The Sand Battery is a large-scale, high-temperature thermal energy storage system that uses sand or similar materials to store energy as heat.

What Is a Sand Battery?

The Sand Battery can change the way we store renewable energy. It offers an efficient way to balance the grid and provide heat without fossil fuels. Learn how this system is helping industries expand the use of wind and solar power while cutting costs and lowering emissions.

The Sand Battery is a large-scale, high-temperature thermal energy storage system that uses sand or similar materials to store energy as heat.

Its primary purposes are storing excess wind and solar energy, participating in grid balancing markets, and producing heat and power without combustion. This technology helps scale up renewable energy sources like wind and solar, enabling companies to meet their climate targets while significantly lowering energy costs.

The Sand Battery was invented by Polar Night Energy. The core of the solution is our patented closed loop heat transfer mechanism in a massive solid material thermal energy storage.

The term “Sand Battery” gained widespread attention through a BBC News story on July 5, 2022. The story, produced by Environmental Correspondent Matt McGrath, featured the world’s first commercial Sand Battery in Kankaanpää, Finland.

The World’s First Sand Battery in Finland

Polar Night Energy developed and operates the world’s first commercial Sand Battery in Kankaanpää, Finland, for the energy utility Vatajankoski.

This 200 kW Sand Battery, with an 8 MWh capacity, is a 7-meter tall structure with a diameter of around 4 meters. It uses 100 tons of locally sourced sand as the storage medium and connects to a district heating network, heating homes and commercial buildings, including the municipal swimming pool.

The Sand Battery works alongside a data center whose waste heat warms district heating water. However, the data center alone cannot provide the required temperatures, so the Sand Battery boosts the water’s temperature before it reenters the heating system.

The system has achieved an efficiency of 60–70%, in line with expectations. Larger Sand Batteries will perform much better, as efficiency increases with scale. The approximate round trip efficiency for our 2 MW Sand Battery is 85% and for 10 MW Sand Battery it is 90%.

Design of the Sand Battery

The Sand Battery’s storage unit is an insulated silo, typically 10 to 15 meters tall, with a diameter ranging from 4 to 30 meters, depending on capacity. Its modular structure allows for flexible storage capacity adjustments without extensive redesign.

Charging and discharging occur via heat transfer pipes circulating air in a closed-loop system. The air is heated with resistive heaters, and the flow is controlled by industrial blowers and dampers. When discharging, the air is led through a heat exchanger.

The output is hot water, steam, or air, with temperatures up to 400°C, suitable for 36% of industrial process heat needs. We are also developing a solution to convert stored heat back into electricity. The pipes, buried in the storage medium, are maintenance-free and designed for longevity.

The Storage Medium

The preferred storage medium is sand or similar granular materials unsuitable for construction.

High-density, low-cost solid materials from abundant sources are ideal. This flexibility allows the use of locally available materials or by-products from industrial processes. Someone else’s dirt could be our thermal energy storage medium.

We collaborate with partners to identify new storage media based on sustainability, cost, and thermal properties. One area of interest is the mining industry, where materials typically discarded as mine waste rock could serve as thermal storage. We have experience in conducting the relevant experiments with samples delivered by our partners and clients.

Use Cases for the Sand Battery

Energy utilities and industries are shifting towards climate-friendly energy solutions, and the Sand Battery is versatile enough to integrate with existing infrastructure. Polar Night Energy’s clients include energy utilities, district heating providers, big commercial or residential building operators that need space heating, and industries needing high-temperature process heat, such as:

  • Food & beverage
  • Pulp & paper
  • Textiles & clothing
  • Metal, mining & minerals
  • Chemicals & pharmaceuticals
  • Manufacturing

The Sand Battery is particularly useful for applications that require heat between 60 and 400 °C, a range typically served by oil or gas today.

Climate Action and Energy Innovation

To combat climate change, we need reliable solutions to store energy from renewable sources. The Sand Battery meets this need by being environmentally sustainable, socially responsible, and economically viable.

Polar Night Energy’s innovation has inspired global interest, sparking DIY projects and discussions around clean energy solutions. Since its introduction, the Sand Battery has been featured in major media outlets and educational forums worldwide.

Polar Night Energy was founded in 2018 and has already made an impact on the energy industry with the world’s first commercial Sand Battery. The company is based in Tampere, Finland.

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