Stationary bikes on Vashon - Flickr user biblionaSo this is a bit of a gimmick—but it’s a GOOD gimmick:  a new gym in Portland, OR is using stationary bicycles to produce electricity.  (See here and here for recent press.)

First off, to any naysaying skeptics out there:  there’s absolutely nothing wrong with recapturing a bit of power that would otherwise be wasted.  So I don’t want to hear any talk-radio crank poo-pooing the idea.  (Not that they’d ever listen to me—I just wanted to get this out of the way early.)

Second, and perhaps more importantly,  this is a perfect example of the sort of creativity the market’s capable of.  Once we set responsible limits on climate-warming emissions, we’ll find all sorts of ways, large and small, to eliminate energy waste, and do more work with less fossil fuels.  Stationary bike-generators are just small examples of all the nifty stuff we can do when we let ourselves imagine new solutions to energy woes.

That said, since I’m an incurable geek, I just had to run the numbers.  How much power can a person actually generate from one of those stationary bikes?

Answer:  not much, unfortunately.

  • According to Calorielab.com, exercising on a stationary bike requires a rider to produce somewhere between 50 and 250 watts of power.   A wattage of 50 is considered “very light effort”—just enough to get your heart rate above resting, I suppose.  A wattage of 250 is considered “very vigorous effort.”

    That sounds about right to me.  Tour de France rider Floyd Landis (later caught doping) sustained an average of 232 watts over the course of the tour.  Of course, that’s over a long race with lots of downhills; peak output during short bursts can be much higher. Super-biker Lance Armstrong could pump out about 500 watts for 20 minute bursts.

    But Armstrong, obviously, is pretty abnormal.  For the average gym rat looking for a cardio workout, I think that 150-200 watts would probably be in the ballpark.  And let’s further assume that the generators are about 90 percent efficient—meaning that 90 percent of the mechanical energy from the bike actually gets turned into usable electricity.

    Doing the math, a 45 minute ride at moderate-to-vigorous effort produces about 120 watt-hours of power.  How much is that?  Enough to:

    • Run a 100-watt bulb for a little over an hour.
    • Run 4 compact fluorescent bulbs for the same duration.
    • Run an aquarium pump for a day.
    • Power a small frost free fridge for about a half hour (give or take.)

    You get the drift.  Gym-rat power probably won’t do much more than keep the machines running and help keep the lights in the gym on.  It certainly won’t heat the water for an after-workout shower.

    The cost savings are pretty slim, too.  Portland General Electric’s peak power rates are about 11 cents per thousand watt-hours.  So 45 minutes of biking produces only about a penny’s worth of electricity.  And that’s where the “gimmick” part comes in: I have to wonder if the cost and energy used to outfit bikes with generators really balances out the relatively small amount of electricity that’s generated.  Maybe it does.  But the question definitely runs through my mind.

    And here’s another wrinkle.  Imagine if, instead of riding a stationary bike attached to a generator, the gym rat had ridden a real bike in place of a car trip.  That’s a much, much bigger energy saver, since cars are surprisingly bad at converting fuel into forward motion.  A ten-mile bike trip reduces gas consumption by half a gallon—the equivalent of about 18,300 watt-hours, compared with the 120 watt-hour output of a stationary bike generator.  Measured per unit of energy, biking instead of driving is, oh, about 150 times more eco-friendly than using a stationary bike generator. If what you really care about is saving energy, look to replace some car trips with bike trips, if you can.

    Still, if you’re looking for an eco-friendly place to get a nice indoor workout in Portland, I’d check this gym out.  It sounds like a cool idea, and a nice place to get a workout.

    Bike photo courtesy of Flickr user Bibliona under a Creative Commons license.