of Denmark and Greenland shows that down to 3000 m in Denmark there is heat to theoretically be able to ensure the country’s heating need for hundreds of years.

Denmark has ambitious goals in terms of a climate-neutral society, where the supply of electricity and building heat energy is of importance. The submitted plans and visions are proposals on how geothermal energy could play a major roll in the Danish energy supply, especially in a longer perspective.

Finally, three aspects have been chosen to present the ability to accelerate the expansion of geothermal energy in Denmark:

1. The cost of a geothermal project is usually high and there is a substantial risk that unpredictable geological conditions can turn a geothermal project into a total failure. Insurances for geothermal projects are available in Germany, however not in Denmark.

2. A new drilling technique, known as spallation drilling, may change the conditions and development for deep geothermal projects.

3. Today the area of use for geothermal sources is district heating, a possible development may be geothermal electric power production in Denmark, viewed in a longer perspective.

1 Vurdering af det geotermiske potentiale i Danmark (2009)

SammanfattningDetta arbete kommer att beröra allmän kunskap kring geotermiska källor, vad de är och hur de kan nyttjas för produktion av energi och elektricitet. Fokuseringen kommer att vara på den rådande situationen i Danmark och arbetet avslutas med att behandla en möjlig dansk framtida utveckling för geotermi.

Danmark är ett av de länder som satsat mest på utbyggnad av fjärrvärme och idag värms mer än hälften av alla hushåll med värme från fjärrvärme. Huvudstadsregionen arbetar med att bygga ut det existerande nätet samt konvertera de befintliga gasledningarna till vattenledningar.

Utnyttjandet av geotermi varierar stort världen över och vissa länder har särskilt gynnsamma förutsättningar, Danmark är dock inte en av dem. Värmeenergin i den danska grunden når maximalt ca 100 C⁰ vilket kan ses som relativt blygsamt, men det en tillräckligt hög temperatur för att värmen ska kunna utnyttjas i fjärrvärmenätet. Ett samarbete mellan fjärrvärmeföretag i huvudstadsregionen har lett till en geotermisk pilotanläggning var arbete förs kring en eventuell utbyggnation.

En relativt färsk undersökning2 gjord av Danmarks och Grønlands Geologiske Undersøgelse påvisar att det ner till omkring 3000 m i Danmark finns tillräckligt med värmeenergi för att i teorin kunna sörja för landets uppvärmningsbehov under hundratals år.

Danmark har högt uppställda mål gällande ett klimatneutralt samhälle, där försörjning av elektricitet och energi utgör en del. I presenterade planer och visioner finns förslag om att geotermi kan kommer att spela en stor roll i den danska energiförsörjningen, i synnerhet på längre sikt.

Avslutningsvis kommer tre valda aspekter kring möjligheten att driva på utnyttjandet av geotermi i Danmark att presenteras:

1. Kostnader vid geotermiska projekt är höga och kan komma att ses som ett hinder, detta speciellt för länder som inte har särskilt goda geologiska förutsättningar. Försäkringar för geotermiska projekt finns tillgängligt i Tyskland, dock inte i Danmark.

2. En ny borrnings teknik, den så kallade spallations-tekniken, kan komma att ändra förutsättningarna samt utvecklingen för djup geotermi.

3. Idag används geotermiska källor uteslutande till fjärrvärme, en möjlig utveckling sett på lång sikt kan vara geotermisk kraftproduktion i Danmark.

2 Vurdering af det geotermiske potentiale i Danmark (2009)

PrefaceI was accepted to Lunds Tekniska Högskola in 2005 were I have been studying mechanical engineering. This thesis is to represent 30 ECTS out of the total 270 ECTS leading to a Degree of Master of Science.

In January 2010 I moved to Denmark to take my final courses at the Technical University of Denmark as an exchange student. The intention was to stay for one semester but I quickly wanted to find a reason for extending my stay. That is how I came to have a Danish focus on my thesis. I have during this time conducted my work for Lunds Tekniska Högskola but have had my residence in Denmark and have had contact with companies and organizations in Denmark.

I would like to thank the people that have helped me in my work, answered my questions and helped to clear up confusions; Leif Bjelm, professor at Lunds Tekniska Högskola; Svend Frederiksen, professor at Lunds Tekniska Högskola; Lars Gullev, managing director at the VEKS regional district heating company and Steffen B. Moe, managing director at Sønderborg Fjernvarme.

A special thanks goes to my family and friends for believing in me, giving my support and well wishes.

Hanna Elf

Copenhagen 3rd of December 2010

CHP Combined heat and powerCTR Centralkommunernes Transmissionsselskab I/SEGS Enhanced Geothermal Systems3

Energistyrelsen The Danish Energy AgencyGEUS Geological Survey of Denmark and GreenlandHDR Hot Dry RockHGS Hovedstadens Geotermiske SamarbejdeIGA International Geothermal AssociationKE Københavns Energi A/SLTH Lunds Tekniska HögskolaOCR Organic Rankine CycleVEKS Vestgnens Kraftvarmeselskab I/S

3 EGS may also be an abbreviation of Engineered Geothermal Systems and is referring to the same concept as Enhanced Geothermal Systems.

Table of Contents1 Introduction.........................................................................................................................8

1.1 Aim...............................................................................................................................9

1.2 Restrictions...................................................................................................................9

2 Traditional geothermal sources.........................................................................................10

3 Exploiting the geothermal resources.................................................................................12

3.1 Conventional systems.................................................................................................12

3.2 Enhanced Geothermal Systems – EGS......................................................................13

4 District Heating – Technology and the Danish Network..................................................15

4.1 Production..................................................................................................................15

4.2 Distribution.................................................................................................................15

4.3 Utilization in Denmark...............................................................................................16

4.4 The Greater Copenhagen Area...................................................................................17

5 Political ambitions for geothermal energy in Denmark and its possible roll....................19

5.1 Heat plan Copenhagen...............................................................................................19

5.2 Green Energy – The way towards a Danish energy system without fossil fuels.......20

5.3 CO2 Neutral in 2025 – Copenhagen’s Climate Plan...................................................21

6 Geology in Denmark.........................................................................................................23

7 Copenhagen Geothermal Cooperation – Hovedstadens Geotermiske Samarbejde (HGS)25

8 Existing geothermal plants in Denmark............................................................................27

8.1 Thisted........................................................................................................................27

8.2 Margretheholm...........................................................................................................27

8.3 Sønderborg.................................................................................................................28

8.4 Applying for a geothermal project.............................................................................29

9 Insurance of geothermal projects.......................................................................................30

9.1 Existing insurances and aids in Germany..................................................................30

9.2 The development in Denmark....................................................................................32

10 Spallation drilling – A way of lowering the costs for deep geothermal projects?.........34

11 Geothermal power production.......................................................................................36

11.1 An example – A chosen location............................................................................38

12 Discussion......................................................................................................................40

13 Conclusion.....................................................................................................................42

14 References......................................................................................................................43

15 Appendix........................................................................................................................46

15.1 Darcy’s law.............................................................................................................46

15.2 Geothermal permits for applications......................................................................47

15.3 Contents of application...........................................................................................48

15.4 Calculations for estimations of reservoir potential.................................................49

15.5 Lindals diagram......................................................................................................52

1 IntroductionThe utilization of geothermal sources dates back to the Greek and Roman times when warm water was used in medical, domestic and leisure applications. Another example is the early settlers in New Zeeland whom were depending on the geothermal steam for essential parts of their life such as cooking and washing. [1]

Belfort in France is the location where the first measurements of geothermal energy took place in 1740. Although it was not until the twentieth century that humans could understand the phenomena.

Larderello is an area in Tuscany, Italy, which was the first for using geothermal sources resembling those of today. In the beginning of the 19th century a method for a system using the heat in the fluids in an evaporating process in a chemical industry was developed. Hundreds years later a low-pressure steam source was used in order to heat buildings and greenhouses in this part of Tuscany.

The first attempt to generate power from a geothermal source was in 1904 and the location for this was Larderello.

Figure 1 - The "covered lagoon" in Larderello, Italy [28]

Parallel with the development in Italy other countries also began to develop geothermal projects. The first geothermal district heating system came in 1892 and was located in Boise, Idaho, USA. Shortly after, Iceland began to explore geothermal sources, mainly for domestic heating.

The interest for geothermal electric power has grown and today countries worldwide explore the possibilities. Countries like Japan, USA, Philiphines, Indonesia and Italy are some that use power from geothermal sources and in year 2003, 8402 MW was the installed capacity in the world. More countries have the possibility to explore geothermal sources for non-electrical

use and Iceland, France, Turkey, Russia and Japan are some examples. In year 2000 the total energy use during one year from geothermal sources reached around 190 699 TJ4. [2]

1.1 AimThe aim with this work is to present a general knowledge of geothermal energy, some of the current developments within this technology in Denmark and to give suggestions of possible, new areas for the development in Denmark.

