Geothermal heat stored in the earth's subterranean layers can be used to produce thermal or electrical energy.
Geothermal energy: heat & electricity
Two types of geothermal energy can be produced, depending on the temperature of the heat extracted.
Low-temperature geothermal energy (below 150 °C): the energy captured is useful for air conditioning or heating systems in buildings. Geothermal probes capture energy which is used in heat pumps via heat exchangers.
Medium and high temperature geothermal energy (above 150° C): this energy is strong enough to produce electricity or to use directly as heat. Two types of technology are used: either the use of steam reservoirs or hot water such as at the Bouillante power plant in Guadeloupe, or the collection of hot geothermal water that runs through natural underground faults, such as at Soultz-sous-Forêts and Rittershoffen in Alsace.
The Bouillante (Guadeloupe) & Rittershoffen (Alsace) models
Bouillante, in Guadeloupe, is the first geothermal power plant to industrially produce electricity. Hot water is pumped to the surface with an underground probe. As it rises, it loses pressure and becomes steam: at this point, as in other types of energy production, the steam fuels turbine generators, which in turn produce electricity.
Rittershoffen, Alsace is home to the first deep geothermal energy plant for industrial use. Using steam from geothermal heat, it is the first energy plant to directly power the Roquette Group's production site in Beinheim. How it works: 165 °C is drawn up from a depth of 2,500 m. Once it reaches the surface, the heat is extracted, and the water is then reinjected into the ground.
This circuit provides a 100% renewable and non-intermittent energy supply with constant output.
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