Renewable energy from sun and wind is difficult to store. Disused coal mines might be able to help.
Scientists in the Ruhr Valley are considering installing pumped-storage plants in the empty shafts that are more than 1,000 meters deep in places. Excess energy from solar or wind power plants would pump water from the depths to the surface. At night, or when the wind is not blowing, the water would be allowed to fall down again and drive generators. The advantage is that the landscape above the mines would not be involved. And there are more and more disused mines - not only in Germany.
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