Finland has officially scaled its "sand battery" technology from a successful prototype to an industrial powerhouse. In June 2025, the world’s largest operational sand battery was switched on in the municipality of Pornainen. This massive silo, standing 13 meters tall and 15 meters wide, serves as the primary heat source for the town's district heating network, warming homes, the town hall, and even the local library. Developed by Polar Night Energy, the Pornainen battery is ten times larger tha