OK, fine. So I fully admit that this one is a bit lightweight in comparison to issues which I would normally write about. It's certainly not as complex as T. Boone's shenanigans.
Nonetheless, being an avid tennis player anything that could green-up my favorite sport attracts my interest. And since I consider human-powered devices to very nearly be alternative energy devices in an age when sweeping a few leaves from the sidewalk seems to require a gas-powered leaf blower in my neighborhood, I feel justified.
This bit of Rube Goldbergery is created by Daniel Bauen and is "Both cleanly powered and built from 2 recycled bicycles, scrap steel and wood, leaking 5 gallon water jug and a lacrosse stick, our pedal powered tennis ball launcher is a unique innovate or die entry. It allows players varying in skill levels to practice to be better at both tennis and cycling."
Based on the video above it certainly seems to work as designed, and since every other tennis ball machine runs off a battery—which most likely ends up being charged from non-renewable sources—this is a comparatively green option. However, I have to ask: Since you have to have another person down the other end of the court to pedal the device, why not just have them feed the balls out of hand using a racquet? I always thought that the whole point of these things is so that you can practice by yourself.
Wouldn't a more practical solution be to lobby your local council (or take up a collection from local players) to install a small solar panel at the courts to charge the battery on your existing ball machine? Kudos to Daniel on ingenuity though.