Geothermal
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Geothermal energy is obtained from heat in the Earth, either from solar heating at the surface or from radioactive decay deep underground.

The ground just under the surface of the Earth is always a constant 50-60°F (10-16°C). Geothermal heat pumps take heat from the ground in the winter to heat air or water, and they deliver heat from indoor environments into the ground to cool things down. A ground-source heat pump can drastically reduce or eliminate the need for energy-intensive heating and cooling systems in homes and other buildings.

In some places, hot water and magma are found closer to the surface, sometimes appearing as steam vents or geysers. These underground heat resources are used to meet a variety of heating needs, as well as to power turbines that create electricity.

Steam rising from a geothermal electricity generating station in Northern California.

Image from National Renewable Energy Laboratory