Bricks to batteries: how walls are used to store energy

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Brick buildings store the heat from sunlight and make for hot summer nights.

When the sun goes down, the bricks continue to glow. On summer nights as they do now, they ensure that cities do not cool down at night. This has already proven that the red brick is not only a good building material, but also an energy store - here in the form of heat.

Researchers at Washington University in St. Louis have now also used the stones to store electricity. "We bought bricks for 65 cents each at the hardware store," says study author and chemist Julio D'Arcy. The researchers then turned these into "intelligent stones" that can store energy and, for example, supply devices with electricity.

The study authors developed a special coating for this. It consists of nanofibers of an electrically conductive plastic (PEDOT) and penetrates the porous interior of the stones, according to the study, which was published in the journal "Nature Communications".

Rust as an aid

The conductive plastic network got into the stones via a detour. The researchers soaked their bricks in a liquid that contained components of the material. The iron oxide contained in the bricks - also known as rust - acted as a catalyst, so that the components of the liquid combined to form a solid plastic.

"The polymer layer stays in the brick and acts as a kind of ion sponge that stores and conducts electricity," says D'Arcy. The bricks could thus be used as batteries. According to the study, energy could be stored with this method in the future - especially if it is used extensively in house walls.

"PEDOT-coated bricks are ideal, for example, to power emergency lighting in a building," said D'Arcy. For this, solar cells could be connected to the stones. With 50 stones, emergency lighting could work for five hours.

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The red bricks supply the green light-emitting diode with electricity.

The study also produced a "proof-of-concept" that is proof of the basic feasibility of the brick energy storage system: The researchers presented a brick to which a green LED light is connected and is supplied with electricity. However, major tests are still pending.

Volcanic rock instead of bricks

In Germany too, companies and research institutes want to use stones as energy storage in order to advance the energy transition. Because an unsolved problem so far is the lack of electricity storage, which can store huge amounts of electricity on sunny days or in strong winds.

A team of researchers from Siemens Gamesa, the Technical University of Hamburg-Harburg and the local utility Hamburg Energie put Germany's first stone storage system into operation last year: 2000 cubic meters of natural stone were heaped up on the edge of the Port of Hamburg - mathematically a cube with an edge length of almost thirteen meters - to store wind power with it.

In doing so, generation is to be decoupled from consumption in order to mitigate fluctuation, for example due to calm or strong winds. However, the Hamburg warehouse does not use bricks, but around 1000 tons of volcanic rock.

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