A recent /. post pointed to an article about a new type of photovoltaic device (solar pannel) that is somewhat transparent and can function as a glass covering much like modern skyscrapers are clad with. It allows 10% of the suns rays to pass (which doesn’t sound like much.) and can also function as a video screen (which the 10% thing and the light absorbtion of the PV would hurt the performance of.) I’m not sure about the video part, but otherwise they seem pretty cool.