Startup is building a giant sand battery in Finland

A Finnish startup has announced plans to build a massive sand battery — demonstrating the potential of the medium to help the world fully transition to clean energy.

The challenge: Solar and wind are cheap, clean, and plentiful sources of energy, but they’re also variable. To run a fully renewable power grid, we need to be able to store excess solar or wind power for use when there’s a shortfall.

We need a safe way to store renewable energy across seasons.

Some wind and solar farms already do this using lithium-ion batteries — the same kind found in your smartphone. Those “self-discharge,” though, meaning they constantly lose a bit of the energy they store. As a result, we can only store energy in them for days or weeks at a time (the fact that they sometimes catch fire isn’t great, either). 

Lithium batteries can fill one important gap, covering hour-to-hour and day-to-day fluctuations, but we also need a safe way to store renewable energy across seasons — then we fill up our energy stores during the windy spring or sunny summer for use at other times of the year.

Sand battery: Instead of storing renewable energy in traditional batteries, Finish startup Polar Night Energy has developed a system for storing it as heat in sand, which can handle temperatures in excess of 1832 F (1000 C). 

Polar uses insulated containers to hold the sand, keeping it hot for months. The heat can be tapped on demand for district heating systems, which deliver hot air or water directly into people’s homes. The heat can be used to boil water to spin electricity-generating turbines, too, but the conversion process results in a major loss of energy, meaning it’s less efficient. 

Going commercial: In 2022, Polar began operating the world’s first commercial sand battery in the Finnish town of Kankaanpää. It holds about 100 tons of sand, heated to 1112 F (600 C). That equates to 8 MWh of thermal energy — enough to provide heat and hot water to more than 100 homes through the town’s district heating system.

Polar has now announced plans to build a sand battery that’s 10 times bigger than the Kankaanpää one in Pornainen, Finland. After spending about 13 months building and testing the battery, Polar will hand it over to Loviisan Lämpö, the company that runs the municipality’s district heating system.

Loviisan Lämpö currently relies on a mix of oil, renewables, and wood chip combustion to provide heat to Pornainen, but execs say the sand battery will allow it to reduce its reliance on wood chips by about 60% and eliminate oil completely.

“It’s exciting to build a large-scale thermal energy storage, which will also act as a primary production plant in Pornainen’s district heating network,” said Liisa Naskali, COO at Polar Night Energy. “This is a significant step in scaling up the sand battery technology.”

The big picture: Sand batteries might not be as efficient for generating electricity as they are for heating, but they could still have a huge impact on climate emissions — about 9% of the heat needed for buildings and industry comes from district heating systems, and 90% of those rely on fossil fuels.

We could then supplement the sand batteries with another alternative form of storage, such as flow batteries, to generate electricity from renewables year-round — completing the transition to a clean energy future.

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