A groundbreaking energy storage technology is entering the testing phase in Finland, as engineers prepare to evaluate a “sand battery” capable of converting stored heat back into electricity.
Developed by Polar Night Energy, the system stores renewable energy by heating sand or similar materials to temperatures of around 400°C. Until now, this stored heat has primarily been used for district heating, steam production, or hot air generation.
The new version of the technology takes a significant step forward by enabling the reverse process—transforming heat back into electrical power. To achieve this, the system operates at even higher temperatures, aiming to improve overall efficiency.
According to co-founder and CEO Tommi Eronen, the upgraded battery is fundamentally different from its predecessor. One key change is its horizontal design, replacing the earlier vertical, silo-like structure. Its efficiency is expected to range between 30% and 35%, comparable to some conventional power generation systems.
Despite this moderate efficiency, the technology offers a major advantage when combined with heat production. In such cases, total energy utilization can reach up to 90%, making it particularly attractive for industrial use.
The pilot project is being conducted in Valkeakoski, about 150 kilometers north of Helsinki. Construction began in October 2025, with testing expected to run for approximately two and a half years. During this period, engineers will explore multiple technical approaches, including the development of materials capable of withstanding higher temperatures.
However, cost remains the primary challenge. As noted by COO Liisa Näskälä, the high upfront investment could deter potential customers, especially given the availability of cheaper alternatives.
While the concept is considered technically feasible, its future will depend on whether it can achieve economic viability. If successful, it could play a key role in balancing power grids, reducing emissions, and accelerating the transition away from fossil fuels.