The word geothermal comes from the Greek words geo (earth) and therme (heat).
Mount St. Helens
On May 18, 1980, Mt. St. Helens, an active volcano in Washington, erupted, providing a vivid display of the energy contained within the Earth. Most volcanic activity occurs around the Pacific Ocean's rim, the Ring of Fire.
Volcanic energy cannot be harnessed (controlled and collected), but in a few places heat from the earth, called geothermal energy, can be collected. Usually, engineers try to collect this heat in the rare places where the Earth's crust has trapped steam and hot water. Here, they drill into the crust and allow the heat to escape, either as steam, or as very hot water. Pipes carry the hot water to a plant, where some of the steam is allowed to "flash," or separate from the water. That steam then turns a turbine - generator to make electricity.
Geothermal energy was first used to produce electricity in Italy in 1903. At the end of 2004, there were 43 power plants producing electricity from geothermal energy in the USA. Most of these are located in California and Nevada; Utah has two geothermal plants and Hawaii, formed by volcanic eruptions, has one. Generation from geothermal sources is therefore "site specific," meaning it's only possible in a few places under unique geologic conditions. One such site in California, called The Geysers, can produce almost as much electricity as all the other geothermal sites combined.
Geothermal energy can be used as an efficient heat source in small end-use applications such as greenhouses, but the consumers have to be located close to the source of heat. The capital of Iceland, Reykjavik, is heated mostly by geothermal energy.
Geothermal energy has a major environmental benefit because it offsets air pollution that would have been produced if fossil fuels were the energy source. Geothermal energy has a very minor impact on the soil - the few acres used look like a small light-industry building complex. Since the slightly cooler water is reinjected into the ground, there is only a minor impact, except if there is a natural geyser field close by. For this reason, tapping into the geothermal resources of Yellowstone National Park is prohibited by Law.
Last Revised: April 2006
Sources: Energy Information Administration, Electric Power Annual 2004, .
The National Energy Education Development Project, Intermediate Energy Infobook, 2005.