Storing Power in Molten Aluminum Lakes

Germany’s sprint toward renewable energy makes wholesale power cheap, even free, when the sun is shining and the wind is blowing. When the weather’s gray, prices spike. The system doesn’t yet have dedicated storage equipment capable of holding large amounts of renewable energy. Trimet Aluminium, Germany’s largest producer of the metal, is experimenting with one answer: using its vast pools of molten metal as storage batteries .

Making aluminum is extremely power-intensive. To yield each ton of the metal, derived from bauxite that’s been converted into molten aluminum oxide, Trimet needs roughly 14 megawatt-hours, or about €500 ($624) worth of power. Multiply that by 500,000, the number of tons of aluminum Trimet produced using electrolysis last year, and that’s a lot of power and money humming through the company’s plant in the western German city of Essen.