Matthew Miller

mrmiller@lsj.com





EAST LANSING – The exceptional thing about Richard Lunt's clear pieces of plastic is that they don't look like anything more than clear pieces of plastic.

What they are is a step toward solar-powered smartphones and tablets that never need to be plugged in and buildings that harvest a sizable chunk of the electricity they use, a technology for harnessing the energy of the sun without blocking the view.

"I grew up just outside of Boston, but I went to the city a lot," said Lunt, who is a professor of chemical engineering and materials science at Michigan State University. "When you look around a big city, there's a lot of glass."

And a lot of surface area that could be used to produce energy, given the right technology.

Lunt and another researcher designed a transparent photovoltaic cell in 2011 while he was a postdoctoral researcher at the Massachusetts Institute of Technology. It was fabricated with organic semiconductors that absorb energy from infrared light, a part of the light spectrum that we can't see with the naked eye, and designed to be coated onto standard window glass.

The material he's working on now is meant for a less expensive sort of device known as a luminescent solar concentrator.

Germany's significant investment in solar technology over the past decade and China's rush to serve that market have reduced the cost of photovoltaic cells, but they're still not cheap. Solar concentrators can be. They're basically sheets of plastic that capture some fraction of the solar spectrum and radiate it out as a glow toward their edges where it is converted into electricity by photovoltaic strips.

The technology dates back to 1970s, but earlier iterations used dyes to absorb the light. They never caught on, in part because few people wanted to spend their days behind colored windows. Lunt keeps a bright pinkish-orange example in his office for inspiration.

His plastic uses both organic salts and nano­structured materials precisely tuned to absorb light from the ultraviolet and infrared parts of the spectrum and to radiate it out at different but equally invisible wavelengths.

The efficiency is just 1 percent, but Lunt thinks it can go as high as 7 percent. The efficiency of conventional silicon solar cells is closer to 18 percent, but the solar concentrators would have other advantages.

"The system should be exceptionally low cost due to its simplicity," Lunt said, easy to fabricate with existing industrial processes, able to piggyback on the installation processes that already are part of putting up a building. And, of course, transparent.

"People have done building-integrated photovoltaic since the 1990s," said John Perlin. He is the author of "Let It Shine: The 6000-Year Story of Solar Energy" and is overseeing the installation of solar cells at the University of California, Santa Barbara.

"They've done overhangs and canopies over rooftops and actually putting solar cells in various aesthetic ways into the windows."

But the Holy Grail, he said, has been "a clear solar cell-type structure to convert sunlight into electricity that also would reduce the heating of the building," by blocking infrared rays, a solar cell that could be placed over a window, a more efficient version of what Lunt already has in his lab.

Windows that harvest solar energy are unlikely to be a sole solution to our energy needs, Lunt said. "It will probably be one of several key tools in making our world more renewable."

But the impact could be sizable. "In some of the early simulations that we've been working on to look at the impact, depending on the shape and the orientation and the location of the building," he said, "it looks like it could be anywhere from 10 to up to 50 percent of a building's energy demand that you can get in both the electricity generation and the heat management savings."

After developing the transparent photovoltaic cell at MIT, Lunt co-founded a company called Ubiquitous Energy. The firm, based in California, now is working to commercialize the solar concentrator.

Lunt estimates that it could be on the market within five years.

"One of the hardest challenges that we have now," he said, "is keeping up with the excitement."

At a glance

Michigan State University professor Richard Lunt has created a solar concentrator that has one distinct advantage over previous versions of the technology: it's transparent.

The concentrator uses plastic impregnated with organic salts and nanostructured materials precisely tuned to absorb light from the parts of the spectrum that are invisible to the human eyes and to radiate it out at different but equally invisible wavelengths.

The technology is a step toward solar-powered smart phones and tablets that never need recharging and buildings that harvest a sizable chunk of the electricity they use.