In a small town in southern Finland, a gigantic silo filled with crushed rock holds an unexpected promise: clean, inexpensive heat stored for months. The world’s largest sand battery has officially begun operations, evolving from an idea conceived by two friends in 2018 into a pioneering facility aimed at solving one of the greatest challenges of renewable energy: large-scale storage .
A sand battery. In a region where the sun does not always shine and the wind does not consistently blow, the need for energy storage in renewable resources becomes imperative. The thermal battery of Polar Night Energy , built alongside the urban heating plant in Pornainen and managed by Loviisan Lämpö, was officially inaugurated on June 11, 2023, as reported by Euronews. This innovative battery has a thermal storage capacity of 100 MWh , with an efficiency rate between 85% and 90% .
Ten times larger. The new cylindrical structure stands 13 meters tall and 15 meters wide , filled with approximately 2000 metric tons of crushed soapstone —a byproduct of Finnish chimney manufacturing. This pulverized rock, stored in an insulated silo, serves as a massive thermal energy accumulator, capable of meeting heating demands for an entire week in winter or an entire month in summer, as noted by TechCrunch.
How can it be made of sand? Although it may sound sophisticated, the principle is relatively simple. Electricity—preferably sourced from solar or wind—is used to resistively heat air, which, in turn, transfers heat to the sand in the silo. Due to its high density and heat retention capacity , the sand can hold that heat for days or even months at temperatures up to 500 °C . When required, the system releases the hot air to heat water for the urban heating network.
In the case of Pornainen, it provides thermal energy to public buildings, households, and even the municipal pool, as highlighted by Euronews. All control and energy performance prediction is managed by an advanced heat transfer model that calculates optimum loading and unloading in real time.
Reducing the use of wood chips. This new structure is designed to reduce the reliance on wood chips for urban heating by 60% , potentially eliminating up to 160 tons of CO2 annually. Additionally, it’s worth noting that the sand used is not construction sand but recycled soapstone, a local byproduct. Polar Night Energy co-founder Markku Ylönen explained in an interview with Euronews that the material must meet certain thermodynamic criteria, but it does not necessarily have to be sand. Any dense granular material can work, paving the way for circular economy models and alleviating pressure on river ecosystems.
Connected to the electricity market. The battery exists within the energy reserve service, and the company is currently developing a pilot project to convert the stored heat back into electricity, which could further enhance the flexibility of the energy system. Furthermore, it has a significantly lower estimated storage cost compared to lithium-ion batteries , according to TechCrunch.
A new paradigm shift. In the face of a climate crisis, it seems that the future of energy may not solely depend on lithium, hydrogen, or large solar parks, but also on forgotten materials like sand. From the heart of Finland, a silent battery is already warming homes, libraries, and schools.
As citizens and policymakers increasingly recognize the importance of sustainable energy solutions, innovations like the sand battery could represent a turning point in energy consumption and production. Such technologies not only promise to reduce emissions but also offer efficient and affordable alternatives to traditional energy sources.