Polar Night Energy, a Finnish technology company, has activated the world’s largest commercial sand battery in Pornainen, Southern Finland. The facility was commissioned by local district heating company Loviisan Lämpö and represents a novel approach to long-duration energy storage for renewable power grids.
The installation consists of a 13-meter-tall industrial silo containing 2,000 metric tons of crushed soapstone, a byproduct from local fireplace manufacturing. During periods of excess renewable energy generation, the system uses clean electricity to power a heating element that superheats air to temperatures between 400°C and 600°C. Embedded pipes circulate this heated air through the soapstone, which retains the thermal energy with minimal loss due to its high heat capacity. The soapstone can maintain stored energy for weeks or months, providing substantial operational flexibility.
When heating demand increases or electricity prices spike, the system releases stored energy by drawing cool air through the internal pipes to extract heat. This thermal energy is transferred through a heat exchanger to produce hot water, which is then distributed through the local district heating network. The facility supplies thermal energy sufficient to warm homes, schools, and public buildings for approximately 5,000 Pornainen residents for one week during winter months and nearly a month during summer periods.
The system operates using automated software with artificial intelligence that monitors real-time electricity spot-market prices. This capability allows the battery to charge when electricity is abundant or negatively priced and discharge during peak demand periods, optimizing financial returns. Polar Night Energy reports the installation has reduced greenhouse gas emissions by nearly 70 percent and lowered wood chip consumption by approximately 60 percent. Unlike lithium-ion batteries, sand batteries do not degrade over time and require no rare-earth materials, offering a sustainable, cost-effective solution for seasonal and long-duration storage.
Polar Night Energy previously operated a smaller pilot project in Kankaanpää in 2022 with 0.1 MW and 8 MWh capacity. The company is developing a significantly larger 250 MWh capacity system in Vääksy, expected to begin operations in summer of 2027. Industry analysts note that long-duration energy storage is becoming increasingly critical as grids integrate larger volumes of intermittent renewable generation, with thermal storage technologies gaining commercial traction as alternatives to conventional lithium-ion systems.
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