Geothermal power

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Geothermal power (from the Greek roots geo, meaning earth, and thermos, meaning heat) is energy generated from heat stored in the earth, or the collection of absorbed heat derived from underground.

Prince Piero Ginori Conti tested the first geothermal generator on 4 July 1904, at the Larderello dry steam field in Italy.[1] The largest group of geothermal power plants in the world is located at The Geysers, a geothermal field in California, United States.[2] The Philippines and Iceland are the only countries to generate a significant percentage of their electricity from geothermal sources; in both countries 15-20% of power comes from geothermal plants. As of 2008, geothermal power supplies less than 1% of the world's energy.[3] The most common type of geothermal power plants (binary plants) are closed cycle operations and release essentially no Greenhouse gas emissions; geothermal power is available 24 hours a day with average availabilities above 90% (compared to about 75% for coal plants). [4]


Geothermal technologies

Geothermal energy methods.

Geothermal resources range from shallow ground to hot water and rock several kilometres below the Earth's surface, and even further down to the extremely hot molten rock called magma. Wells over 1.5 km deep can be drilled into underground reservoirs to tap steam and very hot water that can be brought to the surface for use in a variety of applications.

Geothermal technologies include:

  1. Conventional geothermal
    • Binary cycle power plants, which pass moderately hot geothermal water by a secondary fluid with a much lower boiling point than water. This causes the secondary fluid to flash to vapor, which then drives the turbines. This is the most common type of geothermal[5], both ORC and Kalina cycles are used.
    • Hot dry rock geothermal energy: Using deep wells into hot rock, a fluid is heated and used to generate power. Also known as EGS or Enhanced Geothermal Systems
    • Dry steam plants, which directly use geothermal steam to turn turbines;
    • Flash steam plants, which pull deep, high-pressure hot water into lower-pressure tanks and use the resulting flashed steam to drive turbines; and
  2. Direct heat: Hot water near Earth's surface can be piped directly into facilities and used to heat buildings, grow plants in greenhouses, dehydrate onions and garlic, heat water for fish farming, and pasteurize milk. Some cities pipe the hot water under roads and pavements to melt snow. District heating applications use networks of piped hot water to heat buildings in whole communities.[5]
  3. Geothermal heat pump: Almost everywhere, the upper 10 feet (3.0 m) of Earth's surface maintains a nearly constant temperature between 10 and 16° celsius (50 and 60° F). A geothermal heat pump system consists of pipes buried in the shallow ground near a building, a heat exchanger, and ductwork into the building. In winter, heat from the relatively warmer ground goes through the heat exchanger into the house. In summer, hot air from the house is pulled through the heat exchanger into the relatively cooler ground. Heat removed during the summer can be used as no-cost energy to heat water.[5]


Krafla Geothermal Station in northeast Iceland

Geothermal power requires no fuel, and is therefore virtually emissions free[6] and insusceptible to fluctuations in fuel cost. And because a geothermal power station doesn't rely on transient sources of energy, unlike, for example, wind turbines or solar panels, its capacity factor can be quite large; up to 90% in practice.[7]

It is considered to be sustainable[7] because the heat extraction is small compared to the size of the heat reservoir. While individual wells may need to recover, geothermal heat is inexhaustible and is replenished from greater depths. 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.[7]

Geothermal has minimal land use requirements; 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.[8]. It also offers a degree of scalability: a large geothermal plant can power entire cities while smaller power plants can supply more remote sites such as rural villages.[6]


From an engineering perspective, the geothermal fluid is corrosive and, worse, is at a low temperature compared to steam from boilers. By the laws of thermodynamics this low temperature limits the efficiency of heat engines in extracting useful energy during the generation of electricity. Much of the heat energy is lost, unless there is also a local use for low-temperature heat such as greenhouses, timber mills, and district heating. However, since this energy is almost free once the plant is established, the efficiency of the system is not as significant as for a coal or other powered plant.

There are several environmental concerns behind geothermal energy. Construction of the power plants can adversely affect land stability in the surrounding region. This is mainly a concern with Enhanced Geothermal Systems, where water is injected into hot dry rock where no water was before. Dry steam and flash steam power plants also emit low levels of carbon dioxide, nitric oxide, and sulphur, although at roughly 5% of the levels emitted by fossil fuel power plants. However, geothermal plants can be built with emissions-controlling systems that can inject these substances back into the earth, thereby reducing carbon emissions to less than 0.1% of those from fossil fuel power plants. Hot water from geothermal sources will 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.

