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Geothermal power

Geothermal power
technological advances have dramatically expanded the range and size of viable resources, especially for direct applications such as home heating. Geothermal wells tend to release greenhouse gases trapped deep within the earth, but these emissions are much lower than those of conventional fossil fuels. As a result, this technology has the potential to help mitigate global warming if widely deployed.[1] Prince Piero Ginori Conti tested the first geothermal generator on 4 July 1904, at the Larderello dry steam field in Italy.[2] The largest group of geothermal power plants in the world is located at The Geysers, a geothermal field in California, United States.[3] As of 2004, five countries (El Salvador, Kenya, the Philippines, Iceland, and Costa Rica) generate more than 15% of their electricity from geothermal sources.

The Nesjavellir Geothermal Power Plant in Iceland
Renewable energy

Biofuel Biomass Geothermal Hydropower Solar power Tidal power Wave power Wind power

Twenty-four countries generated a total of 56,786 GWh (204 PJ) of electricity from geothermal power in 2005, accounting for 0.3% of worldwide electricity consumption. This output is growing by 3% annually, thanks to a growing number of plants as well as improvements in their capacity factors. Because a geothermal power station does not rely on transient sources of energy, unlike, for example, wind turbines or solar panels, its capacity factor can be quite large; up to 90% has been demonstrated.[4] Their global average was 73% in 2005.[1] The global capacity was 10 GW in 2007. Geothermal electric plants have until recently been built exclusively on the edges of tectonic plates where high temperature geothermal resources are available near the surface. The development of binary cycle power plants and improvements in drilling and extraction technology has opened the hope that enhanced geothermal systems might be viable over a much greater geographical range. A demonstration project has recently been completed in Landau-Pfalz, Germany, and others are under construction in Soultz-

Geothermal power (from the Greek roots geo, meaning earth, and thermos, meaning heat) is power extracted from heat stored in the earth. This geothermal energy originates from the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface. It has been used for space heating and bathing since ancient roman times, but is now better known for generating electricity. About 10 GW of geothermal electric capacity is installed around the world as of 2007, generating 0.3% of global electricity demand. An additional 28 GW of direct geothermal heating capacity is installed for district heating, space heating, spas, industrial processes, desalination and agricultural applications.[1] Geothermal power is cost effective, reliable, and environmentally friendly, but has previously been geographically limited to areas near tectonic plate boundaries. Recent


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Geothermal power
furnaces.[5] Geothermal heat pumps can be used essentially anywhere. There are a wide variety of applications for cheap geothermal heat. The cities of Reykjavík and Akureyri pipe hot water from geothermal plants under roads and pavements to melt snow. District heating applications use networks of piped hot water to heat buildings in whole communities.[5] Geothermal desalination has been demonstrated.

Geothermal electric power plants have been limited to the edges of tectonic plates until recently. sous-Forêts, Australia. France and Cooper Basin,

Environmental Impact

Direct Application
Approximately seventy countries made direct use of a total of 270 PJ of geothermal heating in 2004. More than half of this energy was used for space heating, and a third was used for heated pools. The remainder was used for industrial and agricultural applications. The global installed capacity was 28 GW, but capacity factors tend to be low (around 20%) since the heat is mostly needed in the winter. The above figures include 88 PJ of space heating extracted by an estimated million geothermal heat pumps with a total capacity of 15 GW. Global geothermal heat pump capacity is growing by 10% annually.[1] Direct application of geothermal heat for space heating is far more efficient than electricity generation and has less demanding temperature requirements. It may come from waste heat supplied by co-generation from a geothermal electrical plant or from smaller wells or heat exchangers buried in the shallow ground. As a result it is viable over a much greater geographical range than electricity generation. Where natural hot springs are available, the water may be piped directly into radiators. If the shallow ground is hot but dry, earth tubes or downhole heat exchangers may be used without a heat pump. But even in areas where the shallow ground is too cold to provide comfort directly, it is still warmer than the winter air. Seasonal variations in ground temperature diminish and disappear completely below 10m of depth. That heat can be extracted with a geothermal heat pump more efficiently than it can be generated by conventional

