Sand batteries: Finland’s radical answer to renewable energy woes

A small town in southern Finland has turned to the world’s largest commercial sand battery to solve the most critical problem facing renewable energy: intermittency.

Measuring 13 meters high and 15 meters wide, this eye-catching facility uses 2,000 tonnes of crushed soapstone to store clean energy in the form of heat, delivering 100 megawatt hours of thermal energy.

This is enough to provide the 5,000 residents of Polnainen with almost a month’s worth of heat needs during the summer and about a week’s worth of heat needs during the winter.

The giant sand battery, commissioned by Finnish district heating company Loviisan Lämpö and developed by Polar Night Energy, was launched last year as part of the introduction of flexible heat production technology and the reduction of carbon emissions produced by regional district heating networks.

Polar Knight Energy said the project is estimated to have reduced greenhouse gas emissions from heating networks by almost 70% and the use of wood chips by about 60%. The existing wood chip power plant continues to operate as a backup and peak load facility.

Polar Night Energy CEO Tommi Eronen said Polunainen had previously relied on burning oil and wood chips for its heating needs, but the town’s sand batteries can now provide combustion-free heating for most of the year.

“We’re moving from a world where large power plants produced energy to a world where solar and wind produce energy, and that requires a lot of storage,” Eronen told CNBC in a video call.

“We hope that the majority of those storage units will be sand cell-type storage units that do not require rare earth materials, similar to many chemical batteries such as lithium-ion batteries.”

The Polunainen project is about 10 times the size of the previous version, which was launched domestically in 2022, reinforcing the potential for sand batteries to play a more prominent role in reducing emissions domestically and internationally.

Batteries are widely expected to play a pivotal role in the energy transition, and sand batteries in particular have shown promise for regional heat storage, but scaling up this technology faces significant hurdles. Notable criticisms include their ability to efficiently convert heat back into electricity and their relatively low energy density compared to traditional batteries.

Essentially, sand battery technology acts as something similar to a giant thermos flask with heat storage material.

The first step is to pull electricity from the grid when there is enough wind or solar power, and then heat the sand to very high temperatures. Heavily insulated silos trap that heat for days or weeks before releasing it via a heat exchanger into the hot water of the local district heating network.

“The three steps, and the key to it all, is that by using sand, we can have a delay between when we use electricity and when we use steam,” Annette Hoglund Donnes, chief commercial officer at Polar Night Energy, told CNBC on a video call.

“This delay is a business advantage because we can heat the sand when electricity is cheap, and we can use the steam during the day when it would normally be very expensive to generate steam from the grid, when everyone else is using steam,” she added.

Hägglund Danes compared the process of charging a mobile phone at night, considering that it can be cheaper than during the day.

Asked if the project could be replicated internationally, Hoglund-Dönes said Polar Night Energy had been approached by teams on “every continent”, particularly communities dependent on fossil fuels such as coal and oil.

Climate scientists have repeatedly warned that fossil fuel use must be drastically reduced to curb global warming, with the burning of coal, oil and gas identified as the main cause of the climate crisis.

Jan Rosenau, professor of energy and climate policy at the University of Oxford in the UK, agreed that electrothermal storage technologies such as sand batteries are likely to be replicated around the world.

“It doesn’t require rare earths or critical raw materials, and the advantage is that you can charge the battery when electricity is cheap and discharge it whenever you need heat,” Rosenau told CNBC.

“They can also be stored for longer periods of time, sometimes days or even weeks, rather than just two or four hours like lithium-ion batteries.”

For example, critics of renewable energy often point out that technologies such as solar and wind only produce energy when the wind is blowing or the sun is shining.

Energy storage systems such as batteries play a vital role in smoothing out interruptions in renewable energy by absorbing excess solar and wind power and supplying it when production slows down.

Mikko Paajanen, CEO of Loviisan Lämpö, ​​said that sand batteries can help clear this energy transition hurdle.

“The important thing is that we can separate the electricity procurement and the production of district heating, because in the winter a single charge of the battery can provide heating for a week, and in the summer it can last for a month,” Pajanen told CNBC in a video call.

“So we can take advantage of low spot prices.”

Loviisan Lämpö’s CEO said the company aims to produce between 55% and 60% of municipal district heating production from sand batteries in the first months of this year, up from around 30% in 2025.

Finland’s Climate Minister Sari Murtala described the sand battery project in Pornainen as a “very exciting and innovative example” of how to solve energy storage challenges.

Murtala told CNBC: “When I also visited the factory when it opened, I understood that they are also developing solutions for using electricity now and perhaps in the future. This is of course a breakthrough, and this will be something that many people will find valuable.”