Geothermics is the science of the earth's internal heat. Most people don't realize that heat is produced within the crust and upper mantle of the earth's surface by decaying radioactive elements. Deep circulating water and subtle movements of molten rock diffuse this geothermal energy to the earth's surface, where its purposes range from therapeutic hot springs to space heating and industrial drying processes.
Tuscany, Italy first tapped into this natural source of energy to develop electric power in 1904. Tuscany still continues to draw from geothermal energy and other places around the world have followed their lead. Geothermal fluids are now heating buildings in Idaho, Oregon, Icelandic city Reykjavik, Budapest, and Paris suburbs.
The United States owns claim to the world's largest geothermal complex at the Geysers of northern California. The Geysers produce enough geothermal energy to provide electricity to the entire San Francisco metropolitan area. Other geothermal energy plants are popping up in Nevada, Utah, and Hawaii, for a total United States capacity of around 2800 megawatts at last calculation. Geothermal electricity is becoming a worldwide phenomenon, with geothermal capacity systems already installed in eighteen countries.
So how does geothermic energy actually work? The earth's natural hot water and steam are used in three basic ways to generate electricity. The world's most common method happens in flash-stream power plants, where steam is separated out from hot geothermal water and then travels through insulated pipes into turbines. The second method involves dry-steam power plants, where reservoirs tap directly into the hot steam, and the steam drives the turbines directly. The third method uses binary power plants, which run geothermal water through a heat exchanger. Heat is then converted to a working fluid which drives the turbines to produce electricity. A fourth method exists, but it is quite rare and uses hybrid power plants where the binary and flash methods are combined.
There is a potential revolutionary concept at work here and experiments are currently underway to further the use of geothermal energy. Fenton Hill conducted one test program from 1970 to 1996, where he tried drilling into hot, dry rock just a few kilometers below the earth's surface. He injected high pressure surface water to fracture the rock, and then pumped in cold water to become superheated. Then he brought the superheated water back to the surface and converted it with a heat exchanger to produce electricity. There are a handful of other experiments being carried out in Australia, Britain, Germany, Japan, France, and Switzerland.