A practical idea for storing green energy – sand

When you come up with a simple, practical and ecologically sound idea that can help the world upscale renewable energy, you attract lots of attention.

That’s what happened to four young Finnish engineers who developed and installed the world’s first ‘sand battery’ in a Finnish community. Finland will be producing 25% of its electricity by 2025, and switching to green power has become urgent as Russia weaponizes non-renewable energy. 

Thanks to two BBC stories, their sand battery went viral, and their Polar Night Energy website is getting a lot of attention. So much that they have had to tell visitors that the company doesn’t have products for individual homes as yet.

Developing batteries that can store green energy long-term has become a kind of holy grail in energy terms. It is the missing link between moving from using increasingly expensive non-renewable resources like oil, gas and coal to generate power, to using lower-cost wind and solar power reliably year-round.

“Solar and wind power is basically already really competitive in terms of energy price per produced energy unit,” Polar Night Energy co-founder and chief technology officer Markku Ylönen told Dezeen. “The only problem with them is that you can’t really choose when it’s produced.” 

Their answer is a simple one. They’ve created the world’s first commercial scale sand battery, now at work in the Vatajankoski power plant, 270 km north-west of Helsinki. 

A 7m (23ft)-high steel structure contains 100 tonnes of low-grade builders’ sand, two district heating pipes and a fan. Using renewable electricity, the sand is heated to 600C using a resistance heater. A fan circulates the hot air around the sand through heat exchange pipes. 

Thick insulation keeps the battery’s internal temperature at 600C (1,112F), even when it is freezing outside. “We don’t want to lose any heat; the average winter temperature is below 0C (32F) in Kankanpää,” says Ville Kivioja, lead scientist at Polar Night Energy.

When full, the battery stores 8 MWh of thermal energy. When demand rises, the battery discharges about 200 kW of power – enough to provide heating and hot water for about 100 homes and the public swimming pool in Kankaanpää, supplementing power from the grid. The battery is charged overnight when electricity prices are lower.

Just Have A Think has a really good explanation of how this works.. 

The battery is four metres in diameter, seven metres high and contains 100 tonnes of sand, but future batteries could be 20 metres across and 10 metres high, which would give the battery one gigawatt hour of storage capacity – equal to one million kilowatt hours (kWh), says Dezeen. Several sand batteries of a standardised size could be placed around larger cities to service larger populations.

It fascinates me that this innovative idea came from four young people who were concerned about climate change and recognized a potential solution in their national traditions.

Tommi Eronen, Markku Ylönen, Liisa Naskali and Ville Kivioja bonded as children over a shared passion for athletics, belonging to the same club in Tampere, southern Finland. As they got older, they saw how winters had become shorter and warmer, and they became keen to tackle climate change.

Traditional Estonian fireplace, J. & P. Parikas, Wikimedia.

In 2016, Eronen was researching energy storage in water when he read an article about traditional Finnish fireplaces, made from stone and sand. “It got me thinking: would a solid material, rather than water, be more suitable for storing solar and wind energy?”

He and Ylönen started developing the sand battery prototype and tested the pilot in Eronen’s grandfather’s garden near Tampere. They recruited their childhood friends from the athletics club to start Polar Night Energy. And in July, they installed the first commercial sand battery at the Vatajankoski power plant in Kankaanpää. They’re getting ready to install a second sand battery for another district heating company in Finland which will be ten times larger. It will have 2MW in heating power and 500MWh in storage capacity. 

Half of Finland’s 5.5 million people are connected to a district heating network, which is common in Europe but much less so in the US or the UK. But the battery has potential far beyond heating homes, says project manager Liisa Naskali. “When scaled up, it will be available for use in all kinds of industrial processes that require high heat: bakeries, laundries [and] steelworks.”

The team calculates that their battery is eight to 10 times cheaper than a lithium battery which stores the same amount of energy. To generate 8 MWh of energy using the Kankaanpää sand battery costs about $200,000, says Eronen. A lithium-ion battery storing 8 MWh of energy would cost at least $1,600,000, he says.

By 2023, Polar Night Energy aims to be “a truly global company, constructing sand batteries all over the world”, Eronen says.


Climate change: ‘Sand battery’ could solve green energy’s big problem. BBC, Jul. 5, 2022

How a sand battery could transform clean energy. BBC Future Planet, Nov. 3, 2022.

Finnish “sand battery” offers solution for renewable energy storage. Dezeen, Jul. 14, 2022

The sand battery that heats your home, NOT the planet. Just Have a Think, Aug. 21, 2022.

Profile image: Tampere, Finland. Eetu-Pekka Myöhänen, Wikimedia.