Finnish City Inaugurates 1 MW/100 MWh Sand Battery

There are more ways to store energy than just using batteries. Some are using fire bricks, particularly for process heat for industries that rely on high heat in manufacturing. Others propose an arrangement of massive concrete blocks that move up and down like the weights of a giant grandfather clock, converting kinetic energy to potential energy and back again. In Finland, two intrepid engineers began experimenting with a sand battery a few years ago.

As we reported when the first prototype was unveiled three years ago, the idea of a sand battery began with two Finnish engineers, Markku Ylönen and Tommi Eronen. The concept is simplicity itself. Make a really big pile of sand. Heat it with excess renewable electricity to around 500°C (932°F), then use that heat later to heat homes, factories, even swimming pools. They say the sand can stay hot for 3 months or more. The pair have founded Polar Night Energy, which constructed a prototype consisting of 100 tons of sand inside what looks like a silo in the town of Kankaanpää.

Many Americans are unfamiliar with the concept of district heating, but it is widely used in other counties, especially in Scandinavia where keeping schools, municipal buildings, arenas, factories, and homes warm in winter is a challenge.

Loviisan Lämpö is a Finnish district heating company that supplies district heating to customers in Loviisa, Pukkila, Pornainen, and Pyhtää. It has collaborated with Polar Night on a new sand battery — one that is much larger than the prototype — which began operating in the city of Pornainen in southern Finland this month, where it is expected to reduce carbon emissions from district heating by 70 percent.

Previously, the majority of heat needed for the system came from burning oil, but that has now been completely eliminated. The system will continue to burn wood chips to supplement the sand battery. Wood chips are at least carbon neutral, although not an ideal solution since it takes years for trees to grow but only minutes for the chips to burn.

At the commissioning ceremony for the new battery, Mikko Paajanen, CEO of Loviisan Lämpö, said, “A couple of years ago, we started considering how to take district heating in Pornainen to the next level. It would have been easy to simply replace the old wood chip power plant with a new one of the same kind, but that didn’t align with our goals. We evaluated every possible alternative, and the Sand Battery proved to be the best option.”

The battery is a 42 foot tall, 50 foot wide steel cylinder filled with 2,000 tons of crushed stone. According to Fast Company, when extra renewable electricity is available, the system uses it to heat up the crushed stone, where it is stored until needed. Then the heat from the battery travels to other buildings through a system of pipes filled with hot water. Each building has its own equipment to distribute the heat to radiators, floor heaters, or other heating devices.

“We have already learnt that our system has even more potential than we initially calculated. It’s been a positive surprise,” said Ylönen after the prototype was placed in service. “Whenever there’s a high surge of available green electricity, we want to be able to get it into the storage really quickly.” The need to use energy more wisely was driven home for Finns after Russia stopped providing electricity, methane, and oil to Finland when it voted to join NATO. Finland and Russia share a common border.

Sand Battery Is Simple & Efficient

The sand battery is simplicity itself. “We just heat air and [circulate it] through sand,” says Liisa Naskali, COO of Polar Night Energy. But materials other than sand can be used. The new battery actually uses crushed soapstone chips from a local fireplace manufacturer. Sand, or other material crushed into sand-size particles, has the ability to store heat for weeks. Unlike some other batteries, the system doesn’t rely on chemicals, doesn’t degrade, and won’t catch on fire. In operation, the sand battery has demonstrated a round trip efficiency of 90 percent.

Inside the steel tank, a heat exchanger and a closed loop system are used to circulate the heat. Software runs heaters when electricity prices are low. So far this summer, the district heating operator has paid only about 10 percent of the average price of electricity because heating the system only occurred at optimal times. That helps make the technology cost competitive, although the initial installation cost is fairly high.

Polar Night is now in talks with other district heating companies and factory owners with a need for high temperature process heat. For the company, the project in Pornainen is a critical proof point. “This is really important for us because now we can show that this really works,” a spokesperson for Polar Night said.

Investment Opportunities

Polar Night and its partners see a bright financial future for sand batteries because they can participate in electricity reserve markets, reduce dependence on single energy sources in heat production, and serve as an excellent example of sector integration between electricity and heat.

“For us, the sand battery is a great commercial investment, but we also wanted to boldly support an innovative solution that benefits customers, the municipality, and the entire electricity market. This is a concrete example of a cost efficient and sustainable investment. If it works here, it will work anywhere,” said Sauli Antila, the investment director at CapMan Infra, the corporate owner of Loviisan Lämpö.

The profitability of the sand battery is based on charging it according to electricity prices and Fingrid’s reserve markets. Its large storage capacity enables balancing the electricity grid and optimizing consumption over several days or even weeks. The reserve market operations and optimization of the Pornainen Sand Battery are managed by the software unit division of Elisa Industriq.

“The Pornainen plant can be adjusted quickly and precisely, and it also has a remarkably long energy buffer, making it well suited for reserve market optimization. Our AI solution automatically identifies the best times to charge and discharge the Sand Battery and allocates flexibility capacity to the reserve products that need it most. Continuous optimization makes it a genuinely profitable investment,” explained Jukka-Pekka Salmenkaita, vice president of AI and special projects at Elisa Industriq.

Polar Night has a clear vision for the future. Construction of an electricity production pilot will begin in the coming weeks in Valkeakoski, Finland, and the company is in active negotiations for several large-scale thermal storage projects in district heating, hot air, and process steam production. “Industrial applications are particularly promising, especially where heat above 100°C is required, something electric boilers and heat pumps cannot provide,” said Polar Night COO Liisa Naskali.

This technology is never going to replace grid-scale battery storage, but could be useful in many situations where battery storage is not. A comment on the YouTube video below complained, “Not a word about return on investment in the presentation. That means it’ll never pay off. They just wasted taxpayers’ money to stroke their own egos.” MAGAlomaniacs are everywhere these days.