Germany helped make solar power cheap. As of June this year, it boasts 1 million homes that have installed rooftop solar panels. That means the country produces a lot of renewable energy—sometimes more than it can use.

At such times, German grid operators have had to pay neighboring countries or grids to use the excess electricity. Since the beginning of this year, German grids have accumulated 194 hours (paywall) with negative power prices.

Now Germany is turning to energy storage as a solution to the problem of excess electricity. On Aug. 28, an energy ministry official attended the commissioning (link in German) of the 100,000th home to install a battery-storage system that’s connected to the grid.

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