The world’s largest sand battery has just been turned on. The battery, which is simple in design, can store heat during periods of excess renewable energy. It then stores the heat and can deliver it on demand, enabling municipalities to eliminate fossil fuels from the heating network.

With this approach, Finnish company Polar Night Energy can store 1,000 megawatt-hours of heat for weeks at a time, losing only around 10% of the heat.

A new way to store renewables

The world has already become pretty good at producing renewable energy. The problem now is storing it. Some periods have more sun or more wind, and you end up with excess energy. If we could store that and use it at a later time, it would truly unlock renewables as the driving source of electricity on the planet.

The problem is that storing this excess isn’t easy at all. Lithium batteries work well for some applications, but they’re expensive and cause their own environmental problems. So instead, a team from Finland looked for a much lower-tech alternative: sand.

A sand battery uses sand or crushed rock to store heat. This stored head can later be used for various purposes. It might not be as imposing as a large lithium-ion battery, but this 2,000 metric ton battery helped a Finnish town eliminate the costly and polluting oil it was previously using.

The economic case is compelling. It’s hard to think of a cheaper material than sand. In fact, in this case, the sand was basically trash discarded by a Finnish fireplace maker. The sand is stored in a silo-type structure and then an electrical current is passed through it. Sand isn’t a conductor so it resists the current, creating heat in the process. This hot air is circulated through the container, heating the sand to 400-500 degrees Celsius. The battery can store this heat for weeks or months, discharging the hot air when needed. For now, this energy is used to heat homes, offices, and even a nearby swimming pool. It’s a simple but efficient process.

“There’s really nothing fancy there,” says Markku Ylönen, one of the pioneers behind the technology. “The complex part happens on the computer; we need to know how the energy, or heat, moves inside the storage, so that we know all the time how much is available and at what rate we can discharge and charge.”

The Spark of Invention

The battery is the brainchild of four Finnish innovators: Tommi Eronen, Markku Ylönen, Liisa Naskali and Ville Kivioja. The four met as children as they were all involved in athletics in southern Finland. They’d cheer on each other during events in their teenage years. Then, as they grew up, they were more and more concerned about climate change and decided to do something about it.

The spark happened when Eronen was working on his master’s thesis and was reading about water storage systems (where you heat water to store energy). “It got me thinking: would a solid material, rather than water, be more suitable for storing solar and wind energy?” Eronen says. Together with Ylönen, he started working on a prototype. The prototype was built in Eronen’s grandfather’s garden. Then, they recruited their childhood friends and set up Polar Night Energy.

In 2022, they installed the first commercial sand battery. It turned out to be a timely idea as it happened right as Russia cut off gas supplies in retaliation for Finland joining NATO. The project became a strong and timely example of how renewable energy can be used in new ways.

Ever since 2022, the first sand battery has been in operation in the town of Kankaanpää, proving that the technology works. At 13 meters high and 15 meters wide, the new sand battery in the town of Pornainen is around 10 times larger. Overall, the battery can store 1,000 megawatt-hours of heat, enough to power around 260 homes.

The new battery is expected to slash district heating emissions by nearly 70%, or around 160 metric tons of carbon dioxide equivalent emissions per year.

Can this be scaled?

The success in Pornainen raises a critical question: can sand batteries work at scale, outside Finland?

The short answer: yes — but with some caveats.

The core idea is simple and adaptable. Sand is widely available, and many communities already rely on centralized heating systems, especially in colder regions. The concept doesn’t depend on cutting-edge components or rare materials. This makes sand batteries attractive for countries looking to decarbonize without waiting for next-generation tech.

But not every country has Finland’s energy mix or heating infrastructure. Pornainen has a grid that’s already largely clean, with 70% of Finland’s electricity coming from nuclear and renewables. That means charging the battery is low-carbon to begin with. In countries where the grid still relies heavily on coal or gas, charging a sand battery would simply shift emissions upstream.

Still, the economics are hard to ignore. The latest battery in Pornainen likely cost far less than a lithium-ion system of comparable capacity. Back in 2022, the company estimated their earlier unit cost just $25 per kilowatt-hour of storage — about a quarter the price of lithium-ion. The new system uses industrial scrap — soapstone from a fireplace maker — as its core material. This promotes circularity and keeps costs low.

Another factor is that sand batteries pair best with existing district heating networks. These centralized systems heat water and pump it to homes and offices — legacy infrastructure common in Northern and Eastern Europe, but rarer in North America. Where those networks exist, sand batteries could plug in relatively easily. They could be used in other contexts too, but would require some adaptation.

Scaling sand batteries may not require a single global design. Instead, it could mean regional variations based on what’s cheap, local, and already in place. For Finland, that means soapstone and district heating. For others, it might mean crushed brick, slag, or even volcanic rock.

But it can work. Markku Ylönen, one of the inventors, is hopeful. “We want to build a hundred times larger storages around the world as fast as possible,” he says.

And if sand batteries can deliver on that vision, they won’t just store energy. They’ll store resilience.