Solar panels and wind turbines are everywhere these days, but the sun doesn’t always shine and the wind doesn’t always blow. Meaning, the more panels and turbines you build, the more you need a backup for rainy days (literally). Storing excess solar and wind energy would be ideal, but conventional batteries wear out quickly, sometimes catch fire, often leak toxic crud and leave behind heavy metal waste when they go. That leaves unconventional batteries — say, power cells built out of something cheap, plentiful and nonflammable that’s also utterly nontoxic. Maybe, since we’re dreaming here, even safe enough to eat. Make that, safe enough to eat and drink, and somewhere Jay Whitacre’s ears perk up. For the past five years, the Carnegie Mellon professor and a team of engineers at his startup, Aquion Energy, have been developing a long-lived, eco-friendly and inexpensive battery out of nothing more than salt water and other simple components. This isn’t a battery that will juice your phone or your car, at least not directly; instead, it’s intended for big power farms that could soak up excess electricity during the day — for instance, from home solar systems — and then shoot it back out at night when the sun’s down. The French consulting firm Yole Développement figures this “stationary storage” market could be a $13.5 billion opportunity by 2023, compared with less than $1 billion this year.