1.2 RestrictionsShallow geothermal energy is retrieved from the ground at depth down to around 400 m and is mainly used as heating systems. Ground source heat pumps are one of the main methods for this purpose. [3]

There are discussions on whether when discussing geothermal energy, heat from depths down to 400 m should be included. The opinions among professionals working in this field differ on this issue. In this project shallow geothermal energy will not be a part of the definition geothermal energy.

4 Heat from shallow geothermal sources are included in the 190 699 TJ/year.

2 Traditional geothermal sourcesThe word geothermal originates from the Greek language, geo meaning earth and thermos meaning heat. According to the Danish Energy Agency 2009:4 geothermal energy is defined as renewable energy, as in the field of contemporary technology and social systems in time-scales, it can reproduce itself.

Geothermal energy has its source within the earth and is not reliant on the sun or other time dependent factors. This means that it is possible to extract heat at all hours of the day all year around. The heat that is stored in the subsurface is mostly originated from the time when the earth was formed and form natural radioactive decay processes taking place in the ground. There are three essential main factors for having geothermal energy of the traditional kind, the first being an aquifer containing water, secondly the fluid itself and thirdly a heat source that will heat up the fluid. The aquifers, or reservoir as they also can be called, are often covered by impermeable rocks which retains the fluid and prevent it from moving upwards. These seals are connected with a recharge area, placed at the surface of the earth, that helps replace the water that do escape.

Figure 2 - Schematic figure over a geothermal system [28]

When talking about aquifers for geothermal energy the concepts of porosity and permeability are of great importance. The amount of cavities in the rock will determine the porosity of the aquifer whilst permeability is the ability to transmit water. It is important that both porosity and permeability exist in an aquifer used as a geothermal source. Both conditions have to be present, one without the other is not sufficient.

Porosity is defined as the fraction between the volume of cavities over the total volume, and will be presented as a percentage.

∅= VcV T [%]

Permeability is traditionally measured in Darcy [D] but the SI unit is m2. Permeability may be determined by Darcy’s law [Appendix 14.1] or through estimation using empirically derived formulas.

1 D ≈ 10-12 m2

What the end-product will be is determined by the enthalpy5 of the fluid. However it is often temperature that is used when talking about geothermal energy and in many cases it is sufficient enough to say that temperature and enthalpy goes hand in hand. Geothermal sources can be divided into three different categories depending on enthalpy (temperature) as follows:

High enthalpy – water and steam with temperatures over 180-200 °C

Medium enthalpy – water and steam with temperatures between 100-180 °C

Low enthalpy – water and steam with temperatures below 100 °C

The geothermal fluid that is being brought up to the surface has been in contact with the rocks for several hundreds or even millions of years. Dissolved solids, such as carbonates, sulphates and chlorides, exist in the fluid and may represent around 1%. The geothermal fluid is often referred to as brine and this is due to dissolved solids. Other matters as well can be found in the brine, which and in what amount depending on the location and depth. Silica, heavy metals and sodium are some examples. The design of the plant is vital in order to avoid problems in the operation and to make sure that the brine, with its solids, does not leak out in to the surroundings.

In the early phase of a geothermal project when wells are being drilled noise will occur and this can be seen as noise pollution. Nevertheless when a plant is taken into operation noise will rarely be a problem, since a geothermal plant has the same noise level as any other form of plant.

Geothermal plants have had problems with the smell of “rotten eggs” which is caused by leaking hydrogen sulfide. However with state-of-the-art technology the plants of today have lowered the environmental impact with re-injection. This leads to no or little need to handle waste water, e.i. the toxic brine. A closed cycle has minimized the corrosion and scaling problems connected with geothermal plants. This has lead to lower emissions, minerals and particles are not deposited in the nature and prevent the aquifers from drying out.

CO2 is one of the important greenhouse gases and geothermal sources contain significant amounts of the gas. A survey made by IGA in 2002 shows that CO2 emissions from geothermal plants can vary largely in levels, from 4 g/kWh to 740 g/kWh. IGA has presented a weighted average of 122 g/kWh for a geothermal plant, which can be compared with 460 g/kWh for a natural gas fired plant and 960 g/kWh for a coal fired plant. [1]

5 Enthalpy is defined as the heat content of a substance per unit mass

3 Exploiting the geothermal resourcesThe heat that is extracted origin from the rocks, and actually as much as 90% of the heat in an aquifer is found in the rock and not in the water. The rocks are seen as poor conductors and large heated areas are needed in order to extract a sufficient amount of heat. With increasing depth the temperatures will raise but the conditions for porosity and permeability will deteriorate. [1]

Traditionally are aquifers down to 3000 m being used, but EGS is a new and up-coming technique that collects heat at depth between 3 and 10 km.

3.1 Conventional systemsAs discussed in section 2, geothermal sources are found in underground reservoirs and in Denmark the depth of the reservoir ranges from 800 m to 3000 m6.

To access the warm fluid boreholes are drilled into the aquifer from where the fluid is retrieved to the surface, often with help from pumps, shown with a simple sketch in figure 3. The fluid can then be used in steam turbines or for direct use, e.g. district heating, depending on its temperature. It is seen as less difficult to deal with warm water then steam, due to lower pressure and temperature for the water. When the heat from the fluid has been extracted it is re-injected into the ground through a second borehole, now with a lower temperature. [1]

Figure 3 -- Simple schematic figure showing how the heat form the warm water stored in the aquifer is transferred through a heat exchanger, here to a district heating system.

6 The larger depth is chosen after calculations showing that the risk for unsatisfied porosity and permeability is too large at depths over 3000 meters and the upper limit is chosen in order to ensure reservoir water with a minimum temperature of 20 degrees.

Aquifer

Heat Exchanger

Brine from aquifer

Geothermalt heated water for district heating

Return water for reheating

Production well

Injection well

3.2 Enhanced Geothermal Systems – EGSEGS goes further down in the ground then a conventional geothermal system, into crystalline rock where there is little or no natural fracturing for water to flow through. This is usually at depths ranging between 3-10 km. The overall concept of extracting heat is still equivalent to the previously described, see figure 4.

A borehole into the hot basement rock is drilled, this rock has a limited permeability and therefore also a limited amount of fluid that flows through. This is often referred to as hot, dry rock which also is a common name used in literature for this type of systems. Then cold water is injected under high pressure in order to obtain fractures in the subsurface and to open up already existing fractures. Water continues to be pumped into the well to extend the fractures and forming a large network, creating an artificial reservoir. A second well is drilled where the injected water will be brought up to the surface, now with a higher temperature due to heat transfer from the hot rock. Additional production wells are often drilled so that a larger amount of heat may be extracted from the subsurface. [4]

Figure 4 - Picture showing a geothermal system in hot dry rock [29]

In a majority of the literature no distinction between EGS and HDR (Hot Dry Rock) is made, but it is mostly chosen to refer them to the same type of technical solution. There is no real physical difference between the two. Hot dry rock is the oldest concept where two wells are drilled and a network of fractions created by water under pressure will connect the wells. EGS

is structured in the same way but strives to create a larger volume of fractures and use more production wells.7

Soultz-sous-Forêts is a pilot plant located just north of Strasbourg in France, close to the German border. Here, three wells have been drilled into the crystalline basement rock and temperatures above 200°C have been measured at a depth of 5000 meters. [5]

Depth of production wells 5 000 mDepth of injection well 5 000 mSpacing of the holes 600 mDelivery temperature 180°CPlanned capacity 4.5 MWe

7 E-mail correnspondens with Leif Bjelm, professor in engeneering geology at LTH, Lund Sweden

4 District Heating – Technology and the Danish NetworkDistrict heating is widely spread in Denmark and is one the most common ways of heating households and other buildings. The technology invites for a number of different sources and where water is the most used medium for heat transportation.

4.1 ProductionThere are different types of sources and production plants where a cogeneration plant or combined heat and power, CHP as it also can be called, is widely used. Other sources can for instance be waste heat from industrial processes or the use of energy form the sun and geothermal energy. The source for a production plant can vary and that is due to the district heating systems ability to take care of many different sources. A mix of production plants is often used in a district heating system in order to cover both base load and peak load.

In a CHP both electricity and heat is produced and 70-95% of the fuel will be converted in to a useful product in comparison to 25-45% if it only was power generation. The fuel used for combustion may vary largely when looking at different countries. In the Greater Copenhagen Area coal, oil, biomass, natural gas and waste are used as fuels.

