In the global push toward a clean energy future, battery technology has taken centre stage. Yet not all energy needs to be stored as electricity. Enter the sand battery: a simple, scalable, and surprisingly elegant solution to the problem of storing renewable energy as heat. While lithium and flow batteries dominate headlines, sand-based thermal storage may quietly become one of the most important tools in the transition to net zero, especially in colder climates and industrial sectors.

At its heart, a sand battery is a thermal energy storage system. It uses resistive heating elements to convert surplus renewable electricity into heat, which is then stored in a large mass of sand. Sand is cheap, abundant, non-toxic, and capable of withstanding extremely high temperatures – up to 1000°C in some designs. Once heated, the sand is housed in a well-insulated steel or concrete silo, where it can retain thermal energy for days, weeks, or even months. The stored heat can later be extracted and used directly in heating systems or, in some cases, converted back into electricity.

The real beauty of sand batteries lies in their efficiency and affordability. When used for heating applications, such as district heating networks or industrial processes, they achieve thermal round-trip efficiencies of 80 to 95 percent. This puts them in a strong position compared to chemical batteries, especially where the end-use is heat rather than electricity. Converting heat back into electricity is less efficient, often below 40 percent, which limits their utility as pure power storage. Yet, for countries with long, cold winters, and industries dependent on high-temperature heat, sand batteries could be revolutionary.

In Finland, the town of Kankaanpää is already home to the world’s first commercial sand battery, developed by startup Polar Night Energy. The battery stores excess wind and solar power during the summer and discharges it in winter to supply district heat. It’s a practical, real-world demonstration of what this technology can do: provide seasonal storage at a fraction of the cost of chemical alternatives. Think of Canada’s northern and remote coastal communities storing wind and solar energy during the summer, then operating their community heating facilities using sand batteries throughout the winter.  

The potential applications extend well beyond district heating. Many industrial processes: textiles, paper, chemicals, and food production, rely heavily on thermal energy. Today, most of that heat comes from burning fossil fuels. Sand batteries offer a clean alternative, especially when paired with renewables. They’re also ideal for off-grid and remote locations, where reliable heat can be hard to come by.

Compared to other storage technologies, sand batteries stand out for their low cost and long-duration potential. They’re not a replacement for lithium batteries or pumped hydro, but are a crucial complement. As more nations seek to decarbonize not just electricity, but also heating and industry, sand batteries will likely find a permanent place in the energy landscape.

Simple, scalable, and rooted in abundant natural materials, sand batteries remind us that sometimes the most advanced solutions are also the most grounded. In the race toward a sustainable energy future, this humble pile of sand might just be one of our best bets.