What renewable energy source uses underground heat to generate electricity or provide heating?

Geothermal energy uses heat from inside Earth to generate electricity or provide heating.

Earth’s internal heat comes mainly from leftover heat from planetary formation and the radioactive decay of elements in the crust and mantle. In places where hot water or steam lies near the surface, wells can bring that energy upward. Steam may drive a turbine directly, or hot water can heat a secondary working fluid in a binary-cycle plant.

Geothermal heat is also used without producing electricity. District heating systems, greenhouse heating, bathing facilities, and ground-source heat pumps all make use of underground heat. Heat pumps can operate in many climates because shallow ground temperatures are relatively stable.

Geothermal resources are not distributed evenly. High-temperature electricity projects are especially common near tectonic plate boundaries and volcanic regions, including Iceland, Indonesia, New Zealand, and parts of the western United States. Unlike solar and wind, geothermal plants can provide steady output, but drilling costs and local geology limit development.