In a CHP, figure 5, the fuels will be fired in order to heat water that is converted to steam (1) which will pass through a turbine (2) which in turn runs the generator (3) where power is generated. The steam is then cooled down in a condenser (5) and the heat in the condensate is transferred to the district heating net (6). [6]

Figure 5 - Schematic figure over a CHP [30]

4.2 DistributionThe heat is distributed to the customers in pipelines mostly located in the ground and figure 6 shows a simple sketch over the pipelines between the production plant and the end-users. Pipes above ground do exist but are often not chosen because it is seen as aesthetically disturbing in the landscape and there is a risk of sabotage. In order to handle peak loads and smaller interruptions, an accumulator can be used in the net where hot water can be stored for shorter periods of times. Typical temperatures on the water in Scandinavia are between 70-120°C in the supply line and 40-65°C in the return line. With help from heat exchangers the heat can be transferred from the water in the distributions pipes to the buildings. Once the heat

from the pipelines has been transferred to the building it will be used in for example radiators and to heat the tap water.

Figure 6 - Schematic figure over supply (red) and return (blue) [31]

The most common medium of transport is hot, pressurized water; it is not expensive, has easy access and is seen neither as corrosive nor toxic. Sometimes steam is used instead. When comparing a net based on hot water with a steam based net under similar conditions a steam based net tends to lead to greater heat losses. This leads to problems, particularly in extended district heating systems. Generally, hot water is preferred today.

There are a numerous number types of pipelines for district heating systems and the trend goes towards prefabricated pipes. This reduces the time needed to assemble the pipe in the ground at the site, which is especially crucial in cities where interference in traffic etc. can cause problems. The type of pipe is determined by the diameter and to some extent the conditions in the ground. A pipe is designed with an inner tube where the medium flows, this is covered with insulation and finally a cover to protect the insulation from ground forces that can shorten the life-span. [6]

4.3 Utilization in DenmarkDistrict heating in Denmark is the most common way to supply heat to dwellings and other buildings and stands for more than half of the supply. The production of district heating in Denmark mostly comes from centralized CHP, almost 50%, while the other half is covered by decentralized CHP, district heating plants and secondary producers such as industries and waste treatment facilities. The total production for district heating during 2008 was 123.7 PJ, that is 33.9% more then in comparison with the level in 1990. The final heat usage can be divided into three areas; household, trade and service, and finally industry. Looking at energy flows for Denmark for earlier years, the relationships between the three areas can be seen as constant. Households are the largest area consuming half of what is produced, while trade and services, and industry are covered by 23% and 7% respectively. Losses include the heat consumption at refineries and distribution losses. This can be seen in diagram 1.

Diagram 1 - Values in [PJ] showing the origin of the heat and the end users [32]

There has been a large change in what fuel that is being used for district heating during the last 30 years. It is the use of natural gas and renewable energy that has increased leading to a decrease in the use of oil and coal. 21 MW heat is produced in geothermal plants and is added to the district heating network. [7]

46%

28%

22%4%

Fuels used for production

Renewable etc.Natural gasCoalOil

Diagram 2 - Showing the fuels used for district heating production where renewable etc. is made up by 8.9 % waste, 35.4% biomass and 2.1% other where geothermal sources is one part [32]

4.4 The Greater Copenhagen AreaThe district heating system in Copenhagen has a long history and is one of the largest networks in the world. It started in the mid 1920’s and has grown ever since. Today around 150 km of double-piped net covers just over 98% of the heat demand in the municipality of Copenhagen, supplied by the company Københavns Energi A/S (KE). As seen in the map in figure 7, there are two regional district heating companies, Vestgnens Kraftvarmeselskab I/S (VEKS, blue color) and Centralkommunernes Transmissionsselskab I/S (CTR, red and yellow). Additionally, a smaller network to the north-west is indicated by green color.

Central CHP 55,4

Decentral CHP 26,6

Secondary Producers

22,8

District Heating

Plant18,8

123,7

Final heat

usage 98

Losses 25,7

Households 61,2 Trade &

Services 28,6Industries 8,2

Figure 7 – The district heating system in the Greater Copenhagen Area [33]

Approximately one third of the fuel in the district heating system come from biomass and waste incineration, while the remaining two thirds are covered by fossil fuels. The major plants that produce heat to the net in the Greater Copenhagen area are four CHP plants; Amagerværket, Avendøreværket, H.C. Ørstadværket and Svanemølleværket, and three waste incineration plants; Amagerforbrændningen, Vestforbrændningen and KARA/NOVEREN.

Water is not the only fluid being used in the district heating system, steam (seen as yellow in figure 7) covers one third of the heating demand. Hospitals and industries in the central parts of the city were the ones that were originally supplied with steam, but it came to be extended to the dwellings nearby when the steam pipe was established. KE is in the process of converting the steam system into a water system. [8]

The two transmission companies VEKS and CTR buy heat from the producing plants mentioned above. Then the heat is transferred through the transmission net to distribution companies, such as KE, whom are the ones to buy the heat from the transmission companies. It is then the distribution companies that distribute heat to consumers. [9]

5 Political ambitions for geothermal energy in Denmark and its possible roll

Several plans and visions for the future energy supply in Denmark have been made. In these plans the presented goals will lead to a use of renewable source in a larger extent and a reduction in CO2 emissions.

The Danish government has a vision of a future society independent of fossil fuels. With the Kyoto protocol Denmark, along with other countries, has committed itself to a reduction of 8% of the emissions relative to 1990 levels. Denmark has made further commitments, a reduction of 21% of the emissions relative to 1990 levels.

As a part of the vision of a future society independent of fossil fuels the Danish government is working on goals to reach a share of 20% of renewable energy in gross energy in 2011, and 30% of renewable energy of the total energy in 2020. A change of fuel will not alone reach the goals, energy conservation and energy efficiency are two strategies that will help reducing the energy consumption. In order to have a safe long-term supply it is desirable to have a reduction in energy consumption through energy conservation, energy from renewable sources and a well working cooperation within Europe. [10]

5.1 Heat plan CopenhagenVEKS, CTR and KE have together produced a report on the future heating demand in the Greater Copenhagen Area, “Heat Plan Copenhagen” (Varmeplan Hovedstaden), giving different scenarios as examples. There is an intended goal that in 2025 energy from renewable sources should be double the amount in comparison to today8, which would mean at least 70% of the total energy shall origin for renewable sources. Four scenarios are set for the time span up until 2025 and a perspective for 2050 is set.

The baseline scenario – This is a scenario where no larger changes are being done. The development is based on the existing rules for taxes and charges, and no larger efforts are being made in order to reduce the use of energy.

Savings and decentralized technology – This scenario shows the efforts in reducing the use of energy. It also shows the possibilities for using the excess heat and the establishment of other heat sources.

Increased heat market – In this scenario it is shown how a conversion from natural gas to district heating for dwellings may look like. Some of the increased heating in the Copenhagen area will be covered with heat form geothermal sources.

Renewable energy, savings and conversion - Here, the idea is to combine the possibility of reducing the use of energy and to convert into district heating. In this scenario it is meant for geothermal energy to be used to reduce dependency on biomass.

8 The report was distributed in September 2009

The scenario for 2050 is based on the last mentioned scenario (Renewable energy, savings and conversion) and it is here assumed that none of today’s existing heat producing plants still are in use, also the district heating is supplied with 100% renewable energy. Is it assumed that heat from the sun and geothermal energy takes a larger part in the district heating system, as shown in figure 8. [9]

Geo- thermal

Heat Pumps

Electrical Elements

Bio Oil Waste Bio Mass Sun Waste Heat

0

2

4

6

8

10

12

PJ/y

ear

Figure 8 - Production for district heating in 2050 divided into different sources Area [33]

5.2 Green Energy – The way towards a Danish energy system without fossil fuels

The Danish Commission on Climate Change Policy presented a report with suggestions on how Denmark will become independent of fossil fuels. The vision addresses two larger challenges, one focusing on how to reduce the greenhouse gases and the second focus on the security of energy supply due to a growing use of energy. The Heads of State and Government in the EU has proposed a goal that would limit the global heating to a maximum of 2 degrees and that the greenhouse gases from industrialized countries has to be reduced with 80-95% by 2050 in comparison with the levels in 1990.

The work of the Danish Commission on Climate Change Policy has been focused on 9 main areas that further on have lead to 40 recommendations. In these nine areas mentioned, subjects are for example; the year 2050 is realistic, there should be flexibility with openness to new technologies and a conversion must start now.

