Who uses geothermal energy

Geothermal energy

Temperatures are very high deep below the surface of the earth. This is associated with enormous amounts of heat that are stored in rock and earth layers as well as underground water reservoirs. Some of them are visible at volcanoes, hot springs and geysers.

The energy from geothermal energy is used both in the form of heat and to generate electricity. However, it has the smallest share of the renewable energies used worldwide. Their great advantage compared to hydropower, solar or wind energy, however, is their reliable and constant availability regardless of the time of day or weather conditions; in addition, the extraction of geothermal energy has little effect on the surface environment.

Geothermal power plant

As experience shows, the deeper one penetrates into the interior of the earth, the warmer it gets. In Central Europe, the heat increases by around three degrees per 100 meters of depth. The temperature in the earth's core reaches around 5000 to 7000 degrees Celsius.

There are two main sources that generate this heat. On the one hand, it consists of residual heat that was generated during the formation of the earth through the compression of the material from which it is made. On the other hand, the heat comes from the radioactive decay of the elements thorium-232, uranium-235, uranium-238 and potassium-40, which occurs mainly in the earth's crust and in the mantle, which is up to 2900 kilometers deep. The upper limit for heat generation from radioactive sources was determined by the Japanese neutrino detector KamLAND in 2012 and by the neutrino detector Borexino in the Gran Sasso laboratory at the beginning of 2013, a value of 4500 billion watts. The major part is the decay of uranium and thorium.

There are different ways of using these geothermal heat sources. It is easiest when the heat is already available in the underground as steam or hot water, which can then be transported to the surface via a bore, similar to the way geysers work in nature. In general, however, a distinction is made between two types of geothermal energy: near-surface geothermal energy and deep geothermal energy.

Near-surface geothermal energy

Geysers - evidence of geothermal energy

When the geothermal energy is used close to the surface, it is drilled up to 400 meters deep, so water with a temperature of up to 25 degrees Celsius can be pumped and the building and technical system heated or cooled. For this purpose, a closed pipe system is inserted into the boreholes, through which water is continuously pumped. As a result, underground heat is transferred to the water and transported to the surface, where it is brought to the temperatures required for the respective use by means of heat pumps.

Deep geothermal energy

There are two different types of deep geothermal energy: hydrothermal and petrothermal systems at depths of 3,000 to 7,000 meters. Hydrothermal systems start at water-bearing layers, the so-called aquifers. Here the hot thermal water is used directly for energy generation.

Petrothermal systems, on the other hand, use the warmth of the hot deep rock. The majority of Germany's geothermal resources are stored in these systems. However, the generation of energy takes place differently than with near-surface geothermal energy.

In the so-called hot-dry-rock process, for example, water is pressed into the hot rock through bores at a pressure of up to 150 bar, with many crevices and channels popping up in the rock. The system of natural and artificial cracks created in this way forms an underground heat exchanger. Water is then pumped through this canal system from above. The water absorbs the warmth of the hot rock, heats up in the process and is then carried back to the surface. It reaches the earth's surface at temperatures well over 100 degrees Celsius and can then be used to generate electricity.

According to geological estimates of the potential of petrothermal systems, there is so much energy available in Germany in the depth range of 3,000 to 7,000 meters that the population could theoretically be supplied with electricity and heat for a good 10,000 years with today's consumption.