Credit: Polar Night Energy

A silo of sand could be the key to using renewable energy more efficiently according to an experiment in Finland. The first commercial “sand battery” could store heat for several months before using it to heat water.

The project aims to tackle one of the big problems with energy generation methods such as solar and wind that have varying outputs. Ideally any excess could be stored for future use, but doing so with lithium batteries has financial and physical limitations.

The Finnish project uses electricity derived from solar and wind energy, which would otherwise go to waste, to heat up a silo of low grade sand to 500 degrees Celsius. This can be kept for several months with little heat loss, then discharged as hot air. This then heats a district heating network in the town of Kankaanpää, which circulates hot water to heat homes and offices.

The main limitation is that using the stored heat to directly generate electricity is far less efficient, meaning at the moment it’s more useful as a replacement source for situations where electricity is normally used to generate heat. As well as water-based building heating, this includes several industrial processes.