Geothermal energy is energy that comes from the heat of Earth. Most geothermal energy is converted to electric power. Geothermal energy is available in areas near geological faults and hot spots. Near these areas, molten material called magma from deep beneath Earth’s surface penetrates the planet’s crust. The magma heats rocks several miles or kilometers below the surface. It also heats aquifers (layers of porous material filled with ground water). These underground formations are also called geothermal reservoirs. They may reach temperatures over 570 °F (300 °C). Geothermal wells reach these aquifers and convey the geothermal fluid to a power plant on the surface. The wells are typically made of systems of steel pipes, This fluid is either water or steam, at high pressure and temperature. The term geothermal energy is also used to refer to the direct use of geothermal waters (hot springs). It may also refer to heat drawn from the ground by heat pumps.
The power plant uses a steam turbine or similar device to convert heat from the geothermal fluid to electric power. Geothermal power plants have the potential to produce power more cheaply than plants that use oil, gas, or nuclear fuel. Rainwater that seeps back into the geothermal reservoir replenishes the fluid consumed by the geothermal plants. Thus, geothermal energy is considered a renewable energy source.
Regions near geological faults tend to experience earthquakes. Engineers design geothermal plants so that they will remain structurally sound if earthquakes occur near them. Planners may place the buildings near sources of fresh water to assure a supply of water for cooling.
The first geothermal power plant was built in 1904, in Lardorello, Italy, near Volterra. Today, a number of countries operate geothermal plants. Countries with such plants include El Salvador, Greece, Iceland, Japan, Mexico, New Zealand, the Philippines, and the United States. The Geysers Geothermal Field, near Healdsburg in northern California, is one of the largest geothermal power producers. It generates enough power to supply a city the size of San Francisco.
See also Energy supply (Geothermal energy) ; Renewable energy .
