This invisible film could let your windows produce power

Source: Christa Marshall, E&E News reporter • Posted: Monday, October 30, 2017

See-through materials placed on windows or other glass surfaces could harness as much solar power as traditional panels and potentially be used everywhere from electric cars to skyscrapers, according to a study this week in Nature Energy.

Michigan State University engineers reported that transparent solar devices could produce power from the estimated 5 billion to 7 billion square meters of available glass surface in the United States, which receive enough solar energy to provide 40 percent of national electricity.

The technology could operate while being invisible, allowing it to be placed on infrastructure or windows without affecting natural lighting or altering the view, the review study said.

“These are not being manufactured commercially yet but they are on their way. We expect that they will be lower cost than traditional modules by piggybacking on the existing structural infrastructure,” Richard Lunt, study co-author and associate professor of chemical engineering and materials science at Michigan State University, said in an email.

The materials developed in the lab contain man-made molecules that harvest only ultraviolet and near-infrared light and allow visible light to pass through. Theoretically, they could be deployed anywhere there is glass, such as on the sides of buildings, vehicles, awnings, mobile electronics or even billboards, said Lunt.

“Once you realize you can make clear solar panels, it really sparks the imagination. They could be all around us without us even knowing, turning our cityscapes into solar farms,” he said. “We expect to see these applied in buildings in the next couple of years.”

The Michigan team started a company, Ubiquitous Energy Inc., that is working on commercializing transparent solar materials, he said. The technology utilizes thin films that can lay over glass or plastic. In the lab, modules powered small fans and other equipment.

Previous companies have tested transparent photovoltaics by punching holes in traditional panels, but the transparency of those devices was not enough to allow them to blend into architecture, and they were still bulky like rooftop units, according to Lunt.

Robert Tenent, an emerging buildings technologies expert at the National Renewable Energy Laboratory, said it is “very reasonable” to see a technology like this make it out of the lab.

“Some of what is going on has similarities to existing dynamic ‘smart’ window technologies, which are currently emerging in the marketplace, albeit slowly. Growing adoption in that market, should help ease things for the photovoltaic window concept,” Tenent said.

Tenent’s NREL colleague Lance Wheeler agreed there is commercial potential, although buildings would need to be better designed to take advantage of this type of technology at scale. That makes the automotive industry “a nice fit in the interim,” Wheeler said.

NREL is working on three different projects on transparent solar. Tenent said most of the major architectural and automotive glass companies NREL has spoken with are “very interested.”

Yet there is skepticism. Current applications at Michigan State are about 5 percent efficient, meaning they have been able to demonstrate turning that level of solar energy into electricity. Comparatively, traditional solar panels are 15 to 18 percent efficient.

Jenny Chase, an analyst at Bloomberg New Energy Finance, said transparent materials would have to be “really cheap” to make up for the lower efficiency. There is also not a shortage of roof space right now for traditional panels, she said.

With 5 percent efficiency, “is it worth putting the wires in?” she asked.

Lunt said current technology is at about a third of its potential, meaning it could reach the current efficiency of rooftop solar with more research.

Research outlined in the Nature Energy study was funded by the National Science Foundation and the Department of Education.