Polar Night Energy''s Sand Battery is a large-scale, high-temperature thermal
Renewable Energy Integration (Wind and Solar Farms) Wind and solar farms
Finnish startup Polar Night Energy and local Finnish utility Vatajankoski have together built the world’s first commercial sand-based, high-temperature heat storage system that can be powered by solar and wind.
Polar Night Energy’s heat storage system is a 23-foot-tall steel container filled with 100 tons of sand. (Polar Night Energy uses the lowest grade of sand that isn’t used in construction.) Hot air blown through pipes heats the sand in the steel container by resistive heating.
The sand is able to store heat at around 500–600C (932–1,112F) for months, so power generated in the summer can be used to heat homes in the winter. Polar Night Energy says it has 100 kW of heating power and 8 MWh of energy capacity. Here’s how it’s meant to work with renewables:
This first sand battery, which is in the town of Kankaanpää, is connected directly to the grid and runs when the electricity is cheapest – that’s usually when renewables are powering it. It’s also next to a data center, which produces waste heat that is pumped into the sand battery. In the future, the energy-storage silo can and should be directly connected to wind or solar sources of power.
When energy prices are higher, the sand storage system discharges heat that warms water for Vatajankoski’s district heating system. The water is then pumped around homes, offices, and the town’s swimming pool.
This innovation is a part of the smart and green energy transition. Heat storage can significantly help to increase [the presence of] renewables in the electrical grid. At the same time we can prime the waste heat to usable level to heat a city. This is a logical step toward combustion-free heat production.
The US National Renewable Energy Laboratory is investigating sand’s potential for energy storage, but the Finns got there first. Polar Night Energy is in talks with other local utilities and is planning to raise more funding to expand.
Read more: The world''s first CO2 battery for long-duration energy storage is being commercialized [update]
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Michelle Lewis is a writer and editor on Electrek and an editor on DroneDJ, 9to5Mac, and 9to5Google. She lives in White River Junction, Vermont. She has previously worked for Fast Company, the Guardian, News Deeply, Time, and others. Message Michelle on Twitter or at michelle@9to5mac . Check out her personal blog.
Polar Night Energy, a startup in Finland, has developed technology for warming up buildings with solar-generated heat stored in sand. The team uses thermal modeling to optimize the design of their heat storage and distribution systems, which are helping Finnish cities reduce their consumption of nonrenewable heating fuels.
By Alan PetrilloFebruary 2022
As we try to objectively study nature, we are often reminded of how natural forces affect us personally. We can sit at a desk and consider heat in its various forms, but we might be distracted if our toes are cold! When we turn up the heat in our homes and workplaces, we must balance our personal need for warmth with the global impact of burning fossil fuels like oil, gas, coal, and biomass. Anthropogenic climate change confronts humanity with a challenge: How can we keep warm now as we try to prevent our world from overheating in the future?
It is a daunting question that a startup called Polar Night Energy, in the small and chilly nation of Finland (Figure 1), is attempting to answer. In a region known for long, dark winter nights, Polar Night Energy is building a system in the city of Tampere that can heat buildings with stored solar energy — all day, all night, and all winter long. The apparent contradictions do not end there. In an era of complex cleantech solutions, often made from rare and expensive materials, Polar Night Energy''s heat storage and distribution system consists of simple ducts, pumps, valves, and sand. The novel system shows potential for tackling global problems in a patient, thoughtful, and human-scaled way.
Big problems demand big solutions, and there is perhaps no bigger 21st-century problem than climate change. To meet this challenge, many governments and organizations are investing in new technology to help lessen the use of fossil fuels. These initiatives have largely focused on renewable electric power generation, distribution, and storage.
"When you ask people about cleaner energy, they think of electricity," says Tommi Eronen, CEO of Polar Night Energy. "But we also have to cut emissions from heating." Out of Finland''s energy-related emissions, 82% come from heating domestic buildings (Ref. 1). "We want to replace all of that if we are to have any hope of meeting our global climate goals," Eronen says.
The spirit of "Think Globally, Act Locally", a mantra associated with the 1960s, lives on with Polar Night Energy''s team of innovators. Their journey began with a question posed by its founders, Tommi Eronen and Markku Ylönen, when they were university classmates: "Is it possible to build an energy-self-sufficient and cost-effective hippie commune for engineers using only solar power?" After graduation, the project they codenamed "Hippie Commune" became Polar Night Energy, with Eronen as CEO and Ylönen as CTO.
What began as a lighthearted (but serious) student project led to a 3 MWh/100 kW pilot plant in the Finnish city of Tampere, which began operation during the winter of 2020–2021. The system uses electricity to heat air, which is then circulated through an exchanger that heats water and distributes it to multiple buildings in the city''s Hiedanranta district (Figure 2).
Inside the system, electrically powered resistive heating elements heat air to more than 600°C. The hot air is circulated through a network of pipes inside a sand-filled heat storage vessel. The hot air then flows back out of the vessel into a heat exchanger, where it heats water that is then circulated through building heating systems. The sand''s heat storage capacity ensures that even when the resistive elements are cool, the circulating air is still hot enough to keep the water (and buildings) warm.
"We only have pipes, valves, a fan, and an electric heating element. There is nothing special here!" Eronen says, laughing.
Multiphysics simulation software helped shape Polar Night Energy''s heat exchanger design (Figures 5–6). Eronen says, "We built a particular model to explore a design idea: What if we created a super hot core of sand surrounded by heating ducts around the perimeter?" By modeling fluid flow and heat transfer effects in the COMSOLMultiphysics® software, the Polar Night Energy team could quantify its design''s comparative advantages and drawbacks. "The simulation confirmed that the ''hot core'' design was good at storing heat for very long periods of time," says Eronen. "But for our intended operational cycle, it makes more sense to evenly distribute hot air ducts throughout the sand storage vessel," he explains.
The sheer scale of Polar Night Energy''s sand-based heat storage system makes simulation software indispensable. "We cannot possibly build full-size prototypes to test all of our ideas. We need predictive modeling to answer as many questions as possible, before we commit to assembling all this equipment — and all this sand!" Eronen says. "It is essential for us to use these immensely powerful tools."
"We want to license this technology. If you operate a power plant, please contact us," Eronen says with a laugh. On a more serious note, he adds, "We have to get away from all kinds of combustion, even biomass. We need to protect and restore forests so they can keep removing carbon from the air. Because climate change is happening so fast, we want our ideas to spread as quickly as possible."
Statistics Finland, "Over one-half of Finland''s electricity was produced with renewable energy sources in 2020", November 2021.
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