Geothermics

Geothermics, science pertaining to the earth's interior heat. Its main practical application is in finding natural concentrations of hot water, the source of geothermal energy, for use in electric power generation and direct heat applications such as space heating and industrial drying processes. Heat is produced within the crust and upper mantle of the earth primarily by decay of radioactive elements. This geothermal energy is transferred to the earth's surface by diffusion and by convection movement of magma (molten rock) and deep-lying circulating water. Surface hydrothermal manifestations include hot springs, geysers, and fumaroles. Hot springs have been used since ancient times for therapy and for recreational purposes. Early Norse settlers in Iceland brought water from nearby hot springs into their shelters by means of wooden conduits.

Steam produced from the naturally hot fluid that exists in geothermal systems is an alternative to pressurized steam produced in power plants by burning fossil fuels, by utilizing nuclear energy, or by other means. Modern drilling in geothermal systems reaches concentrations of water and steam, heated by much deeper magma, at depths up to 3000 m (10,000 ft). Steam is purified at the wellhead before being transported in large, insulated pipes to turbines.

Geothermal energy was developed for electrical power in 1904 in Tuscany (Toscana), Italy, where power production continues today. Geothermal fluids are also used to heat groups of buildings in Budapest, Hungary; a Paris suburb; all of Reykjavík and other Icelandic cities; most of Klamath Falls, Oregon; and (since 1890) part of Boise, Idaho.

The world's largest geothermal power complex is in the U.S. at The Geysers of northern California. As of 1991, The Geysers had a generating capacity of approximately 1400 megawatts (MW), enough to satisfy most of the electrical demand of the San Francisco metropolitan area 170 km (105 mi) to the south. Geothermal power plants are operating at other sites in California, Nevada, Utah, and Hawaii, for a total U.S. capacity of approximately 2800 MW in 1990. The U.S. has an estimated total potential of 23,000 MW for 30 years, based on all known hydrothermal systems hotter than 150° C (300° F). A possible technique for development of geothermal energy was tested in New Mexico by drilling into hot, dry rock beneath a quiescent volcanic system and injecting surface water that returns as superheated steam. Worldwide, installed geothermal capacity in 18 countries was about 5800 MW in 1990, and as much as 9000 MW is planned by 1995.