An innovative thermal energy storage system could help Europe transition away from natural gas dependence.
In Pornainen, a Finnish municipality an hour from Helsinki, a massive sand-filled storage unit is set to revolutionize district heating. Developed by startup Polar Night Energy, this system stores renewable energy as heat, eliminating the need for fossil fuels in the local heating network.
With a capacity of 100 MWh, the structure—standing 13 meters tall and 15 meters wide—holds 2,000 tons of crushed soapstone, a byproduct of construction materials. It is ten times larger than the company’s 2022 pilot project and is expected to meet the heating demands of Pornainen’s 5,000 residents while cutting emissions by 70%.
How It Works
When wind or solar power exceeds demand, the surplus electricity heats the sand to 600°C (1,112°F) via resistive heating and a circulating air system. The tank’s insulation retains this heat for months. When needed, the hot air is transferred to the district heating network, supplying homes, businesses, and public spaces.
“Burning fuels is no longer a sustainable solution for the climate or environment,” said Liisa Naskali, COO of Polar Night Energy. “Our technology proves there are viable alternatives to combat climate change.”
Flexible Storage & Sustainable Backup
While a full charge from ambient temperature takes four days, the battery continuously tops up with excess renewable energy. In winter, a single charge could heat the city for a week; in summer, up to a month. As a backup, Pornainen will maintain a biomass (wood chip) boiler for peak demand periods.
With expansion plans in Finland and abroad, Polar Night Energy aims to position its invention as a scalable clean heating solution. According to the IEA, heating accounts for 50% of global energy use, and in Europe, it still largely relies on gas, oil, and biomass.
Alongside other storage technologies—such as lithium batteries, pumped hydro, or gravity-based systems—sand batteries could become a key pillar in decarbonizing urban heating, especially in regions with renewable energy surpluses.
“We won’t solve the climate crisis alone,” acknowledged Naskali, “but every innovation brings the world closer to a cleaner future.”
—With data from the International Energy Agency (IEA).
By: Nestor Castillo, ForAllTechNews Director
Photo Credit: Polar Night Energy