An industrial-scale sand battery in Finland’s Pornainen can cover about one month of the city’s heating needs in summer and one week in winter.
Polar Night Energy
A small town in southern Finland has turned to the world’s largest sand battery to solve what many see as a critical problem facing renewable energy: downtime.
Standing 13 meters tall and 15 meters wide, this eye-catching facility uses 2,000 tons of crushed soapstone to store clean energy in the form of heat to provide 100 megawatt hours of thermal energy.
That is enough to provide the 5,000 inhabitants of Pornainen with about one month of heat demand in summer – and about one week of demand in winter.
Commissioned by the Finnish heating company Loviisan Lämpö and developed by Polar Night Energy, the large sand battery was launched last year as part of a campaign to introduce variable heat generation technology and reduce carbon emissions produced by the regional heating network.
Polar Night Energy said the project is estimated to reduce greenhouse gas emissions from the heating network by around 70% and reduce the use of wood pellets by around 60%. The existing wood burning plant still serves as a back-up and bulk load facility.
Tommi Eronen, CEO of Polar Night Energy, said that Pornainen previously relied on burning oil and wood chips for its heating needs – but the city’s sand battery has been able to provide heat that does not burn for most of the year.
“We’re transitioning from a country where large power plants used to produce energy to where solar and wind produced energy, so we need a lot of storage,” Eronen told CNBC in a video call.
“We hope that a large part of those reserves can be a type of sand battery where we don’t need rare earth materials, like many chemical batteries, like lithium-ion batteries.”
The Pornainen project is 10 times larger than the previous version that was launched in the country in 2022, strengthening the potential for sand batteries to play a more prominent role in reducing pollution both indoors and outdoors.
Battery storage is widely expected to play a key role in the energy transition – and sand batteries in particular have shown promise for regional heat storage, but scaling up this technology faces major hurdles. Some notable criticisms include their ability to efficiently convert heat back into electricity and their low energy density compared to traditional batteries.
How does this work?
Basically, sand battery technology works like a giant thermos with heat storage elements.
The first step is to take electricity off the grid where there is a lot of wind or solar power, before heating the sand to very high temperatures. A highly sealed tank keeps that heat trapped for days or weeks before it is released through heat exchangers to the warm water of the district heating network.
“Three steps — and the key to everything is sand enables you to delay between the time you’re using electricity, and you’re using steam,” Polar Night Energy chief commercial officer Annette Höglund-Dönnes told CNBC via video call.
“That delay is an advantage for your business because you can heat the sand when electricity is cheap, and you use steam when it would normally be more expensive to produce steam from the grid, which is during the day when everyone uses it,” he added.
The industrial-scale sand battery at Pornainen in Finland stands 13 meters long and 15 meters wide. The facility uses 2,000 metric tons of crushed soapstone to store clean energy in the form of heat.
Polar Night Energy
Höglund-Dönnes compared the process to charging a cell phone overnight as this can be less expensive than during the day.
Asked if this work could be done in other countries, Höglund-Dönnes said that Polar Night Energy has been contacted by groups from “every continent,” especially communities that rely on fossil fuels, such as coal and oil.
Climate scientists have repeatedly warned that drastic reductions in fuel consumption will be needed to stop global warming, with the burning of coal, oil and gas identified as the main driver of the climate crisis.
Renewable interval
Jan Rosenow, a professor of energy and climate policy at the University of Oxford in the UK, agreed that electrothermal storage technologies, such as sand batteries, could be replicated around the world.
“You don’t need exotic earth, valuable raw materials and the beauty is that you can also charge the battery when the electricity is cheap and go out whenever you need heat,” Rosenow told CNBC.
“And you can store it for a long time, not just two hours or four hours like lithium-ion batteries, but potentially days and maybe even weeks.”
Critics of renewable energy, for example, often point out that technologies like solar and wind only produce power when the wind blows or the sun shines.
Energy storage systems such as batteries play an important role in smoothing the renewable cycle by absorbing excess solar and wind production and sending it out when production declines.
Mikko Paajanen, CEO of Loviisan Lämpö, said that the sand battery helps to clear this difficulty of changing energy.
“The main thing is that we can separate the purchase of electricity from the production of district heat because now we are able to deliver this heat in winter for one week, with one battery charge, and in summer, for up to one month,” Paajanen told CNBC via video call.
“So, we can use the lower prices very well.”
The manager of Loviisan Lämpö’s said that the company aims to produce between 55% and 60% of the heating production of the municipal district from the sand battery in the first few months of this year, from about 30% in 2025.
Finland’s Climate Minister Sari Multala described the Pornainen sand battery project as a “very encouraging” and innovative example of how to solve the energy storage challenge.
“I understood when I visited this facility when it was opened that they are now developing solutions for maybe using electricity in the future, which would be, of course, breaking – and this is going to be something that a lot of people will see the value of,” Multla told CNBC.
