In a quiet corner of southern Finland, a pile of sand is quietly rewriting the future of renewable energy.
The town recently switched on what’s now the world’s largest “sand battery” , a deceptively simple system built by Finnish startup Polar Night Energy that could help solve one of the trickiest problems in the clean energy transition: storage.
Unlike oil, coal, or even natural gas, renewable sources like solar and wind don’t show up on demand. The sun fades, the wind stills, and grids are left scrambling. That’s where the sand battery steps in.
Housed inside a steel silo the size of a small apartment block, roughly 100 feet long and 40 feet wide, sits a mountain of sand heated to blazing temperatures of 600°C (1,112°F). The trick is simple: excess energy from wind farms and solar panels is funneled into the battery, heating the sand through a network of pipes. The sand holds onto this heat for months, ready to be tapped when the skies go dark or calm.
When the town needs it, cool air is blown through the same pipes, capturing the stored heat and turning it into hot water, steam, or air that can be fed directly into the district heating system. With a heating capacity of 10 megawatts, it can churn out enough warmth to keep homes and buildings toasty during Finland’s long winters.
“This technology is proving successful here,” says Matteo Chiesa, a professor of mechanical and nuclear engineering at Khalifa University, who has been following the project. “And it has strong potential elsewhere.”
The genius of the sand battery lies in its materials: cheap, abundant, and ancient. Humans have been using sand and bricks to trap heat for centuries, think of wood-fired ovens that stay warm long after the fire dies. Polar Night Energy has simply scaled that idea up to industrial levels, wrapping it in steel and pairing it with renewable power.
There are limitations. The system isn’t yet optimized for households, and seasonal storage, capturing summer’s solar bounty to release in the depths of winter, remains a future goal. But the promise is clear.
Imagine stockpiling sunshine in July, then releasing it as heat in January. That’s what sand batteries could make possible, and in a world racing toward net-zero carbon goals, that’s not just a clever trick. It’s a potential game-changer.
