Geothermal energy has existed since the Earth was created and represents the internal energy of the Earth.
The earth consists of a core, a mantle and a crust. The mantle, the layer between the core and the crust, consists of a glowing liquid rock material called magma. When magma breaks through the surface of the earth, through a volcano, it is called lava.
At every 100 m depth, the temperature of the rocks rises by 3 degrees C. When we descend to a depth of 3000 m, we would reach the boiling point of water.
Deep below the surface the water sometimes reaches the hot rock and turns into steam. Hot water can reach a temperature of over 150 degrees C without turning to steam because it is under high pressure. When this hot water reaches the surface through a crack in the earth’s crust, we call it a hot spring, or if it erupts into the air, a geyser.
Hot springs are used around the world as spas, for health and recreational purposes. Hot water from the depths of the Earth can heat greenhouses and buildings. In Iceland, which is known for its geysers and active volcanoes, many buildings and pools are heated by geothermal hot water.
Electricity generation using geothermal energy
Hot water and steam from the depths of the earth can be used to produce electricity. Geothermal wells are drilled and pipes are lowered into hot water. Hot water or steam (under lower pressure hot water turns into steam) rises with these pipes to the surface. A geothermal power plant is like any other power plant, except that steam is not produced by burning fuel but is extracted from the ground. The further procedure with steam is the same as with a conventional power plant: the steam is fed to a turbine that drives the rotor of an electric generator. After the turbine steam goes to the condenser, it condenses (liquefies) so that the water thus obtained is injected back into the geothermal source.
Geothermal heat pumps (heat pumps)
Although the temperature in the depths of the earth is high, the surface layer of the earth is not so hot. At the first 3 m below the surface, for example, the temperature is constant and is between 10 and 16 degrees C. A geothermal or “surface” heat pump can take advantage of the difference in surface temperature and the Earth’s interior to heat or cool buildings. Pipes are laid in the ground near the building through which the working medium flows and is used for heat exchange between water and soil, and is therefore called a heat exchanger. In winter, heat from the ground through a heat exchanger heats the air flowing into the building. In summer, the process goes the other way around: the hot air from inside the building passes through the heat exchanger to the relatively colder ground. The heat removed from the air in summer can be used to heat water.