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Select Citation Style Copy Citation Share to social media Written by John W. LundEmeritus Professor of Civil Engineering and Emeritus Director of the Geo-Heat Center, Oregon Institute of Technology, Klamath Falls, Oregon. Private consultant in geothermal engineering and civil engineering.
John W. Lund Fact-checked by The Editors of Encyclopaedia BritannicaEncyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.
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geothermal power, form of energy conversion in which geothermal energy—namely, steam tapped from underground geothermal reservoirs and geysers—drives turbines to produce electricity. It is considered a form of renewable energy.
While humans have long made direct use of geothermal energy as a source of heated water, the first geothermal electric power generation took place in Larderello, Italy, with the development of an experimental plant in 1904. The first commercial use of that technology occurred there in 1913 with the construction of a plant that produced 250 kilowatts (kW). Geothermal power plants were commissioned in New Zealand starting in 1958 and at the Geysers in northern California in 1960. The Italian and American plants were “dry steam” facilities, where low-permeability reservoirs produce only steam that can be sent to a power plant through pipes and used for power generation right away. In New Zealand, however, high-temperature and high-pressure water emerges naturally as a mixture made up of 80 percent superheated water and 20 percent steam. This superheated water is separated from the mixture and flashed into steam for electricity generation. Most geothermal plants at present are of this “wet steam” type.
Although geothermal energy is abundant, geothermal power is not. With wide-scale adoption using current technology, it is estimated that about 8 percent of the world’s electricity could be produced by using geothermal resources. In addition, nearly 40 countries, most of which are located in Africa, the Pacific, and Central and South America, could conceivably meet all of their electricity needs by using geothermal resources. In the first quarter of the 21st century, geothermal energy was used to produce electricity in 27 countries, the leaders being the United States, the Philippines, Indonesia, Turkey, Mexico, New Zealand, and Italy. In 2020 geothermal power plants in the United States produced more than 8,831 gigawatt-hours, and in 2021 these plants had an installed capacity of more than 3,600 megawatts (MW)—the most of any country. California and Nevada had the most installed geothermal capacity, accounting for about 95 percent of U.S capacity. Still, in 2022 geothermal energy accounted for only 0.4 percent of all electricity generated in the U.S. In 2021 Kenya was the eighth highest geothermal electricity producer and had the largest percentage share of electricity generation from geothermal energy—generating more than 40 percent of the country’s annual electricity supply. Many geothermal fields have utilization factors of about 95 percent (equivalent to 8,322 full-load operating hours annually), the highest for any form of renewable energy.
