While solar and wind power are now the cheapest sources of energy across the world, energy storage remains one of the biggest hurdles preventing a full switch to renewables. This is because it’s still quite expensive to use batteries for storing power. A startup, however, has figured out a new way to store energy by using the force of gravity on hills instead of batteries.

The new system, developed by RheEnergise, works in a similar way to existing hydropower plants that pump water up mountains when energy is cheap, and then release it to spin turbines and thus generate electricity when it’s needed.

But while a hydropower plant can sometimes take longer than a decade to build, and makes economic sense only on steep hills, the new system can be built much faster and it can be located on smaller hills, making it suitable for more areas.

What’s also different is that, instead of using water, the novel system pumps a fluid that’s two and a half times denser. This means that it can store the same amount of energy on a smaller hill, such as a former mine. The pipes can also be stored underground so they don’t deface the scenery in more pristine areas.

“As the energy grid is transitioning to accommodate these distributed generation technologies, you also need a distributed storage technology, so you store it more locally to where it’s been produced,” says Stephen Crosher, chief executive of RheEnergise.

On top of it all, the new systems are economically sound. According to Crosher, depending on the area, the cost of the renewables together with the new storage system could already be competitive with energy generated by fossil fuel stations.

The company has mapped out 9,500 sites in the UK with hills suitable for the new technology and is now raising funds for a pilot plant.