Geothermal energy is heat extracted from the Earth. A wide range of temperatures can be suitable for using geothermal energy, from room temperature to above 300° F. This heat can be drawn from various depths below the surface, ranging from the shallow ground (the upper 10 feet beneath the surface of the Earth) that maintains a relatively constant temperature of approximately 50° to 60° F, to reservoirs of extremely hot water and steam located several miles deep into the Earth.
Geothermal reservoirs are generally classified as either low temperature (<302°F) or high temperature (>302°F). Commercial electricity production normally requires a high-temperature reservoir capable of providing hydrothermal (hot water and steam) resources, called hydrothermal reservoirs.
Geothermal is distinct from other renewables such as solar or wind because it is a considered a "baseload" technology, providing electricity 24 hours a day, 365 days a year.