Berlin testing salt battery

May 2019—So called salt batteries aren’t using table salt. Instead they’re using calcium oxide which becomes calcium hydroxide in water. It’s used in cement and pickles. In a ghoulish historical connection, the Nazis used it in their freight cars to burn the Jews to death on their trip to the gas chambers.

What’s special about quicklime, as calcium oxide is called, is that it generates a lot of heat when it gets wet. But it can return to a dry state and wait to do it again.

At the Reuter power plant in Berlin, which supplies 600,000 households in the capital with heat, the solution now includes calcium oxide, also known as quicklime. Vattenfall and Swedish start-up SaltX have been taking advantage of a simple chemical reaction that occurs when quicklime 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 — a process not dissimilar to baking — the substance turns back into calcium oxide.

The process essentially mirrors how batteries work, except that instead of electricity, the system stores heat. SaltX says it has also patented a way of covering the quicklime with tiny particles — known as a nano-coating — to prevent it from lumping together after several heating and cooling cycles.