The Uses of Geothermal Energy
Geothermal power (from the Greek words geo, meaning earth, and therme, meaning heat) is energy generated by heat stored beneath the Earth’s surface. It is a developing field where serious energy potential has been identified.The ever growing juxtapose of uses for geothermal energy can be classified into direct uses and electricity generation. The use that can be derived depends on the operating temperature at the source. Direct use requires using geothermal heat directly (without a heat pump or power plant) for non-electricity generation purposes such as heating of buildings, industrial processes, domestic heating, greenhouses, aquaculture, public baths and pools. Direct use can take place at high and moderate to low temperature geothermal resources, depending on the use and scale required.
Even very low temperature resources can be exploited for heat applications using ground-source heat pumps to facilitate space heating and cooling. Research has shown that ground-source heat pumps can be a lucrative investment:
· where there are cold winters or hot summers,
· where electricity is over 12c/kWh,
· where gas is not available and where new construction is taking place. (For more information see GNS Science website).
Almost all high temperature geothermal resources produce a mixture of water and steam at temperatures up to 300ºC, but rarely above that. Commercial geothermal energy operations access geothermal fluids by drilling wells typically 1000 to 3000m deep, while domestic wells for heating are usually only around 100m deep. When hot water above 90 to 100ºC flows up the well, the release of pressure allows some of the fluid to boil into steam, resulting in two-phase mixture at the surface. The water and steam are physically separated before use.
Potential energy use at various indicative field temperatures is:
30-69ºC Thermoculture, Bathing
70-140ºC Space and Water Heating, Drying
140-220ºC Drying, Process Heat, Binary Electrical Plant
220+ºC Steam Turbine and Binary Electricity or Process Steam
