Geothermal energy

Geothermal energy

Geothermal energy

Geothermal energy is a type of renewable energy on a human scale that is obtained from the heat of the interior of the Earth. Equestrian thermal energy can be obtained without the combustion of any material, it is therefore a form of clean energy without carbon dioxide emissions.

The temperature in the inner layers of the Earth remains constant during the different seasons of the year. Generally the inner layers are hotter than the surface in winter and cooler in summer. This is because the surface layers are heated and cooled more easily according to the laws of thermodynamics.

Sometimes this energy is linked to other geological phenomena such as the presence of geysers, volcanoes or hot springs. These phenomena greatly facilitate the possibility of extracting heat in installations near these areas.

To take advantage of it, a fluid was passed through the hot zone, which will heat it sufficiently to turn it into steam. This steam can be used to transform it into mechanical energy by means of a turbine and later in electrical energy.

Applications of geothermal energy

The applications of thermal energy are based on the use of heat energy and the generation of electricity. At a more concrete level, some of the applications of this renewable energy are the following:

  • Air conditioning in summer. In a house with floor heating you can circulate the heating fluid through the subsoil. This water will acquire approximately a temperature of 15ºC that will facilitate the cooling of the house.
  • Heating in winter. For the same reason as in the case of air conditioning. In this case, we will use a heat pump to pass the 15ºC to the 19 or 20ºC in which we want to put the heating. This model is also applicable to greenhouses, animal farms, etc.
  • Production of sanitary hot water for showering, washing clothes, dishes, etc.
  • Production of electricity in power plants.
  • Heat production that can be applied to industrial processes such as heating, drying, evaporation, distillation, sterilization, de-icing, washing and extraction of salts

Production of geothermal energy

The system is based on the temperature difference between the subsoil and the surface. The energy is exchanged in the form of heat - thermal energy - through two closed water circuits that connect them. To obtain heat in winter, the water inside the geothermal collector circuit, which is a plastic circuit arranged in vertical perforations that reach between 80 and 200 meters deep, resorts, driven by a pump, the subsoil to heat up, heats the water in the radiant emitting circuit, a closed circuit that gives the heat in the building. In summer the operation is analogous, but the heat moves in the opposite direction. The efficiency is greater the deeper the subsoil circuit is, since the temperature difference is greater.

To obtain hot water, the collector circuit heats hot water from an open circuit, which comes from the water network and can be stored in one or more tanks. Hot water can also be used to move a turbine, transforming thermal energy (geothermal, thermal from the subsoil) into mechanical energy. Mechanical energy can be used as it is, to move machines, or perhaps in turn transformed into electrical energy: electricity.

For small powers of renewable energy (production of up to 30 kW) and particular uses it is possible to arrange the heat collecting water pipes horizontally and at a shallow depth, that is to say between one and five meters, usually between one and a half and two, by example under a garden. The pump is the size of a refrigerator but it is very quiet, and can be located in the garage, for example.

Type of geothermal sources

Geothermal energy is obtained through the extraction of internal heat from the Earth. There are several areas with thermal waters. These thermal waters can be those used in spas or other centers. These waters are warmed by the temperature inside the Earth. In areas where hot springs are very hot, shallow drilling is done through natural fractures.

Hot water and / or steam can flow naturally, by the impulses of the water and steam flows, but also by pumping. You have to select the method to be used depending on the method that is most economically profitable. There is not a single method to take advantage of this type of energy, since there have been projects that in some countries have had to be rejected due to their economic infeasibility.

Magma - geothermal energy

Magma (molten rock) is a great source of geothermal energy, since rocks are only found in the liquid state at extremely high temperatures. In spite of this, with the technology that is available at the moment it is not possible to take advantage of this type of source, it is economically unfeasible.

The exploitations to extract hot water, usually have an even number of wells, because one of the hot water is extracted and the other one injects water into the aquifer once it has cooled down. This system has several advantages:

  • Unlikely to deplete reservoir water, since as the water is continuously injected, the volume keeps costing.
  • There are no emissions of dissolved gases, since the water circuit is closed, this fact avoids possible contamination on the outside.

Type of deposits according to water temperature

The different types of geothermal energy deposits are classified according to the temperature of their thermodynamic source. In this way we have geothermal energy of high temperature, medium temperature and geothermal energy of low and very low temperature.

High temperature geothermal energy

This type of renewable energy is found in areas where the layer of the crust is still active and the temperature ranges between 150 ° C and 400 ° C. In these cases the steam comes to the surface through a turbine that generates electricity at the be moved by the force of steam. To find an area from which to extract hot water, a geothermal area, you must find an upper layer composed of:

  • Coverage of impermeable rocks, which allow the filtration of water.
  • Aquifer or high permeability deposit, between 300m and 2 km deep.
  • Fractured soil, allows the circulation of fluids by convection, thus the heat transfer reaches the surface.
  • Magmatic heat source, at a depth between 3 km and 15 km and at a temperature between 500 ° C and 600 ° C.

The perforations that have to be done to extract the hot water are almost equal to those that are made to extract oil from the wells.

Medium temperature geothermal energy

The temperature of the fluids of the aquifers is much lower, at temperatures ranging between 70 ° C and 150 ° C, for which the steam-electricity conversion efficiency is much lower, in this case it is necessary to add a volatile component. This type of geothermal energy can be transformed into small power plants, but it is in the distribution through the urban network where the use is maximum, it is used for heating and cooling, with absorption machines. This is used for the production of electricity, it is necessary that the fluid is between 120 ° C and 180 ° C.

Low temperature geothermal energy

It is used in large areas, in larger areas than the one that works at high or medium temperatures. It can be found in sedimentary basins, the fluid of these basins is at a temperature between 50 ° C and 70 ° C.

Very low temperature geothermal energy

It is used to serve domestic, urban and agricultural needs. The fluids that can be found are at temperatures between 20 ° C and 50 ° C.

Both geothermal energy at low temperature and geothermal energy at very low temperature are very useful for urban heating systems, through closed circuits.

Geothermal power plants

The geothermal power plants have the function of generating electricity from the thermal energy of the Earth's interior. For this, they have heat exchangers with the aim of generating steam. With the steam pressure a turbine is activated obtaining mechanical energy. The mechanical energy obtained by the turbine can easily be converted into electrical energy by an electric generator.

The main geothermal plant is located in Tuscany, near the city of Pisa and is called Central Geothermal Larderello. An image of the central one in the central part of a valley and the vision of kilometers of pipes of a meter of diameter that go towards the thermal power station show the landscaping impact that it generates.

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Last review: January 3, 2018