In this report two lager recommendations are given on how Denmark will become independent from fossil fuels. The first is to become more energy efficient, this through developments in technology and a better use of electricity. Secondly the future energy shall be from renewable sources where the energy system shall be based on electricity, mainly from windmills. Additional energy will come from biomass and may also origin from other

renewable sources such as geothermal energy and solar heat. Figure 9 shows how the share between energy sources may look like in the future in comparison to today.

A suggestion for a future society without fossil fuels is that houses are heated with district heating and heat pumps where the energy comes from windmills. The heat in the district heating system will have its origin from biomass, solar heat and geothermal energy. [11]

Figur 9 - Share in energy sources, 2008 vs. 2050 [34]

5.3 CO2 Neutral in 2025 – Copenhagen’s Climate PlanThe municipality of Copenhagen has published a climate plan (København CO2 neutral i 2050 – Københavns Klimaplan) with visions of a CO2 neutral city in 2025 presenting initiatives on how to reach the goals.

The first step toward a carbon neutral city in 2025 is to reduce the carbon emissions by 20% relative to the levels in 2005 until 2015. It will be a challenge but an assessment that has been carried out shows that it is possible. The climate plan shows desirable implementations within different areas such as energy supply, transport, buildings, everyday life and the development of the city. This plan shows a vision of becoming a leading actor in the field of renewable resources and the technologies that come with it.

A reduction of 20% in carbon emissions corresponds to 508 000 million tonnes CO2/year less than in 2005. This goal will be reached by for instance a conversion in energy production from fossil fuels to renewable sources and a reduction in energy consumption.

The statement that the municipality of Copenhagen will be carbon neutral in 2025 means that the net emissions will be zero. The plan presents 50 concrete initiatives on how to reach the goal. It can be read that biomass will replace coal, a new CHP and new windmills will be built, heat from geothermal energy will be increased and an improvement in waste incinerations and district heating network will help reduce the carbon emissions. Table 1 gives an overview of the potential in reduction for different measures.

Measures Potential in reduction, tonnes CO2

Energy savings 230 000Energy savings in the municipality’s own operations

19 000

Conversion of biomass 300 000Geothermal 25 000Solar heating 1 000Heat pumps and electrical elements 65 0000Improved waste separation 9 000Increased windmill capacity 925 000Urban development 30 000Reduction of transport 150 000

Table 1- The potential of these measures are based on the carbon levels in 2005 [35]

The vision according to this plan is to expand the existing geothermal plant at Margretheholm to a so called star plant. By doing that the heat capacity is expected to be five to six times larger then it is today. The plant will have eleven boreholes and the heat will be distributed to the district heating network in Copenhagen and account for about 11% of the heating use in the city. [12]

6 Geology in DenmarkOne can learn about the underground by collecting various information, for example through seismological investigations and by studying already existing wells. By combining this knowledge an estimation of the underground can be given, it will be possible to estimate the geological conditions and decide whether the area is suitable for geothermal projects. In order to get an accurate valuation it is vital to have knowledge about the structure of the underground such as thickness, depth and possible faults and this is collected through seismological investigations. While knowledge concerning porosity, permeability, temperature and salinity mainly comes from existing wells, preferably from well close by as the underground can show large variations within the same area.

Five reservoirs holding possible geothermal qualities have been detected in Denmark; Frederikshavn reservoir, Haldager reservoir, Gassum reservoir, Skagerrak reservoir and Bunter reservoir, which are all being presented in Figure 10.

The Bunter reservoir and the Gassum reservoir are two reservoirs covering the larger parts of Denmark, but it is indicated that all reservoirs holds good conditions. This is based on data from the already existing plants and recently performed investigations. Thus, there are large amounts of geothermal sources to be explored in Denmark. [13]

Figure 10 - Map showing the different formations and placement of geothermal plants [36]

Investigations done by Aarhus University gives rough indications for the Danish reservoirs seen per km, an increase in temperature with around 30°C which is being made visual in diagram 3. Further, it is indicated that there will be an increase in salinity with around 10% per kilometer and that the permeability is around 1D at 1 500m depth and will then be halved for each 300m. This puts Denmark’s geothermal resources into the low-enthalpy category meaning that it is not suitable for power production. [14]

GEUS has compiled data from several drillings which has lead to the following formula on the relationship between permeability and porosity in Denmark.

Permeability = 196 449 * (Porosity in fraction)4.3762 [mD]

The data is collected from all over the country, but no special regard considering depth has been taken into account and this formula can only give an indication of the permeability when the porosity is known. [13]

Diagram 3 - The diagram shows temperature data from drillings made in Denmark, the black line shows a temperature gradient of 30 °C/km and the green line shows a generalized temperature gradient of around

28 °C/km where it is estimated that the surface temperature is 8 °C. [37]

7 Copenhagen Geothermal Cooperation – Hovedstadens Geotermiske Samarbejde (HGS)

In 1996 an energy action plan, Energi 21(Energy 21), was carried out by the then current government and this plan was the start of Copenhagen Geothermal Cooperation (Hovedstadens Geotermiske Samarbejde - HGS). A committee was established in order to investigate how Denmark could use geothermal resources in a way to reduce emissions from carbon dioxide. One of the conclusions was to set up a pilot plant in Copenhagen as the area has a well functioning district heating network and a large heating demand which could allow an integration of geothermal energy in the future. [15]

HGS was formed in 1999 with the intention to introduce and supply the Greater Copenhagen Area with district heating from geothermal energy. VEKS, CTR, KE and DONG Energy are the four companies that joined together to form HGS and Diagram 4 shows the shares in percentage. HGS is the cooperation that runs the geothermal plant at Margretheholm, Amager in Copenhagen.

18 %

18 %

18%

46 %

HGS in percentage

VEKSCTRKEDONG Energy

Diagram 4 - Shares in HGS

In 2008 an investigation made by HGS showed that the geothermal reserves in the three main reservoirs could cover between 30-50% of the heat demand during several thousands of years. [16]

An investigation about a possible expansion of geothermal energy in Denmark has been made and carefully studied. Every second year there will be agreed with the Danish Energy Agency on which concrete work that shall be preformed with consideration to resources and economics for new establishments. The latest report covers the possibility of building a star plant. A star plant has multiple wells from one well site, all in different directions reaching different parts of a reservoir, see figure 11. Four locations were looked extra into and the location at Amager in Copenhagen was chosen. The reason for wanting to continue on to the next phase at Amager is based on four major reasons; the reservoir is well known and has been producing heat in more then five years, there are less investments for connection pipes in comparison with other locations, it is the lowest total investment in relation to production in the subsurface and there is a low heat price. [17] [27]

Figure 11 - A star plant with five production wells (red) and six injection wells (blue)[38]

8 Existing geothermal plants in DenmarkThe first geothermal plant was established in 1984 and today two operating plants exist in Denmark, Thisted and Margretheholm, a third is being established in Sønderborg. The two most wide-speeded reservoirs, Gassum and Bunter are being used and warm water is collected at different depth with a variation in temperature. The plants are found in different areas of the country, marked with red stars in figure 10 in section 6, and the total capacity which is produced is around 21 MW.

Locality Flow Rate [kg/s] Temperature [°C] Capacity [MW]Inlet Outlet

Thisted 61 44 11 7Margretheholm 73 73 17 14

Table 2 - Showing maximum utilization and capacity for existing plants

8.1 ThistedThe geothermal plant in Thisted was the first one in Denmark and is located in the north western parts of Jutland. The pilot plant has delivered heat to the district heating network since 1984 when it was taken into operation. Since the start the amount of extracted heat has been increased and today 7 MW can be transferred to the net. Figure 12 shows a schematic overview for the plant. The plant pumps water from the Gassum sandstone aquifer at a depth of 1 250 m, the brine has a temperature of 44°C and a salinity of 15%.

With help from heat pumps and heat exchangers the heat can be transferred from the brine to the water circulating in the district heating net. The brine is then re-injected into the aquifer with a temperature of 11°C in order to be reheated. The heat pump that is being used is driven by the temperature difference between the driving heat and the transferred heat. [13]

Figure 12 - Schematic figure over the geothermal plant in Thisted [39]

8.2 MargretheholmThe plant is located at Amager in Copenhagen, the eastern part of Zeeland, just next to the Amager CHP plant. The location is only meters away from the water and the plant was taken into operation in 2004. The location was chosen so that an easy access of driving heat for the absorption heat pumps was possible as well as the closeness to the sea water. The plant uses a reservoir in the Bunter Sandstone Formation at 2 500 m depth with a water supply at around 73°C and a salinity of 19%. After having transferred heat to the net the brine is re-injected into the aquifer at a temperature of around 17°C. A schematic overview for the plant is shown in figure 13.

