This is a 13-metre silo in a small, Finnish town in the Pornainen region, which is home to a 2000-ton sand battery marking one of Europe鈥檚 boldest climate pivots. On June 11, 2025, the system officially went live, eliminating oil from the town鈥檚 heating network and reducing carbon emissions by approximately 70%, equivalent to around 160 tonnes per year. This is not a pilot; it鈥檚 a working model, and one that doesn鈥檛 rely on lithium, cobalt or even complex chemistry. It doesn鈥檛 even store electricity. Instead, it stores excess renewable energy as heat using crushed soapstone and then delivers it back to the homes through the district.
So, how does the battery that is currently made out of rock outperform the technology that we鈥檝e spent decades refining? And can it reshape how Europe thinks presently and reshape how Europe feels about energy security and independence?鈥
Why heat storage changes the equation
Most people would think of batteries as devices or things that store electricity. Like lithium-ion, pumped hydro, and even hydrogen, these technologies are designed to capture the energy and store it. But the biggest energy use in Europe is staying warm.
This is where this project breaks the mould because it鈥檚 a sand battery that holds a hundred MWh of thermal energy, which is enough to heat the entire town through the winter, charging from solar or wind power when it鈥檚 cheap or abundant.
The secret is that the battery utilises crushed soapstone and stores energy as high-temperature heat with an efficiency of 85 to 90%.
Then that heat is piped directly into the existing district heating network, which bypasses the inefficiencies of converting it back to electricity.
This method is a clean, low-loss, scalable solution to a problem that most energy headlines do not currently talk about: how to decarbonise heat.
The economic edge
This entire sand battery is built without lithium, with no cobalt, nickel, or rare earth dependency. The entire system is built around soapstone, which is a crushed byproduct from Finnish industry, a cheap, non-toxic material. That鈥檚 what makes it viable, because it鈥檚 not just about clean energy; it鈥檚 also about low cost and local infrastructure.
The system charges when electricity prices on Finland鈥檚 electricity market dip, it absorbs the excess solar and wind when the supply peaks.
This AI-powered control system 鈥 developed in partnership with Elisa 鈥 decides when to charge and how much heat to release, optimising both energy use and cost.
It鈥檚 a financially stable system that requires no fuel, no imports, no price spikes, and, unlike most battery technology, it does not degrade over time.
Built to scale
What makes the Pornainen battery more than just a local success story is that the model can travel because the materials are simple, the storage mechanism is passive, and the concept involves converting surplus electricity into storage heat. It does not require advanced grid overhauls or rare minerals.
It鈥檚 opening doors for regions across Eastern Europe, Germany, the Baltic, and even parts of Spain for them to rethink anything local heating, not with subsidies but with circular infrastructure.
This is energy that鈥檚 cheaper, more stable, and less vulnerable to global shocks. It鈥檚 a blueprint and not a premium export.
What it can鈥檛 do yet
For all its promises, this sand battery isn鈥檛 a miracle yet. It can鈥檛 power your lights, charge your car, or even keep the lights on. It does store heat, not electricity, and that limits where and how it fits into the broader energy transition.
So, regions without district heating networks will find this model harder to implement. While thermal-to-electric conversion, which is sometimes called power-to-heat-to-power or P2H2P, is possible in theory, it is inefficient and experimental.
There are also environmental questions to address
If you scale this technology rapidly, will the extraction or processing of sand along with this alternative pose ecological risks?
And how do you balance the decentralised deployment with oversight in order to prevent stagnating performance?
In other words, this works best when it鈥檚 local, modest, and integrated 鈥 not rushed into being the next exportable climate fix.
Still, what鈥檚 impressive is what it replaces. In Pornainen, oil is now zero. Emissions are down 70%. And all of it happened without rare materials, high maintenance, or international fuel contracts.
The world鈥檚 biggest battery is better than a small Finnish town that most people have never heard of, while the world races to electrify everything, Finland solves part of the energy puzzle by storing what鈥檚 often ignored heat.
And it鈥檚 done not by billion-dollar breakthroughs but with local material, surplus power, and even a clear plan to use what鈥檚 already there. This has to be the future of clean energy, and it was hiding in the ground all along.