🕒 Last updated on July 17, 2025
In a small Finnish town called Pornainen, a groundbreaking invention is turning heads around the world. Finland has just unveiled the world’s largest sand battery—a giant structure that stores heat made from renewable energy inside crushed stone.
Finland Builds the Biggest Sand Battery in the World
This clever new battery isn’t just a scientific wonder—it’s already helping heat homes and buildings in the town, all while cutting pollution and saving money.
The Finnish business Polar Night Energy constructed the enormous sand battery. It stands about 43 feet tall and 49 feet wide, and it’s filled with 4.4 million pounds of crushed soapstone, a special kind of rock left over from fireplace manufacturing. This battery can hold a huge amount of heat—341 million BTUs (British Thermal Units)—and it gives off heat continuously at 3.4 million BTUs per hour. That’s enough to keep an entire town warm during Finland’s long, freezing winters.
This isn’t Finland’s first sand battery, but it is ten times bigger than their first one, which launched in 2022 in another town. This newer system is now part of the Loviisan Lämpö district heating network, meaning the heat from the battery flows into pipes that warm homes and buildings in Pornainen. Since the battery started running, the town has stopped using oil for heating and has cut back on burning wood chips by 60%. The old biomass boiler is now only used during very cold spells when extra heat is needed.
How the Sand Battery Works
The idea behind the sand battery is simple but powerful. When there’s extra electricity from solar panels or wind turbines—like during sunny or windy days—the system uses that electricity to heat air. This hot air then flows through pipes inside the soapstone, warming it up to temperatures between 932°F and 1112°F. The special soapstone holds this heat extremely well.
Thanks to its strong insulation, the battery can store the heat for weeks or even months without losing much. When it gets cold outside, the system blows air through the hot stones again, picking up the heat and using it to warm water in the town’s heating pipes.
Charging the battery from cold takes about four days, but usually, it just gets topped up with any extra electricity that’s not being used. This way, no energy goes to waste, and the heat is always ready when needed.
The soapstone is a smart choice. It’s more efficient than regular sand and is leftover material from fireplace factories in Finland. Using this waste material fits into the idea of a circular economy, where nothing goes to waste and old materials are given new life.
The battery has a thermal efficiency of up to 99%, meaning it hardly loses any heat. When it’s charging and discharging, there’s only about 10–15% energy loss, which is very low. For heating buildings via the district network, the battery’s maximum operating temperature of 752°F makes it ideal.
Cutting Carbon and Costs in a Smart Way
The environmental benefits of the sand battery are already clear. Since it started running, Pornainen has reduced its carbon emissions by 70%, which equals about 352,740 pounds of CO₂ per year. That’s like taking nearly 70 cars off the road every single year.
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Burning fewer wood chips also means less chopping down of trees and a big cut in air pollution. Plus, no more oil is needed to keep the town warm, which saves money and helps protect the planet.
But the battery isn’t just good for the environment—it also helps the local economy. By using heat made from free, renewable electricity, the town can lower heating bills for residents. And because this is a homegrown Finnish invention, it shows the world that Finland is a leader in clean energy technology.
This project has also drawn attention from people and companies across the globe. It shows what can happen when smart ideas and renewable energy come together. The sand battery doesn’t just store heat—it stores hope for cleaner, smarter energy everywhere.
With its massive size, smart use of waste materials, and real-world impact, Finland’s sand battery is a shining example of how even the simplest materials—like crushed stone—can change the world when used in the right way.