Here, 14 MW can be produced and this is equivalent to a bit more than 1%, or the consumption of around 4 600 dwellings, of the total energy used in the district heating system in Copenhagen (steam net from KE is not included). An additional 13 MW from the Amager CHP used for the three absorption heat pumps (driving heat) can be added and giving a total of 27 MW that can be put in to the district heating system. [14][18]

Figure 13 - Schematic figure over the geothermal plant at Margretheholm [40]

8.3 SønderborgThe plant at Sønderborg in the south of Jutland is still under development and does not produce heat to the local district heating net. Seismological surveys indicate that the geothermal source has a thick reservoir and that nearly a third of the district heating demand can be covered by heat from geothermal energy. The plant will, at best, be able to start producing heat in autumn 2011. [19]

There has been borehole made down to 2 500m, but it was at 1 200m in the Gassum sandstone formation that the best conditions was found with water at a temperature of 48°C. This is lower then the expected 64°C that studies had suggested was possible at 2 000m depth. It will not be possible to reach over 10MW, but the total will be more then 6MW which is the plants lower restriction. [20]

There were no plans on drilling deeper and there are uncertainties whether a more suitable reservoir could be found at larger depths. The found source was good enough to continue the project, i.e. the temperature held a sufficient level.9

8.4 Applying for a geothermal projectCompanies and organizations with plans on establishing a geothermal plant will have to send an application to the Danish Energy Agency. The location of the project has to be in an area not already covered by an existing geothermal permit. The available areas can be seen at a map over Denmark, distributed by the Danish Energy Agency, where the already chosen areas are marked. (Appendix 14.2)

New from October 2010 is that it will be possible to apply for new permits twice a year, with deadlines first of February and first of September every year. Now to start with, new permits will be approved in areas with existing district heating networks or in close connection with one, another possibility is to place it were it is planned for a coming district heating network. As a starting point the permits will be approved for a period of six years which can be extended for the extraction and production. The extended permission will be for the expected lifetime of the plant, but a maximum of 30 years is set.

The application shall contain certain information (Appendix 14.3) in order to be valid and to be able to make a proper assessment. A fee of 25 000 DDK will be charged which is not refundable. [21]

9 E-mail correspondence with Steffen B. Moe, Director at Sønderborg Fjernvarme

9 Insurance of geothermal projectsThere are large risks associated with drilling and the high costs, being made visible in diagram 5, unfortunately make geothermal projects to high risk projects. In order to make geothermal projects more attractive and to have more companies exploring the possibilities, the thought is that more aid and insurances in this field will help the development and growth.

68%

13%

8%

3%

8%

Costs

Drilling costs

Investigations/Studies

Administration/Engineering

Land/Access

Other

Diagram 5 - Costs for geothermal projects, European Commission (1999) [41]

As brought to attention in section 5 Denmark have high-reaching visions for the future. In order to reach a CO2 neutral society, Denmark seeks to shift from fossil fuels to renewable fuels. There will according to several plans be a large focus on energy and power from biomass and wind. Geothermal energy is mentioned as one of the renewable sources in the planned conversion. Looking at the existing geothermal plants in Denmark and comparing their capacity to what might be needed for the future, it is clear that the geothermal capacity need to increase during the coming 40 years.

The reason for insurances is for projects becoming more interesting and less risky, thus help in increasing the use of geothermal energy in Denmark as the plans and visions wishes for the future.

9.1 Existing insurances and aids in Germany“Germany is currently the most mature insurance market for deep geothermal reservoir risks.”

- Marcel Stäheli, director of Weather and Energy Underwriting at Swiss Re10

The market in Germany can be divided in two, private insurance market and the German federal risk mitigation program. Where the private market is covered by insurance companies 10 Investing in Geothermal (Article, downloaded 2009-02-01); Kai Sametinger, Renewable Energy Focus http://www.renewableenergyfocus.com/view/886/investing-in-geothermal/

such as Munich Re and Swiss Re to mention some, and insurance brokers such as Marsh and Willis. The difference between private insurances and insurance brokers is that the private side acts as a direct insurer while a broker spreads the risk between different partners, having one taking the leading role.

In the sector of private insurances it is common to let the customer decide the sum of expected investment which they want to insure. There are several requirements to fulfill when looking for a risk insurance and it may occur differences between various companies. The requirements are as follows:

A project description A geological feasibility study Seismic investigations A development concept Drilling path and well design Stimulation and hydraulic test program The power plant and heat use concept All necessary permits Information on contractors and key personnel Business plan Report on the probative value of all data by an independent expert An estimated probability of success

In Germany there is something called a POS-study and this study gives information on well testing from statistical evaluations, giving an estimation on the possibility for a successful project. A large part of the private insurances require this external report as a part of the application.

The German federal risk mitigation program works in addition to the private insurance market and strives for a faster development of geothermal projects. This program only addresses deep geothermal projects, i.e. projects with wells deeper then 400 metes. The program is built up by three modules each covering different areas; technical drilling risks, general project risks and exploration risks. These modules are to cover both heat and power projects while only heat projects can apply for the subsidies.

There are two main differences in comparison to the private insurance market. The first thing is that no POS-study is necessary, giving projects outside the traditional geographical area a chance. The second large difference is that the federal mitigation program uses subsidized long-term loans with a low interest rate.

In the module for the technical drilling mitigation the risk of excess drilling costs can be covered to some extent. In this way the risk of additional expenses beyond the initial costs can be lowered. The risk of cost increase and/or business risks may be covered by the general project risks module. But this module is only available for projects connected to power, that are being able to apply for credits from 10 to 15 million Euros. The module with exploration

risk mitigation is new and allows projects to apply for loans up to 16 million Euros, but covering at the most 80% of the drilling costs. [22]

9.2 The development in Denmark“District heating companies should not expect governmental help to cover the risk of geothermal projects”

- Lykke Friis, Climate and energy minister

Climate and energy minister Lykke Friis recently stated that it is not time now for new support systems, nor for a governmental insurance scheme for geothermal projects. It was also said that there exist two geothermal plants in Denmark, a third is under construction in Sønderborg, and that the Danish Energy Agency currently deals with six applications. This according to Lykke Friis states that geothermal energy is valued to be competitive with other renewable sources and she also says that the district heating companies themselves has to lower the risk by taking out an insurance policy. [23]

The author’s perception of the general opinion is that there is a large uncertainty related to seismological surveys and a large risk connected with drilling. Further, it can be said that smaller companies and organizations do not have the same possibility to take a chance due to the large sums involved and that a failure can have large consequences. Despite that, the comment from the minister of energy clearly states that there will be no governmental insurance for geothermal projects in the near future.

A group consisting of directors and technical specialists within the field has been formed in order to work with the problems related to geothermal projects and what can be done to minimize the problems. During a day of information connected to geothermal energy in Denmark held at the House of District Heating (Fjernvarmens Hus) this group was presented on paper and it was said that they will continue with the work, especially with the insurances. At the same time a representative from the working group presented their work that has been done so far and concluded the knowledge of the actual situation in Denmark.

They have been in contact with different actors in Germany and Marsh is one of them. This in order to see how the system works there and what they have learnt so far is that it is possible to insure geothermal projects, that all projects are to be valued individually, the insurance premium will depend on the risk and that the project shall formally be approved by GEUS or the equivalent organization in Germany (expertise opinions). With that knowledge it is possible to take one step forward and see what will be of interest to insure. Here the working group has decided to divide it into three sections; responsibility for the environment, the drilling phase and operation. Examples of private insurances that the working group has started working with and what might be real in the future are presented below. The ideas do not exist more than on paper and further work has to be done.

Drilling Risk Insurance; the premium will be calculated from the total price of the drilling project and it is hoped that it will cover the risk for losses and damage whilst drilling.

Lost-in-hole; this will be an additional insurance to the Drilling Risk Insurance and is to cover costs for typical things such as a drill head, drive motor and measuring instruments that can be lost in to the hole.

Exploration Risk Insurance; this is a performance warranty insurance that will insure extra costs connected with the amount of water, the temperature of the water and placement of the pump.

Other insurances mentioned were All Risk Insurance for surface facilities, Liability Insurance and Operating Insurance.

10 Spallation drilling – A way of lowering the costs for deep geothermal projects?

Conventional drilling works well in softer rocks but when dealing with harder rocks problem starts to occur. The drill bit used for crushing and grinding the rock in conventional drilling experience more wear and the drilling rates are too low when drilling in hard rock. This leads to a longer total time for drilling, and frequent bit replacement adds further to the total time spent on the drilling phase.

The costs for drilling are large as seen in diagram 5, in section 9 and the costs increases with depth of the wells. At depths that are relevant to EGS wear on the drill is large caused by the hard rock and maintenance can also be more difficult.

