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Sci-Tech Dictionary:

geothermal energy

(¦jē·ō′thərm·əl ′en·ər·jē)

(geophysics) Thermal energy contained in the earth; can be used directly to supply heat or can be converted to mechanical or electrical energy.

 
 
Sci-Tech Encyclopedia: Geothermal power

Thermal or electrical power produced from the thermal energy contained in the Earth (geothermal energy). Use of geothermal energy is based thermodynamically on the temperature difference between a mass of subsurface rock and water and a mass of water or air at the Earth's surface. This temperature difference allows production of thermal energy that can be either used directly or converted to mechanical or electrical energy.

Commercial exploration and development of geothermal energy to date have focused on natural geothermal reservoirs—volumes of rock at high temperatures (up to 662°F or 350°C) and with both high porosity (pore space, usually filled with water) and high permeability (ability to transmit fluid). The thermal energy is tapped by drilling wells into the reservoirs. The thermal energy in the rock is transferred by conduction to the fluid, which subsequently flows to the well and then to the Earth's surface.

There are several types of natural geothermal reservoirs. All the reservoirs developed to date for electrical energy are termed hydrothermal convection systems and are characterized by circulation of meteoric (surface) water to depth. The driving force of the convection systems is gravity, effective because of the density difference between cold, downward-moving, recharge water and heated, upward-moving, thermal water. A hydrothermal convection system can be driven either by an underlying young igneous intrusion or by merely deep circulation of water along faults and fractures. Depending on the physical state of the pore fluid, there are two kinds of hydrothermal convection systems: liquid-dominated, in which all the pores and fractures are filled with liquid water that exists at temperatures well above boiling at atmospheric pressure, owing to the pressure of overlying water; and vapor-dominated, in which the larger pores and fractures are filled with steam. Liquid-dominated reservoirs produce either water or a mixture of water and steam, whereas vapor-dominated reservoirs produce only steam, in most cases superheated.

Although geothermal energy is present everywhere beneath the Earth's surface, its use is possible only when certain conditions are met: (1) The energy must be accessible to drilling, usually at depths of less than 2 mi (3 km) but possibly at depths of 4mi (6–7km) in particularly favorable environments (such as in the northern Gulf of Mexico Basin of the United States). (2) Pending demonstration of the technology and economics for fracturing and producing energy from rock of low permeability, the reservoir porosity and permeability must be sufficiently high to allow production of large quantities of thermal water. (3) Since a major cost in geothermal development is drilling and since costs per meter increase with increasing depth, the shallower the concentration of geothermal energy the better. (4) Geothermal fluids can be transported economically by pipeline on the Earth's surface only a few tens of kilometers, and thus any generating or direct-use facility must be located at or near the geothermal anomaly.

Equally important worldwide is the direct use of geothermal energy, often at reservoir temperatures less than 212°F (100°C). Geothermal energy is used directly in a number of ways: to heat buildings (individual houses, apartment complexes, and even whole communities); to cool buildings (using lithium bromide absorption units); to heat greenhouses and soil; and to provide hot or warm water for domestic use, for product processing (for example, the production of paper), for the culture of shellfish and fish, for swimming pools, and for therapeutic (healing) purposes.

The use of geothermal energy for electric power generation has become widespread because of several factors. Countries where geothermal resources are prevalent have desired to develop their own resources in contrast to importing fuel for power generation. In countries where many resource alternatives are available for power generation, including geothermal, geothermal has been a preferred resource because it cannot be transported for sale, and the use of geothermal energy enables fossil fuels to be used for higher and better purposes than power generation. Also, geothermal steam has become an attractive power generation alternative because of environmental benefits and because the unit sizes are small (normally less than 100 MW). Moreover, geothermal plants can be built much more rapidly than plants using fossil fuel and nuclear resources, which, for economic purposes, have to be very large in size. Electrical utility systems are also more reliable if their power sources are not concentrated in a small number of large units.

