Geothermal Power

A way into the future?

Jonathan Bailey

24th February 2005

Outline

• Introduction • What is geothermal energy?• Utilization of geothermal energy• The Southampton CHP Scheme• Projections

Introduction

• Developments in alternative energy sources sparked by – Threats of traditional energy resource exhaustion– Drive to self-sufficiency– Growing concern for the environment

• Drive to find alternative energy sources that are widely available, versatile, renewable, and have limited impact on the environmental

Traditional Utilization of Geothermal Energy

• Natural releases of geothermal energy have been utilized for centuries: – Balneology

• Healing • Hygiene

– Domestic services (e.g. Cooking, laundry)• Native New Zealanders

– Mineral extraction• geothermal water can contain useful minerals

– Boric acid, sulfur, vitriol or aluminum

• Ex. Etruscans extracted boric acid from boiling springs and used it for making enamels

What is Geothermal Energy?

• Heat generated by natural processes occurring within the earth

• Hot springs and mud pots are natural phenomena that result from geothermal activity

Photo: www.geothermal.marin.org/

Where Can Geothermal Energy be Harnessed?

• Technology today allows for small scale harnessing everywhere – Heat pumps

• Different areas have different thermal gradients and thus different utilization potentials

• Higher thermal gradients correspond to areas containing more geothermal energy

• Photo: www.geothermal.marin.org/

What is Geothermal Energy?

• The centre of the Earth is around 6000 degrees Celsius - hot enough to melt rock. Even a few kilometres down, the temperature can be over 250 degrees Celsius. In general, the temperature rises one degree Celsius for every 36 metres you go down. In volcanic areas, molten rock can be very close to the surface and in such areas geothermal energy has been used for thousands of years for cooking and heating.

Geothermal Fields• Geothermal field - thermal area where permeable rock

formations below ground contain a working fluid without which the area could not be exploited (Armstead, 1978)

• Geothermal field characterizations:– Semi-thermal field- produces water up to 100oC from drilling

depths of 1-2 km – Wet hyper-thermal field (water-dominated)- produces

pressurized water > 100oC– Dry hyper-thermal field (vapor-dominated)- produces dry

saturated, or slightly superheated steam at P > Patm

• By exploiting geothermal fields, particularly hyper-thermal fields, geothermal energy can be harnessed on a large scale

Geothermal Fields: Expected Locations

• Semi-thermal fields typically found in areas having abnormally high temperature gradients

• Hyper-thermal fields generally located at tectonic plate boundaries in seismic zones

Energy Utilization: Semi-Thermal Fields

• Hot fluid exploited from semi-thermal fields can be directly transported to needed areas by intricate systems of pipes – District heating – e.g. Southampton

• Uses heat exchanger

– Farming applications– Industrial usages

Geothermal Usages

• Semi-thermal fields– District heating

• Building/hot water heating• Sidewalk clearing

– Farming applications• Ex. Greenhouses in Iceland

– Industrial usages

• Hyper-thermal fields (supply high grade heat)– Electric Power Generation

Photo: Sitewalk in Klamath Falls, Oregon (www.geothermal.marin.org/)

Currently…

• Individual power plants operate at capacities ranging between 100kW and 100MW (World Bank, 2004)– Dependent on energy resource and power demand

• Over 8200 megawatts of electricity from geothermal plants supply energy to 60 million people in 21 countries (Nemzer, 2001)– most countries classified as developing nations

Uses of Geothermal Energy• There are three main

ways of tapping geothermal energy:

1) Direct use: Geothermal heat found near the surface of the Earth can be used directly for heating buildings (CHP), like the programme in Southampton

2) Electricity production:

• There are three types of power plant that can convert geothermal energy to electricity, depending on the temperature of the geothermal fluid used. All three use a turbine that is driven by steam, which then drives a generator to produce electricity.

Electricity Generation

– Thermal energy associated with high temperature fluids extracted from hyper-thermal fields may be converted into mechanical work and then electricity (Wahl, 1977)

– Thermal energy is converted into mechanical work by expanding hot fluid

– Electrical energy generally produced by a generator powered by an expansion machine producing mechanical work in the form of a rotating shaft

– Expansion machines• Steam turbines• Piston-driven engines

3) Geothermal heat pumps

The relatively constant temperature of the top 15 metres of the Earth's surface (or ground water) can be used to heat or cool buildings indirectly. The pump uses a series of pipes to circulate fluid through the warm ground. When the ground is warmer than the buildings above, the liquid absorbs heat from the ground, which is then concentrated and transferred to the buildings. This can also be used to heat domestic water. However, is this solar or geothermal energy?