A so called hydrothermal spallation drilling is a new method which is currently being developed. This new method may in the future allow deeper wells, where the ground consists of harder rocks, with increased efficiency and at lower costs. Diagram 6 shows the predicted cost for spallation drilling in comparison with conventional drilling.

Diagram 6 - Predicted cost for spallation drilling compared to conventional drilling [42]

Spallation drilling will make the rock fracture by using water jets at extremely high temperatures. At the end of a body, a combination of a flame and evaporated water is forced

trough a nozzle targeted towards the crystalline rock, see figure 14. The hot flame will cause tension and inner natural existing flaws will expand to cracks. Due to stress imposed by the warm water thin flakes, so-called spalls will break away. In conventional flame-jet drilling a high velocity gas stream is used for removing the spalls.

Figure 14 – Showing the principal for spallation drilling [43]

Preformed tests show a possibility for improvement in drilling in hard rock when using spallation drilling instead of conventional drilling and the drilling rates have shown to be 5-10 times faster. When using spallation drilling the tools do not come in contact with the rock and therefore wear and damage will not occur in the same extent as for conventional drilling. This can reduce the time spent on replacement on worn drill bits and can in turn minimize the time spent on the drilling phase. [24]

11 Geothermal power productionInformal contacts with professionals in the field of geothermal energy indicate that they so far do not see that EGS can be a part of the Danish energy system. As explained in section 6, geological surveys and researches of the Danish underground indicate large thermal resources down to a depth of around 3 km. These layers can be expected to be relatively porous and reach temperatures up to around 100 °C, thus temperatures not especially suitable for electricity production. The utilization of geothermal sources in Denmark has historically been focused, and is still the only purpose, on producing heat for district heating and not for electrical power production. On this background it only seems natural that so far little, or none, has been done in terms of exploring the possibilities to drill deeper or to explore the possibilities for geothermal power production.

Other countries have however started to produce electricity using a brine at similar temperatures or slightly higher. These smaller plants can reach values up to a couple of hundreds of kW or in some cases a few MW.

A plant in Neustadt-Glewe, in the northern parts of Germany shows an example of this. As seen in figure 15 it is a combined plant, producing both heat and power. The brine is approximately 98°C when it reaches the surface and power can be generated from ORC11 plant. This plant can bring the brine to the ORC system and/or let it pass a heat exchanger for supply to district heating, in a combined serial and parallel operation mode. [25]

Figure 15 - A schematic picture over the combined heat and power plant in Neustadt-Glewe [44]

11 ORC is a system where an organic fluid is used; this fluid has a lower boiling point then water and allows cycle heat recovery from low temperature sources.

In Germany, there has been more interest in exploring options such as EGS and OCR. This comes more natural considering the current conditions in the country where district heating only serves around 12%12 of the heating market which is significantly lower then in Denmark. Also, in general the temperature gradient is higher than in Denmark. The Federal Ministry for Environmental, Nature Conservation and Nuclear Safety in Germany has presented a report on geothermal sources and existing plants, calculations give rough values for temperature gradients with values up to 50°C/km.13 While another source present possible temperature gradients up to 60°C/km in the south-west parts of the country, where Landau for example is located.14

When reasoning in general geological terms, this author has understood that the conditions of the subsurface in Denmark can not be assumed to deviate significantly from those of Germany. As explained in section 9 new drilling techniques are being invented and presented. The spallation technology shows possibilities of lowering the costs for drilling at larger depths. One may speculate on this background that deep geothermal technology intended for electricity generation could be feasible, whether it is in connection with district heating or not.

So why should one consider geothermal power generation in Denmark when the conditions are favorable for district heating?

One could propose that deep geothermal energy should be seen as quite attractive in Denmark and further use the knowledge that comes with an expansion of geothermal energy as a catalyst for deep geothermal technologies in the future for this country.

As mentioned in the visions for a climate neutral society, renewable sources and wind in particular, set out the base for this. Energy extracted from wind can be unpredictable as there might not be wind every day and therefore there are good reasons to supplement with another type of renewable source, for example geothermal. The point here is not to argue for geothermal power generation to be utilized rather than geothermal district heating. It should rather be seen as a supplement that can grow gradually. If the geothermal production should have a chance to reach a reasonable level within 30-40 years it is necessary to start investing now.

Another reason can be that it in the longer run there will be a tendency for buildings using less energy for heating. That in combination with the fact that the usage of electricity will probably not be decreased in the future, can lead to that the utilization of geothermal energy for district heating alone will reduce the base for combined heat and power production.

12 District heating in Germany – a survey about the German heat market and it’s legal framework (Information brochure, 2005); AGFW - The Energy Efficiency Association for heating, cooling and cogeneration, http://www.agfw.de/201.0.html

13 Tiefe geothermie in Deutschland (Report, 2007); Bunderministerium für Umwelt, Naturschuts und Reaktorsicherheit, http://www.erneuerbare-energien.de/files/pdfs/allgemein/application/pdf/broschuere_tiefe_geothermie.pdf

14 Tiefe geothermie im Oberrheingraben (HDP) (PDF-file, downloaded 2010-11-30); VBI - the German Association of Consulting Engineers

With the direction of geological surveys one can search for locations with indication of good geothermal sources for power production and at the same time see to the interests of district heating. Should the particular location turn out not to be suitable for power production, will it not necessary mean that the project has failed. The possibility for heat production to a district heating network can be seen as a fall-back option lowering the risks for having a failed project.

Further can the issue of deep geothermal systems in Denmark be viewed from an energy policy angle. What has been said here above should be interpreted as an assumption that deep geothermal systems soon will become less expensive. This is an optimistically point of view and the future deep geothermal may possibly be expensive, for instance expressed in DKK/MW. Further, the knowledge and experiences from geothermal district heating will contribute to a well functioning base for the future energy generation.

11.1 An example – A chosen locationBy defining the amount of heat being present in a reservoir, it is possible to quantify the reservoirs and give an estimation of the potential. The prognoses can not be taken with too large certainty as the geological conditions in the underground are complicated and can not be seen as linear. [13]

Following in this section are calculations made for an area east of Odense (area 7, Appendix 14.4) for the Gassum Reservoir. The chosen area has not been allowed a permit for geothermal investigations and is therefore free for applications. The location is close to residential areas connected to existing district heating networks and operating plants, with several companies being present. Also, the University of Southern Denmark is located close by giving an opportunity to a close contact with professors and other employees. Students at bachelor-, master- and PhD levels can be given the chance to closely study a geothermal system and thereby spread the knowledge connected to geothermal systems.

H1 = R0 × H0 (1)

R0 = 0.33×[(Tt-Tr)/(Tt-T0)] (2)

H0 = [(1-Φ) ×ρm×cm+ Φ ×ρw×cw] × [Tt-T0] ×ΔZ×A (3)

Φ = 0.25

Tt = 75.5°C

ΔZ = 69.3 m (99 m × 0.70 = 69.3 m)

The chosen location with an estimated gross thickness of 99 m will at the depth of 2400 m, result in an estimated potential of H1= 3.54 GJ/m2 by using the formulas (1), (2) and (3). The temperature will increase with depth and in turn increase the estimated potential.

EGS ranges between 3 and 10 km and if assuming the same temperature gradient as in diagram 3, ~28°C/km, temperatures around 150°C can be found at a depth of 5000 m, table 3

shows the calculated results. But for this location it has to be taken into consideration that a structural ridge is dominating in the area and will affect the possible geothermal potential. Temperatures at this level are suitable for power production and once the hot brine has passed trough a turbine for power generation it can be used again for other purposes, such as district heating. Or as seen in figure 15, serial and parallel connections can be used as in the plant in Neustadt-Glewe.

Depth [m] Temperature [°C]3000 92.54000 120.95000 149.36000 177.77000 206.18000 234.5

Table 3 - Showing increase in temperature with growing depth, based on values from Diagram 3 and assuming that the temperature gradient stays constant.

The Lindal diagram (Appendix 14.5) describes and gives examples on possible applications depending on the temperature of the geothermal water and steam. The diagram ranges form low temperatures where fish farming may be an alternative, through space heating at intermediate temperatures to high temperatures which is suitable for power generation. [26]

This diagram can be used as a base if wanting to use the “same” heat more then once. In an area where both power and heat is needed one might find more areas of use, such as for greenhouses and baths.

Power productio

n> 140°CHeat for district heating~ 80 °CGreenhouse~ 60 °C

Swimingpools

~ 30 °C

12 DiscussionHistorically, district heating has played a large roll in Denmark not least in the Copenhagen metropolitan area where the already large amount of buildings supplied by district heating is planned to expand on the disadvantage of natural gas supply. The increased use of district heating will according to several visions have biomass as a main base. It can in the long run seem risky to become too dependent on this kind of energy supply alone and an expansion of, for example geothermal energy can be viewed as a good compliment.

