A scalding hot 'sand battery' is now heating a small Finnish town

A small municipality in southern Finland recently installed the world's largest "sand battery" to supply the town's heating.

The new sand battery, designed by Polar Night Energy, is effectively a giant sandpit encased in a roughly 43 foot tall by 49 foot wide (13 by 15 meter) steel container.

The sand is heated using closed-loop heat transfer pipes and this heat is trapped by two layers of steel sandwiching an insulation layer. The energy is then extracted by blowing cool air through the pipes, capturing the heat to generate hot water, steam or hot air.

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Renewable energy sources, such as solar and wind power, differ from traditional energy sources, like oil and coal, because they do not contribute to the carbon footprint — making them essential for reaching net zero by 2050.

But solar and wind power is not constantly available, with supply waxing and waning over the course of each year. This makes it critical to find ways of storing renewable energy for use during periods of shortfall in the energy supply.

"The main challenge to large-scale implementation of renewable energy is energy storage," Matteo Chiesa, a professor of mechanical and nuclear engineering at the Khalifa University of Science and Technology in Abu Dhabi who was not involved in the project, told Live Science.

Related: How to store renewable energy

By channelling excess energy from the grid and locally produced solar and wind energy to heat up sand to a whopping 842 degrees Fahrenheit (450 degrees Celsius), this new sand battery can store heat energy for potentially months on end, Polar Night Energy representatives say.

With a heating power of 1 megawatts — meaning it can provide 1 million joules of energy per second — it can output temperatures of 140-752 degrees F (60-400 degrees C).

"It’s proving successful in Finland," Chiesa said, adding that there’s strong potential for it to succeed elsewhere.

Heating using the power of sand

Using sand and sand-like materials to retain heat is an age-old phenomenon, with brick ovens being popular worldwide. This is because sand — which is most commonly made up of a combination of silicon and oxygen — is readily available globally. It can be heated to extremely high temperatures before it melts, and retains its heat for a long time.

Sand batteries are not batteries in a conventional sense as they do not directly produce electricity. Instead, they are thermal energy storage systems, meaning they are charged up using renewable energy, which is then stored as heat energy for use when energy demand exceeds supply.

Chiesa said that the Polar Night Energy design is "very robust," but the current configuration would be too expensive to translate over to household contexts, which face similar energy storage challenges.

"Every single time you add metal, you add costs," he said. "Ideally, we should design the sand battery’s porosity so that air can be distributed evenly throughout all pores without relying on expensive materials."

Chiesa also noted that Polar Night Energy does not currently provide seasonal storage, instead using its system to store energy for shorter durations — primarily to balance fluctuations in wind power generation.

Thermal energy storage systems like this are well-suited for storing renewable energy seasonally because it takes so long for sand to lose its heat.

"A battery that enables you to store summer solar energy and use it during winter — when heating demand is highest — is a powerful solution for seasonal energy needs," Chiesa said.

Editor's Note: This story was updated on Friday, Sept. 12 at 12:19 p.m. EDT to correct the size of the plant, the temperatures it reaches and the power it outputs.