Finnish Sand Battery Technology Converts Stored Renewable Energy into Grid Power

Engineers in Finland have commenced testing of an advanced sand battery system designed to convert stored thermal energy back into electrical power for grid distribution. The technology, developed by Polar Night Energy, represents a significant evolution from the company’s existing thermal storage solutions, although questions remain regarding commercial viability and investment costs.

The established sand battery model stores renewable electricity by heating sand and similar materials to temperatures reaching 400 degrees Celsius. This thermal energy is subsequently extracted to provide hot water, steam or heated air. The new power-to-heat-to-power iteration operates at substantially higher temperatures to enhance efficiency, with precise operating ranges currently under investigation as part of the pilot programme.

Tommi Eronen, co-founder and chief executive of Polar Night Energy, described the new system as fundamentally different from the existing power-to-heat version. Whilst specific details remain confidential, the configuration represents a key departure from previous designs. The power-to-heat-to-power sand battery employs a horizontal arrangement rather than the vertical silo structure of its predecessor.

The system’s efficiency depends upon scale and integration with existing infrastructure. Polar Night Energy anticipates efficiency levels between 30 and 35 per cent, comparable to combustion-based power plants. For context, fossil fuel-based combustion facilities in the United States achieved average efficiency of 39 per cent in 2023.

The technology aims to balance grid demand, reduce emissions and decrease reliance on fossil fuels whilst providing a pathway to large-scale, cost-effective energy storage. The new battery will generate both heat and electricity, potentially increasing overall system efficiency to approximately 90 per cent, according to Eronen. This dual output makes the technology suitable for industries requiring both forms of energy, including utility companies.

The pilot project is currently underway in Valkeakoski, a Finnish municipality approximately 150 kilometres north of Helsinki. Construction began in October 2025, with testing scheduled to commence within weeks. The pilot phase will extend for roughly two and a half years, although Polar Night Energy has already begun developing commercial product designs.

Liisa Naskali, chief operating officer at Polar Night Energy, confirmed that engineers will trial various technological solutions during the pilot project to enable future electricity production. This includes developing materials capable of withstanding elevated operating temperatures and exploring new design configurations.

Investment cost presents the primary barrier to commercial deployment. Naskali acknowledged that the substantial capital requirement discourages potential customers, particularly given the availability of cheaper alternatives such as wood-chip boilers. She noted that whilst a power-to-heat-to-power sand battery is technically achievable, identifying an economically viable and technologically efficient solution remains the central challenge. The technology’s complexity is evidenced by the absence of comparable systems in commercial operation.

The development represents a significant advance in thermal energy storage technology, offering potential benefits for grid stability and renewable energy integration. However, the project’s commercial success will ultimately depend upon demonstrating cost-effectiveness relative to existing energy storage and generation alternatives.