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:: Underground pumped storage plants: Green power from the mines

Solar and wind energy have many ecological advantages, but also a big problem: if the wind doesn't blow or the sun doesn't shine, they produce no electricity. Then conventional power plants have to step in. An interdisciplinary team from the University of Duisburg-Essen and the Ruhr-University Bochum, both inGermany, is researching new methods to save the green power to bidge such times. Dr. Ulrich Schreiber (Geology), Dr. Eugene Perau (Geotechnical Engineering), Dr. André Niemann (Water Engineering) and Professor Dr. Hermann-Josef Wagner (Energy Systems) are developing a proven technology to store energy: the pumped storage plant.

The principle is well known: the plant leads water from higher reservoirs through turbines in deeper pools and thus generates electricity when needed. In times of surplus of wind or solar energy the water is pumped back to the upper reservoir until the next bottleneck. These systems need large differences in altitude and lots of space. Therefore in Europe they are mainly used in the mountains of Norway and the Alps.


But especially in these zones, areas for large basins are as rare as electricity consumers. In comparison there is no lack of space and electricity demandin the Rhine-Ruhr region. It is the largest metropolitan region in Germany with more than ten million inhabitants. But there areno mountains in this part of the country. "Nevertheless, we havethe necessary difference in altitude," said Professor Schreiber.


What he is talking about are actual and former coal mines - the Ruhr coal field is the largest coal supply in Europe. But due to economical factors, coal mining there will probably come to anend in 2018. Prof. Schreiber and the other scientists are thinking of using the abandonded mines for underground pumped storage plants. The novelty of their approach is that the basins are at ground level or underground. The water is passed to the depth through the old tunnels or pipes.


"Our idea needs no mountains orcliffs. It could be used almost anywhere," said Professor Perau. The researchers are working on basically three different variants. In the first variant the shafts of coal mines are lined with a pipe system.


In the cavities a closed storage system could be built, which is equiped with different shafts to lift the water. In times of high electricity demand water is passed in a central shaft through a turbine to produce power. In times of high wind activity or intense solar radiation, the surplus of electricity could be used to raise the water again. Depending on the design of the system the geothermal energy can be utilized by heat exchangers, too.


A structurally simpler version is probably the use of open-castmining holes as they occur primarily in the production of brown coal. Already during the mining phase itself, which sometimes goes down 400 meters below ground level, the pipe system andthe cavities have to be built. The turbines can then gradually be installed with the backfill. Finally, the mine will be covered with over burden material and the upper reservoir can be established. The same principle can be implemented in coastal regions,which have a steep relief to the ocean basins. This is especially interesting for coasts, where a high photovoltaic power generationis possible, for example at the Red Sea.


Yet the research is in its early stages. But, the first calculations of the scientists show that there is a remarkable potential, especially in the case of open-cast mines. However, the idea needs support, as Professor Niemann knows: "To implement our project, we need partners in the industry."

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