The fact that human power using the major muscle group, (legs) can produce 75 watts on a sustained basis leads us to several interesting conclusions:
1. Human muscle power can never provide more than a tiny fraction of the power that each American typically uses. Assuming that a person could ride an hour a day with health benefits, but much more than that would seriously interfere with other activities, we can expect a person to produce 75 kWh of energy a day. A very conscientious American consumer is proud to say that "My family of four uses, on average, 4.7 kilowatt hours (kWh) of electricity per day." [1] That is 1.175 kWh per person so the hour's exercise would produce 4% of her energy needs. This shows that a person who wants to live off of human muscle power must cut their energy consumption by an additional 96%. Another way to look at this is that based on grid supplied power, a person riding a bike would produce about 1 cent worth of power per hour, compared to buying grid power. Make that 2 to 3 cents per hour in places where power is very expensive. Do you see why our wages and standard of living are so greatly tied to cheap energy availability?
2. This analysis shows why the standard of living is so low in countries that depend on human muscle or even animal muscle for their energy. This means that we Americans need to learn to live on much less power than we do or else find a way to provide clean and cheap energy for ourselves and the world. (Windmills and solar are at best a limited solution).
3. Using energy wisely could consist of biking to work when weather permits. 75 watts powers a bike rather nicely, compared to the 5-8 KW for an electric car. [2] You could ride the bike to work, (1/2 hour each way at 15 MPH), or you could generate 2.5-4 kWh of energy on your home bike generator, and use that power to drive to work, (15 minutes each way). But to generate that much energy would take you 48 hours on the bike. The dramatic difference is because riding the bike avoids hauling a ton or more of steel and plastic back and forth to work.
4. Exercise machines that actually consume power seem to be a very wasteful approach. I suggest that one use the bicycle generator to power a TV set, (75 watts is about what they consume), and thus only watch TV when the bike is being ridden. That would provide a motivation for exercise and limit the time one spends on mind numbing entertainment.
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