Yet another "renewables and batteries are looking good" story

From Science, a report about a Harvard team that has come up with a cheaper, safer, set of chemicals to use in a "flow battery" which could have domestic application for storing roof top solar power.   The big question - whether it will end up cheaper to run than Tesla's lithium home storage - is not answered, and it sounds like the system could take up more space, but still:

The Harvard team realized that a possible bromine replacement was a charge-carrying molecule called ferrocyanide, which sounds dangerous but is actually used as a food additive. Ferrocyanide, however, dissolves in alkaline solutions, not acidic ones. So Aziz and his colleagues tweaked the chemical structure of their quinone—ripping off a couple of sulfur groups and replacing them with pairs of hydrogen and oxygen atoms—in the end converting the compound into one that readily dissolves in an alkaline solution.

The scheme worked, and as the researchers report today in Science, the battery readily stores power with only components that are cheap, abundant, and nontoxic.

For now, Aziz notes the alkaline quinone battery stores only about two-thirds of the energy per volume as the previous acid-based version. But because it doesn’t require expensive materials to deal with bromine, it’s likely to be far cheaper to produce and friendlier to use. “This is chemistry I’d be happy to put in my basement,” Aziz says. And that may not be far off. A flow battery using the new quinones and ferrocyanide would likely only have to be the size of a couple of hot water tanks to store the energy produced by a conventional home rooftop solar array.