Krafla Geothermal Station in northeast Iceland Geothermal fluids drawn from the deep earth may carry a mixture of gases with them, notably carbon dioxide and hydrogen sulfide. When released to the environment, these pollutants contribute to global warming, acid rain, and noxious smells in the vicinity of the plant. Existing geothermal electric plants emit an average of 122 kg of CO2 per MWh of electricity, a small fraction of the emission intensity of conventional fossil fuel plants.[6] Some are equipped with emissions-controlling systems that reduces the exhaust of acids and volatiles. In addition to dissolved gases, hot water from geothermal sources may contain trace amounts of dangerous elements such as mercury, arsenic, and antimony which, if disposed of into rivers, can render their water unsafe to drink. Geothermal plants can theoretically inject these substances, along with the gases, back into the earth, in a form of carbon capture and storage. Construction of the power plants can adversely affect land stability in the surrounding region. Subsidence has occured in the Wairakei field in New Zealand[7] and in


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Staufen im Breisgau, Germany.[8] Enhanced geothermal systems can trigger earthquakes as part of the hydraulic fracturing process. The project in Basel, Switzerland was suspended because more than 10,000 seismic event measuring up to 3.4 on the Richter Scale occurred over the first 6 days of water injection.[9] Geothermal has minimal requirements for land use and freshwater. Existing geothermal plants use 1-8 acres per megawatt (MW) versus 5-10 acres per MW for nuclear operations and 19 acres per MW for coal power plants.[10]. They use 20 litres of freshwater per MWh versus over 1000 litres per MWh for nuclear, coal, or oil.[7]

Geothermal power

Geothermal power requires no fuel, and is therefore immune to fluctuations in fuel cost, but capital costs tend to be high. Drilling accounts for most of the costs of electrical plants, and exploration of deep resources entails very high financial risks. At present, the construction of a geothermal electric plant and well costs about 2-5 million € per MW of capacity, while operational costs are 0.04-0.10 € per kWh.[11] Geothermal power offers a degree of scalability: a large geothermal plant can power entire cities while smaller power plants can supply rural villages or heat individual homes.[12] Chevron Corporation is the world’s largest producer of geothermal energy. Other companies as Reykjavik Energy Invest build geothermal energy plants around the world. [13]

Enhanced geothermal system accumulates solar energy (i.e. warms up) during the summer, and releases that energy (i.e. cools down) during the winter. The seasonal energy stored this way is much smaller in total scale and less dense, but the heat flow rates are much higher, more easily accessible, and evenly distributed around the world. A geothermal heat pump can extract enough heat from shallow ground anywhere in the world to provide wintertime home heating. Electricity generation requires high temperature resources that can only come from deep underground. The heat must be carried to the surface by fluid circulation, either through magma conduits, hot springs, hydrothermal circulation, oil wells, drilled water wells, or a combination of these. This circulation sometimes exists naturally in the most favorable areas where the crust is thin: magma conduits bring the heat close to the surface, and naturally occurring hot springs bridge the last gap to the surface. If no hot spring is available, a well must be drilled into a hot aquifer. Away from tectonic plate boundaries the geothermal gradient is 25-30°C per km of depth in most of the world, and wells would have to be drilled several kilometers deep to permit electricity generation.[1] The quantity and quality of

The heat content of the earth is 1031 Joules[1]. This heat naturally flows up to the surface by conduction at a rate of 40 TW, and is replenished by radioactive decay at a rate of 30 TW.[14] These flow rates are more than twice the rate of human energy consumption from all primary sources, but most of it is too geographically diffuse (0.1 W/m2 on average) to be recoverable. The Earth’s crust effectively acts as a thick insulating blanket which must be pierced by fluid conduits (of magma, water or other) in order to release the heat underneath. In addition to heat emanating from deep within the Earth, the top 10 m of the ground


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recoverable resources improves with drilling depth and proximity to tectonic plate boundaries. In ground that is hot but dry, or where water pressure is inadequate, it is possible to inject a fluid to stimulate production. Two boreholes are bored into a candidate site, and the deep rock between them is fractured by explosives or high pressure water. Water is pumped down one borehole and steam comes up the other. Liquefied carbon dioxide may also be used. This concept is called hot dry rock geothermal energy in Europe, or enhanced geothermal systems in North America. A much greater resource potential may be available from this approach than from conventional tapping of natural aquifers.

