By mid-2024 sand batteries had moved from curiosity to small commercial use. The best-known example was in Kankaanpää, western Finland, where Polar Night Energy and the local utility Vatajankoski had been running a sand-based heat store since 2022. A second, much larger unit was being built for the district heating network in Pornainen, in southern Finland’s Uusimaa region.
The principle is simple. When electricity is cheap, usually because wind or solar output is high, it is passed through resistive heaters, much like the element in a kettle, which heat a large insulated silo of sand or crushed rock to several hundred degrees. The heat is drawn back out when it is needed, typically to warm water for a district heating network. Sand works well because it is cheap, does not degrade with repeated heating and can hold very high temperatures in a well-insulated container for days or weeks.
The Kankaanpää unit is modest: about 100 tonnes of sand, 8 MWh of storage and 200 kW of heat output. It also raises the temperature of waste heat from a data centre so it can enter the heating network. Polar Night Energy puts its overall efficiency at roughly 60–75%.
What happened next
- Late 2024: Construction in Pornainen progressed and the silo was filled by the end of October 2024. Instead of sand it uses about 2,000 tonnes of crushed soapstone, a by-product of a Finnish fireplace manufacturer.
- June 2025: The Pornainen battery entered service for heating company Loviisan Lämpö and was inaugurated that summer. Rated at 1 MW of heat output and up to 100 MWh of storage, with a maximum temperature of 400°C, it has more than ten times the storage capacity of the first unit. It became the main heat source for the town’s network, with a wood-chip boiler kept for backup and peaks.
- November 2025: Utility Lahti Energia agreed to build a 2 MW / 250 MWh sand battery at Vääksy, using about 2,400 tonnes of local sand.
- June 2026: After its first year, Polar Night Energy reported that the Pornainen unit had run above 85% efficiency with no interruptions to heat supply, cut the network’s emissions by about 70% and ended oil use. The company says it bought electricity for charging at well below the average spot price. These figures come from the company and its customer.
- Mid-2026: Foundations were under way at Vääksy, with commissioning due to begin in spring 2027.
The record so far also shows the limits. Sand batteries are best at delivering heat, not electricity. Turning stored heat back into power would need a turbine or similar heat engine, losing a large share of the energy, and the commercial Finnish units supply heat only. They work best where there is an existing district heating network or an industrial heat demand nearby, and where electricity prices swing enough to make cheap charging worthwhile. The storage is also measured in days to weeks of demand, not a whole winter.
We are not aware of any operating sand battery in the UK as of October 2026. British heat networks are far less widespread than Finnish ones, which narrows the obvious market, although industrial heat users may be a better fit. For comparison with other approaches, see our pages on gravity energy storage, pumped storage hydropower and the environmental impact of battery technologies.
Why it matters for UK energy
Heating accounts for a large share of UK energy use, and periods of surplus wind power are becoming more common. Thermal stores like these offer a low-cost way to turn that surplus into heat. Their usefulness in Britain will depend on how quickly heat networks and electrified industrial heat develop.