UC Berkeley, Lawrence Berkeley National Lab will one day make windows work like solar panels

BERKELEY, Calif. (KGO) -- A breakthrough by a UC Berkeley professor at Lawrence Berkeley National Laboratory could one day help tall buildings use dramatically less energy, by using their windows to generate electricity.

The research, funded by the U.S. Department of Energy, comes from the lab of chemistry professor Peidong Yang, who showed us some small squares of orange-tinted glass. One was hooked up to electrodes under a microscope, with a bright light shining on it.

"At a lower temperature, they are transparent," he said. "Basically, they are windows, transparent windows. Then, when the temperature is a little bit higher, they become colored."

Smart glass that darkens is nothing new -- Boeing's latest airplanes have it in place of mechanical shades on passenger windows. But that glass requires electricity. A voltage must be applied to get it to change color. Instead of using electricity, Yang's glass creates it.

"It's generating electricity, generating power," he said, showing us a voltmeter connected to the glass sample that was reading 1.2V -- about the same voltage as a rechargeable AA battery.

In the next room, Yang's research team demonstrated the way the crystalline structure of the coating on the glass changes with temperature. Heated up to about 100 degrees Celsius, the clear glass took 30 seconds to take on an orange tint and become ready to generate power. Placed in a damp box to cool off, the orange glass turned clear in about 10 seconds.

Yang said it's not hard to imagine the uses.

"As a transparent window, as a shade, and as a solar panel," he said.

While homes and warehouses can be covered in solar panels, tall buildings don't have all that roof space. But they do have big, beautiful windows, often covering nearly their entire surface. Yang says this kind of glass could one day be perfect for Dubai, where the buildings are tall and the summers are hot.

"In the earlier morning, it's a window that's transparent, then in the afternoon, when the temperature is a little higher, it automatically becomes a shade, meantime collecting electricity out of the solar radiation," he said.

One reason the material could be so attractive for building is that it's easy to make. The team demonstrated in the lab what could one day be done in a factory at much larger scale: applying a liquid semiconductor to a flat piece of glass, then spinning it rapidly to spread the solution evenly across the surface. It's a process also used in the making of computer chips.

Prof. Yang's team is already working to make the glass in different colors -- currently, an assortment of warm tones ranging from yellow to brown -- and get the material to start changing at a lower temperature -- about 50 degrees Celsius, to more closely match conventional solar panels.

There's one other change that will need to happen: the early samples of this smart glass are about 7 percent efficient at converting solar energy into electricity, Yang said. Today's best commercial solar panels are about 20 percent efficient.

While he hopes the new technology will match and even beat that number one day, Yang said given the energy smart tinted windows will save by reducing the need for air conditioning, the technology could begin to make commercial sense once it reaches efficiency levels above 10 percent.