The missing piece of the renewable-power jigsaw may now have been found in the form of a new type of flow battery.
THERE is nothing so expensive, some cynics suspect, as free fuel. It is not that turning wind and sunlight into electricity is itself that costly, provided you pick the right places to do it. But it is not reliable. The wind does not always blow, and even in the most cloud-free desert night falls with monotonous regularity. Political commitments to use large quantities of renewables, such as several European countries have made (see following story), thus risk the lights going out. The search therefore has been on for a cheap way to store energy transduced from sun and wind when it is plentiful, so that it can be used when it is not.