A small municipality in southern Finland recently installed the world’s largest “sand batteries” to supply the town’s heating.
The new sand battery, designed by Polar Night Energy, is effectively a huge sandbox wrapped in a steel container of about 100 x 40 feet (30 x 12 meters).
The sand is heated using closed loop heat transfer pipes, which is trapped in two layers of steel sandwiched between the insulation layers. Energy is extracted by blowing cold air into the pipe, capturing heat and generating hot water, steam, or hot air.
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Renewable energy sources such as solar and wind power are essential to reach net zero by 2050, unlike traditional energy sources such as oil and coal, as they are not contributing to carbon dioxide emissions.
However, solar and wind power output is constantly unavailable, and supply waxes and declines annually. This makes it important to find ways to store renewable energy for use during periods of shortages in the energy supply.
“The main challenge for large-scale implementation of renewable energy is energy storage,” Matteo Chiesa, professor of mechanical and nuclear engineering at Khalifa University of Science and Technology in Abu Dhabi, who was not involved in the project, told Live Science.
Related: How to preserve renewable energy
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By deriving excess energy from the grid and heating the sand to a whopping 1,112 degrees (600 degrees Celsius), the new sand battery is capable of storing thermal energy for potentially several months, says Polar’s Night Energy Representative.
A heating power of 10 megawatts (meaning that it can provide 10 million joules of energy per second) can output an output temperature of 140-752 degrees F (60-400 degrees C).
“It has proven successful in Finland,” Chiesa said.
Heating using the power of sand
Using materials like sand and sand to retain heat is a traditional phenomenon, and brick ovens are popular all over the world. This is because sand, which is most commonly made up of a combination of silicon and oxygen, is easily available worldwide. It can be heated to very high temperatures before it melts, and keeps the heat for a long time.
Sand batteries do not produce electricity directly, so in the traditional sense it is not a battery. Instead, they are thermal energy storage systems. That is, it is charged using renewable energy. This is stored as thermal energy for use when energy demand exceeds supply.
Chiesa said Polar Night Energy Design is “very robust,” but the current configuration is too expensive to translate into a home context facing similar energy storage challenges.
“Every time you add metal, you add a cost,” he said. “Ideally, the porosity of sand batteries should be designed so that air can be distributed evenly across all pores without relying on expensive materials.”
Chiesa also said Polar Night Energy does not currently provide seasonal storage and instead uses the system to store energy for a shorter period, primarily to balance fluctuations in wind power.
Such thermal energy storage systems are suitable for storing renewable energy seasonally, as it takes a lot of time for sand to lose heat.
“A battery that can store solar energy in the summer and use it in the winter — when the heating demand is the highest — is a powerful solution to seasonal energy needs,” says Chiesa.
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