Image: Polar Night Energy

Finland has inaugurated the world’s largest sand battery, a 1 MW/100 MWh thermal storage system developed by Polar Night Energy.

The industrial-scale unit, located in Pornainen, began operations in June after being commissioned by district heating company Loviisan Lämpö. It now serves as the main production facility for the company’s district heating network, fully replacing the area’s old woodchip plant during the summer months.

Polar Night Energy reported that the battery has met performance expectations and exceeded guaranteed efficiency targets in its first months of operation.

A sand battery stores clean electricity as heat in sand or other solid materials. The Pornainen installation measures nearly 13 meters tall and 15 meters wide, delivers 1 MW of thermal power, provides 100 MWh of storage capacity, and contains about 2,000 tons of crushed soapstone.

The company said the battery can also participate in electricity reserve markets, charging in response to electricity prices and Fingrid’s reserve market signals. With its large storage capacity, the system enables energy consumption to be optimized over days or weeks, while also supporting grid balancing.

Finland’s Minister of the Environment, Sari Multala, highlighted the role of thermal storage in reducing emissions and improving system flexibility: “Energy storage plays an important role in the energy transition, where combustion-based production is phased out and society moves toward carbon neutrality. The Pornainen sand battery is a great example of how the clean transition can be advanced through the electrification of district heating networks.”

Polar Night Energy is currently in negotiations for several large-scale thermal storage projects for district heating, hot air, and process steam production. Chief Operating Officer Liisa Naskali noted that industrial applications are particularly promising in cases where heat above 100 °C is required, beyond the limits of electric boilers and heat pumps.