BY THE OPTIMIST DAILY EDITORIAL TEAM In a small Finnish town with a big climate goal, an unassuming tower of sand is quietly storing solar and wind energy all while making a powerful statement about clean tech innovation. Pornainen, in southern Finland, is now home to the world’s largest sand battery: a 13-metre-high, 15-metre-wide thermal storage system built by Finnish company Polar Night Energy. Capable of holding 100 megawatt-hours (MWh) of heat, the new battery will slash emissions from the town’s district heating network by nearly 70 percent and phase out the use of oil. “Our goal is to be climate neutral by 2035, and the sand battery is a major step toward that,” says Mikko Paajanen, CEO of Loviisan Lämpö, which operates the heating system. With its large-scale rollout, the battery is now the network’s main energy provider. Wood chip use is expected to drop by 60 percent, while an existing biomass boiler will offer backup during energy demand spikes. The surprising power of sand The Pornainen battery isn’t Finland’s first foray into sandy storage. In 2022, Polar Night Energy launched a smaller prototype in Kankaanpää, just as Russia cut off gas supplies. The timing made a strong case for homegrown, renewable energy solutions. Engineers and co-founders Markku Ylönen and Tommi Eronen came up with the idea in 2018. “We were talking about how—if we had the liberty to design a community for ourselves—how could we solve the energy problem?” said Markku. “Especially here in the north, you run into the problem of energy storage.” Sand turned out to be the perfect candidate: affordable, abundant, and surprisingly spacious when it comes to storing heat. Lithium batteries, while useful in certain situations, fall short for large-scale energy storage due to cost and environmental concerns. Sand, by contrast, can store heat for days or even months at a time. How does a sand battery work? The system is relatively straightforward. A tower is filled with low-grade sand and heated using excess electricity from solar or wind power. This is done via resistive heating, where friction from the electrical current generates heat. That hot air then flows through a heat exchanger, charging the sand. Stored at around 500 degrees Celsius, the heat is held until needed. When temperatures drop, the battery releases the hot air to warm water in the town’s district heating system. In Kankaanpää, it helps heat homes, offices, and even the local swimming pool. “There’s really nothing fancy there,” Markku explains. “The complex part happens on the computer; we need to know how the heat moves inside the storage, so we know how much is available and at what rate we can discharge and charge.” What makes this one different? The Pornainen system is about ten times larger than the Kankaanpää model. It’s built using crushed soapstone, a by-product from the Finnish fireplace company Tulikivi. As project manager Naskali notes, “The soapstone they use is a very Finnish thing.” And it’s not just nostalgic; it’s practical. Soapstone meets the density and heat tolerance needed to store thermal energy efficiently. “We always choose the storage medium based on the customer’s needs,” says Naskali. “Examining and testing different materials is crucial for us to use options that are cost-effective and support the circular economy.” Mayor Antti Kuusela is a proud supporter. “This project has gone very smoothly,” he says. Town buildings like the school, library, and town hall all run on district heating. “Pornainen wants to be a front runner in sustainable energy solutions.” In summer, the battery can meet nearly a month’s heating demand; in winter, about a week’s. Each year, it’s expected to eliminate 160 tonnes of carbon dioxide equivalent emissions. Can sand really save the world? Well, maybe not all sand. A Dutch study recently warned that demand for construction sand will surge by 45 percent in the next 40 years, with harmful impacts on rivers and lakes. But Polar Night Energy isn’t after beach sand. “We wanted to find something that can be sourced nearly everywhere in the world,” said Markku. Their solution is to use any sand-like material that meets thermodynamic standards. That flexibility keeps costs low and helps promote sustainable sourcing. With successful pilots in Kankaanpää, Tampere, and now Pornainen, the company has big dreams. Earlier this year, it announced a pilot in Valkeakoski to explore converting thermal energy back into electricity. International expansion is also on the horizon. “We want to build a hundred times larger storages around the world as fast as possible,” Markku asserted. From backyard brainstorms to international headlines, Finland’s sand battery movement is proving that sometimes the simplest materials can offer the smartest solutions.The post How Finland’s giant sand battery is storing clean energy (and cutting emissions by 70 percent) first appeared on The Optimist Daily: Making Solutions the News.