Geothermal resources are reservoirs of hot water that exist at varying temperatures and depths below the Earth's surface. Wells a mile or more deep can be drilled into underground reservoirs to tap steam and very hot water that can be brought to the surface for use in a variety of applications, including electricity generation, direct use and heating and cooling.
The ground is a good insulator and stores the heat as energy. Pipes are run through a large area several feet underground. Water is heated as it passes through these pipes. New drilling technologies are being researched and developed to capture the heat in deeper areas.
Magma (layers of melted rock from the Earth’s crust) deep in the Earth’s core heats nearby rock and rainwater that has seeped into the ground. Some of this hot water reaches the Earth’s surface in the form of geysers or hot springs. Most stays trapped in porous rocks and cracks underground in geothermal reservoirs.
Geothermal specialists drill into these reservoirs to access the hot water and steam and use it to generate electricity at geothermal power plants. The heated water and steam produces enough power to spin turbine generators that make electricity.
Geothermal heat pumps use the Earth’s relatively stable underground temperature to heat and cool buildings with very little energy use or environmental impact. The pumps, which use pipes buried next to buildings, circulate water or other liquids to either heat the buildings using energy from the Earth’s crust or cool the buildings by pulling heat from them and transferring it to the Earth. This form of heating and cooling is used in the US, Sweden, Romania, Japan and other countries around the globe.