Geothermal energy belongs to renewable energy sources (RES) and is considered the most environmentally friendly type of energy since its generation does not lead to the emission of greenhouse gases as well as does not require large areas of land (DiPippo, 2005; Massachusetts Institute of Technology, 2006; Glassley, 2015). Other advantages concern the possibility of continuous energy production, extracting energy anywhere on Earth, no need to store primary energy, and availability of an almost inexhaustible source of energy.
There are several types of geothermal resources:
- Hydrothermal Resources are most common type where hot water or steam is extracted from underground permeable reservoirs. Those can be further categorized as either ‘dry’ or ‘wet’ steam fields, ‘hot-water’ fields, or ‘warm-water’ field, depending on characteristics. Their reserves are relatively small.
- Deep Geothermal Heat refers to resources that are contained mainly in waterproof hot dry rocks (HDR) that are located at depths of 3–10 km (or more) at temperatures up to 350°C. The reserves of exactly Deep Geothermal Heat are practically inexhaustible. However, the development of this type of energy is at the stage of scientific research and pilot projects due to the enormous complexity, comparable in scale to coping with thermonuclear energy. The Enhanced Geothermal Systems (EGS) is an application to utilize the heat of dry materials, involving the creation of geothermal reservoirs by drilling deep wells and then injecting water into the hot rocks to create steam or hot water. However, the EGS concept is applicable to any other geothermal systems where there is a lack of water or insufficient permeability.
- Geopressured resources are deep sedimentary rocks containing high-pressure brine and gas, that can be used to generate electricity from deep beneath the Earth's surface. Geopressured reservoirs are characterized by three important properties that make them potentially attractive for geothermal exploitation: (1) very high pressure, (2) high temperature, and (3) dissolved methane.
- Magma resources – the magma or molten rock contains tremendous amount of heat. This heat can be tapped into for energy – no safe efficient technology exists.
Geothermal energy is used both for producing electrical energy and supplying heat, including direct utilization of heat. Geothermal energy is among the cheapest energy sources. Despite the obvious attractiveness, the contribution of Earth's heat to world energy is negligible, which definitely does not correspond to its potential. There is hope for the predominant contribution of this type of energy in the future, especially due to the need to make drastic decisions in the fight against climate change.
DiPippo, R. (2005) Geothermal Power Plants. Principles, Applications, and Case Studies, Elsevier, Oxford, England, 450 p.
The Future of Geothermal Energy in the 21st Century Impact of Enhanced Geothermal Systems (EGS) on the United States. Report. (2006), Massachusetts Institute of Technology. 358 p.
Glassley, W.E. (2015) Geothermal Energy: Renewable Energy and the Environment, 2nd ed., Energy and the Environment, Abbas Ghassemi, Series Editor, CRC Press, Taylor & Francis Group, 410 p.
- DiPippo, R. (2005) Geothermal Power Plants. Principles, Applications, and Case Studies, Elsevier, Oxford, England, 450 p.
- The Future of Geothermal Energy in the 21st Century Impact of Enhanced Geothermal Systems (EGS) on the United States. Report. (2006), Massachusetts Institute of Technology. 358 p.
- Glassley, W.E. (2015) Geothermal Energy: Renewable Energy and the Environment, 2nd ed., Energy and the Environment, Abbas Ghassemi, Series Editor, CRC Press, Taylor & Francis Group, 410 p.