Sick energy: Has the small Finnish town finally found the substitute for oil and gas?
The company Polar Night Energy has built a 13-meter-high tower in the town of Pornainen containing compressed sand reservoirs, which "absorb" cheap electricity from wind and solar, and release it on demand. The reservoir already generates 55%–60% of the local district heating and reduces gas usage by 80%, and the ability to convert the heat back into electricity is now being tested.
Most residents of the small Finnish town of Pornainen are not even aware that they live next to one of the world's most innovative energy inventions. On the outskirts of the town, against the backdrop of the Scandinavian forest, stands a 13-meter-high cylinder-like structure containing 2,000 tons of crushed soapstone, heated to temperatures of up to 500 degrees Celsius. This is the largest sand battery in the world, produced by the Finnish company Polar Night Energy, and it suggests that the solution to one of the main problems of the renewable energy era — storage — may be hidden beneath our feet.
Solar and wind cannot solve the problem alone; during night hours and in the absence of wind, renewable energy sources stop producing electricity. The common solution — lithium-ion batteries — involves mining rare raw materials and enormous costs. Polar Night Energy has proposed a completely different approach: to convert excess and cheap electricity from wind and sun into heat, store it in sand, and release it on demand.
"We are moving from a world where large power plants produced the energy to a world where sun and wind produce it, and therefore we need a huge amount of storage," Polar Night Energy CEO Tommi Eronen told CNBC.
The sand tower is connected to the local power grid. During hours when electricity prices are low, electrical elements heat the sand. The heat is stored there, with insulation that allows the temperature to be maintained for weeks. A heat exchanger leads the heat to the city's district heating network — the same pipes that heat homes, public buildings, and businesses. According to data presented by the Finnish company Loviisan Lampo, which operates the reservoir in Pornainen, the facility is capable of providing heat for a whole week from a single charge in winter, and up to a month in summer. Today, it covers between 55% and 60% of the town's district heating production.
The project in Pornainen is ten times larger than a previous experimental reservoir that Polar Night Energy built in 2022 in the town of Kankaanpää, just as Russia stopped gas supplies to Europe. Now the company is working on building an even larger reservoir of 250 megawatt-hours, which is expected to be completed in the summer of 2027 and will be connected directly to the district heating network of the city of Valkeakoski. According to estimates, the reservoir will reduce the greenhouse gas emissions of the local heating network by about 60% per year and reduce the use of natural gas by about 80%.
At the same time, a new experiment is underway in the city of Valkeakoski: a "sand-to-power" project — another stage that seeks not only to release heat but also to convert it back into electricity. The project, costing about 4.2 million euros, is in the testing phase.
What distinguishes the Finnish solution is its simplicity and abundance: sand is one of the most common and cheap raw materials in the world, it is resistant to extreme temperatures, and it does not wear out or lose its value over time, unlike chemical batteries. Alongside the enthusiasm, those involved in the field warn that initial investment costs can deter customers, and that the ability to convert heat back into electricity has not yet been proven on a commercial scale. Moreover, sand reservoirs are mainly suitable for district heating networks, which do not exist in every country.
