In a move that could fundamentally change the landscape of renewable energy storage, Finland has officially activated the world’s largest “sand battery” in the southern municipality of Pornainen. Developed by Finnish startup Polar Night Energy, the industrial-scale thermal energy storage system can store enough heat to warm an entire town for a week, providing a stable and emissions-free alternative to fossil fuels.
The new sand battery, a towering structure measuring 13 meters tall and 15 meters wide, contains 2,000 tons of crushed soapstone—a byproduct of the Finnish fireplace industry. Unlike traditional chemical batteries that store electricity, this innovative system stores heat. It operates by using excess electricity from renewable sources, such as wind and solar, to heat air to temperatures as high as 600°C. This superheated air is then circulated through pipes within the insulated tank, transferring the thermal energy to the crushed stone.
When the town’s district heating network requires warmth, the process is reversed. Air is blown through the pipes, absorbing the stored heat and transferring it to the network’s water supply. The system, with a thermal output of 1 megawatt and a storage capacity of 100 megawatt-hours, is now the primary heat source for the Pornainen community.
This groundbreaking project directly addresses a key challenge of renewable energy: intermittency. By storing surplus energy during periods of high wind or sunshine, the sand battery ensures a consistent and reliable heat supply even when the sun isn’t shining or the wind isn’t blowing. According to Polar Night Energy, the system’s efficiency has already exceeded initial targets, and it is expected to reduce the municipality’s CO2 emissions from district heating by nearly 70%, while completely phasing out the use of oil and significantly reducing the consumption of wood chips.
Polar Night Energy is already in talks for new projects, with plans to explore a future where the stored heat can be converted back into electricity, potentially making this technology a true “game-changer” for global energy grids.
