Because of the intermittency of renewable energy like wind and solar power, storing large amounts of electricity is a necessity for the decarbonization of our energy system. However, we still don’t have enough batteries to compensate for renewable energy slumps across the planet. When thinking about the biggest utility-scale energy storage installations, a huge cylindrical lithium ion battery powered light bulb may go off in your head. But what if I told you the world’s largest battery taps into water rather than lithium? Can an old technology, even one still learning new tricks, be the answer? Let’s see if we can come to a decision on this.