Sometimes it’s not sunny enough to depend on solar power, or windy enough to turn the windmill. So, Finnish researchers have devised a year-round, 24/7 energy source: a battery made from sand.

Markku Ylönen and Tommi Eronen are the young engineers who came up with the idea of building a sand battery. They founded a company called Polar Night Energy to develop their concept. Now, they’ve installed their first sand battery in the Vatajankoski power plant in Kankaanpää, a town in southwest Finland.

Related: Global sand crisis caused by urbanization, reports UN

So how do you build a sand battery? Polar Night poured 100 tons of low-grade builder’s sand into a silo. Then they charged the sand battery with cheap solar or wind energy until it’s 500 degrees Celsius. As anybody who’s ever burnt their soles on a hot beach knows, sand stores heat very well. Polar Night’s plan is in its name: they want to use that hot sand to warm homes and other buildings through Finland’s long, cold winter nights.

As the sand warms up, a heat exchanger in the sand will circulate the hot air until it’s distributed throughout the sand battery. Ylönen and Eronen say their battery will be able to keep the sand at a toasty 500 degrees Celsius for several months.

Since green energy is hard to come by in winter, that’s when the price shoots up. Polar Night plans is to charge their sand battery before the days get short. “Whenever there’s this high surge of available green electricity, we want to be able to get it into the storage really quickly,” said Ylönen, as reported by BBC.

Most batteries require lithium—which is expensive and intensive to extract from the earth—so scaling up production of sand batteries could be one more useful tool in the fight against ruining the planet beyond human habitation. But we can’t get too excited. A recently released UN report named sand the Earth’s second most exploited resource after water, and warned of a global sand crisis. Used for constructing roads and buildings, sand is our most mined material.

Via BBC

Lead image via Pexels