A sand battery is a type of thermal energy store. When electricity is cheap, often because wind or solar output is high, it powers resistive heaters that warm a large insulated silo of sand or crushed rock to several hundred degrees. The heat is drawn out later, typically to heat water for a district heating network. Despite the name, it stores heat, not electricity, and the commercial units built so far supply heat only.
How it works
Air or another fluid is heated by electric elements and circulated through the sand, which absorbs the heat. To discharge, cooler air is blown through and the hot air passes through a heat exchanger into the heating network. Sand and crushed rock are cheap, do not wear out with repeated heating and cooling, and can hold high temperatures for days to weeks in a well-insulated container. Turning the heat back into electricity would need a turbine or similar engine and would lose a large share of the energy.
Plants in Finland
The Finnish company Polar Night Energy has built the best-known examples:
| Site | In service | Size |
|---|---|---|
| Kankaanpää | 2022 | About 100 tonnes of sand, 8 MWh storage, 200 kW heat output |
| Pornainen | 2025 | About 2,000 tonnes of crushed soapstone, up to 100 MWh storage, 1 MW heat output |
| Vääksy (Lahti Energia) | Under construction, commissioning due from spring 2027 | 250 MWh, 2 MW |
After its first year, the company reported that the Pornainen unit ran above 85% efficiency and cut the local network’s emissions by about 70%. These figures come from the company and its customer, not an independent assessment.
UK status
We are not aware of an operating sand battery in the UK as of October 2026. The technology suits places with a district heating network or an industrial heat user nearby and electricity prices that swing enough to make cheap charging worthwhile. Heat networks are much less common in Britain than in Finland, which narrows the obvious market for now.
Read more: Sand batteries: storing renewable electricity as heat.