Geothermal energy

— Geothermal technologies use renewable energy resources to generate electricity and direct use of heat while producing very low levels of greenhousegas (GHG) emissions. Geothermal energy is the thermal energy stored in the underground, including any contained fluid, which is available for extraction and conversion into energy products. Electricity generation, which nowadays produces 73.7TWh (12.7GW of capacity) worldwide, usually requires geothermal resources temperatures of over 100 ◦C. For heating, geothermal resources spanning a wider range of temperatures can be used in applications such as space and district heating (and cooling, with proper technology), spa and swimming pool heating, greenhouse and soil heating, aquaculture pond heating, industrial process heating and snow melting. Produced geothermal heat in the world accounts to 164.6TWh, with a capacity of 70.9GW. Geothermal technology, which has focused for decades on extracting naturally heated steam or hot water from natural hydrothermal reservoirs, is developing to more advanced techniques to exploit the heat also where underground fluids are scarce and to use the Earth as a potential energy battery, by storing heat. The success of the research will enable energy recovery and utilization from a much larger fraction of the accessible thermal energy in the Earth’s crust.