A geothermal power plant is used to generate electricity using the heat that occurs naturally below the surface of the Earth. These plants have existed since the early 1900s and can be built in any area that has access to a geothermal reservoir. Most of these are found along the boundaries of the tectonic plates. There are three ways that a geothermal power plant can be used to transform heat from the Earth into energy, and all of them involve the use of steam powered turbines.
In 1904, the first geothermal power plant was built in Tuscany, Italy. At this site, steam was already erupting through the Earth's crust, which made it easy to harness and transform this energy into electricity. Prior to this, energy from geothermal reservoirs was used as a heat source, though it was not stored for later use.
The most common type of geothermal power plant is one that pumps hot water up from the geothermal reservoir and then transforms it into steam that is used to move a turbine. This type of plant is called a flash steam plant. Once the steam cools and turns back into liquid water, it is usually put back into the system to be heated by the Earth again. In most cases, it is necessary to drill to between 1 and 2 miles (1.6 and 3.2 km) below the surface in order to reach a supply of water that is under enough pressure to make this type of plant run.
Another common type of geothermal power plant uses steam that is captured to move a turbine as it escapes the earth's crust. These plants, which are called dry steam plants, do not require drilling because steam, often in the form of geysers, erupts naturally. Binary cycle power plants may also be used as geothermal power plants. In these plants, hot water from below the surface of the Earth is used to transform another liquid into steam.
In most cases, there is very little pollution created by a geothermal power plant. The main byproduct of the majority of them is water, which is itself often captured and recycled for later use. Impurities and other chemicals that are found in the water below the Earth's surface can be captured before the water is released into the environment in order to decrease the amount of pollution the plant causes. These plants often emit less than 5% of the pollution that plants which burn fossil fuels do.