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 use hot water from springs or reservoirs located near the surface of the earth.
- Electricity generation power plants require 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 surface of the earth.
- Geothermal heat pumps use stable ground or water temperatures near the earth's surface to control building temperatures above ground.
Direct use of geothermal energy
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 natural healing powers.
Geothermal energy is also used to heat buildings through district heating systems. Hot water near the earth's surface can be piped directly into buildings and industries for heat. A district heating system provides heat for most of the buildings in Reykjavik, Iceland.
Industrial applications of geothermal energy include food dehydration, gold mining, and milk pasteurizing. Dehydration, or the drying of vegetable and fruit products, is the most common industrial use of geothermal energy.
The United States produces the most electricity with geothermal energy
The United States leads the world in the amount of electricity generated with geothermal energy. In 2014, U.S. geothermal power plants produced about 17 billion kilowatthours (kWh), or 0.4% of total U.S. electricity generation. In 2014, seven states had geothermal power plants.
Share of U.S. geothermal electricity produced by each state, 2014:
Geothermal energy contributes a significant share of electricity generation in several countries
Twenty seven countries including the United States had geothermal power plants in 2012, which generated approximately 68 billion kWh of electricity. The Philippines was the second-largest geothermal power producer after the United States at 10 billion kWh of electricity, which equaled approximately 15% of the country's total power generation in 2012. Iceland, the seventh-largest producer at 5 billion kWh of electricity, produced 30% of its total electricity using geothermal energy.