The Renewability of Geothermal Energy

Abstract

International organisations have class$ed geothermal energy as a renewable energy source, but it is sometimes stated that this is not the case. The meaning of the concepts ôrenewable energy sourcesö and ôsustainable energy prodction ö is discussed in this paper. Comparkon is made with the resources of lydropower andfish stocks in order to clariifl the meaning of the two concepts. It is f o d that the rate of energy recharge to geothermal systems is the most critical aspect for the classifcation of geothermal energy as a renewable energy source. In the exploitation of natural geothermal ytems, the recharge of energy takes place by advection of thermal water at the same time scale as the proahtion ji-om the resource. This justiies the classifcation of geothermal energy as a renewable energy source. In the case of hot dry rock and evenrually some of the hot water aqugers in sedimentaty basins, the energy recharge is only by ihermal conduction d due to the slowness of this process, hot diy rock andsome sedimentary reservoirs should be considered as finite energy sources.