The most common process is the steam flash process, which incorporates steam separators to take the steam from a flashing geothermal well and passes the steam through a turbine that drives an electric generator. A more efficient utilization of the resource can be obtained by using the binary process on resources with a temperature less than 360°F (180°C). This process is normally used when wells are pumped. The pressurized geothermal brine yields its heat energy to a second fluid in heat exchangers and is reinjected into the reservoir. The second fluid (commonly referred to as the power fluid) has a lower boiling temperature than the geothermal brine and therefore becomes a vapor on the exit of the heat exchangers. It is separately pumped as a liquid before going through the heat exchangers. The vaporized, high-pressure gas then passes through a turbine that drives an electric generator. See also Electric power generation.

 
Britannica Concise Encyclopedia: geothermal energy

Power obtained by using heat from the Earth's interior. Most geothermal resources are in regions of active volcanism. Hot springs, geysers, pools of boiling mud, and fumaroles are the most easily exploited sources. The ancient Romans used hot springs to heat baths and homes, and similar uses are still found in Iceland, Turkey, and Japan. Geothermal energy's greatest potential lies in the generation of electricity. It was first used to produce electric power in Italy in 1904. Today geothermal power plants are in operation in New Zealand, Japan, Iceland, Mexico, the U.S., and elsewhere.

For more information on geothermal energy, visit Britannica.com.

 
Science Dictionary: geothermal energy

Energy obtained by tapping underground reservoirs of heat, usually near volcanoes or other hot spots on the surface of the Earth.

  • At present, little of the world's energy supply is obtained from these sources.

    •  
    Wikipedia: geothermal power
    Krafla Geothermal Station in northeast Iceland
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    Krafla Geothermal Station in northeast Iceland


    Renewable energy

    Geothermal power is energy generated by heat stored beneath the Earth's surface. As of 2007, geothermal power supplies less than 10% of the world's energy.[1] Geothermal comes from the Greek words geo, meaning earth, and therme, meaning heat. Prince Piero Ginori Conti tested the first geothermal power plant 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 in The Geysers, a geothermal field in California.[3]

    Electricity generation

    Three different types of power plants - dry steam, flash, and binary - are used to generate electricity from geothermal energy, depending on temperature, depth, and quality of the water and steam in the area.[4] In all cases the condensed steam and remaining geothermal fluid is injected back into the ground to pick up more heat. In some locations, the natural supply of water producing steam from the hot underground magma deposits has been exhausted and processed waste water is injected to replenish the supply. Most geothermal fields have more fluid recharge than heat, so re-injection can cool the resource, unless it is carefully managed.

    Flash steam

    Flash steam power plants use hot water above 182°C (360°F) from geothermal reservoirs. The high pressure underground keeps the water in the liquid state, although it is well above the boiling point of water at sea level. As the water is pumped from the reservoir to the power plant, the drop in pressure causes the water to convert, or "flash", into steam to power the turbine. Any water not flashed into steam is injected back into the reservoir for reuse.[4] Flash steam plants, like dry steam plants, emit small amounts of gases and steam.[5]

    Flash steam plants are the most common type of geothermal power generation plants in operation today. An example of an area using the flash steam operation is the CalEnergy Navy I flash geothermal power plant at the Coso geothermal field.

    Binary-cycle

    The water used in binary-cycle power plants is cooler than that of flash steam plants, from 107 to 182°C (225-360°F)[5]. The hot fluid from geothermal reservoirs is passed through a heat exchanger which transfers heat to a separate pipe containing fluids with a much lower boiling point.[4] These fluids, usually Iso-butane or Iso-pentane, are vaporized to power the turbine.[6]. The advantage to binary-cycle power plants is their lower cost and increased efficiency. These plants also do not emit any excess gas and, because they use fluids with a lower boiling point than water, are able to utilize lower temperature reservoirs, which are much more common. Most geothermal power plants planned for construction are binary-cycle.[6]

