Renewable thermal storage is gaining prominence again in Finland with the development of a new system based on sand that promises to drastically reduce the use of fossil fuels. Lahti Energia and Polar Night Energy announced the construction of an industrial unit that will operate within the Vääksy district heating network.
The project will have a storage capacity of 250 MWh and a thermal power of 2 MW. Once operational, it will become the largest Sand Battery installed globally. Its goal is to ensure stable, accessible, and very low-emission heat for local residents.
The initiative is framed within an energy context marked by climate variability and the need for simple, robust, and combustion-free storage solutions. Sand appears as a suitable resource due to its availability, low environmental footprint, and thermal properties.
Renewable storage for urban heating
The new Sand Battery will supply thermal energy to the Vääksy network and will allow for a reduction of about 60% in emissions associated with the use of fossil fuels. The system will help reduce natural gas consumption by up to 80% and decrease biomass dependency.
The mechanism involves heating thousands of tons of sand using renewable electricity to exceed 500 °C. That heat is stored for long periods, even months, without significant losses or chemical processes.
This technology also offers rate stability, as heat can be charged during low-demand hours or when renewable energy is more abundant. In this way, the system reduces exposure to the volatility of the electricity market.
Expanding Finnish technology
Polar Night Energy will be responsible for the installation, with construction starting in 2026 and finishing in 2027. The structure will reach 14 meters in height and use about 2,400 tons of local natural sand. Lahti Energia supports the initiative with financial backing from the energy innovation program of Business Finland.
The system does not start from scratch. A similar battery operates successfully in Pornainen, where it demonstrated operational stability and a sustained capacity to store heat for long periods. This performance encouraged new investments and agreements to expand the use of the technology.
The Finnish advancement also received international recognition, including its entry into the list of the Best Inventions of 2025 by TIME magazine and various awards related to industrial sustainability. The sand battery thus consolidates itself as a scalable energy alternative for industries and urban thermal networks.
A step towards decarbonizing heat
The incorporation of this system will have a direct impact on emission reduction and the transition towards a combustion-free energy model. By decoupling heat production from fossil fuels, urban heating gains resilience and predictability.
The technology also opens the door to industrial applications requiring high temperatures. Storage at over 500 °C allows for replacing thermal processes traditionally fueled by gas, fuel, or biomass, expanding the possibilities of heat electrification.
Additionally, the system provides flexibility to the electrical grid, as it can absorb renewable surpluses at critical moments. This improves the balance between generation and demand and supports the expansion of sources like wind and solar.
How does a Sand Battery work?
The Sand Battery is a thermal storage system that uses an insulated tank filled with sand or another granular material. Renewable electricity heats the material through resistors, and the heat is retained internally due to its low thermal conductivity.
The sand can remain hot for months, and the system does not require chemical reactions or scarce materials. This simplicity reduces costs and avoids impacts associated with mining extraction or complex manufacturing processes.
Its ability to reach very high temperatures makes it a valuable option for urban heating and industries needing stable and safe heat.
Differences between sand batteries and lithium batteries
1. Type of energy stored
- Lithium batteries: store electrical energy.
- Sand batteries: store thermal energy (heat), not electricity.
2. Materials and environmental impact
- Lithium: requires intensive mining, chemical processing, and sensitive components.
- Sand: is abundant, cheap, and does not require complex processes or critical inputs.
3. Main application
- Lithium: ideal for electric mobility and electrical backup.
- Sand: useful for urban heating, industrial processes, and thermal network balancing.
4. Lifespan and maintenance
- Lithium: suffers chemical degradation over time.
- Sand: does not degrade; can be reused for decades without significant loss.
5. Safety
- Lithium: risk of overheating or fire if damaged.
- Sand: does not present a combustion risk and operates without chemical reactions.
