Heated Sand: the battery that bridges the seasons

Jan 03, 2024

Sustainability - The sand battery is relatively simple, cheap, and can store heat for up to several months.

In the energy transition Polar Night Energy offers an innovative solution: sand batteries. These high temperature thermal energy storages use sand, a material that can hold its temperature for months, bridging the gap between summer’s surplus and winter’s demand. The process involves the use of insulated steel silos filled with sand and heat transfer pipes. Electricity, ideally clean and cheap, is used to charge the sand up to a maximum temperature of 600 degrees Celsius. The stored heat can be extracted by blowing cool air through the pipes, which heats up for use in various applications. A sand-based system can store several times the amount of energy compared to water tanks of a similar size. These systems can be used for industry or to heat homes through district heating systems.

With the increasing adoption of renewable energy sources, there is an urgent need to solve the problem of power variability. The solution, it seems, may not be in complex technology, but in one of the most common substances on earth: sand. Polar Night Energy, a Finnish company, has been pioneering the use of sand batteries, an innovative method of storing thermal energy. These batteries, which are essentially insulated steel silos filled with sand, provide a straightforward and scalable solution to an issue that has long vexed the renewable energy industry.

The principle behind sand batteries is simple: electricity, either from the grid or local production, is used to heat the sand to high temperatures—up to 600 degrees Celsius. The sand then retains this heat for a significant amount of time, releasing it when needed. Because sand can hold its temperature for months, these batteries can help to bridge the gap between the energy-abundant summer months and the colder, more energy-demanding winter months.

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Using sand as a medium for energy storage offers a number of advantages. For one, sand is readily available and low-cost, making it an attractive alternative to more expensive and resource-intensive batteries. More importantly, sand can store several times the amount of energy compared to water tanks of a similar size, thanks to its ability to withstand high temperatures. This makes sand batteries a highly space-efficient solution, particularly for industrial applications.

But the benefits of sand batteries go beyond their cost and storage capacity. For businesses and industries including energy utilities, building operators, and various manufacturing sectors, sand batteries present a versatile solution. By converting the stored heat into process steam or district heating water, these batteries can be used for a wide range of purposes. However, it is important to note that while the heat can be converted back into electricity using turbines, this process requires additional investments and has inherent losses.

In the Finnish town of Kankaanpää, the world’s first sand battery is already in operation. Developed by Polar Night Energy in collaboration with the local energy utility Vatajankoski, the sand battery stores excess wind and solar energy. This battery, which can store 8 megawatt hours of thermal energy, has been used to power the central heating system for the district. When energy prices are high, the hot air in the battery is used to warm the water, which is then pumped to offices and homes in the region.

The success of the sand battery in Kankaanpää has not gone unnoticed. The technology is receiving positive attention, and Polar Night Energy aims to expand its innovation to more locations. These sand batteries are a significant step forward in the transition to a more sustainable and reliable energy supply. As the world moves away from fossil fuels and towards renewable energy sources, the sand battery could be a game changer in the way we store and use energy.