Finland s Bold Fix for Renewable Intermittency: The World s Largest Commercial Sand Battery

Finlands sand battery tackles renewable intermittency

A small southern Finnish town has deployed what developers say is the worlds largest commercial sand battery to address one of the most persistent obstacles in the energy transition: intermittency. The industrial-scale facility in Pornainen stores clean energy as heat and can deliver 100 megawatt-hours (MWh) of thermal energy, enough to cover nearly a month of the towns heating needs in summer and roughly one week in winter for its 5,000 residents.

Standing 13 meters tall and 15 meters wide, the silo contains 2,000 metric tons of crushed soapstone. The system was commissioned by district heating company Loviisan Lämpö and developed by Polar Night Energy, which launched the project last year as part of a strategy to introduce flexible heat production and reduce carbon emissions from the local district heating network.

Polar Night Energy estimates the sand battery has cut greenhouse gas emissions from the heating network by almost 70% and reduced wood-chip consumption by about 60%. An existing wood-chip plant remains available as a backup and for peak loads.

Tommi Eronen, CEO of Polar Night Energy, told CNBC that Pornainen previously relied on oil and wood chips for heating. The sand battery now delivers combustion-free heating for the majority of the year. Were changing from a world where big power plants were doing the energy production to where solar and wind are producing the energy, then we need a massive amount of storage, Eronen said. He added that sand batteries avoid reliance on rare-earth and other critical materials required for many chemical batteries, including lithium-ion systems.

How the technology works and its potential

The sand battery operates like a giant thermos. When wind or solar generation is abundant and electricity is cheap, electrical heaters raise the temperature of the sand to very high levels. The silo is heavily insulated to retain heat for days or weeks. When heat is required, the stored energy is discharged through heat exchangers to produce steam or hot water for the district heating network.

Annette Höglund-Dönnes, Polar Night Energys chief commercial officer, described the process as analogous to charging a phone overnight when electricity prices are lower and using that charge during the day. The key commercial advantage is the time-shift between charging and discharging: operators can charge when spot prices are low and use the heat when grid prices are high.

The Pornainen installation is roughly ten times larger than an earlier Finnish pilot launched in 2022, demonstrating the technologys scalability for regional heat storage. The company says teams from every continent have contacted them about replication, particularly communities that remain dependent on coal, oil or other fossil fuels.

Experts see sand batteries as a promising tool for long-duration thermal storage. Jan Rosenow, professor of energy and climate policy at the University of Oxford, highlighted that electrothermal systems do not require rare earths and can store energy for days or potentially weeksfar longer than typical lithium-ion batteries, which are optimized for two-to-four-hour durations.

Nonetheless, sand batteries face limitations. Critics point to inefficiencies when converting heat back to electricity and to relatively low energy density compared with chemical batteries. These constraints make sand batteries especially suitable for regional heat applications rather than compact, high-power electric storage.

Loviisan Lämpös CEO, Mikko Paajanen, said the sand battery allows the company to separate electricity procurement from district heating production. With one full charge the system can supply a weeks winter demand and up to a months summer demand, enabling better use of low spot prices. The company planned to produce roughly 55%60% of the municipalitys district heating from the sand battery in the first months of this year, up from about 30% in 2025.

Finlands Climate Minister Sari Multala called the project a very inspiring example of energy storage innovation and noted developers are exploring ways to recover electricity from such systems in the future, which would be a potentially groundbreaking enhancement.

As countries work to curb greenhouse gas emissions from burning coal, oil and gasthe primary drivers of climate changelong-duration storage solutions will play a crucial role in decarbonizing heat production and stabilizing grids dominated by variable renewable power. The Pornainen sand battery underscores one pragmatic, material-light approach to that challenge, particularly for district heating systems in cold climates. Whether the model scales beyond regional heat networks and addresses electricity-conversion inefficiencies will determine how central sand batteries become in the broader rollout of clean energy systems.