hot sand? The ability of sand to store heat has inspired a new type of battery. A team of engineers in western Finland (Markku Ylönen and Tommi Eronen) have installed the world’s first fully functional ‘sand battery’, which can store renewable energy for several months.
A very basic concept
We catch a very large pile of sand. We heat it with excess renewable electricity to around 500ºC; then we use that heat to heat homes, factories, and even swimming pools. They say that the sand can stay hot for 3 months or more.
The company is called Polar Night Energy and it has completed its first installation of 100 tons of sand in what looks like a large silo four meters wide and 7 meters high, in the city of Kankaanpää. When this sand is heated, using a simple heat exchanger buried in the middle, this device is capable of storing an impressive 8 megawatt-hours of energy, at a power rating of 100 kW, with the sand heated to around 500 -600 degrees Celsius.
Instead of individual furnaces in each building, the heat is generated at a central location and distributed to homes, factories and businesses through a system of underground pipes and conduits.
It is a very efficient system.
The researchers say it could help solve the problem of how to store renewable energy, such as wind and solar, since it can be used when the sun isn’t shining or the wind isn’t blowing. The sand, which can reach temperatures of 600°C, offers an alternative to lithium-ion batteries, which rely on expensive and relatively scarce metals and can only store a limited amount of energy.
“It’s really easy to convert electricity into heat,” says Markku Ylönen, CTO of Polar Night. “But going back from heat to electricity, that’s where turbines and more complex things are needed. As long as we use heat as heat, it’s still very simple.” The company claims an efficiency factor of up to 99 percent, the ability to store heat with minimal loss for months, and a lifespan of decades.
Currently, the battery powers the district’s central heating system. When energy prices are higher, the hot air from the battery can be used to heat water and then pump it to offices and homes in the region.
“The hot water from the storage is mixed with the main line, so we will provide a fraction of the heat needed to keep the city warm. The fraction varies according to the time of the year, since the heating load of the district heating network depends to a large extent on the ambient temperature”, they explain from Polar Night.
The researchers are thinking about how they can scale up their idea and also use it to generate electricity and heat. Polar Night Energy says it can design a sand battery for every need, from a single building to an entire city. Each system is individually tailored to customer requirements and designed based on simulations using COMSOL Multiphysics software, 3D transient heat transport models, and real-life input and output data. Systems can be buried underground to preserve space if project surface area is limited and each system is fully automated.
Referencia: Polar Night Energy
