Over the past several years, a number of companies and institutions have been developing technologies that could allow windows to double as solar panels. These have included EnSol’s metal nanoparticle-based spray-on product, RSi’s photovoltaic glass and Octillion’s NanoPower window. Last September, Maryland-based New Energy Technologies joined the party by demonstrating a 4 x 4 inch (10.2 x 10.2 cm) prototype of its SolarWindow product. This Tuesday, the company unveiled a working 12 x 12 inch (30.5 x 30.5 cm) prototype, which takes it significantly closer to becoming commercially-viable.

As is the case with EnSol’s technology, SolarWindow incorporates a spray-on photosensitive film. It is applied at room temperature, allows the window to remain transparent, and is capable of generating electricity from both artificial and natural light – the company's intention is that it would be used primarily on the exterior of windows, where it would be exposed to sunlight.

While the details of how the system works aren’t being fully disclosed, the company has stated that the film “replaces visibility-blocking metal [used in most solar panels] with environmentally-friendly and more transparent compounds."

New Energy Technologies claims that SolarWindow is superior to similar products in that its coating doesn’t have to be applied at a high temperature or in a vacuum, it is less than one-tenth the thickness of other “thin films,” and the solar cells used in each window are the world’s smallest functional models – less than a quarter the size of a grain of rice. It is also said to outperform other technologies by up to ten-fold when it comes to generating electricity from artificial light.

Although precise figures on efficiency aren’t available, the company estimates that when applied to the facade of an office tower, its product could generate over 300 percent the energy savings of traditional rooftop panels.

New Energy Technologies has also received some publicity for its experimental MotionPower system, that generates power from traffic driving over small plates embedded in roads.