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Sand Batteries

A company in Finland has brought on line a high-temperature heat storage installation, using crushed local soapstone, to store off-peak and renewable energy for use during peak demand periods

SL Staff C

• 2 min read
Insulation and claddidng being added to a large cylinrical steel tank that is under construction
Sand Battery under construction for Loviisan Lämpö in Pornainen, Finland. Image courtesy of Polar Night Energy

We recently wrote about a project that stores high-temperature heat from renewables in insulated containers filled with slag from steel-making, heat which is used for making crisps1.

Another project, employing the same principle of high temperature thermal energy storage, but with a different technology, has recently come online in Finland. Polar Night Energy of Finland has completed what it calls a “sand battery” to supply heat for the Loviisan Lämpö district energy system for the town of Pornainen, Finland2.

The sand battery for this project is a large, insulated cylindrical tank 13m high (42 ft) by 15m diameter (49 ft), filled with about 2,000 tonnes of crushed soapstone, a by-product of local industry. The soapstone in this project is heated to 400 °C, although the system can store heat at up to 600 °C, depending on the use case.

Aerial view of large cylindrical tank alongside two smaller industrial building, set in a forest clearing
Completed Sand Battery installation in Pornainen, Finland. (Image courtesy of Polar Night Energy.)

The system in Pornainen heats the rock with electricity, either produced from local renewable sources, or purchased from the grid at low cost in off-peak times. The heat is released back to the district energy system (at a lower temperature than it is stored at) when needed. The company claims an in-out efficiency of 80% for the system3.

GIF showing conceptually how energy is stored during periods of low demand and released during high demand
Conceptual illustration of energy being stored during periods of low demand and released during high demand. GIF courtesy of Polar Night Energy

The sand battery in Pornainen can deliver peak heating a a rate of 1 MW (3.4 million BTUH, or British Thermal Units/Hour), equivalent to about 50 average home furnaces. It has a storage capacity of 100 MWh (3.4 MMBTU, or Million British Thermal Units). The company anticipates the project will cut the heating network’s total emissions by 160 t CO2e (carbon dioxide equivalents) per year by reducing demand on the existing woodchip power plant.

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 Sweet Lightning has no affiliation with any products or manufacturers mentioned in this article.

Reading

  1. https://sweetlightning.ghost.io/storing-energy-from-renewables-and-or-waste-heat-for-industrial-processes/
  2. Polar Night Energy. “World’s Largest Sand Battery Now in Operation,” June 11, 2025. https://polarnightenergy.com/news/worlds-largest-sand-battery-now-in-operation/.
  3. https://polarnightenergy.com/reference/solution-for-clean-energys-big-problem/ Polar Night Energy. “Sand Battery.” Accessed June 23, 2025. https://polarnightenergy.com/sand-battery/.

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