Geothermal power

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Thermally active area, New Zealand.

Geothermal power is electricity generated by utilizing naturally occurring geological heat sources. It is a form of renewable energy.


Types of geothermal sources

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Geothermal energy sources.

Geothermal power is generally harnessed in one of three ways. Large scale electrical generation is possible in areas near geysers or hot springs by utilizing naturally occurring steam, superheated ground water or using geothermal heat to heat a heat-transfer fluid. Experiments are in progress to determine if a fourth method, deep wells into "hot dry rocks", can be economically used to heat water pumped down from the surface. A hot dry rock project in the United Kingdom was abandoned after it was pronounced economically unviable in 1989. HDR programs are currently being developed in Australia, France, Switzerland and Germany. Magma (molten rock) resources offer extremely high-temperature geothermal opportunities, but existing technology does not allow recovery of heat from these resources.

Electrical generation

Geothermal-generated electricity was first produced at Larderello, Italy, in 1904. Since then, the use of geothermal energy for electricity has grown worldwide to about 8,000 megawatts of which the United States produces 2700 megawatts. The largest dry steam field in the world is The Geysers, about 90 miles north of San Francisco began in 1960 which produces 2000 MWe. 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 Santa Clara Electric. 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.

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. 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 produce about 570 megawatts.

Geothermal power is generated in over 20 countries around the world including Iceland (producing 17% of its electricity from geothermal sources), the United States, Italy, France, New Zealand, Mexico, the Philippines, Indonesia 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 B.C, where a 100 MWe facility might be developed at that site.

Water injection

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. In at least one location, this has resulted in small but frequent earthquakes (see external link below). This has led to disputes about whether the plant owners are liable for the damage the earthquakes cause.

Heat depletion

Although geothermal sites are capable of providing heat for many decades, eventually they are depleted as the ground cools. [1] ( 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 15 TWh per year over 100 years, compared to the current production of 1.2 TWh per year. [2] (


Currently there are few geothermal resource areas capable of generating electricity at a cost competitive with other energy sources, such as natural gas and coal. Some do not have a high enough temperature to produce steam and others don't have the water to produce steam, which is necessary for current plant designs. Geothermal areas without steam are called hot dry rock areas and methods for exploiting them are continuing. Also, instead of producing electricity, lower temperature areas can provide space and process heating. As of 1998, the U.S. has 18 district heating systems, 28 fish farms, 12 industrial plants, 218 spas and 38 greenhouses that use geothermal heat.


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