Finnish startup Polar Night Energy is building an industrial-scale thermal energy storage system in southern Finland. The 100-hour, sand-based storage system will use crushed soapstone, a by-product from a fireplace manufacturer, as its storage medium.

Finnish startup Polar Night Energy has announced that construction is proceeding according to plan on its thermal energy sand-based storage system in the municipality of Pornainen in southern Finland. The 1 MW system will supply thermal energy for Loviisan Lämpö’s district heating network.

Once in operation, it will be capable of storing up to 100 MWh of thermal energy – a capacity equivalent to almost one month of heating demand in the summer and one week of demand in Pornainen in the winter. Polar Night Energy said its Sand Battery works as a high-power, high-capacity reservoir for excess wind and solar energy, storing energy in sand as heat.