Today geothermal energy is used modestly in Denmark and is exclusively used for district heating. With two existing plants 21MW can be produced, but this will be increased in the future as one project has recently completed its drilling, an existing plant plans for an expansion and currently six applications are being handled. To this it can be added that a large interest was shown from district heating companies and companies in the energy field at an information meeting held on geothermal district heating at Fjervarmes Hus about geothermal development and possibilities in Denmark, a meeting this author attended.

The Geological Survey of Denmark and Greenland has presented a survey that indicates good geological conditions and that down to 3 km, heat can be found that theoretically can ensure the country’s heating need for thousands of years ahead. This clearly shows that geothermal energy is something to be reckoned with. No surveys have been made for depths deeper than 3 km and no one can for certain say what temperatures that might be found there. But if assuming that the temperature gradient stays constant it can be possible to find temperatures high enough for viable power generation at around 5 km. This can, however, not be seen as definite due to large differences in the ground and the fact that the conditions in the ground can not be seen as linear. At these depths the technology EGS is applied and it is becoming more and more frequently used.

It is costly to complete a geothermal project and the outcome may not be as predicted, thus large amounts of money can be lost. The costs for drilling increases non-linear with depth, and drilling in hard rock leads to wear and damage on the drill bits which further increases the cost. The large risks associated with geothermal projects can be intimidating for companies, especially the smaller ones that not have the same possibility to take a chance. A failed project can have devastating results.

Insurances may just be what is needed in order to make geothermal projects more attractive. Through risk mitigation more companies and organizations will be given a chance to take part of the development that is being undertaken. Germany is one of the countries that have reached the furthest with insurances and governmental aid. They are leading the way and other countries strive to achieve the possibility of offering the same help. Denmark has relatively recently started working on how to establish an insurance premium that will invite for more geothermal projects. This is a vital step if geothermal is to be a large part of the future energy supply as indicated in several visions. There will as of today be no governmental aid in Denmark and this is based on the fact that one plant is being established and another six are applying for permission to start investigations. Geothermal projects are seen as competitive with other renewable sources. At the same time geothermal energy is said

to be the future, but the development for the future can seem far away when so many companies can not take part in the extent they may wish for.

The new technology, spallation drilling, can come to lower the costs for the drilling phase significantly, not only through less time spent on drilling but also through less wear and damage on drill bits. If this turn out to be the case, this new technology may help in making geothermal project more attractive. It will ensure easier access to greater depths and by that higher temperature, which in turn will enable better conditions for heat supply and a possible power production. Spallation drilling is still not commercially available on the market today, but several companies are working on developing it further, and laboratory tests have proved that the basic principals work well. This can result in a bright future within this field.

Power from geothermal sources is found at different places around the world, mostly in volcanic active areas. But thanks to EGS, power is starting to be produced as well in areas with less favorable conditions and there are several good examples. Denmark has made no investigations of the ground at depths larger than 3 km, much due to the focus on geothermal district heating. There is no doubt, however, that higher temperatures are to be found at depth larger than 3 km, so here in Denmark. A wish and goal for the future is to have a secure energy supply from renewable sources, and with that comes the need for several different sources and not being reliant on a few. It is true that drilling deeper in hope of finding high temperatures combined with conditions for establishing sufficient permeability, that can be used for power production and may not always turns out to be as successful as predicted. Still, in such cases the found conditions can be sufficient enough for district heating. This means that the whole project should not necessarily be seen as a failure since the wells can be used. There is also the possibility of having both power and heat produced at the same plant and this work has given an example in Neustadt-Glewe.

Just as the visions are for the future so are the suggestions of development. But in both cases, for it to be real in 30-40 years a change need to start now. EGS lies possibly even further in the future in Denmark, but a good development in geothermal district heating with insurances and new drilling technologies will for sure make a well functioning base when one is ready to take the next step.

13 ConclusionThe exploration of geothermal resources started almost 40 years ago in Denmark and today a modest 21 MW is produced. As mentioned before, in order to reach the high stated visions for the future efforts must be accelerated already now. This in order to multiply dramatically from the modest 21 MW from geothermal sources and attain goals set for the future. Heat and possible power in a longer perspective, from underground sources will constitute a good compliment to biomass and wind. Denmark is not the only country to invest in biomass and prices will probably be increase. The downside with wind mills is the fact that it is not always windy and they can, and will, have days where nothing is being produced. Geothermal plants on the other hand produce heat and/or power steadily all hours of the day, every day, making it a reliable source.

A main problem with geothermal projects is the large risks in the initial phase. It is costly and not all companies have the capital to invest, risking seeing it is lost because of non favorable conditions in the ground. Insurances and aid is vital in order to make geothermal projects more attractive. Denmark has started the work on how to apply insurances, but it is necessary that the government show their interest. Not only by saying that geothermal sources are the future, but by helping geothermal sources becoming the future. A continuous work for improving the conditions around insurances is of great importance.

Spallation drilling is a new technology under development which shows possibilities for decreasing costs connected to drilling. Hopefully will this technology continue to be developed and frequently used in future projects. More research and development is needed in this area and the growing interest for geothermal sources will show how successful it will turn out to be.

EGS is not considered relevant in Denmark today and no investigations have been made in order to get an estimation of the underground at depths over 3 km. However, it can not be ruled out that power production from geothermal sources can be viable in Denmark in the future. The work with geothermal district heating will make out a good base for this when one is ready to take the next step, geothermal power production.

Further studies that can be done in order to enlighten the knowledge around geothermal sources are investigations of the underground at depths larger than 3 km. Another aspect is the possibility of using ORC for power production in Denmark.

14 References[1] Renewable Energy – Power for a sustainable future, Chapter 9 - Geothermal Energy

(Oxford University Press, 2004); Geoff Brown and John Garnish

[2] What is geothermal energy? (website, 2004); Mary H. Dickson and Mario Fanelli, Istituto di Geoscienze e Georisorse, CNR, Pisa, Italy, http://www.geothermal-energy.org/314,what_is_geothermal_energy.html

[3] Technological Status of Shallow Geothermal Energy in Europe (Report, 2007); Walter J. Eugster and Burkhard Sanner

[4] How an Enhanced Geothermal System Works (website, 2010); U.S. Department of Energy, http://www1.eere.energy.gov/geothermal/egs_animation.html

[5] Tiefe geothermie in Deutschland (Report, 2007); Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit

[6] Fjärrvärme – Teori, teknik och funktion (Studentlitteratur, 1993); S. Frederiksen and S. Werner

[7] Energistatistik 2008 (Yearly report, 2009); Energistyrelsen

[8] District heating in Copenhagen: An energy efficient, low carbon, and cost effective energy system (Information brochure, downloaded 2010-07-27); Københavns Energihttp://dbdh.dk/images/uploads/pdf-diverse/District_heating_in_Copenhagen.pdf

[9] Varmeplan Hovedstaden – Analys af den fremtidige fjernvarmeforsyning i hovedstadsområdet (Report, 2009); VEKS, CTR, KE

[10] Dansk klima- og energipolitik (website, downloaded 2010-07-27); Energistyrelsen,http://www.ens.dk/da-DK/Politik/Dansk-klima-og-energi-politik/Sider/dansk-klima-og-energipolitik.aspx

[11] Grøn Energi – vejen mod et dansk energisystem uden fossile brændsler (Report, 2010); Klimakomissionen

[12] København CO2-neutral i 2025 – Københavns Klimaplan (Report, 2009), Miljø Metropolen (Teknik- og Miljøforvaltningen)

[13] Vurdering af det geotermiske potentiale i Danmark (Report, 2009); A. Mathisen, L. Kristensen, T. Bidstrup, L.H. Nielsen, GEUS

[14] Geothermal Development in Denmark, Country Update WGC 2005 (Report, 2005); Allan Meahler and Jesper Matengaard

[15] Geotermisk varme i hovedstaden (website, downlodeded 2010-08-03); VEKS, http://www.veks.dk/Om%20VEKS/Varmeproduktion/Geotermi.aspx

[16] Hovedstadsområdets Geotermiske Samarbejde (HGS) (website, downlodeded 2010-08-03); DONG Energy, http://www.dongenergy.com/geotermi/anlaeg/amager/pages/om_hgs.aspx

[17] Prioritering af lokaliteter for et geotermisk stjerneanlæg (Report, 2010); HGS

[18] Om anlægget (website, downloaded 2010-07-12); DONG Energy, http://www.dongenergy.com/geotermi/anlaeg/amager/pages/om_anlaegget.aspx

