Photo: Chris Barile

New ‘Smart’ Windows Could Help Consumers Cut Energy Costs

Stanford engineers find a quick way to darken glass.

By Diana Aguilera

Want a new way to make your house energy-efficient? “Smart” windows may be your answer. A recent window prototype developed by Stanford engineers can change from transparent to dark — and vice versa — in less than a minute, saving potential users up to 20 percent in heating and cooling costs.

“I think this is something people are going to love — the possibility that you could just push a button and have the tinting of a window change,” says Stanford professor of materials science and engineering Michael McGehee, senior author of a study, published in Joule in August, that explains how the 4-inch-square prototype works. The first author on the paper is Christopher Barile, a former Stanford postdoc who is now an assistant professor of chemistry at the University of Nevada-Reno.

Existing self-tinting windows can take more than 20 minutes to dim and lose their opaqueness over time, McGehee says. They also tend to be expensive and have a blue tint. Whereas those windows are made of materials that change color when charged with electricity, the new prototype blocks light when a small electrical current triggers the movement of a copper solution over its conductive glass plates. The advance in technology eliminates the blue tint, does not degrade and is cheaper to make.

Before scaling up, the researchers are working to expand the surface area of the windows and to reduce manufacturing costs. They expect the technology to be useful not only in homes but also in sunglasses, cars and airplanes, and they’re already in discussions with manufacturers about commercialization.

“Success came faster than we expected,” McGehee says. •