Polar Night Energy’s first commercial sand-based high temperature heat storage is now in operation at Vatajankoski power plant area.

The world’s first commercial solution to store electricity in the sand as heat to be used in a district heating network, the heat storage is producing low emission district heating to the city of Kankaanpää in Western Finland.

The actual heat storage is about four meters wide and seven meters high steel container that has an automated heat storage system and a hundred tons of sand inside. As a material, sand is durable and inexpensive and can store a lot of heat in a small volume at a temperature of about 500–600 degrees Celsius.

The heat storage has 100 kW of heating power and 8 MWh of energy capacity.

Vatajankoski uses the heat provided by the storage to prime the waste heat recovered from their data servers which are intended for high-performance computing. Depending on the season, the temperature of the 60-degree waste heat from the servers must be raised to 75–100 degrees before it is fed into the district heating network.

Markku Ylonen, one of the two founders of Polar Night Energy, said the new battery marked a milestone for a low-cost technology.

“Many of the components can be bought off the shelf,” he said. “The intelligence of the system lies more in the design part — in the plumbing and in how we model how the heat will be stored.”

The aim now is to build much larger versions. “If we scale it up, it’s really beneficial for us in terms of physics,” Markku Ylonen added.