    Enhanced Geothermal Systems

    Main article: Hot dry rock geothermal energy

    Enhanced Geothermal Systems (EGS), also known as Hot-dry-rock systems, involve pumping water into hot rocks in the earth, rather than harvesting hot water already in the earth. This type of geothermal system has many advantages over the others, as it can be used anywhere, not just in tectonically active regions. However, it requires deeper drilling than the other forms of geothermal energy harvesting.[7]

    Advantages

    Geothermal energy offers a number of advantages over traditional fossil fuel based sources. From an environmental standpoint, the energy harnessed is clean and safe for the surrounding environment.[8] It is also sustainable because the hot water used in the geothermal process can be re-injected into the ground to produce more steam. In addition, geothermal power plants are unaffected by changing weather conditions.[9] Geothermal power works continually, day and night, providing baseload power. From an economic view, geothermal energy is extremely price competitive in some areas and reduces reliance on fossil fuels and their inherent price unpredictability.[10] Given enough excess capacity, geothermal energy can also be sold to outside sources such as neighboring countries or private businesses that require energy. 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.[11]

    Disadvantages

    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 Hot dry rock geothermal energy Enhanced Geothermal water into hot dry rock where no water was before.[12] Dry steam and flash steam power plants also emit low levels of carbon dioxide, nitric oxide, and sulfur, although at roughly 5% of the levels emitted by fossil fuel power plants.[11] Geothermal plants can be built with emissions-controlling systems that can inject these gases back into the earth, thereby reducing carbon emissions to less than 0.1% of those from fossil fuel power plants.[7]

    Although geothermal sites are capable of providing heat for many decades, eventually specific locations may cool down. It is likely that in these locations, the system was 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. Some interpret this as meaning a specific geothermal location can undergo depletion, and question whether geothermal energy is truly renewable, but if left alone, these places will recover some of their lost heat, as the mantle has vast heat reserves. The government of Iceland states: "It should be stressed that the geothermal resource is not strictly renewable in the same sense as the hydro resource." It estimates that Iceland's geothermal energy could provide 1700 MW for over 100 years, compared to the current production of 140 MW.[13]

    Potential

    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.[4] 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.[14]

    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'.[15]

    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.[14]

    The MIT report calculated the world's total EGS resources to be over 13,000 ZJ, of which 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 energy needs for several millennia.[14]

    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. There seems no reason why the steam should not feed an existing coal, oil or nuclear fired generating plant.

    Drilling at this depth is now routine for the oil industry (Exxon announced an 11 km hole at the Chayvo field, Sakhalin. Lloyds List 1/5/07 p 6). The technological challenges are to drill wider bores and to break rock over larger volumes. Apart from the energy used to make the bores, the process releases no greenhouse gases. Compared to the difficulties of developing other forms of energy supply such as nuclear, wind, wave, solar etc.

    Other important countries are China, Hungary, Nicaragua, Iceland, and New Zealand. There is also a planned site in Adelaide, Australia that is over 1km long.

    History of development

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

    Prince Piero Ginori Conti tested the first geothermal power plant on 4 July 1904, at the Larderello dry steam field in Italy.

    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.[16]

    In 1960, Pacific Gas and Electric began operation of the first successful geothermal power plant in the United States at The Geysers. It lasted for more than 30 years and produced 11 MW net power.[16]

    Development around the world

    Geothermal power is generated in over 20 countries around the world including Iceland, the United States, Italy, France, Samogitia (Lithuania), New Zealand, Mexico, Nicaragua, Costa Rica, Russia, the Philippines, Indonesia, the People's Republic of China and Japan. Canada's government (which officially notes some 30,000 earth-heat installations for providing space heating to Canadian residential and commercial buildings) reports a test geothermal-electrical site in the Meager Mountain-Pebble Creek area of British Columbia, where a 100 MW facility could be developed.

