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‘A very Finnish thing’: Big sand battery starts storing wind and solar energy in crushed soapstone

Big sand battery starts storing wind and solar energy

The world’s largest sand battery has started working in the southern Finnish town of Pornainen. Capable of storing 100 MWh of thermal energy from solar and wind sources, it will enable residents to eliminate oil from their district heating network, thereby cutting emissions by nearly 70 per cent.

Sand batteries are getting bigger in Finland

The new 1 MW sand battery has a precursor. In May 2022, Polar Night Energy rigged a smaller design to a power station in Kankaanpää town. Launched just as Russia cut off gas supplies in retaliation for Finland joining NATO, the project was a timely example of how renewable energy could be harnessed in a new way.

How do sand batteries work exactly?

A tall tower is filled with low-grade sand and charged up with the heat from excess solar and wind electricity. This works by a process called resistive heating, whereby heat is generated through the friction created when an electrical current passes through any material that is not a superconductor. The hot air is then circulated in the container through a heat exchanger. The sand can store heat at around 500C for several days to even months, providing a valuable store of cheaper energy during the winter. When needed, the battery discharges the hot air - warming water in the district heating network.

How is the sand battery serving people in Pornainen?

Having refined its charging algorithms, Polar Night Energy has now successfully scaled up the storage tech in Pornainen. Many of the town's buildings, including the comprehensive school, town hall, and library, rely on district heating. In total, the sand battery is expected to knock off 160 tonnes of carbon dioxide equivalent emissions per year. The battery’s thermal energy storage capacity equates to almost one month’s heat demand in summer and a one-week demand in winter in Pornainen.

Is sand a sustainable material?

In Pornainen, Polar Night Energy has found a sustainable material in crushed soapstone; a by-product of a Finnish company’s manufacture of heat-retaining fireplaces. Polar Night Energy has big ambitions to take its technology worldwide, and is currently in "active discussions" with both Finnish and international partners. Earlier this spring, the company announced a pilot in Valkeakoski to explore the conversion of stored thermal energy back into electricity.