[19] Geotermiske boringer i Sønderborg udskydes (website, 2009); Sønderborg Fjernvarme and DONG Energy, http://www.sonderborg-fjernvarme.dk/getfile.php?objectid=72286

[20] Geotermi-anlæg hænger på millionregning efter ubrugelige undersøgelser (article, 2010-06-12); Magnus Bredsdorff, www.ing.dk

[21] Indkaldelse af ansøgninger i henhold til undergrundsloven (Guideline bookleet, 2010); Energistyrelsen

[22] Geothermal Risk Mitigation Schemes in Germany (Report, 2010); Horst Kreuter and Christina Schrage, GeoThermal Engineering GmbH

[23] Lykke Friis: Varmeselskaber må selv forsikre sig mod tab på geotermisk varme (Article, 201-11-11); Claus Djørup, www.ing.dk

[24] Hydrothermal spallation drilling and advanced energy conservation technologies for engineered geothermal systems (Report, 2009); Chad R. Augustine, Massachusetts Institute of Technology

[25] Combined heat and power plant – Neustsdt-Glewe (Report, 2005); John W. Lund, Geo-Heat Center

[26] In Memory of Baldur Lindal, (Article, 1997); Ingvar B. Fridleifsson, (President of IGA, Reykjavik, Iceland), GHC Bulletin

[27] Geothermal reserves and sustainability in the Greater Copenhagen Area (Report, 2010); Jesper Magtengaard and Allan Mahler

Figures, diagrams and tables

[28] What is geothermal energy? (Report prepared 2004), Mary H. Dickson and Mario Fanelli Istituto di Geoscienze e Georisorse, Pisa, Italy, http://www.geothermal-energy.org/314,what_is_geothermal_energy.html

[29] Images of Hot Rock Energy Systems (website downloaded 2010-11-28), Hot Rock Energy, http://www.hotrockenergy.com/images-of-hot-rock-energy-systems.html

[30] Så fungerar ett värmeverk (website downloaded 2010-07-15), Vattenfall, http://www.vattenfall.se/sv/sa-fungerar-ett-varmeverk.htm

[31] Fjärrvärme - Vad är fjärrvärme och hur fungerar det? (website downloaded 2010-07-15), Rindi Energi, http://www.rindienergi.se/fjarrvarme.php

[32] Values from the report Energistatistik 2008, The Danish Energy Agency

[33] Varmeplan Hovedstaden – Analys af den fremtidige fjernvarmeforsyning i hovedstadsområdet (report, 2009); VEKS, CTR, KE

[34] Grøn Energi – vejen mod et dansk energisystem uden fossile brændsler (report, 2010); Klimakomissionen

[35] København CO2-neutral i 2025 – Københavns Klimaplan (report, 2009), Miljø Metropolen (Teknik- og Miljøforvaltningen)

[36] Geothermal Development in Denmark, Country Update WGC 2005 (report, 2005); Allan Meahler and Jesper Matengaard, DONG Energy

[37] Vurdering af det geotermiske potentiale i Danmark (report, 2009); A. Mathisen, L. Kristensen, T. Bidstrup, L.H. Nielsen, GEUS

[38] Geotermisk energi – Bidrag til national energiplan (Power Point, 2009), Jesper Magtengaard, http://ida.dk/News/Dagsordener/Klima/Klimaplan2050/Documents/IDA%2020012009/Foredrag%20til%20IDA%20Energiplan_jesper%20M090120.pdf

[39] Om anlægget (website, downloaded 2010-11-28), DONG Energy, http://www.dongenergy.com/geotermi/anlaeg/thisted/pages/om_anlaegget.aspx

[40] Om anlægget (website, downloaded 2010-11-28), DONG Energy, http://www.dongenergy.com/geotermi/anlaeg/amager/pages/om_anlaegget.aspx

[41] Geotermisk energi – en vit bok för Sverige (Report, 2006), Herbert Henkel

[42] Our advantage (website, downloaded 2010-11-28), Potter Drilling, http://www.potterdrilling.com/technology/advantage/

[43] Spallation Drilling for Deep Heat Mining (Power Point 2007), T. Rothenfluh, K. Prikopskô & P.R. von Rohr, Swiss federal Institute of Technology Zurich

[44] Erdwärmenutzung in Neustadt-Glewe (website, 2004), Energieforum, http://www.energieforum.ru/de/erneuerbare_energien/geothermie/projekte_deutschland/

15 Appendix

15.1 Darcy’s law

Darcy’s law gives Q [m3/s] which is the total discharge, κ is the permeability, A the cross-sectional area, (Pb-Pa) is the pressure drop, μ is the viscosity and L being the length over which the pressure drop is taking place.

[Wikipedia]

The hydraulic conductivity (Kw) is to be found in a version of Darcy’s law as follows

Q = AKw HL , where

Q the volume of water flowing in unite time

A cross-sectional area

H/L hydraulic gradient, the change in head per meter of distance

[Godfrey Boyle (2004); Renewable Energy – Power for a sustainable future, Geoff Brown and John Garnish, Chapter 9 - Geothermal Energy]

Typical porosities and hydraulic conductivities

Material Porosity [%] Hydraulic conductivityClay 45-60 <10-2

Silt 40-50 10-2-1Sand, volcanic ash 30-40 1-500Gravel 25-35 500- 10 000Mudrock 5-15 10-8 -10-6

Sandstone 5-30 10-4-10Limestone 0.1-30 10-5-10Solidified lava 0.001-1 0.0003-3Granite 0.0001-1 0.003-0.03Slate 0.001-1 10-8-10-5

15.2 Geothermal permits for applications

Map over Denmark showing areas in which it is possible to apply for a permission to investigate the geothermal possibilities and a chance of establishing a geothermal plant.

15.3 Contents of application

1. Name, address and contact person for all participating partners, and the percentage distribution between the parties.

2. If there is more then one company shall information exist on which company will lead the work (operator).

3. Information on the forms of the companies- Economical information, for example accounting for the last three years,

information on ownership, composition of the board and name of the director

- Possible link and ownership with other companies- Information on possible parent company

4. Information on the companies’ previous experience connected to geothermal energy and district heating production.

5. Description of the companies technical expertise concerning the activities they are about to implement (geological mapping and evaluation, seismological surveys, drilling, establishment and operation of district heating systems, etc.). If the companies do not have the expertise it shall be described how this will be secured by such involvement of consultants.

6. A map showing the applied area, attached with a list for the coordinates for the area, identified as geographic coordinates based on ED 50.

7. Description of the works needed to clarify the geothermal potential of the applied area, including a work program which outlines the work which the companies will undertake to implement the timetable.

8. Description of the geological and geothermal conditions of the applied area, indicating applicants’ data bank.

9. Geological / geophysical maps and any interpreted seismic lines covering the applied area.

10. Brief description of existing district heating supply in the trade area and / or plans for changes.

15.4 Calculations for estimations of reservoir potential[Formulas and maps are from Vurdering af det geotermiske potentiale i Danmark (2009); GEUS, A. Mathisen, L. Kristensen, T. Bidstrup, L.H. Nielsen]

H1 = R0 × H0 (1)

R0 = 0.33×[(Tt-Tr)/(Tt-T0)] (2)

H0 = [(1-Φ) ×ρm×cm+ Φ ×ρw×cw] × [Tt-T0] ×ΔZ×A (3)

Tt = Temperature at the top of the aquifer [°C]

Tr = Temperature of the re-injected water, set to approximately 20°C

T0 = Temperature at the surface, normally 8°C in Denmark

Φ = Effective porosity

ρm = Density for matrix, 2650 [kg/m3]

cm = Heat capacity for matrix; 880 [J/kg K]

ρw = Density for water; 1000 [kg/m3]

cw = Heat capacity for water, 4180 [J/kg K]

ΔZ = Net sand thickness (= Gross thickness × Net gross ratio) [m]

A = Surface area [m2]

Part of table 1, chapeter 5.

Map showing the 7 different areas defined from structural elements combined with geographical locations.

Map showing the expected prevalence of the Gassum reservoir, the chosen location in section 3.3.2.2 is pointed out with a red arrow.

15.5 Lindals diagram

Baldur Lindal (1918-1997) was an engineer from Iceland who graduated as a chemical engineer from Massachusetts Institute of Technology. He worked with geothermal research during many years in Iceland and has published a large number of papers on the use of geothermal energy. He has worked out a diagram that describes and gives examples on possible applications depending on the temperature of the geothermal water and steam.

[In Memory of Baldur Lindal, (1997); GHC Bulletin, Ingvar B. Fridleifsson (President of IGA, Reykjavik, Iceland)]