    Africa

    Geothermal power is very cost-effective in the Rift area of Africa. 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) run by geothermal specialist geothermal specialist Ormat. 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.

    Australia

    Main article: Geothermal energy exploration in Central Australia

    Iceland

    Main article: Geothermal power in Iceland

    Iceland is situated in an area with a high concentration of volcanoes, making it an ideal location for generating geothermal energy. Over 26% of Iceland's energy is generated from geothermal sources. In addition, geothermal heating is used to heat 87% of homes in Iceland.[17]

    New Zealand

    Main article: Kawerau geothermal power station
    Geothermal power plant in Valencia, Negros Oriental, Philippines
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    Geothermal power plant in Valencia, Negros Oriental, Philippines

    Philippines

    The US 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. [18][19] 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.[20] 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 2.02 million kilowatts of geothermal power, while the Philippines can generate 1.93 million kilowatts. (Italy is third with 0.79 million kilowatts). [21] Early statistics from the Institute for Green Resources and Environment stated that Philippine geothermal energy provides 16% of the country's electricity.[22] 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.[21] Leyte is one of the islands in the Philippines where the first geothermal power plant started operations in July 1977.[19]

    United Kingdom

    Main article: Geothermal power in the United Kingdom
    The West Ford Flat power plant is one of 21 power plants at The Geysers
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    The West Ford Flat power plant is one of 21 power plants at The Geysers

    United States

    Main article: Geothermal energy in the United States


    The United States is the country with the greatest geothermal energy production.[23]

    The largest dry steam field in the world is The Geysers, 72 miles (116 km) 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 renewable 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 megawatts.

    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

    References

    1. ^ January 2007 IEA Fact sheet: "Renewables in Global Energy Supply"
    2. ^ THE CELEBRATION OF THE CENTENARY OF THE GEOTHERMAL-ELECTRIC INDUSTRY WAS CONCLUDED IN FLORENCE ON DECEMBER 10th, 2005 in IGA News #64, April - June 2006. Publication of UGI/Italian Geothermal Union.
    3. ^ [1] Calpine Corporation page on The Geysers
    4. ^ a b c Geothermal Technologies Program: Geothermal Power Plants. U.S. Department of Energy. Retrieved on 2007-09-11.
    5. ^ a b
    6. ^ a b Geothermal Energy for Electric Power
    7. ^ a b
    8. ^ Geothermal Energy
    9. ^ Kenya Looks Underground for Power
    10. ^ Overview, U.S. Department of Energy
    11. ^ a b Geothermal Energy
    12. ^ "Energy search goes underground", Yahoo! News, Associated Press, 2007-08-06. Retrieved on 2007-09-11. 
    13. ^ RESPONSE OF WAIRAKEI GEOTHERMAL RESERVOIR TO 40 YEARS OF PRODUCTION, 2006 (pdf) Allan Clotworthy, Proceedings World Geothermal Congress 2000. (accessed 30 March)
    14. ^ a b c The Future of Geothermal Energy, Idaho National Laboratory
    15. ^ Geothermal Energy Association - Washington, DC (http). Retrieved on 2007-02-07.
    16. ^ a b A History of Geothermal Energy in the United States. U.S. Department of Energy, Geothermal Technologies Program. Retrieved on 2007-09-10.
    17. ^ Energy Statistics in Iceland. Orkustofnun (Iceland Energy Authority). Retrieved on 2006-09-20.
    18. ^ Geothermal Education Office - The Philippines
    19. ^ a b Birsic, R.J. The Phillipines geothermal success story Geothermal Energy(vol. 8, Aug.-Sept. 1980, p. 35-44)
    20. ^ World Geothermal Congress 2000
    21. ^ a b IGA: What is Geothermal Energy?
    22. ^ Institute for Green Resources and Environment: Asian Geothermal Symposium
    23. ^ All About Geothermal Energy - Current Use. Geothermal Energy Association. Retrieved on 2007-01-25.

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