1. Publisher: Earthscan, UK Homepage: www.earthscan.co.uk/?tabid=101808
Energy and the New Reality, Volume 2: C-Free Energy Supply Chapter 5: Geothermal Energy L. D. Danny Harvey
Publisher: Earthscan, UK Homepage:
This material is intended for use in lectures, presentations and as handouts to students, and is provided in Powerpoint format so as to allow customization for the individual needs of course instructors. Permission of the author and publisher is required for any other usage. Please see for contact details.

2. The temperature increases with increasing depth in the Earth’s crust at a typical rate of 20 K/km

3. Types of geothermal resources:
Hydrothermal – hot water or steam in confined aquifers, under pressure
Geopressurized – hot, high-pressure brines (saline water) with dissolved methane
Hot dry rock (or “enhanced geothermal systems”, EGS)
Magma

4. Figure 5.1 A hydrothermal geothermal resource
Source: Barbier (2002, Renewable and Sustainable Energy Reviews 6, 63–65,

5. Geothermal energy can be used:
Directly for heating
To generate electricity

6. Geothermal Energy For Electricity Generation (1990-2014)
Source: Renewable Energy World, May-June 2016

7. Existing and planned (as of end-of-2015) geothermal electricity generation capacity by country
Source: "2016 Annual US and Global Geothermal Power Production Report"

8. Figure 5.2 Agricultural uses of heat

9. Figure 5.3a US subsurface temperature at a depth of 6.5 km
Source: MIT (2006, The Future of Geothermal Energy: Impact of Enhanced Geothermal systems (EGS) on the United States in the 21st Century)

10. Figure 5.3b Temperatures encountered at a depth of 5 km in Europe
Source: GAC (2006, Trans-Mediterranean Interconnection for Concentrating Solar Power, Final Report, GAC)

11. Figure 5.4a Creil geothermal district heating (near Paris)
Source: Brown (1996, Renewable Energy, Power for a Sustainable Future, Oxford University Press, Oxford)

12. Figure 5.4b Creil geothermal district heating
Note the use of a heat pump to extract extra heat from the 35⁰C water returning
from the top set of 2000 apartments, allowing another 2000 apartments to be
heated while making the return flow even colder (10⁰C). The colder return flow
allows more heat to be extracted from the hot (60⁰C) water taken from the ground
before it is returned than would otherwise be possible (the geothermal loop is
in contact with 10⁰C water instead of 35⁰C water, and so is cooled down to 25⁰C).
Source: Brown (1996, Renewable Energy, Power for a Sustainable Future, Oxford University Press, Oxford)

13. Technologies for converting geothermal heat into electricity:
Dry steam
Single, double and triple flash
- both of these are suited for high-__temperature resources
Binary cycle/organic Rankine cycle
- can use low-temperature resources (down __to 100⁰C)

14. Figure 5.5a Dry steam geothermal power
Source: Brown (1996, Renewable Energy, Power for a Sustainable Future, Oxford University Press, Oxford)

15. The purpose of the cooling tower shown in the previous slide is to make the steam exiting from the turbine as cool as possible, so that it has low pressure – this allows more energy (as electricity) to be extracted from the turbine). The cooling tower produces cool water by forcing evaporation of some of the water that is fed to it. The water lost through evaporation needs to be continuously replaced. (cooling towers are used in coal and nuclear power plants, which also have steam turbines)

16. Geothermal power plant with cooling tower

17. Geothermal power plant with cooling towers

18. Figure 5.5b Single-flash geothermal power
Source: Brown (1996, Renewable Energy, Power for a Sustainable Future, Oxford University Press, Oxford)

19. Figure 5.5c Binary-cycle geothermal power (there are two completely separate flow loops, where only heat is transferred between them in a heat exchanger)
Source: Brown (1996, Renewable Energy, Power for a Sustainable Future, Oxford University Press, Oxford)

20. Figure 5.5d Double-flash geothermal power
Source: Brown (1996, Renewable Energy, Power for a Sustainable Future, Oxford University Press, Oxford)

21. Figure 5.6 Enhanced geothermal system (EGS)
Source: Mock et al (1997, Annual Review of Energy and Environment 22, 305–356)

22. Drilling: To a depth of 10 km is possible
6 km might be a limit to the depth that is economical
The USGS estimated that EGS between depths of 3-km could supply 500 GW of power (compared to about 1000 GW total power capacity today in the US).
Exploration costs can add up to 15% of the total cost of a geothermal project, and the success rates in the early stages can be only 50-60% - so early-stage government support is needed to reduce financial risks to investors

