Finnish Engineers Launch Pilot of Advanced Sand Battery Designed to Return Stored Heat to Electric Grid

Polar Night Energy begins testing a sand battery in Finland that converts stored heat back into electricity, aiming for 90% total system efficiency.

By: AXL Media

Published: Apr 7, 2026, 4:41 AM EDT

Source: Information for this report was sourced from Live Science

A New Frontier in Thermal Energy Storage

Engineers in Finland are preparing to test a sophisticated sand battery designed to convert stored thermal energy back into electricity for the national grid. Developed by Polar Night Energy, this pilot project in Valkeakoski represents a significant evolution of existing technology that previously focused solely on heat delivery. According to Tommi Eronen, CEO of Polar Night Energy, the new model differs fundamentally from its predecessors by utilizing a horizontal configuration rather than a vertical silo, allowing for higher operating temperatures and expanded utility.

Technical Shifts in Energy Conversion Efficiency

The power-to-heat-to-power system operates by heating sand-like materials to temperatures exceeding 752 degrees Fahrenheit. While the electrical efficiency of this conversion is expected to reach approximately 30% to 35%, similar to traditional combustion power plants, the overall system efficiency is projected at 90%. This high rating is achieved by capturing and utilizing the byproduct heat for industrial steam or hot water alongside electricity production. This dual-output capability is intended to help stabilize the electrical grid while reducing a community's reliance on fossil fuels.

Infrastructure and Construction Timeline

Construction on the pilot site began in October 2025, with active testing slated to begin within the coming weeks. The experimental phase is scheduled to last approximately two and a half years, providing engineers with the data necessary to refine the technology for commercial use. During this period, the team will focus on trialing new materials capable of withstanding the intense thermal stress required for efficient power generation. Polar Night Energy is already developing designs for a scaled-up commercial product based on these preliminary findings.