Thermal energy is stored passively and i great quantities by the earth itself. Harnessing this stored thermal energy for productive use has actually been practices since the days that humans lived in caves. Over the centuries we have used both the thermal insulating and thermal storage capacities of earth to our benefit. In many areas, including Canada’s prairies during the settelment period of the 19th century, earth sheltered structures provided isolated farmers and communities shelter against Canada’s frigid winters.
Mire recently, new technologies including geo-exchange and ground source heat pumps have been designed and built both in urban and isoluted areas to harvest the earth’s latent stored heat.