Geothermal power
4 kilometres (2 mi) generally incur drilling costs in the tens of millions of dollars. The technological challenges are to drill wide bores at low cost and to break rock over larger volumes. Geothermal power is considered to be sustainable[4] because the heat extraction is small compared to the Earth’s heat content, but extraction must still be monitored to avoid local depletion.[18] Although geothermal sites are capable of providing heat for many decades, individual wells may cool down or run out of water. The three oldest sites, at Larderello, Wairakei, and the Geysers have all reduced production from their peaks. It is not clear whether these plants extracted energy faster than it was replenished from greater depths, or whether the aquifers supplying them are being depleted. If production is reduced, and water is reinjected, these wells could theoretically recover their full potential. These mitigation strategies have already been implemented at some sites. The long-term sustainability of geothermal energy production has been demonstrated at the Lardarello field in Italy since 1913, at the Wairakei field in New Zealand since 1958, and at The Geysers field in California since 1960.[4]

At present, only a small percentage of the total potential power is effectively used Estimates of the electricity generating potential of geothermal energy vary greatly from 35 to 2000 GW, depending on the scale of financial investments in exploration and technology development.[1] This does not include non-electric heat recovered by cogeneration, geothermal heat pumps and other direct use. A 2006 report by MIT, that took into account the use of enhanced geothermal system, estimated that an investment of 1 billion US dollars in research and development over 15 years would permit the development of 100 GW of generating capacity by 2050 in the United States alone.[15] The MIT report estimated that over 200 ZJ would be extractable, with the potential to increase this to over 2,000 ZJ with technology improvements - sufficient to provide all the world’s present energy needs for several millennia.[15] At present, geothermal wells are rarely more than 3km deep.[1] Upper estimates of geothermal resources assume wells as deep as 10 km. Drilling at this depth is now possible in the petroleum industry, although it is an expensive process. For example, Exxon has announced an 11-kilometre (7 mi) hole at the Chayvo field, Sakhalin,[16] and a 12 km well has been reported on the Kola peninsula.[17] Wells drilled to depths greater than

Hot springs have been used for bathing at least since paleolithic times.[19] The oldest known spa is a stone pool on Lisan mountain built in the Qin dynasty in the 3rd century BC, at the same site where the Huaqing Chi palace was later built. In the first century AD, Romans conquered Aquae Sulis and used the hot springs there to feed public baths and underfloor heating. The admission fees for these baths probably represents the first commercial use of geothermal power. The world’s oldest geothermal district heating system in Chaudes-Aigues, France, has been operating since the 14th century.[7] The earliest industrial exploitation began in 1827 with the use of geyser steam to extract boric acid from volcanic mud in Larderello, Italy. In 1892, America’s first district heating system in Boise, Idaho was powered directly by geothermal energy, and was soon copied in Klamath Falls, Oregon in 1900. A deep geothermal well was used to heat greenhouses in Boise in 1926, and geysers were used to heat greenhouses in Iceland at about


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the same time.[20] Charlie Lieb developed the first downhole heat exchanger in 1930 to heat his house. Steam and hot water from geysers were used to heat homes in Iceland starting in 1943.

Geothermal power
electric power plant in the United States at The Geysers. The original turbine installed lasted for more than 30 years and produced 11 MW net power. The Geysers are currently owned by four companies: the Calpine Corporation, the Northern California Power Agency, Bottlerock Power, and Western GeoPower. They currently produce over 750 MW of power, making them the largest geothermal development in the world.[19] The binary cycle power plant was first demonstrated in 1967 in Russia and later introduced to the USA in 1981.[2] This technology allows the use of much lower temperature geothermal fields that were previously unrecoverable. In 2006, a binary cycle plant in Chena Hot Springs, Alaska, came on-line, producing electricity from a record low geothermal fluid temperature of 57°C.[25]

