Polar Night Energy and Valkeakosken Energia have announced a collaboration to build a new Sand Battery pilot plant in Valkeakoski, Finland. The pilot will test a next-generation version of the Sand Battery capable of converting stored thermal energy back into electricity, a process known as Power-to-Heat-to-Power (P2H2P). Construction is set to begin in autumn 2025.
The pilot is based on Polar Night Energy’s existing Sand Battery technology, which stores affordable, clean electricity as thermal energy for industrial or district heating needs. This new pilot will test the energy storage system’s ability to convert heat back into electricity and evaluate its efficiency.
Unlike current Sand Batteries used for heat production, the version intended for electricity generation operates at significantly higher temperatures. Achieving these higher temperatures and overcoming the related material technology challenges are key goals for the pilot, which will run through early 2027.
“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.
Valkeakoski was selected as the pilot location due to the strong enthusiasm and support from both Valkeakosken Energia and the City of Valkeakoski, who recognized the project’s potential to strengthen the city’s reputation as a development-driven region.
“We found common ground from the very beginning. Valkeakosken Energia quickly identified a suitable site for the pilot, conveniently located with good transport connections to Tampere. In addition, the heat generated by the pilot can be fed into Valkeakosken Energia’s district heating network, reducing energy waste,” says Markku Ylönen, CTO of Polar Night Energy.
The technology has the potential to significantly cut emissions and make renewable energy sources like wind and solar more reliable and cost-effective. When operational, the new Sand Battery would enable a better match between electricity production and consumption, thereby supporting the growth of wind and solar energy.
“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.
Massive Need for Energy Storage
The efficiency of the P2H2P system depends on factors like plant size, the selected electricity generation process, and how it integrates with existing systems. The expected electrical efficiency is approximately 30–35%, similar to traditional combustion-based power plants. If used in combined heat and power (CHP) production, 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,” says Veli-Matti Pietarinen, Power Plant Specialist at Polar Night Energy.
Construction of the pilot facility will begin in autumn 2025 at Pispantalli in Valkeakoski. The site will feature a thermal energy storage unit and technical building covering nearly the entire plot.
“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.
Based on the pilot’s results and experience, Polar Night Energy aims to deliver commercial-scale electricity production plants in the future. The project will run for 2.5 years and has received support from Business Finland.
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