Some applications of geothermal energy use the earth's temperatures near the surface, while others require drilling miles into the earth. There are three main types of geothermal energy systems:
- Direct use and district heating systems
- Geothermal power plants
- Geothermal heat pumps
Direct use and district heating systems
Direct use and district heating systems use hot water from springs or reservoirs located near the surface of the earth. Ancient Roman, Chinese, and Native American cultures used hot mineral springs for bathing, cooking, and heating. Today, many hot springs are still used for bathing, and many people believe the hot, mineral-rich waters have health benefits.
Geothermal energy is also used to directly heat individual buildings and to heat multiple buildings with district heating systems. Hot water near the earth's surface is piped into buildings for heat. A district heating system provides heat for most of the buildings in Reykjavik, Iceland.
Industrial applications of geothermal energy include food dehydration (drying), gold mining, and milk pasteurizing.
Geothermal electricity generation
Geothermal electricity generation requires water or steam at high temperatures (300° to 700°F). Geothermal power plants are generally built where geothermal reservoirs are located, within a mile or two of the earth's surface.
The United States leads the world in the amount of geothermal electricity generation. In 2021, there were geothermal power plants in seven states, which produced about 16 billion kilowatthours (kWh) (or 16,238,000 megawatthours), equal to about 0.4% of total U.S. utility-scale electricity generation. Utility-scale power plants have at least 1,000 kilowatts (or 1 megawatt) of electricity generation capacity, equal to 0.4% of total U.S. utility-scale electricity generation.
| State share of total U.S. geothermal electricity generation | Geothermal share of total state electricity generation | |
|---|---|---|
| California | 70.5% | 5.8% |
| Nevada | 24.2% | 9.4% |
| Utah | 2.2% | 0.8% |
| Oregon | 1.3% | 2.2% |
| Hawaii | 1.0% | 0.3% |
| Idaho | 0.5% | 0.5% |
| New Mexico | 0.3% | 0.1% |
International geothermal electricity generation
In 2019, 27 countries, including the United States, generated a total of about 88 billion kWh of electricity from geothermal energy. Indonesia was the second-largest geothermal electricity producer after the United States, at nearly 14 billion kWh of electricity, which was equal to about 5% of Indonesia’s total electricity generation. Kenya was the eighth-largest geothermal electricity producer at about 5 billion kWh, but it had the largest percentage share of its total annual electricity generation from geothermal energy at about 46%.
Geothermal heat pumps
Geothermal heat pumps use the constant temperatures near the surface of the earth to heat and cool buildings. Geothermal heat pumps transfer heat from the ground (or water) into buildings during the winter and reverse the process in the summer.
Last updated: March 18, 2022 with preliminary data for the United States from the Electric Power Monthly, February 2022.