Finland Tests Sand Battery That Stores Heat as Electricity

A massive battery filled with sand might sound like science fiction, but it's about to become reality in Finland.

Engineers at Polar Night Energy are testing a revolutionary energy storage system that heats sand to extreme temperatures using renewable electricity, then converts that stored heat back into power for the electrical grid. The new pilot project in Valkeakoski, a town 90 miles north of Helsinki, began construction in October and will start testing within weeks.

The technology builds on an existing sand battery design that already stores renewable energy as heat. The original version heats sand and similar materials to 752 degrees Fahrenheit, then extracts that warmth to provide hot water, steam, or hot air for buildings.

The new power-to-heat-to-power version takes things further by operating at even higher temperatures. It will output both electricity and heat, reaching a combined efficiency of around 90 percent.

The electricity conversion alone achieves 30 to 35 percent efficiency, matching the performance of fossil fuel power plants. For context, combustion power plants in the United States averaged 39 percent efficiency in 2023.

"It's basically totally different" from the existing model, CEO Tommi Eronen explained at the company's current sand battery site in Pornainen. The new design uses a horizontal configuration instead of a vertical silo, though specific details remain under investigation during the two-and-a-half-year pilot phase.

Industries that need both heat and electricity, like utility companies, could benefit most from the technology. The dual output means almost no energy goes to waste.

The Ripple Effect

This innovation addresses one of renewable energy's biggest challenges: storage. Solar and wind power generate electricity when conditions are right, not necessarily when people need it most.

Sand batteries could store excess renewable energy during peak production times, then release it as electricity when demand rises. This helps balance electrical grids without relying on fossil fuel backup power plants.

The technology creates a pathway to large-scale, affordable energy storage while cutting emissions. If successful, it could accelerate the transition away from coal and natural gas for grid stabilization.

During the pilot phase, engineers will test different materials capable of withstanding extreme operating temperatures. They're already designing commercial versions while the pilot runs.

The main hurdle isn't technical feasibility but cost. "The one challenge when selling this to customers is that the investment price is so high," explained Chief Operating Officer Liisa Naskali. Many potential customers currently use cheaper wood-chip boilers for heating.

Finding an economically viable solution remains the key question. "It's doable, but at what price?" Naskali noted.

If the Finnish team cracks the cost equation, sand batteries could help renewable energy finally compete with fossil fuels for reliable, round-the-clock power.