Pedal Power

[Peter Owen]

One of my recurring New Year resolutions is to get a bit fitter so, having yomped up a mountain (read large hill!) yesterday, today I dusted off my fitness bicycle cum rowing machine and spent a life threatening 40 minutes pedalling away for nine miles and, apparently burning off some 300 calories.

Now this seemed like an effort of some consequence to me and I'm wondering if anyone can translate it into electrical power terms and compare it with the output of a diesel, wind or other on-board power generation system. Quite probably inconsequential, I know, but it would certainly help me get a better fix on what all this power stuff means - yet another of my (new) New Year resolutions!

Thanks for your help; see ya!

[Trim50]

I'm guessing that your calorie counter is telling you how many food calories you have burned off during your work-out. As such, 1 food calorie = 1000 thermal calories = 1.1627 Watt-hours of energy for a total of 348.8 Watt-hours of energy. This is enough to power a standard 32"lcd tv for a couple hours or chill your ice box for the day (as long as it is already cold) or heat a small pot of coffee.

For comparison, 1 horsepower = 746Watts. However, due to mechanical efficiencies, it typically requires 2 horsepower to generate 1000 Watts of electricity using a diesel genset. So, a 7 hp, single piston, Kubota diesel can produce the same amount of energy you burned in 40 minutes in approximately 5 minutes.

Even so, the calorie counter isn't considering efficiencies and speed necessary to generate electricity via a generator. I would estimate that you would lose 30 - 40% efficiency through gearing and friction to drive a generator to give you a grand total of 210 - 240 Watt-hours of equivalent electrical energy for your 40 minute workout. This would give you lukewarm coffee or barely enough electricity to watch you favorite episode of Lost.

[Trim50]

Peter,

Sorry man...with further research, it is worse than I thought. Apparently a human on a bicycle is only 25% efficient at generating electricity...you only produced 88 Watt-hours of electrical energy. If you get a small tv you may be able to finish the episode of Lost.

FYI, 1 slice of pizza contains approximately 344 food calories.

[Peter Owen]

Thanks Trim. That certainly put things in perspective. I wasn't actually thinking about turning any boat that I get to own into a pedalo but any idea how the price of diesel compares to that of pizza - I guess plain Margarita would do?

See ya!