How can Flipboard be rated on 200m

Geothermal energy : The longer the line, the shorter the bill

Geothermal energy, also known as geothermal energy, is one of the renewable energy sources, like solar and wind energy. According to the Federal Association of Renewable Energies (BEE) in Berlin, it can be used at almost any location without major structural effort. With a heat pump, the heat present in the earth's interior is brought to light via probes sunk in the ground and used for the building's heat supply.

According to figures from the Federal Geothermal Association (GtV) in Berlin, there were around 230,000 properties in Germany in 2009 that were supplied with near-surface geothermal energy via heat pumps. “According to our estimates, it can be assumed that more than 80 percent of the systems are used in private living areas,” says GtV board member Burkhard Sanner. The remaining plants supplied larger residential complexes and commercial properties.

In near-surface geothermal energy, geothermal energy from depths of up to 400 meters is used. The deeper you drill, the warmer it gets: According to GtV, the temperature in Central Europe increases by around three degrees per 100 meters of depth. But drilling extremely deep is not even necessary with geothermal energy for heating. At 100 meters, the underground is around eleven to twelve degrees. That is enough to heat buildings with a heat pump in winter. At a depth of 400 meters it is around 25 degrees, in the earth's core up to 6000 degrees. The heat is constantly transported to the surface of the earth.

"This energy stored in the earth is inexhaustible by human standards", according to the GtV. Most of it escapes unused: "The earth radiates around four times more energy into the surrounding space every day than we humans are currently consuming," the association calculates. A frightening notion when you consider that the cost of heat from gas and oil is constantly increasing.

According to GtV information, various methods can be considered to bring geothermal energy to the surface. For example, groundwater is pumped up from wells up to 20 meters deep to extract heat. Another method works with geothermal collectors, which are laid on larger areas at a depth of 1.5 meters. Here, heat is extracted from the ground with a heat pump and a circulating liquid. “Energy piles” with integrated heat exchange pipes are in turn placed in the ground as parts of the building foundation in new buildings.

However, geothermal probes have established themselves as the most common type of system in Central and Northern Europe, explains the association. They are drilled vertically into the ground at depths of 50 to 160 meters. The probes consist of double U-tubes made of plastic, which are filled with a heat transfer fluid. It absorbs the heat from the ground, a heat pump pumps the heated liquid up into a heat exchanger. It transfers the heat to the heating system. The cooled carrier liquid is then fed back into the earth and the cycle starts all over again.

Other methods use gas instead of liquid in the geothermal probes, or the probes are driven into the ground at an angle. Without a heat pump, geothermal heating would not work. It works like a refrigerator, only the other way around, explains the Federal Association of Heat Pumps (bwp) in Berlin. Since it is driven electrically, the decisive factor in calculating the costs is how large the heat output of the pump is in relation to the electricity used. Because it usually has to be bought from the supplier. According to the bwp, the energy requirement of modern heat pumps accounts for around 25 percent of the total heating output.

When calculating the costs in new buildings, it should also be noted that the investments due to the expensive geothermal probes and the purchase of the heat pump are higher than for a conventional boiler. However, because only a small part has to be purchased as electricity for the pump operation and most of the energy is obtained for free from the subsoil, "the systems pay off after a few years", according to the GtV. And as oil and gas prices rise, the economic advantage will increase.

If an existing property is to be converted to geothermal heating, the project should always be integrated into a building renovation concept, recommends Christian Stolte from the German Energy Agency (dena) in Berlin. “The decisive factor with a heat pump is that the building is insulated.” Because the goal should be to use as little electricity as possible in order to heat the living space with the heat pump. The less the heat pump has to work, the cheaper it is to generate heat.

If the house cannot be properly insulated, the money can perhaps be used more sensibly. After all, there is still money from the state for retrofitting: According to Stolte, there is funding of 20 euros per square meter of living space for electrically operated heat pumps for single-family houses, but a maximum of 2400 euros. Those who build from scratch, on the other hand, get nothing. (dpa)

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