Lahti Energia Invests in a Sand Battery – Towards Climate-friendly and Cost-efficient Energy

Polar Night Energy and Lahti Energia have agreed on the construction of an industrial-scale thermal energy storage for Lahti Energia’s district heating network in Vääksy, Finland. The new Sand Battery will have a heating power of 2 MW and a storage capacity of 250 MWh, making it the world’s largest sand-based thermal energy storage system once completed.

The Sand Battery will supply heat to Lahti Energia’s Vääksy district heating network. The goal is to provide local customers with energy that is as low-emission and cost-efficient as possible.

The Sand Battery will cut fossil-based emissions in the Vääksy district heating network by around 60% each year, driven by an approximately 80% reduction in natural gas use and a notable decrease in wood chip consumption.

“We want to offer our customers affordable district heating and make use of renewable energy in our heat production. The scale of this Sand Battery also enables us to participate in Fingrid’s reserve and grid balancing markets. As the share of weather-dependent energy grows in the grid, the Sand Battery will contribute to balancing electricity supply and demand”, says Jouni Haikarainen, CEO of Lahti Energia.

A Sand Battery is a high-temperature thermal energy storage system that uses sand or a similar solid material to store renewable energy.

“The negotiations went extremely well, and we are excited to begin working with Lahti Energia. It is incredible to once again build the world’s largest Sand Battery. This represents a major step forward for both organizations toward achieving our emission-reduction goals,” says Tommi Eronen, CEO of Polar Night Energy.

Towards a Cleaner Energy System

Polar Night Energy will act as the main contractor for the construction project. On-site work will begin in early 2026, and the Sand Battery will be completed in summer 2027.

“We are truly proud to collaborate with a major energy company like Lahti Energia. This project is not only an important reference for us but also another step toward cleaner heat production in demanding high-temperature applications,” says Tommi Eronen.

The energy storage medium of the Sand Battery will be approximately 2,400 tons of locally available natural sand. Sand is well suited for this purpose and enables storage tempe­ratures above 500 degrees Celsius.

Once completed, the Sand Battery will be about 14 meters high and 15 meters wide. A separate technical building will be constructed next to it. Lahti Energia has received energy aid for the project from Business Finland.

Polar Night Energy’s previous Sand Battery built for Loviisan Lämpö in Pornainen has been operating for half a year and has demon­strated strong, reliable performance in real-world operation. The company is currently in negotiations for several additional Sand Battery projects for district heating as well as industrial applications.

Polar Night Energy’s technology has recently received significant recognition. The Sand Battery was selected for TIME magazine’s list of the Best Inventions of 2025 and has been honored in compe­titions such as the Capgemini Nordic Sustai­nability Tech Award and the Mission Innovation Net-Zero Industries Mission special award at the COP30 climate conference. These inter­national recog­nitions highlight the growing relevance of high-temperature thermal storage as a key enabler of industrial decar­bo­nization.