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The world’s first commercial sand battery could solve green energy’s biggest problem: storage

Have you ever been to the beach on a swelteringly hot day, and the sand almost burned your feet?

Sand has low specific energy, meaning it does not need that much energy from the sun to warm. When outside temperatures are only 75 degrees Fahrenheit, sand can be over 100. At an ambient 90 degrees, sand can be a burning 120. Finnish startup, Polar Night Energy, is taking this beach day mishap, and turning it into sustainable energy through giant sand batteries.

As Fast Company reports, a device like Polar Night Energy’s sand battery does not exist anywhere else in the world. It’s exactly what you’re picturing: a towering gray battery filled with 100 tons of super-heated sand. The sand is heated using renewable electricity like solar or wind and can store heat for months.

The device is ideal for homes in need of heat in places where it’s not sunny or windy, “to enable the upscaling of solar and wind,” Markku Ylönen, cofounder and CTO of the startup, told Fast Company. At specific times of day when the sun is shining and the wind is blowing, solar panels and wind turbines often produce more energy than the grid needs. The excess energy can be stored in lithium-ion batteries, but they are still relatively expensive.

Lithium-ion batteries also have a large physical footprint, and can only cope with limited amounts of excess power. Instead, Polar Night Energy has turned to storing renewably-powered heat long-term in order to reduce emissions from traditional heating methods.

But their applications don’t stop at homes. In factories, industrial processes that require high heat currently run on fossil fuels. Instead, sand batteries could help store heat. The sand can be heated to 752 degrees Fahrenheit, and with some tweaks to system infrastructure, this temperature could double.

Polar Night Energy’s approach isn’t complicated. When sand is extremely hot, it naturally retains heat, and the company takes advantage of that. A giant pile of low-grade sand is siloed into a strong container. This container is either a tower with extra thick walls or an underground pit. It could even be built in an old mine. Sand is then heated with hot air that blows through pipes.

Sand is everywhere, making it the ideal material, Ylönen says. “It’s cheap, and you can build large storage for scaling it up.” Water is also cheap and can store heat, but has higher specific energy than sand, meaning that it can not reach as high a temperature. Sand, on the other hand, loses little heat over time.

The company says that future facilities may be built near wind farms. Located in the Finnish town of Kankaanpää, their first sand battery is connected directly to the grid, running when electricity is the cheapest. The battery is also next to a data center that produces waste heat to be pumped into Polar Night Energy's system. The device is installed at the Vatajankoski power plant, which operates the district heating system, BBC reports. The battery here draws sand from a nearby sand pit. Through the system, the battery discharges hot air through a network of pipes to heat water, heating individual homes, offices, and even the local swimming pool.

Like existing battery storage systems, sand batteries can store solar energy generated during sunny summer days, but the ideal use, Ylönen is making use of wind energy, which in Finland is most abundant during the winter. The project is really all “about helping the wind and solar sectors to grow,” he told EuroNews. “We think that this is just one of the key components to make a society with a really high production of wind and solar power.”

The system is already competitive with gas. Finland gets most of its gas from Russia. However, Russia has recently halted its gas supply due to Finland’s decision to join NATO, and the country is now looking for greener ways to provide electricity.

Still, one of the biggest questions is if this technology can be scaled up to a point where it makes a difference.

Polar Night Energy plans to build a larger scale system, 100 times the size of the first, to be competitive with burning biomass, the process by which Finland currently produces most of its heat. The startup is currently in conversation with district heating managers in Finland and Sweden for expansion. While Polar Night Energy’s technology is patented, Fast Company notes, that all parts are “available off-the-shelf from manufacturers,” so its possible that sand batteries will spread quickly. Research groups such as US National Renewable Energy Laboratory, have already been looking at sand as a viable form of battery for green power.

“Finland has to be the proving ground since we’re building a physical product,” Ylönen told Fast Company. “But we want to spread the technology around the world as fast as possible.”

"It's a bit crazy, if you wish, but I think it's going to be a success,” Pekka Passi told BBC. Passi is the managing director of the Vatajankoski power plant. "It's really simple, but we liked the idea of trying something new, to be the first in the world to do something like this.”

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