Today I was talking to the Bicycle Man. You ever meet one of those elderly academic gentlemen who knows nearly everything, and can figure out the rest in picoseconds? Well, the Bicycle Man's father is one of those. The man made a bundle of money by patenting a specific form of the linear air track with a triangular shaped top to it, and donated half of that money to build the observatory at my undergrad school, which he proceeded to do with his own hands.
Well, the Bicycle Man is just as much a genius when it comes to bikes, but he's recently been working with some engineering students at the local University. A couple of them had a really awesome idea. Piezoelectric crystals are crystals that vibrate when a current is applied (I believe this is how most watches work these days), and apparently can also do the opposite and create a charge when vibrated. This particular group wanted to cover a wall with them and use sound to generate electricity to power things - it'd essentially be a solar panel with sound rather than light, or maybe a sonar panel.
And here's where Bicycle Man Sr.'s genius comes in: in the time it took him to blink he announced to Bike Man Jr. that it wouldn't work. Why not? you ask. B/c he quickly calculated that normal sound waves contain only something like 1W/m2 of power, and therefore you'd need a prohibitive amount of the sonar panels to get out any useful energy, even if we assumed perfect efficiency! Too bad, it was a great idea.
My prediction for the future though is that we will start lining the outsides of houses with solar panels. But it will take a while until the process of building them becomes cost effective enough that people are willing to do it.