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250MWh 'Sand Battery' to start construction in Finland

Recorded: Nov. 28, 2025, 1:02 a.m.

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250MWh 'Sand Battery' to start construction in Finland, for both heating and ancillary services - Energy-Storage.News

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250MWh ‘Sand Battery’ to start construction in Finland, for both heating and ancillary services

By Cameron Murray

November 26, 2025

Europe

Grid Scale, Distributed

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Polar Night Energy and Lahti Energia are partnering on the Sand Battery project in Finland. Image: Polar Night Energy / Lahti Energia.

Technology provider Polar Night Energy and utility Lahti Energia have partnered for a large-scale project using Polar’s ‘Sand Battery’ technology for the latter’s district heating network in Vääksy, Finland.
The project will have a heating power of 2MW and a thermal energy storage (TES) capacity of 250MW, making it a 125-hour system and the largest sand-based TES project once complete.
It will supply heat to Lahti Energia’s Vääksy district heating network but is also large enough to participate in Fingrid’s reserve and grid balancing markets.
Polar Night Energy’s technology works by heating a sand or a similar solid material using electricity, retaining that heat and then discharging that for industrial or heating use.
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The project will cut fossil-based emissions in the Vääksy district heating network by around 60% each year, by reducing natural gas use bu 80% and also decreasing wood chip consumption.
It follows Polar Night Energy completing and putting a 1MW/100MWh Sand Battery TES project into commercial operations this summer, for another utility Loviisan Lämpö. That project uses soapstone as its storage medium, a byproduct of ceramics production.
This latest project will use locally available natural sand, held in a container 14m high and 15m wide. Lahti Energia received a grant for the project from state body Business Finland.
Polar Night Energy will act as the main contractor for the construction project, with on-site work beginning in early 2026, and the Sand Battery will be completed in summer 2027.
“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.

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ancillary services, district heating, EnergyStorageEurope, finland, heat battery, sand battery, thermal energy storage

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The construction of a 250MWh ‘Sand Battery’ is underway in Finland, a collaborative project between Polar Night Energy and Lahti Energia. This ambitious undertaking aims to provide district heating services to Lahti Energia’s Vääksy network, while simultaneously participating in Fingrid’s reserve and grid balancing markets. The project utilizes Polar Night Energy’s proprietary ‘Sand Battery’ technology, which involves heating a large volume of sand to store thermal energy. Subsequently, this stored heat can be discharged for either industrial or heating applications.

This particular system boasts a 125-hour duration, making it the largest sand-based thermal energy storage project currently in development. The core of the operation will utilize locally sourced natural sand, contained within a container measuring 14 meters high and 15 meters wide. The project’s overall power output is slated at 2MW, highlighting its substantial contribution to the local energy landscape.

The initiative has received a grant from Business Finland, underscoring its strategic importance. Jouni Haikarainen, CEO of Lahti Energia, emphasizes the project's dual purpose: supplying affordable district heating and leveraging renewable energy sources. Furthermore, the Sand Battery's capacity to participate in Fingrid’s market operations is viewed as crucial for balancing electricity supply and demand, particularly given the increasing reliance on weather-dependent renewable energy sources.

Polar Night Energy will serve as the primary contractor, with construction commencing in early 2026, culminating in completion during the summer of 2027. This project builds upon Polar Night Energy’s earlier success with a 1MW/100MWh Sand Battery TES project at Loviisan Lämpö, which deployed soapstone as its storage medium – a byproduct of ceramics production. The ‘Sand Battery’ reflects a strategic approach towards utilizing readily available resources and contributing to a more resilient energy system.