Although geothermal sites are capable of providing heat for many decades, locations may eventually cool down. For example, the world's second-oldest geothermal generator at Wairakei has reduced production. It is likely that locations like these were designed too large for the site, since there is only so much energy that can be stored and replenished in a given volume of earth. If left alone, however, these places should recover their lost heat, as the Earth's mantle and core have vast heat reserves. Geothermal and biomass are the only two renewable resources which must be carefully managed in order to avoid local depletion.[9] An assessment of the total potential for electricity production from the high-temperature geothermal fields in Iceland gives a value of about 1500 TWh (total) or 15 TWh per year over a 100 year period. The electricity production capacity from geothermal fields is now only 1.3 TWh per year.[citation needed]


At present, only a small percentage of the total potential power is effectively used

If heat recovered by ground source heat pumps is included, the non-electric generating capacity of geothermal energy is estimated at more than 100 GW (gigawatts of thermal power) and is used commercially in over 70 countries. During 2005, contracts were placed for an additional 0.5 GW of capacity in the United States, while there were also plants under construction in 11 other countries.[10]

Estimates of exploitable worldwide geothermal energy resources vary considerably. According to a 1999 study, it was thought that this might amount to between 65 and 138 GW of electrical generation capacity 'using enhanced technology'.[11]

A 2006 report by MIT, that took into account the use of Enhanced Geothermal Systems (EGS), concluded that it would be affordable to generate 100 GWe (gigawatts of electricity) or more by 2050 in the United States alone, for a maximum investment of 1 billion US dollars in research and development over 15 years.[10]

The MIT report calculated the world's total EGS resources to be over 13,000 ZJ. Of these, 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.[10]

The key characteristic of an EGS (also called a Hot Dry Rock system), is that it reaches at least 10 km down into hard rock. At a typical site two holes would be bored and the deep rock between them fractured. Water would be pumped down one and steam would come up the other. The MIT report estimated that there was enough energy in hard rocks 10 km below the United States to supply all the world's current needs for 30,000 years.[10] However, favourable locations for EGS (eg in central Australia) may require wells only 4 kilometres (2 mi) deep.[citation needed]

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.[12] Wells drilled to depths greater than 4 kilometres (2 mi) generally incur drilling costs in the tens of millions of dollars.[citation needed] The technological challenges are to drill wide bores at low cost and to break rock over larger volumes. Apart from the energy used to make the bores, the process releases no greenhouse gases.

Other important countries considered high in potential for development are the People's Republic of China, Hungary, Mexico, Iceland, and New Zealand. A number of potential sites are being developed or evaluated in South Australia that are several kilometres in depth.

History of development

Extraction of geothermal power has been limited to the edges of tectonic plates.

Geothermal steam and hot springs have been used for centuries for bathing and heating, but it was not until the 20th century that geothermal power started being used to make electricity.

Prince Piero Ginori Conti tested the first geothermal power generator on 4 July 1904, at the Larderello dry steam field in Italy. It was a small generator that lit four light bulbs.[13] 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.

The first geothermal power plant in the United States was made in 1922 by John D. Grant at The Geysers Resort Hotel. After drilling for more steam, he was able to generate enough electricity to light the entire resort. Eventually the power plant fell into disuse, as it was not competitive with other methods of energy production.[14]

In 1960, Pacific Gas and Electric began operation of the first successful geothermal 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 the Calpine Corporation and the Northern California Power Agency. They currently produce over 750 MW of power.[14]

Development around the world

Geothermal power is generated in over 20 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. Chevron Corporation is the world's largest producer of geothermal energy. Other companies as Reykjavik Energy Invest also help other countries of setting up geothermal energy plants. [15]


Geothermal energy is only in the exploration and development stage in Australia and not yet a source of usable electrical power.


The largest conventional geothermal resources are located in British Columbia, Yukon and Alberta; these regions also contain potential for EGS Enhanced Geothermal Systems. Initial resource estimates indicate that geothermal energy could meet half of British Columbia's electricity needs. [4]

Canada's government (which officially notes some 30,000 earth-heat installations for providing space heating to Canadian residential and commercial buildings) reports that the most advanced project exists as a test geothermal-electrical site in the Meager Mountain-Pebble Creek area of British Columbia, where a 100 - 300 MW facility could be developed.

The remaining Canadian provinces and territories contain potential for Enhanced Geothermal. Low temperature - or direct heat potential (sometimes called geothermal heating) exist everywhere in Canada.


