I know, I shouldn't care—but when a major newspaper and a professional journalist get goofy about something scientific, I feel an obligation to respond. The latest, from a source that I won't deign to name: a column about the marvelous potential of generating electricity from human motions, specifically pedestrian traffic and similar activity.

Hello? Has anybody heard of conservation of energy? Maybe it's not taught to reporters, but maybe it should be. If any device is producing electricity from people, then it's really producing electricity from the food that those people have eaten—minus all the inefficiency that humans have in digestion, muscular motion, etc.

Look at the numbers: a person ingests a few thousand food-calories per day, which converts into ~10,000,000 Joules/day. Sounds like a lot! But in electrical units that's only ~3 kilowatt-hours, roughly ~30¢ worth of juice. And that assumes 100% efficiency in converting food to useful work. In reality one might hope for a few percent of that, at best. Plus which, do folks want to feel like they're walking uphill or through molasses all the time? To maximize energy capture, that's what they'll have to do. And how much energy is it going to require to manufacture these devices, and how long will they last before they break?

Far be it from me to deprecate the value of exercise, for health and enjoyment. But journalists who rhapsodize about the potential to capture "free" energy from human activity should realize that it's a gimmick, not a game-changer. They've fallen victim to techno-promoters. And it's not even a new notion: does anybody remember self-winding wrist watches? They had a pendulum inside, a weight on a pivot that, via a ratchet mechanism, quietly wound the mainspring as the owner turned his wrist throughout the day.

It's silly to think about generating significant amounts of electricity via people-power. But realistically, motions by the wearer could be used to energize ultra-low-power "smart" garments, like motion-canceling active mechanical structures. Hmmm—perhaps a Brainy Jogbra™ needn't use batteries after all!?

^z - 2010-05-04