The world’s largest sand battery has officially started operating in Pornainen, a small town in southern Finland. This groundbreaking battery, developed by Finnish company Polar Night Energy, stores 100 megawatt-hours of thermal energy from solar and wind power.
At 13 metres high and 15 metres wide, it can hold enough heat to meet one month’s summer demand. It will help cut the town’s carbon emissions by nearly 70 per cent by replacing oil in the district heating network.
“This is a major step toward climate neutrality by 2035,” said Mikko Paajanen, CEO of Loviisan Lämpö, which runs the heating network.
Sand batteries work through resistive heating, a process where electricity warms sand to around 500 degrees Celsius. The stored heat is then used to warm water that circulates through homes, schools, offices, and even swimming pools.
Unlike traditional batteries, sand is a cost-effective and widely available material. In Pornainen, crushed soapstone—a by-product of Finnish fireplace manufacturing—is used as the storage medium.
The new system also means the use of wood chips will drop by 60 per cent. An older biomass boiler will remain on standby for peak demand.
The sand battery was first tested in 2022 in Kankaanpää and has now been scaled up. Polar Night Energy hopes to expand globally and is already planning more projects in Finland and abroad.
“Sand can store energy for days or even months,” says co-founder Markku Ylönen. “Now we just need to build bigger systems, and fast.”
