A lot of sunlight hits tall office buildings, only to go to waste.
Their relatively small roofs don't offer much space for solar panels. A solar array crammed onto the top of a typical office tower could produce, at best, a tiny fraction of the electricity the building and its tenants need.
But what if the building's windows could serve as solar panels?
Pythagoras Solar in San Mateo has developed a window laced with solar cells, a window that generates and saves electricity at the same time.
Thin horizontal rows of silicon cells embedded between dual panes of glass catch light from above. And through a trick of optics, the window blocks direct sunlight from entering the building, cutting the amount of power needed for air conditioning.
"Instead of heating the room, the light generates clean solar power," said Gonen Fink, chief executive officer of Pythagoras. "It's relatively simple and straightforward optics. The challenge is making everything work together."
The window works well enough that earlier this week, Pythagoras won an award from the "GE ecomagination Challenge," an effort by General Electric Co. and several venture capital firms to find and fund promising technologies. Pythagoras was one of five companies given an "innovation award," which comes with a $100,000 grant.
Not a lot of money, to be sure. For Fink, the award's true value lies in the recognition from GE, a company deeply familiar with all manner of energy technologies. Pythagoras has raised $11 million in capital from investors, including Evergreen Venture Partners.
"Mostly for us it's a validation of three things - that the window is unique, that it's feasible and it could have a big impact," he said.
The Pythagoras window belongs to a class of solar equipment known as BIPV - building-integrated photovoltaics. Other companies have marketed solar window awnings and photovoltaic roofing tiles.
"If you look at all the different parts of the building, from the pavement to the panels that make up the exterior to the windows - everything that receives sunlight is a potential solar collector," said Joel Makower, chairman of the GreenBiz Group, a media company focused on sustainable businesses. "And there's a tremendous amount of work, some of it in the lab and a little bit in the market, that's trying to tap into this."
Makower argues that the technologies for buildings, energy, data and vehicles are starting to blend together, a phenomenon GreenBiz calls "Verge." Buildings won't simply be consumers of energy - they'll be producers as well.
"We're definitely looking at buildings as net generators of electricity, at least during some parts of the day," he said.
Other companies are designing their own versions of solar windows. New Energy Technologies Inc., for example, is testing a way to generate electricity using a transparent chemical coating sprayed on glass.
The solar cells Pythagoras uses aren't transparent. Instead, they look like open venetian blinds. They capture about 14 percent of the sunlight's energy.
Fink won't reveal the system's cost per watt. But the company estimates that for a typical customer, the windows will pay for themselves within three to five years. Pythagoras already installed some of the windows at Chicago's Willis Tower, formerly known as the Sears Tower.
"The most important thing for us is the impact this could have," Fink said. "This could change the way buildings are being built."
