In Pornainen, Finland, the world’s largest sand battery has begun operation. Built by Polar Night Energy, the 13-meter-tall and 15-meter-wide tower stores 100 megawatt-hours of thermal energy, accumulating it from solar and wind power. As a result, the city has reduced emissions by 70%, moving away from oil and minimizing the burning of wood chips.
The system uses crushed talc-magnesite, which heats up to 500°C and delivers heat to the city through hot air and a heat exchanger. In summer, a full charge covers the city’s monthly heating needs, while in winter it provides district heating for one week. According to estimates, the system reduces CO₂ emissions by 160 tons per year.
The idea grew out of a simple question from engineers: what readily available material stores heat best? Sand turned out to be more environmentally friendly and cheaper than conventional batteries and does not require rare metals. The first prototype has been working in Kankaanpää since 2022, and the technology is now being scaled up, showing that straightforward solutions can change energy systems for entire cities.
A special value of the project is that it uses not beach or sea sand, but accessible waste from crushed rock materials, so as not to damage shorelines and ecosystems. But the concept itself is inspiring: a house could also be used to heat ordinary sand on a beach.
