Renewables

Geothermal

Geothermal energy technologies use the heat of the Earth for direct-use applications, geothermal heat pumps, and electrical power production. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth’s surface, and down even deeper to the extremely high temperatures of molten rock called magma.

Almost everywhere, the upper 3 metres (10 feet) of the Earth’s surface maintains a nearly constant temperature between 10-16 °C (50-60 °F). Geothermal heat pumps can tap into this resource to heat and cool buildings. A geothermal heat pump system consists of a heat pump, an air delivery system (ductwork), and a heat exchanger - a system of pipes buried in the shallow ground near the building. In the winter, the heat pump removes heat from the heat exchanger and pumps it in to the indoor air delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air in to the heat exchanger. The heat removed from the indoor air during the summer can also be used to provide a free source of hot water.

Wells can be drilled into underground reservoirs for the generation of electricity. Some geothermal power plants use the steam from a reservoir to power a turbine/generator, while others use the hot water to boil a working fluid that vaporises and then turns a turbine. Hot water near the surface of the Earth can be used directly for heat. Direct-use applications include heating buildings, growing plants in greenhouses, drying crops, heating water at fish farms, and several industrial processes such as pasteurising milk.

Hot dry rock resources occur at depths of 5-8 km (3-5 miles) everywhere beneath the Earth’s surface and at lesser depths in certain areas. Access to these resources involves injecting cold water down one well, circulating it through hot fractured rock, and drawing off the heated water from another well.