Global geothermal electric capacity. Upper red line is installed capacity;[11] lower green line is realized production.[1] The 20th century saw the rise of electricity, and geothermal power was immediately seen as a possible generating source. Prince Piero Ginori Conti tested the first geothermal power generator on 4 July 1904, at the same Larderello dry steam field where geothermal acid extraction began. It was a small generator that lit four light bulbs.[21] Later, in 1911, the world’s first geothermal power plant was built there. It was the world’s only industrial producer of geothermal electricity until 1958, when New Zealand built a plant of its own. At this point, the heat pump had long ago been invented by Lord Kelvin in 1852, and the idea of using it to draw heat from the ground had been patented in Switzerland in 1912.[22] But it was not until 1940’s that the idea was successfully implemented. The first commercial geothermal heat pump was designed by J.D. Krocker to heat the Commonwealth Building (Portland, Oregon) in 1946, and Professor Carl Nielsen of Ohio State University built the first residential heat pump two years later.[19] The technology became popular in Sweden as a result of the 1973 oil crisis, and has been growing slowly in worldwide acceptance since then. The development of polybutylene pipe in 1979 greatly augmented its economic viability.[23] As of 2004, there are over a million geothermal heat pumps installed worldwide providing 12 GW of thermal capacity.[24] Each year, about 80,000 units are installed in the USA and 27,000 in Sweden.[24] In 1960, Pacific Gas and Electric began operation of the first successful geothermal

Development around the world
Geothermal electricity is generated in 24 countries around the world including the United States, Iceland, Italy, Germany, Turkey, France, The Netherlands, Lithuania, New Zealand, Mexico, El Salvador, Nicaragua, Costa Rica, Russia, the Philippines, Indonesia, the People’s Republic of China, Japan and Saint Kitts and Nevis. During 2005, contracts were placed for an additional 0.5 GW of electrical capacity in the United States, while there were also plants under construction in 11 other countries.[15] A number of potential sites are being developed or evaluated in South Australia that are several kilometres in depth. When direct use is included, geothermal power is used in over 70 countries.

See also
• Naknek Electric Association

[1] ^ Fridleifsson,, Ingvar B.; Bertani, Ruggero; Huenges, Ernst; Lund, John W.; Ragnarsson, Arni; Rybach, Ladislaus (2008-02-11). O. Hohmeyer and T. Trittin. ed (pdf). The possible role and contribution of geothermal energy to the mitigation of climate change. Luebeck, Germany. pp. 59-80. documenti/IGA/


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Geothermal power

Installed geothermal electric capacity as of 2007 [11] Country USA Philippines Indonesia Mexico Italy Japan New Zealand Iceland El Salvador Costa Rica Kenya Nicaragua Russia Papua-New Guinea Guatemala Turkey China Portugal France Germany Ethiopia Austria Thailand Australia TOTAL Capacity (MW) 2687 1969.7 992 953 810.5 535.2 471.6 421.2 204.2 162.5 128.8 87.4 79 56 53 38 27.8 23 14.7 8.4 7.3 1.1 0.3 0.2 9731.9


[3] [4] [5]

Fridleifsson_et_al_IPCC_Geothermal_paper_2008.pdf. [6] Bertani, Ruggero; Thain, Ian (July 2002). Retrieved on 2009-04-06. "Geothermal Power Generating Plant ^ Lund, J. (September 2004), "100 Years CO2 Emission Survey". IGA News of Geothermal Power Production", Geo(International Geothermal Association) Heat Centre Quarterly Bulletin (Klmath (49): 1-3. http://www.geothermalFalls, Oregon: Oregon Institute of n49.pdf. Retrieved on 2009-05-13. Technology) 25 (3): pp. 11-19, ISSN [7] ^ Lund, John W. (June 2007), 0276-1084, "Characteristics, Development and bulletin/bull25-3/art2.pdf, retrieved on utilization of geothermal resources", 2009-04-13 Geo-Heat Centre Quarterly Bulletin [1] Calpine Corporation page on The (Klamath Falls, Oregon: Oregon Institute Geysers ^ [2], U.S. Department of Energy, of Technology) 28 (2): pp 1-9, ISSN Geothermal FAQ 0276-1084, ^ "Geothermal Basics Overview". Office bulletin/bull28-2/art1.pdf, retrieved on of Energy Efficiency and Renewable 2009-04-16 Energy. [8] Waffel, Mark (March 19, 2008). geothermal/geothermal_basics.html. "Buildings Crack Up as Black Forest Retrieved on 2008-10-01. Town Subsides". Spiegel Online


