An unusual way to store energy

Polar Night Energy specialises in seasonal heat storage, storing wind and solar power generated during summer months as heat to be released during winter. The unexpected twist is that the storage medium is sand.

Why sand? Sand is a cheap and abundant material that can be heated to 1000°C and beyond as part of the storage cycle. A heat transfer system is constructed inside the sand which enables effective energy transportation to and from the storage. Effective insulation between the storage system and the surrounding environment ensures storage periods of up to several months with minimal heat loss.

The size of the storage can vary from tens to thousands of cubic metres, and the system can be installed underground, which saves surface space for other uses such as construction.

This approach to heat storage is very flexible and could be used to heat a single building, to provide a large district-heating network or as part of a self-contained electricity and heating system on an island.

The first commercial sand-based heat storage was commissioned by Vatajankoski, an energy utility based in Western Finland, and will provide heat for a district-heating network in Kankaanpää, Finland. This storage system has 100 kW heating power and 8 MWh capacity.