Polar Night Energy’s sand-based thermal storage system. Image: Polar Night Energy.

The first commercial sand-based thermal energy storage system in the world has started operating in Finland, developed by Polar Night Energy.

Polar Night Energy’s system, based on its patented technology, has gone online on the site of a power plant operated by utility Vatajankoski.

The 4×7 metre steel container contains hundreds of tonnes of sand which can be heated to a temperature of 500-600 degrees Celsius. The sand is heated with renewable electricity and stored for use in the local district heating system.

It has a particularly strong use case in Finland which sees long and very cold winters, and was recently cut off from Russian gas supplies over a payments dispute. The storage system’s developers say it is cheap and easy to build.

The system can discharge a maximum of 100kW of heat power and has a total energy capacity of 8MWh, equating to up to 80 hours’ storage duration, but now authorities want to scale the system to one a thousand times bigger, or 8GWh, according to a report from UK broadcaster BBC.

“This innovation is a part of the smart and green energy transition. Heat storages can significantly help to increase intermittent renewables in the electrical grid. At the same time we can prime the waste heat to usable level to heat a city. This is a logical step towards combustion-free heat production,” said Markku Ylönen, co-founder of Polar Night Energy.

Vatajankoski also uses the heat provided by the storage to prime the waste heat recovered from their data servers so that it can also be fed into the district heating network.

It is the second major thermal storage facility based on a unique (if not novel) technological solution that has progressed this week. Swedish public utility Vattenfall is about to start filling a 200MW-rated thermal energy storage facility, effectively a giant water tank, in Berlin.