If you've ever found yourself in the street with a dying phone and nowhere to power up, you'll be interested in this idea: charging stations, using photovoltaic cells, built into street signs and other existing infrastructure. Called "Street Charge," the proposed setup is the work of Pensa, a New York design group. Asking the question, "How can we use what's already here?", Pensa proposes to add thin solar cells to things like street signs, with USB outlets.
The idea has its weak points: it looks fragile, and would be vulnerable to vandalism as well as the elements. I'm not sure how much electricity the small cells could generate, and how many gadgets they could charge. A phone, computer or tablet needs to charge for longer than most would want to spend sitting on the street.
Considering how coveted the few outlets in airport waiting areas are, this could even create de facto hangout spots, especially since everyone would spend at least five minutes charging their gadget. Add a little table or a bench, a nearby food vendor, and you've got an impromptu cafe, free of charge and powered by the sun. We've considered the idea that "in the future, everything will be a coffee shop." Let's add the street corner to the list.