World’s Largest “Sand Battery” Heats Finnish Town

Pornainen, Finland —(Map)

A town in Finland has begun using the world’s largest “sand battery” to help provide heat. The unusual method of storing energy allows the town to create heat when electricity prices are cheap, and store it for long periods of time. The heat can then be used whenever it’s needed.

Pornainen is a town in Finland with about 5,000 people. Most of the buildings in the town are heated through “district heating”. In a district heating system, hot water is piped into the buildings from a central heating plant. That way, each building doesn’t need to have its own furnace or boiler. The central heating system in Pornainen is run by a company called Loviisan Lämpö.

Until recently, Pornainen’s heat came from burning oil and wood chips. Loviisan Lämpö was looking for ways to cut the pollution it created. They hired a company called Polar Night to build the world’s largest sand battery. In 2022, Polar Night successfully built a smaller sand battery.

A sand battery works because sand (which is really just tiny rocks) can be heated to very high temperatures. In a well-insulated container, sand can hold this heat for a long time.

About 43% of Finland’s energy comes from renewable sources. But renewable energy sources like solar and wind power have a problem – they only produce power part of the time. This means that sometimes there’s more energy than is needed, and sometimes, there’s not enough. The way to solve this problem is to store the energy so it can be used when it’s needed.

That’s where Pornainen’s new sand battery comes in. The huge battery took a year to build. It’s roughly 42.5 feet (13 meters) tall and almost 50 feet (15 meters) across. It can store enough energy to heat Pornainen for about a month in the summer and about a week in the winter.

The battery uses crushed soapstone instead of sand. The rock was waste material from a Finnish company that uses soapstone to make fireplaces. The soapstone can be heated up to 750º Fahrenheit (400º Celsius), and the battery can hold onto this heat for months.

Pornainen began using the sand battery earlier this summer. The sand is heated when electricity costs are at their cheapest. When heat is needed, air is pushed through the super hot sand, heating it. The hot air can then be used to heat water or turn it into steam. Pornainen’s sand battery has been used to warm up homes, government buildings, a library, and a school.

In cold, dark winter months, some wood chips will still be needed, but the battery will cut the amount of wood burned by 60%. Mikko Paajanen leads Loviisan Lämpö. He says, “Our goal is to be climate neutral by 2035, and the sand battery is a major step toward that.”

Currently the sand battery simply turns electricity into heating. But the people at Polar Night are also looking into ways to turn the stored heat back into electricity.