The origin of terrestrial heat is the sum of physical and chemical processes that take place in a different way inside it.
The Earth is a hot body immersed in a cold space that continuously loses temperature at a rate of 130ºC for every 1,000 million years.
Volcanoes and hydrothermal systems that give rise to water surges at high temperatures are the most evident manifestations of the Earth's interior heat that we can observe on the surface.
What processes cause the heat of geothermal energy?
The different processes that originate the Earth's heat are described below, considering the part of the interior of the planet where they take place.
- Latent heat of crystallization: it is the limit between the inner core and the outer core. The inner core is in the solid state while the outer core is in the liquid state. Crystallization reactions occur continuously in the outer nucleus; These reactions are exothermic and therefore create heat. This heat is known as latent heat of crystallization.
- Gravitation. Gravity exerts a compressive force toward the center of the planet, and friction heating is generated in the process of contraction of the earth's mass.
- Remaining heat from the planet's formation: This is the heat, although present, as a result of the collisions between the stellar residues of the protoplanetary disk that gave rise to Earth.
- Friction or kinetic heat: between the outer core and the mantle. It is the energy in the form of heat that is released as a consequence of the friction produced by the different responses that the outer core and the mantle have to the stress field of the Moon and the Sun (tidal forces).
- Exothermic physicochemical reactions: mantle. The high pressures and the high temperature make the minerals unstable and produce continuous phase changes that generate energy in the form of heat.
- Radiogenic decomposition of isotopes: cortex and mantle. The rocks that make up the lithosphere (composed of the crust and the highest part of the mantle) are rich in minerals that contain radioactive elements such as the 235U, 238U, 232Th and 40K isotopes. The decomposition reactions of these isotopes are exothermic. Radiogenic isotope decomposition is the process that brings more heat to the Earth's surface.
It must be taken into account that the Earth's temperature increases inward from a global surface average of 15ºC to more than 5000ºC in the inner core.
What are the types of geothermal reservoirs?
There can be considered that there are three types of geothermal deposits:
- Hot water reservoirs.
- Dry deposits.
- Geysers.
Hot water reservoirs
These deposits can form a source or be underground, contained in an aquifer.
Those that form fountains have been used since ancient times as thermal baths. In general, they tend to have relatively low flow rates.
The underground deposits serve to take advantage of the heat from the interior of the earth. Hot water or steam can flow naturally, by pumping or by impulses from water and steam flows.
There are other reservoirs in which the water comes out in the form of steam. In these, the use is direct to obtain mechanical energy through a turbine.
Dry deposits
In dry deposits, there is an area under the ground, at not excessive depth, with hot materials or stones, in dry conditions. Water is injected through a perforation and it is recovered already hot by another, the heat is used, by means of a heat exchanger and is reinjected again.
What is a geyser?
A geyser is a special type of hot spring that periodically emits a column of hot water and steam into the air.
Geyser formation requires favorable hydrogeology that exists only in some parts of the planet, making them a rather strange phenomenon. There are about 1000 around the planet.
When did geothermal energy start to be used?
At the end of the 17th century the Earth was conceived as a molten mass with a solid crust as a consequence of its cooling. It was not until the 19th century that the first calculations of the age of the Earth based on its thermal evolution were made, and the term geothermal energy was first defined as the scientific discipline that studies terrestrial heat, the origin of this heat , distribution and use.
Precisely, the use of this thermal energy is what has led to the development of geothermal energy. This energy source makes it possible to take advantage of the heat energy of the Earth's interior in different applications using the laws of thermodynamics.