Last Updated 2/12/2003
Overview
Gilligan used it to power the radio, phonograph, and everything else on the island. The reality is that if you're an Olympic cyclist, you might be able to supply .75 KWH indefinitely. Average people can produce less than a third of that. However it is a sustainable source of energy as long as you have food and water.
Energy Available
You can't get out more than you put in (that whole Conservation of Energy thing), so you'll either have to lose weight or eat more when you do this. Based on a 2000 calorie diet, you can produce (or in my case, store) a maximum of 8372 J of per day, or 8.372 KWH per day. Assuming some loss in joint friction and taking into account the energy required to warm your food up to body temperature and process it, losses, etc, that doesn't leave much left over. Good cyclists require 5-10,000 calories a day.
250WH for only as long as you're riding the bike isn't much energy. Even if you rode 12hrs (not likely in my case), you'd produce 3KWH of energy. It would take 5.5hrs to charge a deep cycle battery.
Efficiency
This would seem not to be terribly efficient to me. I haven't seen numbers, but I'd guess that it's less than 25% efficient.
Energy Storage
Energy can be stored in the body indefinitely. If you don't believe me, just look at my ass and you'll change your mind.
Products
WindStream Power Products makes two models - a standalone model good for 125W and a bike stand they say is good for up to 300W. I'm thinking of getting one of these instead of an exercise bike.
Treadmills should be another good source of energy. They already have motors connected to the tread, and it may be possible to convert (or replace) these motors to produce electrical energy.
Ideas
I imagine that adding flywheels (or weight to the bike wheel) would be a good way to simulate actual cycling and to stabilize the output energy.