Denmark has two geothermal power plants, one in Thisted started in 1988, and one in Copenhagen started in 2005.[16][17]


Internal view of the ORC-power plant located in Neustadt-Glewe / Northern Germany

Electricity from geothermal sources is expected to grow in Germany mainly because a law that benefits the production of geothermal electricity and guarantees a feed-in tariff. Less than 0.4 percent of Germany's total primary energy supply came from geothermal sources in 2004. But after a renewable energy law that introduced a tariff scheme of EU €0.15 [US $0.23] per kilowatt-hour (kWh) for electricity produced from geothermal sources came into effect that year, a construction boom was sparked and the new power plants are now starting to come online. However the first German geothermal power plant had been build in 2003 in Neustadt-Glewe located in northern Germany. This plant was not just the first one operating with the ORC-technology Organic Rankine Cycle but also with the lowest temperature.[18]

This first project proved that the generation of electricity from geothermal sources on low temperature levels is possible in Germany. In the same year the TAB (bureau for technological impact assessment of the German Bundestag) concluded that Germany's geothermal resources could be used to supply the entire base load of the country. A conclusion that had been made regarding the fact that geothermal sources have to be developed sustainably because they can cool out if overused.[19]


Iceland is situated in an area with a high concentration of volcanoes, making it an ideal location for generating geothermal energy. 19.1% of Iceland's electrical energy is generated from geothermal sources.[20] In addition, geothermal heating is used to heat 87% of homes in Iceland. Icelanders plan to be 100% fossil fuel-free in the near future.[21]


Geothermal power is very cost-effective in the Rift area of Kenya, Africa. Kenya was the first African country to build geothermal energy sources. Kenya's KenGen has built two plants, Olkaria I (45 MW) and Olkaria II (65 MW), with a third private plant Olkaria III (48 MW). Plans are to increase production capacity by another 576 MW by 2017, covering 25% of Kenya's electricity needs, and correspondingly reducing dependency on imported oil. In Ethiopia there is another plant for geothermal power (in 2008 some experts from Iceland calculated that Ethiopia has at least 1000 MW of that energy). Hot spots have been found across the continent, especially in the Great Rift Valley.


Mexico has the third greatest geothermal energy production with an installed capacity of 959.50 MW by December 2007. This represents 3.24% of the total electricity generated in the country.[22][23][24]

New Zealand

New Zealand has operated geothermal power stations since the 1950s. First developments were at Wairakei and Kawerau (direct heat and power). Other stations include Ohaaki, Rotokawa, Poihipi, Ngawha and Mokai.

New Zealand geothermal fields [5]


Portugal has a geothermal power plant on São Miguel Island, in the Azores islands.


Geothermal power plant in Valencia, Negros Oriental, Philippines

The Geothermal Education Office and a 1980 article entitled "The Philippines geothermal success story" by Rudolph J. Birsic published in the journal Geothermal Energy (vol. 8, Aug.-Sept. 1980, p. 35-44) note the remarkable geothermal resources of the Philippines.[25][26] During the World Geothermal Congress 2000 held in Beppu, Ōita Prefecture of Japan (May-June 2000), it was reported that the Philippines is the largest consumer of electricity from geothermal sources and highlighted the potential role of geothermal energy in providing energy needs for developing countries.[27]

According to the International Geothermal Association (IGA), worldwide, the Philippines ranks second to the United States in producing geothermal energy. As of the end of 2003, the US has a capacity of 2020 megawatts of geothermal power, while the Philippines can generate 1930 megawatts. (Mexico is third with 953 MW according to IGA). [28] Early statistics from the Institute for Green Resources and Environment stated that Philippine geothermal energy provides 16% of the country's electricity.[29] By 2005, geothermal energy accounted for 17.5% of the country's electricity production. [30]. More recent statistics from the IGA show that combined energy from geothermal power plants in the islands of Luzon, Leyte, Negros and Mindanao account for approximately 27% of the country's electricity generation. Leyte is one of the islands in the Philippines where the first geothermal power plant started operations in July 1977.[26]


There is a geothermal plant on the north slope of Mutnovsky volcano in Kamchatka, presumably supplying power to Petropavlovsk-Kamchatsky

Saint Kitts and Nevis

The island of Nevis, long known for its numerous hot springs, commenced drilling for the construction of a geothermal powerplant at Spring Hill, Nevis, in January 2008. When completed (estimated 2010), the plant will supply 50 megawatts of electricity, enough to fulfill all of Nevis' demand (approximately 10 megawatts), and also enough to export to neighbouring Saint Kitts as well as other nearby islands via submarine electrical transmission cables. The project, being undertaken by West Indies Power, will make Saint Kitts and Nevis the first country in the Caribbean to utilize large-scale Geothermal energy, and, when complete, will make Saint Kitts and Nevis one of the least dependent nations in the world on fossil-fuels.[31]


Turkey currently has the 5th highest direct utilization and capacity of geothermal energy in the world.[32]

United Kingdom

There are no geothermal electrical plants in the UK, but there are a small number of geothermal heating schemes in operation.

