Decarbonizing the world’s electricity grids won’t be an easy task, but it is a necessary one if we’re going to mitigate some of the worst effects of climate change. Since wind and solar power are intermittent, part of decarbonizing the grid will involve storing renewable energy for use when the Sun isn’t shining and the wind isn’t blowing.

While day-to-day storage will cover the gaps when the wind slacks or the Sun sets, on grids with more than 80 percent renewable energy you’re also going to want inter-seasonal storage. This is because sun and wind are seasonal, and energy demand is also seasonal—people use a lot more energy in the winter than they do in the spring, because it’s darker and colder outside.

Researchers from the University of Edinburgh and the University of Strathclyde think that one potential step toward seasonal storage should involve identifying large underground saline aquifers where energy could be stored as compressed air. Saline aquifers are usually found underwater; the compressed air will displace some of the water, which can be discarded, as it’s not potable.