Solar or Geothermal??

• While geothermal resources are not spread uniformly, heat pumps can be used nearly anywhere. This answers the question that using a heat pump uses solar energy, as they can be used in places where no geothermal energy is available!

Geothermal in the U.K

• The red areas shown in the figure, are areas of the United Kingdom that are available to place geothermal plants. However, inside our island, we would only be able to introduce programmes like that of Southampton. As we are only a semi-thermal field zone

The Southampton Scheme 1The geothermal heat provided by the well is used as part of Southampton's District Heating scheme , where it works in conjunction with the Combined Heat and Power scheme. Geothermal energy provides between 15-20% of the total heat-input into this scheme.The combined heat and power generators use conventional fuels to make electricity. "Waste heat" from this process is recovered for distribution through the 11km mains network. The district heating scheme in Southampton helps reduce energy bills by 25% and the city's CO2 omissions by 10kt a year. It closely resembles a huge domestic central heating system, with hot, treated water circulating underground from the heat station.

The Southampton Scheme 2

• The borehole is non-polluting (at the moment the used brine is being pumped into the River Test) and costs little to run. The scheme produces enough electricity from its own generator to fuel itself, and there is electricity left over to sell to the electricity board.

The Southampton Scheme 3

• Launched in 1986• Water is found at a

depth of nearly 1.8km and at a temperature of 76ºC

• Saved 180kt CO2 going into atmosphere since opening!

Sadly we cannot have anything as big as this in the UK.

The Problems Are?

• As the U.K. is only on a semi-thermal field we cannot rely upon its resource as a way into the future. The plants we would open in the coming years would provide:

• A) A 25% reduction in CO2 emissions for the areas in question but for how long?

• At best guess a plant opened in the next year would be open for the next 25, this would be self sufficient, but not effect our overall energy needs, as the plant would provide heating/cooling to around 10-20 large buildings. This on the greater scheme of things would have no effect.

Projections: 0 PJ a fair number?

A Graph to Show Projections for Geothermal Electricity Generation in the Future

0

20

40

60

80

100

120

2000 2005 2010 2015 2020 2025 2030 2035

Time (Year)

GJ

valu

e

Projections Explained

• Values in GJ as PJ values too small to graphically show.

• The demand value for 2003 was 9914.8PJ so an input of 0.00008208PJ from a possible geothermal source proves insignificant and this source is therefore not worth investing in!

• References

• Books

• Armstead, H. C. 1978. Geothermal Energy. John Wiley and Sons: New York, p. 1-12, 39-41, 61-141

• Carrington, G. 2002. Basic Thermodynamics. Oxford University Press: New York, p. 31-39.

• Collie, M. J. 1978. Geothermal Energy: Recent Developments. Noyas Data Corporation: New Jersey, p. 35-70, 98-104.

• Gupta, H. K. 1980. Geothermal Resources: An Energy Alternative. Elsevier Scientific Publishing Company: New York, p. 51-98

• Veziroglu, T. N. 1977. Alternative Energy Sources: An International Compendium. Hemisphere Publishing Corporation: New York, p.2577-2598

• Veziroglu, T. N. 1980. Alternative Energy Sources III, Volume 4, Indirect Solar/Geothermal Energy. Hemisphere Publishing Corporation: New York, p. 471-487.

• Wahl, E. F. 1977. Geothermal Energy Utilization. John Wiley and Sons: New York, p. 170-181.

• Websites

• The World Bank Group. 2004. Geothermal Energy. Available at http://www.worldbank.org/html/fpd/energy/geothermal/. Last accessed April 7, 2004.

• US Department of Energy. 2004. Geothermal Technologies Program. Available at http://www.eere.energy.gov/geothermal/. Last accessed April 7, 2004.

• Geothermal Education Office. 2001. Introduction to Geothermal Energy Slide Show. Available at http://geothermal.marin.org/GEOpresentation/. Last accessed April 7, 2004