Finnish town heats up with innovative sand battery storing renewable energy

In the small southern Finnish town of Pornainen, an innovative and surprisingly simple solution is addressing the challenge of storing excess electricity from renewable sources. Developed by the Finnish company Polar Night Energy, a massive "sand battery" is efficiently converting surplus electricity into thermal energy for the town's district heating system.

The facility, standing 13 meters high and 15 meters wide, resembles a silo and is filled with 2,000 tons of crushed soapstone. This material is chosen for its excellent heat absorption and retention properties. The battery has a thermal storage capacity of approximately 100 megawatt-hours, sufficient to provide heating for Pornainen for up to a month during the summer and about a week during the winter months.

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One of the biggest challenges of the energy transition is how to store electricity obtained from sustainable sources. When there is no wind and wind turbines stop, or when there is no sun or it is night, people are dependent on other sources of energy.

The operational principle is straightforward: when wind or solar power generation is high and electricity prices are low, the surplus energy is used to heat air. This hot air then heats the soapstone to temperatures between 500 and 600 degrees Celsius. Thanks to robust insulation, the stored heat can be maintained for days or even weeks. When heating is needed, the stored thermal energy is transferred via a heat exchanger into the district heating network.

This pioneering sand battery system has already led to a significant reduction in harmful emissions, cutting them by 70% compared to the town's previous reliance on oil and pellets for heating. While a biomass power plant remains as a backup, it is now used much less frequently. Finnish Minister for Climate Sari Multala praised the facility as an example of innovative energy storage, highlighting its potential for future development in flexible electricity supply.

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As a climate minister, I think it is a very interesting example of energy storage.