In Finland, a simple material—sand—is being used to tackle one of renewable energy’s toughest problems: long-term storage. The so-called “sand battery,” developed by Polar Night Energy, stores excess wind and solar power by converting it into heat and packing it into large insulated silos filled with sand, where temperatures can climb above 400°C. Until now, this stored heat has mainly been used for district heating, helping warm homes through long Nordic winters. But engineers are now working on the next leap—converting that stored heat back into electricity so it can be fed into the grid when energy demand rises.
This shift could make sand batteries far more versatile, effectively turning them into a full-cycle storage system. New pilot designs are exploring ways to improve efficiency through better heat exchange systems and higher operating temperatures, making it possible to recover usable electricity alongside heat. If successful, the approach could offer a low-cost alternative to conventional batteries for storing energy over days or even weeks. While challenges remain—especially around efficiency losses when converting heat back into power—the idea is gaining attention as a scalable solution, using one of the most abundant materials on Earth to stabilise renewable energy systems. More