Power/Performance Bits: Sept. 20

Energy-harvesting fabric; large-scale artificial photosynthesis.

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Energy-harvesting fabric

Researchers at the Georgia Institute of Technology and Chongqing University in China developed a fabric that can simultaneously harvest energy from both sunshine and motion.

The fabric, just .32mm thick, was constructed using a commercial textile machine to weave together solar cells constructed from lightweight polymer fibers with fiber-based triboelectric nanogenerators.

Fiber-based triboelectric nanogenerators capture the energy created when certain materials become electrically charged after they come into moving contact with a different material. For the sunlight-harvesting part of the fabric, the team used photoanodes made in a wire-shaped fashion that could be woven together with other fibers.

“The backbone of the textile is made of commonly-used polymer materials that are inexpensive to make and environmentally friendly,” said Zhong Lin Wang, professor at Georgia Tech. “The electrodes are also made through a low cost process, which makes it possible to use large-scale manufacturing.”

A bracelet made from fabric woven with special energy-harvesting strands that collect electricity from the sun and motion. (Source: Georgia Tech)

A bracelet made from fabric woven with special energy-harvesting strands that collect electricity from the sun and motion. (Source: Georgia Tech)

In one experiment, the team used a fabric about the size of a sheet of office paper and attached it to rod like a small colorful flag. Rolling down the windows in a car and letting the flag blow in the wind, the researchers were able to generate significant power from a moving car on a cloudy day. The researchers also measured the output by a 4 by 5 centimeter piece, which charged up a 2 mF commercial capacitor to 2 volts in one minute under sunlight and movement.

While early tests indicate the fabric can withstand repeated and rigorous use, researches will be looking into its long-term durability. Next steps also include further optimizing the fabric for industrial uses, including developing proper encapsulation to protect the electrical components from rain and moisture.

Large-scale artificial photosynthesis

Scientists from Forschungszentrum Jülich designed an artificial photosynthesis unit, storing solar energy as hydrogen by splitting water.

Instead of individual components the size of a finger nail that are connected by wires, the researchers have developed a compact, self-contained system constructed completely of low-cost, readily available materials.

“To date, photoelectrochemical water splitting has only ever been tested on a laboratory scale,” said Burga Turan, a solar cell researcher at Jülich. “The individual components and materials have been improved, but nobody has actually tried to achieve a real application.”

With a surface area of 64cm2, the component is still relatively small. The design, however, is flexible. By continuously repeating the basic unit, it would be possible to fabricate systems that are several square meters in size. The basic unit itself consists of several solar cells connected to each other by a special laser technique. “This series connection means that each unit reaches the voltage of 1.8 volt necessary for hydrogen production,” said Jan-Philipp Becker of Jülich. “This method permits greater efficiency in contrast to the concepts usually applied in laboratory experiments for scaling up.”

The photosynthesis system of the Jülich solar cell scientists is compact and self-contained, and the flexible design allows for upscaling. (Source: Forschungszentrum Jülich)

The photosynthesis system of the Jülich solar cell scientists is compact and self-contained, and the flexible design allows for upscaling. (Source: Forschungszentrum Jülich)

At the moment, the solar-to-hydrogen efficiency of the prototype is 3.9%. “That doesn’t sound like much,” admits Turan. “But naturally this is only the first draft for a complete facility. There’s still plenty of room for improvement.” Still, the scientists point out, natural photosynthesis only achieves an efficiency of 1%. Becker is of the opinion that within a relatively short time the design could be increased to around 10% efficiency using conventional solar cell materials. However, there are also other approaches. For instance, perovskites, with which it is already possible to achieve efficiencies of up to 14%.

The design allows for the photovoltaic and electrochemical components to be optimized separately. The researchers patented the concept, which can be to all types of thin-film photovoltaic technology and for various types of electrolyser, and are working toward a market launch.

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