I just thought had a slightly humorous idea for a green technology solution.
Think of your local Gym, lots of people running, cycling lifting weights etc. What if all these various exercise machines were designed to harvest energy. How much do you think a gym might save on it's energy bill, probably not a lot, but I wonder if anyone has everworked out what the average available energy per square foot is generated by a gym. Could be a great differentiator for exercise equipment manufacturers.