Geothermal energy is classified as a renewable resource, where “renewable” describes a characteristic of the resource: the energy removed from the resource is continuously replaced by more energy on time scales similar to those required for energy removal. Consequently, geothermal exploitation is not a “mining” process. Geothermal energy can be used in a “sustainable” manner, which means that the production system applied is able to sustain the production level over long periods of time. The longevity of production can be secured and sustainable production achieved by using moderate production rates, which take into account the local resource characteristics (field size, natural recharge rate, etc.)