How the sand battery that stores green energy produced by wind turbines and solar panels works / Four young engineers think they have found an answer to one of the biggest challenges of green energy

At the end of a winding tree-lined country road in western Finland, four young engineers think they have a possible answer to one of the biggest green energy challenges.

The challenge is to ensure a constant supply of renewable energy throughout the year, during the change of seasons and changing weather conditions. The answer, found at the Vatajankoski power plant, located 270 km northwest of the Finnish capital Helsinki, is extraordinarily simple, abundant and cheap: sand, it transmits BBC.

The Vatajankoski power plant houses the world’s first commercial-scale sand battery. Completely enclosed in a 7 meter high steel container, the battery consists of 100 tons of low quality construction sand, two district heating pipes and a fan. The sand becomes a battery after being heated to 600 ° C using electricity generated by wind turbines and solar panels from Finland, brought by Vatajankoski, the owners of the plant.

Renewable energy powers a resistance heater that heats the air inside the sand. Inside the coil, this hot air is circulated by a fan around the sand through heat exchange tubes.

Thick insulation surrounds the sand, keeping the temperature inside the battery at 600 ° C (1,112 ° F), even when it’s freezing outside. “We don’t want to lose heat; the average winter temperature is below 0 ° C (32 ° F) in Kankanpää, ”says Ville Kivioja, lead researcher at Polar Night Energy, which monitors battery performance online.

The battery stores 8 MWh of thermal energy when fully charged. When the demand for energy increases, the battery discharges around 200 kW of energy through the heat exchange pipes – this is enough to provide heating and hot water to around 100 homes and a public swimming pool in Kankaanpää, integrating energy from the grid. The battery charges overnight when electricity prices are lower.

It’s a low maintenance system, says Kivioja. The company uses cheap, low-quality sand rejected by builders instead of high-quality river sand, which is used in large quantities for construction, leading to a global shortage.

“There is no wear on the tubes [de schimb de căldură] and sand. The fan is the only moving part and is easy to replace if necessary, “says Kivioja.

Sand is a very efficient means of retaining heat over a long period of time, storing energy for months. And there are other benefits. “Sand has a very long life: it can heat up and cool down any number of times,” says Kivioja. “It will get denser after a while, so it needs less space. At that point we can add more sand. “

The sand battery developed by Tommi Eronen (right) and Ville Kivioja (left) provides enough heat for around 100 houses and a swimming pool in Kankaanpää.

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