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 testing whether 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.
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.
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)
US Department of Energy pages on geothermal energy (http://www.eere.energy.gov/geothermal/)
A University of Alaska article on geothermal energy (http://www.uaf.edu/energyin/webpage/pages/renewable_energy_tech/geothermal.htm)
Earthquakes due to geothermal energy production (http://quake.wr.usgs.gov/recenteqs/FaultMaps/122-38.htm) - A real-time one week duration earthquake map that always shows a number of small earthquakes due to water injection and geothermal production - observe the upper left corner (Cloverdale) - this is the site of a geothermal plant called "The Geysers"]
Hot Dry Rock Geothermal Energy Technology (http://www.ees4.lanl.gov/hdr/)
Geothermalenergy was first used to produce electricity in Italy in 1903.
Geothermalenergy can be used as an efficient heat source in small end-use applications such as greenhouses, but the consumers have to be located close to the source of heat.
Geothermalenergy has a major environmental benefit because it offsets air pollution that would have been produced if fossil fuels were the energy source.
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, CA.
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, Nicaragua, Russia, the Philippines, Indonesia and Japan.
Currently there are few geothermal resource areas capable of generating electricity at a cost competitive with other energy sources, particularly natural gas.
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