When Is A Window Not Just A Window?

When is a window just not a window? When it’s a solar energy generator, thanks to solar cells crafted of carbon nanotubes which are so transparent they can be sprayed on window glass and so flexible they can be woven into fabric like window curtains or drapes.

Well, that’s not true either, since the solar cell-coated windows still act as windows, according to researcher/inventor Dr. Mark Bissett of Flinders University School of Chemical and Physical Sciences in Adelaide, South Australia. But these windows, besides offering light, fresh air and a view, also provide energy via the photovoltaic process. And, since windows are up to 75 percent of a modern building’s exterior, the amount of potential energy generated is enormous.

Dr. Mark Bissett

Image via Flinders University

The process of using solar-energy delivery materials on building surfaces is known as BIPV, for Building Integrated Photovoltaics, and promises to provide a wealth of clean, renewable solar energy for the world’s cities. The two drawbacks to traditional solar energy are cost and deployability. Crystalline silicon (c-Si) is tremendously expensive, and it is difficult to affix solar panels to the sides of tall buildings, not to mention the difficulty of making hundreds of the connections needed to deliver the energy inside where it is needed.

Cheap, energy-efficient carbon nanotubes are already being looked at to replace metallic wiring products like copper and silver. Moreover, the conductivity-to-weight ratio (of carbon nanotubes) is greater than most metals, and second only to sodium, the metal with the highest specific conductivity, according to Yao Zhao, the author of a study on specific conductivities at Rice University.

And, while Dr. Bissett doesn’t anticipate BIPV solar energy ever being enough to offset the total energy burden of an office building or skyscraper, adding transparent solar cells to the glass when it is installed (or replaced) could make a very large dent in energy costs (and carbon emissions). All for a process not much more complicated than tinting window glass, using a material which Dr. Bissett expects to be commercially available within a few years time.