World’s Largest Sand Battery Passes First Year Mark

One year after going live in Pornainen, Finland, the world’s largest sand battery has surpassed all performance targets.

Developed by Polar Night Energy for the district heating company, Loviisan Lampo, the innovative thermal energy storage system has achieved complete reliability and slashed local district heating emissions by 70%.

The system utilises a 13-meter-tall insulated steel silo packed with 2 000 tonnes of crushed soapstone, which is recycled industrial waste from a fireplace manufacturer. Excess green electricity from wind and solar is converted into heat and circulated through an internal network of foil-wrapped pipes, heating the core to 500-600 degrees celsius. When energy is needed, the process reverses to deliver environmentally friendly heat to the grid.

The installation proved its durability during Finland’s brutal 2025-2026 winter, which was colder than expected by locals.

The sand silo boasts a round-trip thermal recovery efficiency of 85% and can store a month’s worth of summer heat demand or a week’s worth in winter. Crucially, its massive 100-hour charging window allowed operators to procure electricity at prices 70-80% below the spot market average.

Thanks to the battery, the municipality completely eliminated its oil consumption and cut biomass burning by 60%, fully meeting its public climate targets.

While district heating remains vital for Nordic regions, Polar Night Energy is aiming for global industrial markets – such as food, chemicals, and pharmaceuticals – that require high-temperature process steam. The company has already commenced construction on an even larger facility in Vaaksy, Finland, accelerating the transition away from fossil fuels.

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