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“Green” power plants are often more harmful to the climate than coal-fired power plants

Basically, the functioning of geothermal power plants is quickly explained. Hot water is pumped from the depths to the surface. The heat is then used to drive a turbine, which in turn is connected to a generator. Theoretically, large amounts of clean electricity can be generated in this way. Numerous countries around the world – such as the USA, Turkey and Italy – are relying on such power plants on a large scale as part of the energy transition. Bavaria’s Prime Minister Markus Söder also recently announced that he intends to massively expand this form of energy generation. Not least because it means that under certain circumstances he can do without the construction of wind turbines, which are often highly controversial among local residents. A study by Turkish scientists now points to a crucial difference between theory and practice: the supposedly green geothermal power plants sometimes even cause more climate emissions than coal-fired power plants.

Icelandic geothermal power plant. Image: Gretar Ívarsson / Public domain

The chemical compounds bound under pressure are released

The background: The pumps not only get the hot water out of the ground, but also unwanted by-products. For example, when the water is used to drive a turbine directly, numerous chemical compounds previously bound under pressure are released. This also includes the well-known greenhouse gas CO2. The effect is comparable to opening a previously shaken bottle of mineral water. In many geothermal power plants, the gas released in this way escapes unhindered into the atmosphere, fueling climate change. Things are further complicated by the fact that the climate balance also depends on the rock at depth. The more carbon storage there is, the more CO2 will be released later. In Iceland, for example, the effect is equally small, while the unwanted emissions in Turkey and Italy are considered to be particularly high. The individual climate balance of the power plants can therefore vary greatly.

The more climate-friendly solution is also the more expensive variant

However, the problem just described only applies to geothermal power plants that work with an open cycle. From a purely technical point of view, however, it is also possible to keep the water in a closed circuit. As a result, it always remains under pressure and no chemical compounds are released. However, the hot water does not drive the turbine directly. Instead, a heat exchanger is used to heat a hydrocarbon compound, which in turn drives the turbine. The CO2 remains in the cycle and can then be injected back into the ground together with the water. Most systems operated in Germany already rely on this technology and actually generate green electricity. However, these closed circuits have one disadvantage that is not entirely unimportant: They are significantly more expensive than the open alternatives. From a climate point of view, however, there is actually no alternative.

Via: Wiwo

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