When windows turn into power plants!

Researchers at the Massachusetts Institute of Technology are working on a new system through which the entire surface area of a building's windows could be used to generate electricity, without interfering with the ability to see through them.

The key technology is a photo-voltaic cell based on organic molecules, which harnesses the energy of infrared light while allowing visible light to pass through.

Coated onto a pane of standard window glass, it could provide power for lights and other devices, and would lower installation costs by taking advantage of existing window structures.

Vladimir Bulovic, Professor of electrical engineering in the Department of Electrical Engineering and Computer Science has developed a transparent photo-voltaic system with Richard Lunt, a postdoctoral researcher in the Research Laboratory of Electronics at MIT.

Bulovic says while the technology, which is still at an early stage, may not be the ultimate solution to all the nation's energy needs, it is part of "a family of solutions" for producing power without greenhouse-gas emissions.

"It is attractive, because it can be added to things already being deployed," rather than requiring land and infrastructure for a whole new system.

Using the window surfaces of existing buildings could provide much more surface area for solar power than traditional solar panels, Bulovic said.

In mornings and evenings, with the sun low in the sky, the sides of big-city buildings are brightly illuminated and that vertical "footprint" of potential light-harvesting area could produce a significant amount of power, he said.

Previous attempts to create transparent solar cells have had extremely low efficiency - less than one per cent of incoming solar radiation is converted to electricity.

Some have blocked too much light to be practical for use in windows.

But the MIT researchers have been able to find a specific chemical formulation for their cells that, when combined with partially infrared-reflective coatings, gives both high visible-light transparency and much better efficiency than earlier versions.

The technology can be put to use in new buildings or where windows are being replaced.

Adding the transparent solar cell material to the glass would be a relatively small incremental cost, since the cost of the glass, frames and installation would all be the same with or without the solar component, the researchers said.

With modern double-pane windows, the photo-voltaic material could be coated on one of the inner surfaces, where it would be completely protected from weather or window washing.

Only wiring connections to the window and a voltage controller would be needed to complete the system in a home.

The researchers expect that after further development in the lab followed by work on manufacturability, the technology could become a practical commercial product within a decade.

In addition to being suitable for coating directly on glass in the manufacture of new windows, the material might also be coated onto flexible material that could then be rolled onto existing windows, Lunt said.