Geothermal Energy

Basis of Geothermal Energy

Geothermal Energy or Geothermics is the power extracted from heat stored in the earth. It encompasses energy stored in the earth, as far as it can be extracted and used, and is regarded as renewable energy. Geothermal energy can be used directly to heat and cool as well as for the creation of electricity or as a combination for heat and power generation. Geothermal energy is the term used both for engineering activity as well as the economic study of the thermal condition of the terrestrial body.

Origin of Geothermal Energy

Geothermal energy originates partly (approx. 30-50%) from the residual heat from the time of the original formation of the planet and the rest (approx 50-70%) from the radioactive decay of minerals and from solar energy absorbed at the earth’s surface. The temperature of the earth’s core is, according to different estimates, between 4500 °C and 6500 °C. 99% of our planet is hotter than 1000°C and 99% of the rest is hotter than 100°C. Nearly everywhere, at a depth of 1km, the earth has a temperature of between 35 °C and 40 °C. Under specific geological conditions, for example in present or previous volcanic areas, there are geothermal anomalies. In such places, temperatures can reach hundreds of degrees Celsius.

Residual Heat from the time of the Earth’s formation

The planet Earth was formed from the time of the formation of matter approximately 4.6 - 4.7 billion years ago. Here the material is warmed as the kinetic energy is converted into heat. This thermal energy has been partly sustained up until today due to the low thermal conductivity of the rock and the low heat emission and can be termed as residual heat from the time of the Earth’s formation.

Radioactive Decay Process

This part of geothermal energy dates back to the natural decay in the terrestrial body of existing durable radioactive isotopes, such as Uranium-235 and Uranium-238, Thorium-232 and Potassium. These elements are built in the crystal lattice of specific minerals, for example in the crevices and micas in granite. This output leads to a natural form of nuclear energy. The power which results from the radioactive decay process amounts to approximately 16 -1012 watts. With the average Earth radius of 6371km the geothermal power density of the radioactive decay process of the Earth’s surface of approximately 0.032 watts (32 mw) per square metre of the Earth’s surface. This would constitute approximately half of the terrestrial heat flow.

Heatflow from the Earth’s interior

Heat flow is transported from the deep parts of the earth through heat conduction and also via convection. The terrestrial heat flow, in which the output from the earth per square metre is approximately 0.063 watts/m2; (63mW/m2) (heat flux density). Thus is a relatively small value and indicates that geothermal energy is predominately suitable for decentralised use. In abnormal regions, as for example, volcanic areas, heat flow can be much greater.

Due to the low heat flux density, the use of geothermal energy is mainly used or dissipated from the energy stored in the earth’s crust rather than the energy from the earth’s interior. Use of geothermal energy must be dimensioned so that the cooling of the terrestrial body progresses slowly that during operation time so that the heating plant sinks the temperature to a certain extent thus enabling the system to work economically.