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Soon Windows May Generate Solar Power Too

by Marguerite Darlington
March 17, 2017 | Our Future

When most people hear the word "solar power," they typically picture clunky, awkward solar panels that are as much of an eyesore as they are energy efficient. Tesla has gone a long way to change that perception with its well-designed solar roof tiles, but there's something even more innovative that's being developed by scientists across the globe: windows that generate solar power.

How is that even possible?

Photovoltaic windows—windows that can collect solar energy—are the next frontier in renewable energy technologies. Why? Because they significantly increase the surface area of the building that generates energy without making the building look weird or otherwise unattractive. They blend invisibly into the building, providing energy as well as a window to the world.

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But now scientists have come up with something even better. Researchers at the University of Minnesota and University of Milano-Bicocca have developed and demonstrated a new material—high tech silicon nanoparticles—that are a giant step forward toward windows that efficiently generate solar power. So cool. Even the Department of Energy is excited.

Invisible particles, invisible light

In an article published in Nature Photonics, the researcher team developed technology to embed the silicon nanoparticles into "efficient luminescent solar concentrators" aka LSCs, which are the development that will make windows that efficiently collect solar energy possible. When light shines through the surface, the useful frequencies of light are trapped inside and concentrated to the edges where small solar cells can be put in place to capture the energy.

"Most of the light that is absorbed is invisible, in the ultraviolet frequency," said Samantha Ehrenberg, a graduate research associate at the University of Minnesota College of Science and Engineering.

Once the light is absorbed, it is then redirected back out of the nanoparticles—or luminesced—as near infrared light, which is also invisible to the naked eye, according to Ehrenberg. The redirected light is then available to be converted into energy. Regular silicon particles can't perform this trick, only silicon nanoparticles.

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“In our lab, we ‘trick’ nature by shrinking the dimension of silicon crystals to a few nanometers, that is about one ten-thousandths of the diameter of human hair,” said University of Minnesota mechanical engineering professor Uwe Kortshagen, inventor of the process for creating silicon nanoparticles. “At this size, silicon’s properties change and it becomes an efficient light emitter, with the important property not to re-absorb its own luminescence.”

A new twist on solar power

The idea of solar concentrators and solar cells integrated into building design has been around for decades, but the silicon nanoparticles are the game changer. Until recently, the best results had been achieved using technology based on either potentially toxic elements such as cadmium or lead or rare substances used by so many technologies that it's not clear how long they will be available.

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While most of the light concentrated to the edge of the silicon-based LSC is invisible, we can better see the concentration effect by the naked eye when the slab is illuminated by a “black light.” Photo by University of Minnesota.

"Silicon is the second most abundant element in the Earth's crust," said Ehrenberg. "It's totally natural and nontoxic. We use a powder of a very tiny crystal that ends up looking like a dye or a gel coating on the window if it's very concentrated."

The silicon nanoparticles are produced in a high-tech process using a plasma reactor and formed into a powder. That powder is part of the window's surface. But how well do windows covered in powder work? Just fine, according to Ehrenberg.

"If you imagine how big a soccer ball is, and then you imagine it next to the size of the planet Earth, that's how small a nanoparticle is," said Ehrenberg. "We use the powder like a dye or a gel coating. It's still completely transparent.

Capturing more energy for a fraction of the cost

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University of Minnesota researcher Samantha Ehrenberg uses a plasma reactor to create silicon nanoparticles that are the key ingredient in the solar concentrators. Photo by University of Minnesota.

Researchers say the this new technology can improve the efficiency of photovoltaic windows significantly: they will be able to capture more than 5 percent of the sun’s energy at unprecedented low costs.

So how long until you can walk into Home Depot and buy windows for your home that will reduce your power bill?

"It's hard to say because it really depends on the technology, how easy it is to implement, and the demand for it," Ehrenberg said. "But our hope is that it would be available for consumers in three to seven years."

Marguerite Darlington
Marguerite Darlington has worked in digital marketing and media since 1999, supporting brands like The New York Times, The University of Chicago Booth School of Business, The University of Wisconsin–Madison’s Wisconsin School of Business, Jessica Simpson, ALDO Shoes and various independent entertainment properties. She joined Twin Cities Public Television as Rewire Director in June 2016.
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