United States

The West Ford Flat power plant is one of 21 power plants at The Geysers

The United States of America is the country with the greatest geothermal energy production.[33]

The largest dry steam field in the world is The Geysers, 116 km (72 miles) north of San Francisco. The Geysers began in 1960, has 1360 MW of installed capacity and produces over 750 MW net. Calpine Corporation now owns 19 of the 21 plants in The Geysers and is currently the United States' largest producer of geothermal energy. The other two plants are owned jointly by the Northern California Power Agency and the City of Santa Clara's municipal Electric Utility (now called Silicon Valley Power). Since the activities of one geothermal plant affects those nearby, the consolidation plant ownership at The Geysers has been beneficial because the plants operate cooperatively instead of in their own short-term interest. The Geysers is now recharged by injecting treated sewage effluent from the City of Santa Rosa and the Lake County sewage treatment plant. This sewage effluent used to be dumped into rivers and streams and is now piped to the geothermal field where it replenishes the steam produced for power generation.

Another major geothermal area is located in south central California, on the southeast side of the Salton Sea, near the cities of Niland and Calipatria, California. As of 2001, there were 15 geothermal plants producing electricity in the area. CalEnergy owns about half of them and the rest are owned by various companies. Combined the plants have a capacity of about 570 MW.

The Basin and Range geologic province in Nevada, southeastern Oregon, southwestern Idaho, Arizona and western Utah is now an area of rapid geothermal development. Several small power plants were built during the late 1980s during times of high power prices. Rising energy costs have spurred new development. Plants in Nevada at Steamboat near Reno, Brady/Desert Peak, Dixie Valley, Soda Lake, Stillwater and Beowawe now produce about 235 MW.

See also


  2. ^ [1] Calpine Corporation page on The Geysers
  3. ^ 2008 IEA Key World Energy Statistics: "Total Primary Energy Supply"
  4. ^ "Department of Energy, Geothermal Technologies Program FAQ
  5. ^ a b c "Geothermal Basics Overview". Office of Energy Efficiency and Renewable Energy. Retrieved on 2008-10-01. 
  6. ^ a b Geothermal Energy
  7. ^ a b c [2], U.S. Department of Energy, Geothermal FAQ
  8. ^ [3], U.S. Department of Energy, Geothermal landuse
  9. ^ The New Math of Alternative Energy retrieved 15 February 2009
  10. ^ a b c d The Future of Geothermal Energy, Idaho National Laboratory
  11. ^ "Geothermal Energy Association - Washington, DC". Retrieved on 2007-02-07. 
  12. ^ Lloyds List 1/5/07 p 6
  13. ^ Tiwari, G. N.; Ghosal, M. K. Renewable Energy Resources: Basic Principles and Applications. Alpha Science Int'l Ltd., 2005 ISBN 1842651250
  14. ^ a b "A History of Geothermal Energy in the United States". U.S. Department of Energy, Geothermal Technologies Program. Retrieved on 2007-09-10. 
  15. ^ Reykjavik Energy Invest coordinating other countries with geothermal energy projects
  16. ^ Thisted Varmeforsyning Geotermi
  17. ^ Allan Mahler & Jesper Magtengaard, Proceeding World Geothermal Congress 2005, Geothermal Development in Denmark, Country Update WGC 2005
  18. ^ Geothermal ORC-power modules
  19. ^ study of possible geothermal power production in Germany
  20. ^ "International Energy Agency, Energy Statistic - Electricity/Heat in Iceland in 2005". Retrieved on 2007-04-24. 
  21. ^ "Energy Statistics in Iceland". Orkustofnun (Iceland Energy Authority). Retrieved on 2006-09-20. 
  22. ^ Federal Commission of Electricity of Mexico/Geothermal-electric production 2007
  23. ^ Main aspects of geothermal energy in Mexico
  24. ^ IGA electricity generation for Mexico
  25. ^ Geothermal Education Office - The Philippines
  26. ^ a b Birsic, R.J. The Philippines geothermal success story Geothermal Energy (vol. 8, Aug.-Sept. 1980, p. 35-44)
  27. ^ World Geothermal Congress 2000
  28. ^ IGA electricity generation for Mexico
  29. ^ Institute for Green Resources and Environment: Asian Geothermal Symposium
  30. ^ "International Energy Agency, Energy Statistic - Electricity/Heat in Philippines in 2005". Retrieved on 2007-04-24. 
  31. ^ Geothermal Development Drilling Begins on Nevis
  32. ^ Lund, J (2005). "Direct application of geothermal energy: 2005 Worldwide review". Geothermics 34: 691. doi:10.1016/j.geothermics.2005.09.003. 
  33. ^ "All About Geothermal Energy - Current Use". Geothermal Energy Association. Retrieved on 2007-01-25. 

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