Geothermal energy is the heat from the Earth. It's clean and sustainable. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth's surface, and down even deeper to the extremely high temperatures of molten rock called magma.
The Department of Energy’s Geothermal Technologies Program supports the U.S. geothermal industry in providing diversity, and therefore security, in domestic energy supply options. This support also helps the industry maintain its technical edge in world energy markets, thereby enhancing exports of U.S. goods and services and U.S. job growth. Energy works in partnership with U.S. industry to establish geothermal energy as an economically competitive contributor to the U.S. energy supply.
The Office of Scientific and Technical Information maintains technical reports related to geothermal energy on its Geothermal Energy Technology (GET) subject portal.
Geothermal Energy
Geothermal energy is contained in underground reservoirs of steam, hot water, and hot dry rocks. As used at electric generating facilities, hot water or steam extracted from geothermal reservoirs in the Earth's crust is supplied to steam turbines at electric utilities that drive generators to produce electricity. Moderate-to-low termperature geothermal resources are used for direct-use applications such as district and space heating. Lower temperature, shallow ground, geothermal resources are used by geothermal heat pumps to heat and cool buildings.
Geothermal Heat Pumps
A geothermal heat pump is an electric heat pump that exchanges heat with the ground or ground water, instead of air. This is more efficient because the temperature of the earth 10-15 feet below the surface remains around 55 degrees F throughout the year (the average temperature and range of temperatures depends on location), providing a better heat transfer medium than outdoor air, whose temperature can vary by more than 100 degrees F. An "open loop" geothermal heat pump uses groundwater from a well as the heat source/heat sink. Once it has circulated through the heat pump(s), the water is returned to the ground through the same well, a separate injection well, or through surface discharge. In a "closed loop" geothermal heat pump, water (or a mixture of water and anti-freeze) from the heat pumps is circulated either to horizontal or vertical pipes that are in contact with the earth. After exchanging heat with the ground, the water is circulated back to the heat pumps in a closed loop.
© Dept. of Energy