23. Figure 5.7a CO2 emissions
Source: Barbier (2002, Renewable and Sustainable Energy Reviews 6, 63–65,

24. Figure 5.7b S emissions
Source: Barbier (2002, Renewable and Sustainable Energy Reviews 6, 63–65,

25. By comparison, total world energy use of all kinds is about 600 EJ/yr
Figure 5.10 Amount of heat available at different temperatures and at different depths below the US land surface
By comparison, total world energy use of all kinds is about 600 EJ/yr
Source: MIT (2006, The Future of Geothermal Energy: Impact of Enhanced Geothermal systems (EGS) on the United States in the 21st Century)

26. Cost of geothermal power:
The US Department of Energy website gives a capital cost of $ /kW for small (< 1 MW) powerplants
Maintenance costs of 1-3 cents/kWh
Capacity factor of 0.9 (running the plant more than 90% of the time increases unit maintenance costs)
Result (depending on interest rate and project lifespan):
__3-10 cents/kWh
(by comparison, both solar PV and onshore wind capital costs are now $ /kW, but these plants have lower capacity factors)
However, the given geothermal costs do not include exploration costs and interest incurred during the project development
Source:

27. Development of geothermal energy is risky, so investors expect higher returns
Source: Nathwani and Mines (2015),

28. The “discount rate” is the same as the interest that has to be
paid to investors at this stage, and the interest incurred is
compounded. Because the early stages occur several years
before the project is ready to start producing and selling
electricity, and the interest rate is large, these early stages
contribute a lot to the final cost of electricity.
Source: Nathwani and Mines (2015),

29. Sample cost breakdown, for a 30-MW single flash powerplant operating for 30 years, with wells drilled to a depth of 2 km and 200⁰C:
Exploration, $3.7 million
Confirmation, $29.2 million
Well field development, $49.9 million
Power plant, $71.1 million
Total, $155.5 million
Total with contingencies, $178.8 million
Total with contingencies and accumulated interest on the loans up to the point of startup, $210.4 million
This is a cost of $7000/kW, of which direct construction cost is $4000/kW
The final cost of electricity is 10.9 cents/kWh, of which 2.4 cents/kWh are for O&M, insurance, and taxes.

30. Dependence of costs in the previous example on the temperature at the 2-km depth
(“overnight” cost means the cost without any interest incurred during construction
– as if the project could be built overnight and then immediately start selling electricity)
Source: Nathwani and Mines (2015),

31. From the previous slide, we see that
The warmer the resource, the lower the cost (with hotter water fed into the turbine, the efficiency is higher – so more electricity is produced, thus lowering the cost per kWh)
Flash systems, using ⁰C water, have final costs of 9-13 cents/kWh
Binary-cycle systems, using cooler water (down to 130⁰C), have final costs of cents/kWh

32. Cost to drill a well as a function of depth of well (several production and injection wells would need to be drilled for a 30 MW plant)
Source: Nathwani and Mines (2015),

33. There will be a tradeoff – deeper wells cost more to drill, but deeper wells will tap hotter water, which increases the electricity generation efficiency and hence electricity production, which reduces the unit cost

34. Larger projects have smaller unit costs ($/kWh), but there is not much cost reduction beyond a size of 30 MW (see the dashed lines in the figure below)
Source: Nathwani and Mines (2015),

35. Applications of oil and gas industry expertise to geothermal energy:
Deep drilling
Fracturing of subsurface rocks
Use of high-temperature tools
Use of fibre-optic cables
Preserving the integrity of well holes
As well, it might be possible to develop geothermal energy at pre-existing oil and gas wells.

36. Figure 5.14 Cost of oil, gas and hot dry rock geothermal wells
Source: MIT (2006, The Future of Geothermal Energy: Impact of Enhanced Geothermal systems (EGS) on the United States in the 21st Century)

37. Some brines (salty waters) from geothermal wells are a potential source of Li, Mn and Zn. Li is needed in the preferred battery technology, Li-ion. Zn is widely used and is facing shortages in the future. Sale of such minerals would increase the economic viability of geothermal projects with salty brines, while addressing potential mineral shortages (which would be reflected in higher prices for the minerals).

38. Figure 5.8 Worldwide direct use of geothermal heat and generation of electricity from geothermal energy

39. Figure 5.9 Geothermal share of national electricity production

40. Source: Renewable Energy World, Jan-Feb 2017

41. Geothermal projects, 2006-2015:
118 binary cycle
58 flash cycle
14 dry steam
for a total of 4.4 GW, bringing the total installed capacity to 13.3 GW
(By comparison, total wind capacity at the end of 2016 was almost 500 GW and total solar just over 300 GW – for a total wind and solar of 800 GW)