The World’s Largest Sand Battery : How a Giant Sand Battery is Changing the Game for Renewable Energy

The sand battery, developed by Polar Night Energy, is a simple yet effective concept. When there is excess solar or wind power, the battery stores the energy as heat in a massive silo filled with sand. The sand is heated to a scorching 400 to 500 degrees Celsius, and the heat is retained for weeks with minimal loss due to clever insulation. When warmth is needed, the stored heat is released and piped into homes, offices, and other buildings, reducing the need for fossil fuels.The World’s Largest Sand BatteryIn June 2025, Polar Night Energy launched the world’s largest sand battery in Pornainen, Finland, marking a major step forward in renewable energy storage. This industrial-scale system delivers 1 megawatt of thermal power and stores up to 100 megawatt-hours of heat, making it about ten times more powerful than their original installation. The massive silo, filled with around 2,000 tons of crushed soapstone, stands 13 meters tall and 15 meters wide. It’s capable of providing heat for nearly a month during summer or about a week in winter to the local district heating network. Beyond its scale, the battery plays a critical role in reducing carbon emissions, cutting approximately 160 tons of CO₂ each year.What is a Sand Battery?A sand battery is an innovative energy storage solution that uses sand to store heat generated from excess electricity, particularly from renewable sources like solar or wind power. They are common in colder countries like Finland. Unlike traditional batteries that store electricity, sand batteries store thermal energy, making them especially useful for heating buildings and supporting clean energy transitions.How Sand Batteries WorkThe sand battery operates on a simple yet effective principle of storing energy as heat. At the heart of the system is a large silo filled with sand, often recycled industrial waste from fireplace manufacturing. When there is excess electricity, typically from renewable sources like wind or solar, it is used to heat the sand to very high temperatures. Thanks to excellent insulation, the sand retains this heat for weeks with minimal energy loss. When the need for heat arises, hot air is extracted from the sand and directed into the district heating network, providing a clean and efficient way to warm homes and buildings.Benefits of Sand BatteriesSand batteries offer a smart and sustainable solution for energy storage, especially in the push toward renewable energy. One of their biggest advantages is their ability to store excess power from sources like solar and wind, helping reduce our dependence on fossil fuels. Unlike lithium batteries, sand is cheap, widely available, and environmentally friendly, making it a cost-effective alternative. These systems also help cut carbon emissions and support efforts to combat climate change. Plus, they’re flexible enough to be adapted to different settings and infrastructure, making them a practical option for communities and cities looking for clean energy solutions.The Story Behind Polar Night EnergyPolar Night Energy was founded in 2018 by Tommi Eronen and Markku Ylönen, who first crossed paths in 2013 while studying at Tampere University of Technology. Tommi earned a Master’s degree in Power Plant Engineering, while Markku holds a Ph.D. in Applied Mechanics. Their journey began with a shared vision: they recognized early on that as electricity prices dropped and volatility increased, simply producing more renewable energy wouldn’t be enough to fully decarbonize the energy sector. What the world needed was reliable, high-capacity storage. With limited resources but a bold idea, they brought their vision to life and created the world’s first commercial sand battery. Today, that groundbreaking innovation is ready for global deployment. As they put it: “Join us on our journey!” Polar Night Energy is a Finnish startup revolutionizing renewable energy storage with sand batteries. Their system stores excess electricity as heat in sand, which can be used later for district heating. It’s low-cost, eco-friendly, and highly efficient, using abundant materials and simple technology. Successfully tested in Kankaanpää, Finland, this innovation supports clean energy goals and offers a scalable solution for reducing fossil fuel reliance and cutting carbon emissions worldwide.