Testing to start on 100 MWh sand-based thermal battery in Finland

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.

The new Sand Battery in Pornainen will be filled with crushed soapstone, a by-product of Tulikivi’s heat-retaining fireplace production. A total of 2,000 tons of soapstone will be used in the Sand Battery, equivalent to the weight of about a thousand soapstone fireplaces. The filling process was completed at the end of October.

“We’re very pleased to use a by-product of Tulikivi’s production instead of virgin materials for the Sand Battery, supporting the principles of circular economy. We have high expectations for soapstone’s performance,” says Polar Night Energy CEO Tommi Eronen.

The Sand Battery is delivered as a turnkey project and integrated with Loviisan Lämpö’s district heating network. It will be charged from the electric grid using charging algorithms developed by Polar Night Energy, which the company said will minimize the cost of electricity used for charging, while meeting demand from the district heating network.

“The Sand Battery will significantly reduce the combustion-based energy used in our district heating network, and the collaboration with Tulikivi has added a valuable circular economy aspect to this project,” says Loviisan Lämpö CEO Mikko Paajanen.

The next project phase includes various installation works. Testing of the Sand Battery will begin during the winter, with commissioning set for 2025.

In 2022, Polar Night Energy switched on the world’s first commercial sand-based, high-temperature heat storage system in the Finnish city of Kankaanpää, with 100 kW of power output and 8 MWh of storage capacity. In December 2023, it announced a partnership with Nordic energy company Ilmatar to develop its sand battery with power-to-heat-to-power capabilities.