Chicago's Willis Tower (formerly the Sears Tower) is experimenting with solar windows, and if the pilot works out, they plan to scale to 2 megawatts (MW).
Two windows on the skyscraper's 56th floor were replaced with solar windows developed by Pythagoras Solar last year. Each generates 120 watts of electricity - about the same as a typical solar cell on a roof.
The technology simply sandwiches a solar cell between two panes of glass, and a reflective prism directs sunlight onto the solar cell while also letting daylight through.
Energy harnessed by the transparent solar windows reduces heat gain, and therefore cooling costs as well as generating electricity.
Founded in 2007, Pythagoras Solar makes a solar window that delivers energy efficiency, high power density and optimized daylighting. General Electric awarded Pythagoras with a $100,000 grant to further its technology.
Last month they put 20 windows at the Wisconsin headquarters of Organic Valley, the largest organic farmer coop in the US.
"We hold ourselves to a high standard when it comes to sustainability - it is embedded in our culture. By adopting these innovative windows, we are also helping to pave the way for this technology, which has the merit to become a standard in the design and construction of net zero energy buildings," says Cecil Wright, VP of Sustainability and Local Operations for Organic Valley.
Since solar windows provide diffused light, rather than glare, the company can turn off artificial lights, and since less heat penetrates, they're reducing the energy needed to cool the building.
Another really interesting solar window technology being developed by New Energy Technologies (NENE.OB) and National Renewable Energy Lab (NREL) can produce solar energy in both natural and artificial light. It can power indoor lights, appliances, and even the rotor blades on a small helicopter.