Little piece at National Geographic on the coming technology of transparent solar cells. These are thin organic coatings applied to glass windows that capture mainly ultraviolet and infrared light, so they appear clear. The best efficiencies achieved so far are in the range of 10 percent, compared to 22% for an off-the-shelf solar cell right now, and 33% in the coming generation of hi-tech cells. But the manufacturing process is much cheaper, and when you consider how many square miles of windows we have in the developed world, the potential to deploy this technology is vast. One idea is to coat the glass of smart phones this way, so they would trickle charge whenever exposed to light.
One thing I wonder about is how long these films last -- it would not be difficult to install coated glass panels when a building is first constructed, but if they have to be replaced every five or seven years that would be a big problem.