Geothermal energy is collected by circulating water through rock or pipes underground, bringing heat to the surface that can be used to heat buildings and generate electricity.
A geothermal heat pump can extract enough heat from shallow ground in most parts of the world to provide home heating, but large-scale geothermal electricity generation is most efficient in areas where high temperatures are close to the surface, such as hot springs.
Geothermal power is generally considered a cost effective, reliable, sustainable, and environmentally friendly energy source, but has historically been limited to areas near tectonic plate boundaries. Recent technological advances have dramatically expanded the range and size of viable resources, especially for applications such as home heating.
The Earth's geothermal resources are, theoretically, more than adequate to supply humanity's energy needs, but only a very small fraction may be easily accessed.