Sunita Somvanshi
New Sand Battery Pilot Aims to Convert Heat Back to Electricity in Valkeakoski
A collaboration between Polar Night Energy and Valkeakosken Energia will soon bring a next-generation Sand Battery pilot plant to Valkeakoski, Finland. This pilot will test something new: the ability to convert stored thermal energy back into electricity, a process called Power-to-Heat-to-Power (P2H2P). Construction begins autumn 2025.
The Sand Battery stores cheap, clean electricity as heat. Current versions only deliver this stored energy as heat for industrial or district heating needs. The new pilot aims to complete the cycle by generating electricity from that stored heat.
This isn’t a small tweak – it requires the battery to operate at much higher temperatures (above 600 °C) and overcome serious material challenges. That’s why the pilot will run through early 2027 to fully test these capabilities.
“The energy market is undergoing a fundamental transformation. Bold ideas and practical solutions are needed, and Polar Night Energy’s Sand Battery pilot is a perfect example. We are proud to support and enable this kind of concrete innovation,” says Olli-Pekka Marttila, CEO of Valkeakosken Energia.
Project Details and Specifications
The pilot comes with substantial backing – a €2.1 million grant from Business Finland within a larger €4.2 million R&D program spanning 2.5 years. The thermal capacity target is approximately 10–20 MWh with peak electrical output around 200 kW.
Expected electrical efficiency will reach 30–35 %, comparable to traditional combustion power plants. When used for combined heat and power (CHP), overall efficiency could reach up to 90 %.
“There’s an enormous and growing need for energy storage solutions. Different types of energy storage will be key for industries and energy producers to meet both cost-efficiency targets and climate goals,” explains Veli-Matti Pietarinen, Power Plant Specialist at Polar Night Energy.
Construction will begin at Pispantalli in Valkeakoski, featuring a thermal storage unit and technical building. The site offers excellent railway connections to Tampere, and heat generated by the pilot can feed directly into Valkeakosken Energia’s district heating network.
“It’s exciting to bring this innovation from research into real-world construction. Planning is already underway, and we aim to secure a building permit as soon as possible. Construction will be phased, allowing us to start initial testing early next year,” says Hanna Kallio, Project Manager at Polar Night Energy.
Track Record and Material Innovation
This isn’t Polar Night Energy’s first rodeo. They already operate the world’s first commercial Sand Battery in Kankaanpää since 2022 – an 8 MWh system with 200 kW output achieving 60–75 % round-trip heat-storage efficiency.
The company is also exploring materials beyond sand. The Valkeakoski pilot will test soapstone, a byproduct from Tulikivi’s fireplace manufacturing, with higher thermal conductivity and a circular-economy opportunity. A 100 MWh soapstone-filled system in Pornainen already uses 2,000 tonnes of crushed soapstone.
This approach delivers impressive environmental benefits. Similar installations like Loviisan Lämpö’s 1 MW/100 MWh system are projected to cut district-heating CO₂ emissions by up to 70 %.
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Team Expertise and Recognition
Founded in 2018 by CTO Markku Ylönen and CEO Tommi Eronen at Tampere University of Technology, Polar Night Energy has accumulated significant expertise in thermal energy storage. The company holds multiple patents on high-temperature air-loop heat-exchange systems.
Their achievements haven’t gone unnoticed – they received Finland’s “Productive Idea 2023” award and were showcased on Nasdaq Helsinki and New York’s Times Square. The company has raised €7.6 million in seed funding led by Jonathan Oppenheimer, with Finnish and Swedish investment firms joining to support R&D expansion, team growth, and new pilot sites.
Strategic Collaborations
Valkeakoski’s selection as the pilot location wasn’t random. The city showed strong enthusiasm and support, recognizing the project’s potential to strengthen its reputation as a development-driven region.
“Valkeakoski has made several major investments supporting the energy transition. Our strong electricity and district heating networks, together with excellent railway connections, make us an ideal location for testing new technologies,” says Timo Kärkkäinen, Director of Economic Development for the City of Valkeakoski.
Beyond this pilot, Polar Night Energy has established strategic partnerships. A collaboration with Ilmatar (signed December 2023) will conduct commercial P2H2P trials at wind farm sites, leveraging grid-balancing services.
Based on the pilot’s results and experience, Polar Night Energy plans to deliver commercial-scale electricity production plants in the future, advancing their mission to make renewable energy sources like wind and solar more reliable and cost-effective.
Initial heat-charging tests will start in early 2026, followed by full P2H2P conversion trials through 2027, with plans for a media tour at ees Europe 2025 in Munich (April 29–May 1).
For press images, see the download link, and for general media assets visit Polar Night Energy’s media page.
