Solar and wind power are the glamorous twins of the clean-electricity revolution. It is thrilling to see a field of glistening panels absorbing the sun’s energy or a vast turbine twirling above the ocean. Stationary power storage does not have quite the same allure—think of a large metal shed stuffed with piles of big batteries. Nonetheless, the ability to stockpile energy on a massive scale will be of supreme importance if the world is to wean itself off filthy fossil-fuel power plants. The technology is gradually getting cheaper and attracting investment (see article). But more needs to be done to ensure that it sparks.