Utilization of Geothermal Resources

Geothermal energy is classified as energy in the form of heat below the surface of the solid Earth. Globally geothermal energy is not an important energy resource. Yet, it is important for many countries located in young volcanologically active regions. Geothermal steam is mostly used for power generation and, together with geothermal water, also directly, for example for house-heating, greenhouses, heat pumps, swimming pools and other health applications. Geothermal systems have been classified on the basis of the geological environment in which they occur as systems in volcanolocially young provinces, tectonic systems, systems in sedimentary basins and hot-dry rock. The first three types represent hydrothermal systems, which are characterized by hot fluid in permeable hot rock. With present-day technology they can be economically exploited. Hot-dry rock systems occur in impermeable rock. Today, much effort is being put into refining technology to turn these systems into a usable source of energy. Exploitation of hydrothermal systems involves drillings to bring the hot fluid to the surface. The drilling technology has been partly adapted from the oil industry and partly developed for drilling into volcanic rocks. Geothermal energy is classified with renewable energy resources, both by the European Union and the Department of Energy in the United States. It appears that this classification is not based on the nature of the resource. It is evident that hot-dry rock represents a non-renewable energy source and the renewability of hydrothermal resources is highly variable, and mostly insignificant. The environmental impact of exploitation of geothermal resources is highly variable, ranging from being insignificant in the case of many low-temperature resources (<150°C) to considerable for power generation from high-temperature resources. This includes extinction of surface thermal activity, spoiled scenery, soil erosion and damage to vegetation, land subsidence, induction or enhancement of seismic activity and, visual, noise, thermal and, in particular, chemical pollution.