In the small southern Finnish town of Pornainen, a new kind of power plant has just begun operating. Instead of woodchips or coal, this one runs on sand. The industrial-scale sand battery, inaugurated this week, is now handling heating duties for the municipality and is expected to slash local heating network carbon emissions by up to 70 percent.
The battery was developed by Polar Night Energy, the same Finnish company that built the world’s first commercial sand-based thermal storage system just a few years ago. Standing 13 meters (42 ft) tall and 15 meters (50 ft) wide, this new installation dwarfs its predecessor. With a storage capacity of 100 MWh and a round-trip efficiency of around 90 percent, it’s about ten times larger than the first model and can hold enough heat to supply the entire town for a week.
The principle is simple yet powerful. When excess electricity from wind and solar sources is available, it’s used to heat air in a closed-loop system. This hot air is then pumped into a silo of sand, raising its temperature to 600 °C (1,112 °F). Thanks to the insulating properties of sand, the heat can be stored for months. Later, when needed, cool air is blown back through the silo, where it absorbs the stored heat. At temperatures reaching 400 °C (752 °F), the air can be used to boil water into steam for industrial applications, or to warm water for the town’s district heating through a heat exchanger.
It’s important to note that this battery does not store or deliver electricity directly. Instead, it stores thermal energy. Polar Night Energy has confirmed it is working on systems to convert the stored heat back into electricity, most likely through steam turbines, but for now its role is primarily heating.
The Pornainen battery has actually been in operation since June, and already the company reports it is outperforming initial efficiency targets. Town buildings, including the municipal hall, are now heated by the new storage system, and officials say it will play a central role in helping Pornainen meet its long-term carbon neutrality goals.
