Key Highlights

  • The Pornainen sand battery stores 100 megawatt-hours of thermal energy using 2,000 metric tons of crushed soapstone.
  • The facility has cut greenhouse gas emissions from the local heating network by almost 70%.
  • Wood chip use for heating has fallen by about 60% since the battery's commissioning.
  • Loviisan Lämpö aims to source 55% to 60% of district heating from the battery in early 2026, up from roughly 30% in 2025.

A Novel Approach to Renewable Energy Storage

A small town in southern Finland has turned to the world's largest commercial sand battery to address intermittency, widely regarded as one of the most critical challenges facing renewable energy adoption. Standing 13 meters tall and 15 meters wide, the facility uses 2,000 metric tons of crushed soapstone to store clean energy as heat, providing 100 megawatt-hours of thermal energy, enough to supply the roughly 5,000 residents of Pornainen with nearly a month of summer heat demand and about a week of winter demand.

Commissioned by Finnish district heating company Loviisan Lämpö and developed by Polar Night Energy, the battery launched last year as part of an effort to introduce flexible heat production technology and reduce carbon emissions from the local district heating network, which previously relied on burning oil and wood chips.

Emissions and Fuel Reductions Already Materialising

Polar Night Energy estimates the project has slashed greenhouse gas emissions from the heating network by almost 70% and reduced wood chip use by about 60%, with an existing wood-chip power plant remaining in operation only as a backup and peak-load facility. The Pornainen installation is roughly ten times larger than an earlier sand battery launched in Finland in 2022, reinforcing the technology's potential to scale meaningfully both domestically and internationally.

The system operates similarly to a large insulated thermos, drawing electricity from the grid when wind or solar output is abundant and using it to heat sand to very high temperatures, which the heavily insulated silo retains for days or weeks before discharging heat through exchangers to warm water for the district heating network. This delay between electricity use and heat discharge allows operators to charge the system when electricity is cheap and avoid drawing power during periods when steam production would normally be expensive.

Balanced Considerations Around Scaling the Technology

Proponents argue sand batteries offer a meaningful advantage over conventional chemical batteries since they do not require rare earth materials such as those used in lithium-ion systems, and can store energy for days or potentially weeks rather than the two to four hours typical of lithium-ion storage. Industry figures note that Polar Night Energy has been contacted by interested parties from every continent, particularly communities currently dependent on fossil fuels such as coal and oil.

Even so, scaling the technology faces notable hurdles, including questions around efficiently converting stored heat back into electricity and the technology's comparatively low energy density relative to traditional batteries. These constraints suggest sand batteries may prove most effective as a complement to existing heating infrastructure and other storage technologies, rather than a wholesale replacement across all energy storage applications, particularly where direct electricity generation rather than heat is the primary requirement.

Conclusion

The Pornainen sand battery demonstrates a tangible pathway for reducing emissions in district heating networks while avoiding reliance on rare earth materials central to conventional battery chemistries, though its broader applicability may remain concentrated in heat-focused use cases for now. Whether electrothermal storage technologies like sand batteries can be replicated at meaningful scale internationally, particularly in fossil fuel-dependent regions expressing early interest, may depend on how effectively developers address the technology's current limitations around electricity conversion efficiency and energy density.