We need better, cheaper ways to store solar and wind energy when it’s dark out and the wind isn’t blowing.

One option: Compressing air in underground caverns when energy is abundant, then blowing it back out to create energy when you need it. It’s an old idea, but it has some fundamental problems.

Curtis VanWalleghem, the co-founder and CEO of Hydrostor, thinks his company has solved those problems with a new approach. If he’s right, his firm will help fix the biggest bottleneck slowing down the adoption of solar and wind power.