The's heat turned into energy

2000/11/12 Kortabarria Olabarria, Beñardo - Elhuyar Zientzia

• Geologia

The Earth has an enormous heat reserve inside it: the geothermal potential accumulated in the first 10 kilometers of surface is 2,000 times greater than the world coal reserves. If performed inside the Earth's surface, the average temperature increases by 25ºC per kilometer. In seismic and volcanic areas, the temperature near the surface is high and the use of geothermal energy is very simple.

As diverse energy sources, geothermal energy has long been exploited. 3,500 years ago the Etruscans used thermal waters to fight surface diseases, relax, heat buildings, acquire useful chemicals and cultivate plants. In addition to thermal use, geothermal energy can be exploited industrially. The first experience of this type dates from the beginning of this century and took place in Italy, specifically in the city of Lardarello. In 1904 a geothermal power plant was built in Lardarello. In the 1940s it had a power of 132 MW. During World War II the power plant was completely destroyed, but after the war it was rebuilt. The Lardarello geothermal plant currently has a power of 400 MW to supply more than 500,000 inhabitants.

How is geothermal energy exploited?

Thermal energy can be used by thermal sources, spas, etc., but in this case it cannot be considered as an alternative energy. To do this, consider whether electricity or heating will be used.

To generate electricity you need water vapor or hot water in the subsoil. When what comes out of the ground is water vapor, this steam is directed directly to the turbines to generate electricity. It is the simplest method, but not very abundant, since there are few sources of this type. When what comes out through the pipes is hot water, first you have to separate liquid water from water vapor and then water vapor is used to generate electricity. However, the steam that will affect the turbines according to the different water temperatures is obtained in places where there is thermal energy at high temperature, that is, when the water temperature exceeds 150-200ºC, the water is poured into tanks or tanks and the steam generated in this process is used to power the turbines generating electricity. The water generated in the process is reinjected into the subsoil. This type of plant is located in Lardarello (Italy), New Zealand, Japan, the Philippines, the United States and Mexico.

When the water temperature ranges from 70 to 150-200ºC, it is called medium temperature thermal energy. In these cases, hot water is used to evaporate a more volatile liquid through a heat exchanger, which will be intended for turbines. Also in this case, the water extracted from the soil returns to the subsoil

But in addition to electric power, geothermal energy has another use, so-called direct use. Low or very low temperature thermal energy (between 20 and 50-60ºC and between 50-60 and 70-80ºC respectively) and medium temperature thermal energy are used to heat buildings, greenhouses, fish farms, wood drying plants, etc. (in addition to being used in thermal bath facilities, of course). Although the savings of other fuels obtained from the direct use of geothermal energy depends on water temperature, distance and type of installation, it can reach 80%. In addition, surprisingly, geothermal energy can also be used in summer to set up buildings. In fact, the temperature of the subsoil is very constant and is used to cool the water circulating through the subsoil through the pipe in hot areas during the summer, especially in the United States.

However, these energy acquisition systems have a number of limitations and barriers: on the one hand, it is only possible to drill down to a depth of 3,000 m to make the operation economically viable. On the other hand, installations for the production of electricity or direct use of heat must be close to the source, as heat is lost along the way.

Today geothermal energy is expensive and in countries where the structure of the Earth's crust is appropriate for this, as in Iceland, it is not exploited, but as the technique progresses this type of energy offers more possibilities. From the environmental point of view, this energy source does not pose big problems, which is a characteristic to take into account, since there is not too much human activity that is exploited and does not produce destruction.

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