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NREL: SunStop Window Technology Ready for Market

Sunspot window solar technology Electrochromic windows—which use a jolt of electricity to go from clear to dark—have been available for decades, but an NREL-developed technology is poised to move the industry forward. Photo credit: Dennis Schroeder / NREL

Window glass that can tint on demand, in response to the application of an electronic charge, has been available for some time. But many pricey, commercially-available materials can block only the visible wavelengths of sunlight, allowing the heat-producing component to pass through. However, recent developments in electrochromic windows also enable selective blockage of near-infrared light.

Now, the US Department of Energy’s (DOE) Colorado-based National Renewable Energy Laboratory (NREL) has developed a new technology for smart windows. And serial entrepreneur Loren Burnett has struck a deal with NREL to commercialize the research through his company e-Chromic Technologies, Inc.

The NREL-developed technology called ‘SunStop’ is expected to lead to a flexible film that can be affixed to the interior of an existing window and connect wirelessly to a controller. Once activated, the film will make the window appear reflective from the outside, while scattering reflected heat and light in all directions. Robert Tenent, a senior scientist in NREL’s Chemical and Materials Science Center, said in a press release issued by NREL that the new technology would likely allow significant energy savings over existing electrochromic windows.

Unlike current options, which require customers to replace all existing windows to adopt the new technology, SunStop can fit over an existing window. The film’s position on the window interior will protect it from the elements, and be easier to install.

When seeking a technology with a potentially huge market that wouldn’t take vast time and money to turn into a product, Burnett saw the value in the still-rough technology that was a finalist for the 2015 R&D 100 Awards, or the ‘Oscars of innovation.’ He capitalized on the Obama administration’s Startup America initiative, which simplified the process for him to gain access to NREL’s intellectual property, including an exclusive license for the patents involved.

The technology works similarly to a lithium-ion thin-film battery: Lithium ions move back and forth between conductor layers, creating a charge. A voltage applied to the conductor layers triggers the formation of a reflective metal layer. During initial development of a thin-film device with a reflective layer hypothesized to work in electrochromic windows, applying electricity caused the device to go into a reflective state that could not be reversed. It turned out that the lithium was not compatible with transparent conductor layers.

So the NREL team, consisting of Tenent, Tim Snow and David Alie,  along with e-Chromic’s Judy McFadden, developed a new transparent conductor. The thin metal layer allows allows electrical charge to pass through while remaining transparent, and the reflective state can be turned on and off. “That was the big jump, going from a battery to something you could actually see through,” Tenent said in the NREL article. Proof-of-concept demonstrations showed how it would work sandwiched between glass and as a flexible film.

Burnett, who runs e-Chromic from Colorado, plans to roll out the SunStop technology first to commercial buildings and eventually to residential customers, and intends to have the first product ready in 2017. But first, he is negotiating with an international automobile manufacturer who is interested in embedding e-Chromic technology directly in the windscreens to reflect infrared. Energy that previously would have been used to heat or cool the car would remain in the battery.

How quickly the product catches on will depend, of course, on the price. In the NREL article, Tenent noted that industry surveys and modelling analyses have indicated that prices for these types of windows would have to fall significantly before they could receive widespread market acceptance.

With angel funding and venture capital investment, Burnett continues to work on the technology with a private laboratory in California and “fight for a market share” in an industry that analyst firm NanoMarkets estimated will generate more then $3 billion in revenue by 2022.


About Rachel Berkowitz (5 Articles)
Rachel Berkowitz began her science writing career as the founding contributor to Physics Today's 'Down to Earth' column from 2011-2014. After completing her Ph.D. (2013) in geophysics in Cambridge, England, she took a science writing/communications position at the Lawrence Berkeley National Laboratory. She now divides her time between working on an artificial intelligence start-up company, called i2k Connect, and writing for scientific publications based in the US and Europe. Please visit www.rberkowitz.net to learn about current publications and projects.
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