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Thursday, May 22, 2008


Today's lesson in innumeracy - the solution to global warming is not at hand (or at foot)

I was briefly extremely excited when I read this the other day in eWeek (rhymes, quite appropriately, with "geek") Magazine:
For three days, participants powered 21 bicycle stations to generate more than 12.9 megawatt hours of energy - enough to power more than 12,000 average American homes for an entire year.
Wow, thought I, the solution to global warming and the source of alternative energy is literally under foot (or, more accurately, under waist, in the quads and thighs). Hire the unemployed, or put the armed forces to good use, and we won't need any oil, coal, or nukes at all!

Then I decided to think about the story, unlike the editor who published what was certainly a press release from the company which sponsored this event. If 21 bicycle "stations" (more about that below) ridden for three days could power 12,000 homes, then they could power 4,000 homes with one day of riding, and just one bicycle station ridden for a day could power 200 homes for a year! You could power one home for a year with just 7 minutes of riding!

Really? That seems rather unlikely, doesn't it? Now you can get electricity from bike riding, for sure. If you ever watched the delightful "Living With Ed" [Begley, Jr.] show on TV, you watched him riding his bicycle while pronouncing, "I'm making toast!", as the electricity he generated was fed back into his (solar- and wind-powered) system. But generating enough electricity to run a toaster and enough to run an entire home are two very different things! I've also been told that some fitness centers in Japan are also "collecting energy" from their participants. But how much?

Research tells me that Lance Armstrong can sustainably generate 400 watts of energy. Let's be very generous and use that as our figure, although finding even one more human being that powerful would be hard. 400 watts times 72 hours times 21 bicycles is 0.6 megawatt-hours, a far cry from 12.9 megawatt-hours!

Now this was a try for a Guinness world record, so maybe those bicycle "stations" were not a single stationary bicycle, as I assume, but banks of bicycles. There would have had to have been 21 such banks, or 400 (approximately) bicycles total, meaning, with trading off rides, several thousand bike riders. A group that large would be made up of riders who likely could generate only half of Armstrong's power, if that, putting us in the neighborhood of 10,000 riders needed for this feat. Somehow, I suspect that if 10,000 riders had been involved in this exercise, the article would have mentioned it!

But, as it turns out, the claim about 12,000 homes is wrong even if 12.9 Mwh were generated by 21 superhuman bicycle riders (each with 20 times the power of Lance Armstrong). The average home uses 500 kilowatt hours of electricity per month, or 6000 Kwh (6 Mwh)/year. So 12.9 Mwh would power not 12,000 homes for a year, but two!!

I hope I haven't embarrassed myself by screwing up these calculations, because I'm trying to illustrate a fairly simple point - don't believe everything you read, even if there's no obvious political motive, and especially when numbers are involved! However, you can believe everything you read in Left I on the News - I hope!

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