Can salt – not the kind you put on your food – be used to store heat? A thermal power station in Germany is testing the theory, which goes like this: When calcium oxide becomes wet, the salt-like grains soak up the water, becoming calcium hydroxide and releasing large amounts of heat in the process. By removing the water again, the substance turns back into calcium oxide. Basically mirroring how batteries work, the system stores heat.

According to the research, the pilot project in Berlin can store enough energy to heat about 100 large houses.