Chicago's Willis Tower, formerly known as the Sears Tower, has replaced nearly 20 square feet of glass on the south side of its 56th floor with transparent solar windows as part of a pilot project.
The glass, created from a special photovoltaic glass by Pythagoras Solar, can generate the same amount of energy as a standard roof-mounted PV panel – about 13 watts per square foot.
Expanding the transparent PV glass units onto other sides of the building could potentially generate up to 2 megawatts of solar power per year. However, there are currently no plans to expand the scope of the pilot project into a large-scale installation because the pilot project is not yet complete.
"We're getting very consistent and positive results and it's generating what we expected," says Udi Paret, Pythagoras's vice president of business development. "It's progressing very well."
The glass diffuses the light as it enters the building, which reduces the amount of heat entering the building and cuts down on the cooling costs for the 56th floor.
"A net-zero energy building is the ultimate goal," Paret says. "The solar window is a significant step."