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International (Der Spiegel). zeitgeist/0,1518,541296,00.html. Retrieved on 2009-02-24. [9] Deichmann, N. et al (2007), Seismicity Induced by Water Injection for Geothermal Reservoir Stimulation 5 km Below the City of Basel, Switzerland, American Geophysical Union, 2007AGUFM.V53F..08D [10] [3], U.S. Department of Energy, Geothermal landuse [11] ^ Bertani, Ruggero (September 2007), "World Geothermal Generation in 2007", Geo-Heat Centre Quarterly Bulletin (Klmath Falls, Oregon: Oregon Institute of Technology) 28 (3): pp. 8-19, ISSN 0276-1084, bulletin/bull28-3/art3.pdf, retrieved on 2009-04-12 [12] Geothermal Energy [13] Reykjavik Energy Invest coordinating other countries with geothermal energy projects [14] Rybach, Ladislaus (September 2007), "Geothermal Sustainability", Geo-Heat Centre Quarterly Bulletin (Klamath Falls, Oregon: Oregon Institute of Technology) 28 (3): pp 2-7, ISSN 0276-1084, art2.pdf, retrieved on 2009-05-9 [15] ^ Tester, Jefferson W. (Massachusetts Institute of Technology) et al (14MB PDF). The Future of Geothermal Energy. Impact of Enhanced Geothermal Systems (Egs) on the United States in the 21st Century: An Assessment. Idaho Falls: Idaho National Laboratory. ISBN 0-615-13438-6. future_of_geothermal_energy.pdf. Retrieved on 2007-02-07. [16] Lloyds List 1/5/07 p 6 [17] Cassino, Adam (2003). "Depth of the Deepest Drilling". The Physics Factbook. Glenn Elert. facts/2003/AdamCassino.shtml. Retrieved on 2009-04-09. [18] The New Math of Alternative Energy retrieved 15 February 2009

Geothermal power
[19] ^ "A History of Geothermal Energy in the United States". U.S. Department of Energy, Geothermal Technologies Program. geothermal/history.html. Retrieved on 2007-09-10. [20] Geysers and Energy Retrieved on 2008-04-12 [21] Tiwari, G. N.; Ghosal, M. K. Renewable Energy Resources: Basic Principles and Applications. Alpha Science Int’l Ltd., 2005 ISBN 1842651250 [22] A History of Geothermal [23] Bloomquist, R. Gordon (December 1999), "Geothermal Heat Pumps, Four Plus Decades of Experience", Geo-Heat Centre Quarterly Bulletin (Klmath Falls, Oregon: Oregon Institute of Technology) 20 (4): pp 13-18, ISSN 0276-1084, art3.pdf, retrieved on 2009-03-21 [24] ^ Lund, J.; Sanner, B.; Rybach, L.; Curtis, R.; Hellström, G. (September 2004), "Geothermal (Ground Source) Heat Pumps, A World Overview", GeoHeat Centre Quarterly Bulletin (Klmath Falls, Oregon: Oregon Institute of Technology) 25 (3): pp. 1-10, ISSN 0276-1084, bulletin/bull25-3/art1.pdf, retrieved on 2009-03-21 [25] Erkan, K.; Holdmann, G.; Benoit, W.; Blackwell, D. (2008), "Understanding the Chena Hot Springs, Alaska, geothermal system using temperature and pressure data", Geothermics 37 (6): 565–585, doi:10.1016/j.geothermics.2008.09.001, ISSN 0375-6505, pii/S0375650508000576, retrieved on 2009-04-11

External links
• Energy Efficiency and Renewable Energy Geothermal Technologies Program • Bassfeld Technology Transfer Introduction to Geothermal Power Generation (3.6 MB PDF file) • MIT - The Future of Geothermal Energy (14 MB PDF file)

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Geothermal power

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