Germany, richer than India, has about seventy energy-storage projects, about a third of which collect the output from wind and solar plants into banks of batteries. The price of batteries, like the price of photovoltaics, has been falling. Renewable-energy enthusiasts imagine great warehouses full of batteries, soaking up excess sun power by day, releasing it by night, keeping the lights on in the dark. But no matter how cheap the batteries are, such facilities will involve constructing a second, parallel infrastructure for energy storage, adjacent to the first, for energy production, a costly step for the foreseeable future. Today, as in Mouchot's time, free energy from the sun is surprisingly expensive.