Geothermal Energy

The Sierra Nevada Mountains provide a spectacular backdrop for a cooling tower array at the ORMAT Mammoth Geothermal Power Plant in Central California.

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.^[1] This heat can be drawn from various depths, 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.^[2][3]

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.^[1]

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.^[4]

NREL Geothermal Favorability Map

In 2008, scientists with the U.S. Geological Survey (USGS) completed an assessment of the geothermal resources in the U.S., which indicated:

• 9,057 MWe of identified geothermal resource
• 30,033 MWe of undiscovered potential
• 517,800 MWe of EGS potential

Visit the Geothermal Resources page to view other resource assessments that have been conducted.

Steam billows from separators at Los Azufres Geothermal Complex near Morelia, Michoacan, Mexico

Hydrothermal Systems

Hydrothermal Systems use coincident heat, water, and permeable rock at shallow depths (typically <5 km) to produce electricity.

Enhanced Geothermal Systems (EGS)

Enhanced Geothermal Systems (EGS) are human-engineered hydrothermal reservoirs developed for commercial use.

Sedimentary Geothermal Systems

Sedimentary Geothermal Systems produce electricity from medium temperature, high flow rate geothermal reservoirs in large-basin, sedimentary deposits.

Co-Produced Geothermal Systems

Co-Production systems use hot water byproduct from oil and gas wells (historically an inconvenience and disposal issue) to produce electricity.

Direct-Use Geothermal Systems

Low-temperature water can be used to provide heat for a number of applications, such as pools, spas, greenhouses, fish farms, and mining operations.

Ground Source Heat Pump Systems

Ground Source Heat Pumps are used for space heating and cooling in buildings, using the ground as a heat source in the winter and a heat sink in the summer.