A Finnish company is using the thermal properties of sand to create heat-storing batteries which could play a major part in meeting the world’s energy needs. “My cofounder Markku Ylönen and I met at Tampere University of Technology,” says Tommi Eronen, CEO of Polar Night Energy. “A battery might only be able to store energy for a few hours, but we need to store energy for days,” Eronen says. The Pornainen sand battery began operations in 2025 and is much larger – 100 MWh – and can deliver hot water, steam or air, with output temperatures of up to 400 degrees C (752 F). “In Pornainen we use crushed soapstone to store heat, a byproduct from the company Tulikivi’s fireplace manufacturing,” Eronen says.