These Exercise Machines Turn Your Sweat Into Electricity


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Although the Green Revolution decided not to build custom equipment, that's exactly the approach another entrepreneur in this field has taken. Mike Taggett attended the University of Arizona, where he majored in Latin American studies. He worked as a river guide and started a business making an eyeglass retainer that he'd invented himself. At a trade show sometime in the late 1980s, he had the idea of attracting visitors to his company's booth by bringing a converted exercise machine that would generate electricity and power lights and kitchen appliances. “We made smoothies,” he recalls.

That demonstration was the seed of an idea that grew in Taggett's mind over the next two decades. A few years ago he got to work, and in 2008 he unveiled the Human Dynamo, a custom-designed power-producing stationary bike—with a twist. In addition to the usual pedals, the machine has hand cranks to provide a rigorous upper-body workout and generate even more electricity. With their sprockets chained together, the hand and leg cranks spin at the same speed to turn the bike's 45-centimeter-diameter flywheel about 300 revolutions per minute during a typical workout. A belt connects the flywheel to the generator, which spins at something like 1500 rpm.


You can connect several of Taggett's machines together to drive a single generator. He calls this configuration the Team Dynamo. “You really cut down expense and maintenance because you have one big generator and one electronics package for up to 10 machines,” he says.

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photo showing ReRev generator
Photos: Top, Henry Works; Bottom, ReRev
Energized:Powered by four people, the Team Dynamo machine uses a single generator [top]; elliptical equipment at California State University, Chico [bottom], uses generators by ReRev.

It might feel like a lot if you're generating it, but just how much energy are we talking about here? An elite cyclist can produce more than 400 watts, more than half a horsepower, for an hour or more at a stretch. But the average person, even somebody in good shape, can generate only 50 to 150 watts during an hour of strenuous exercise. If you could capture that power to produce electricity, what would it be good for? Not much, really. It could power a television set for about an hour, which might keep you entertained while you pedaled away to produce the electricity in the first place.

Still, might this be a reasonable way for a gym to offset at least some of its electricity use? Let's assume that the average piece of exercise equipment is in use 5 hours a day, 365 days a year. If each patron generates 100 watts while using it, that machine creates some 183 kilowatt-hours of electricity a year. Commercial power costs about 10 cents per kilowatt-hour on average in the United States, so the electricity produced in a year from one machine is worth about US $18 dollars.


The companies selling the retrofitted equipment say that costs vary on a case-by-case basis, depending on the kind of equipment the gym has and its electrical installation. But according to some reports, it costs a gym at least several hundred dollars—perhaps as much as $1000—to purchase the equipment or equipment modifications needed to harvest this electricity from a single exercise machine. Earning just $18 a year from it means that the initial investment would take decades to pay back. Other energy-conserving investments a gym might consider, such as installing better insulation or adding solar water heaters for the showers, typically have payback periods of several years.

So are these electricity-producing exercise machines merely a marketing gimmick, something to make gym patrons feel good about their workouts? At the moment, that would seem to be the case. Gyms that have embraced the technology say that by advertising themselves as greener than regular gyms—and gyms are notorious power hogs—they can attract environmentally conscious customers. And if enough customers choose that gym rather than another one down the street, the initial investment will pay for itself much faster.

Take the Green Microgym in Portland, Ore. Adam Boesel opened the facility in 2008 with Human Dynamo machines inside and solar panels on the roof. Boesel reports that his gym generates about 36 percent of its own electricity, saving nearly 40 000 kWh per year—although he admits that the savings come mostly from the solar panels.

“People are very receptive,” says Boesel. He even initiated a program called Burn and Earn, which rewards customers with $1 coupons—redeemable for food, beverages, clothing, and other merchandise—for every hour they operate the electricity-generating equipment. The electricity produced certainly isn't worth a dollar to him. And he'll be lucky if he's still in business when the electricity generated from the machines finally compensates for the extra money he spent on them.

But this might change in the not-too-distant future, if the companies selling retrofitted equipment can ramp up volume and bring costs down. Or if the mainstream manufacturers of exercise machines catch the wave and add an electricity-generation option to their products without charging a large premium for it. If including that feature ups the price only $100 or so—a reasonable prospect given the very minor alterations needed—the payback period would rival that of many other conservation measures.

Boesel can't wait. “I hope this technology is in every piece of equipment in 10 or 15 years,” he says. “A few watts here and there from all of us as we sweat may add up to something significant.”

via:  Spectrum

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