Polar Night Energy to build 1 MW sand-based heat storage battery in Finland

Finnish startup Polar Night Energy and Loviisan Lämpö, a district heating company in Finland, plan to construct an industrial-scale thermal energy sand-based storage system in the municipality of Pornainen in southern Finland.

The 1 MW Sand Battery 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.

It will deliver the system as a turnkey project, including testing of the battery, which will be approximately 13 meters high and 15 meters wide. Development and construction are expected to take around 13 months.

The Sand Battery will be 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 battery will also help to reduce annual carbon dioxide emissions from the district heating network of Pornainen by nearly 70%, according to Polar Night Energy. Liisa Naskali, the COO of Polar Night Energy, said the project is “a significant step in scaling up the sand battery technology.”

The thermal energy storage system will use crushed soapstone as its storage medium. Sand batteries can use sand or sand-like materials as a storage material. Polar Night Energy said soapstone conducts heat better than conventional sand. It will get soapstone from Tulikivi, a Finnish company specializing in heat-retaining fireplaces, which produces soapstone as a byproduct of its manufacturing process.

“We always choose the thermal energy storage medium based on the customer's needs. Examining and testing different materials is crucial for us – to use materials that are suitable in terms of properties, cost-effectiveness, and promotion of circular economy,” said Naskali. “Tulikivi is a well-known and traditional company. The soapstone they use is a very Finnish thing.”

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 heating power and 8 MWh of energy 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.