A German coal mine is about to become a massive battery for storing electricity from renewable energy sources. The Prosper-Haniel hard coal mine in the state of North-Rhine Westphalia that provided coal power to German industry since it opened in 1974 will soon be turned into a 200-megawatt pumped-storage hydroelectric reservoir. When completed, the nearly 2,000-foot-deep mine that is set to close in 2018 will essentially act as a giant battery that can store enough power for 400,000 homes. That’s a huge backup that’s much needed in one of the most progressive solar nations in the world.

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This “giant battery” stores energy by continually pumping water between two chambers, an upper and a lower connected via pipes with turbines. During periods of high electricity demand, power is produced by releasing the stored water from the upper chamber through the turbines and into the lower chamber. When demand decreases, pumps refill the upper chamber using the cheaper electricity available from the grid. Plants such as this tend to have a huge efficiency of about 80 percent, while also balancing the load in a larger power system.

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As Bloomberg notes, creating this energy storage facility is a win, win for Germany—as it not only provides a much-needed place to store all that power it’s now producing through renewable energy initiatives, but it will also give a boost to the local economy in nearby Bottrop by providing jobs for many of the miners who would otherwise be out of work when the coal mine is shuttered next year.

Via Bloomberg

Images via Goseteufel, Wikimedia Commons and University of Duisburg-Essen