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How sand batteries are helping cities cut emissions and heat homes

How sand batteries are helping cities cut emissions and heat homes
How sand batteries are helping cities cut emissions and heat homes | Photo: Polar Night Energy

The global challenge of balancing renewable energy production with consistent demand has spurred a wave of innovations. Among the most striking is the industrial-scale sand battery, pioneered in Finland, which is now beginning to demonstrate how simple materials and careful engineering can bridge gaps in the clean energy transition. By converting surplus electricity into stored heat, the system offers a scalable solution for communities that depend on district heating networks.


At the heart of the design is a steel tank filled with ordinary sand or crushed stone. Using resistive heating, electricity warms air that circulates through the tank, raising the sand’s temperature to as high as 600°C. This thermal mass can retain heat for days or even months. When required, the process is reversed: cooler air passes through the tank, absorbs the heat, and transfers it to water via a heat exchanger. The water then circulates through local heating infrastructure, cutting reliance on fossil fuels.


From Kankaanpää to Pornainen

The first commercial unit was commissioned in 2022 in Kankaanpää, Finland. With an energy capacity of 8 MWh, it was designed to prime waste heat from a data centre and integrate with the local district heating system.


The technology has since scaled up dramatically. In August 2025, Polar Night Energy inaugurated the world’s largest sand battery in Pornainen. Using 2,000 tonnes of crushed soapstone, a byproduct of the fireplace industry, the unit boasts 100 MWh of capacity—enough to cover up to a week of winter heating demand for the local network. Importantly, it is expected to reduce emissions by nearly 70 per cent compared to traditional fossil-fuelled heating.


Key strengths of sand batteries

What makes this approach noteworthy is its balance of efficiency, cost and sustainability:


·       Affordable and abundant: sand and soapstone are inexpensive, widely available and chemically inert.

·       Environmentally sound: no toxic by-products are generated, and waste materials can be repurposed.

·       Long-duration storage: unlike batteries that discharge within hours, stored heat can be held for months.

·       Scalable design: larger installations achieve higher efficiencies, making them suitable for towns as well as individual facilities.

·       Grid flexibility: by charging during periods of low demand, sand batteries help stabilise electricity markets while storing excess renewable output.


What is a sand battery ?

Towards a cleaner future

Globally, heating accounts for nearly half of total energy demand, and the sector has been notoriously slow to decarbonise. Sand batteries provide a practical pathway, particularly in colder regions where demand peaks in winter. Analysts note that their relatively low construction cost, combined with potential emission cuts of 60 to 70 per cent, make them a compelling option for municipalities seeking to meet climate targets while ensuring reliable energy supply.


As cities experiment with new energy infrastructures, projects such as those in Finland could mark an important turning point. The technology also aligns with the Sustainable Development Goal on affordable and clean energy, reinforcing its role in a wider transition towards more resilient energy systems.


Further information about similar storage innovations can be found at IEA’s energy storage hub and Fraunhofer’s research on thermal storage.

 

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