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Turning sweat into light

March 2, 2007 By Michael Hopkin This article courtesy of Nature News.

Could 'gym generators' power the way to green electricity?

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Do you spend your free time sweating away in the gym? Ever wonder whether all that energy might be put to better use? Well fear not, because you might soon find yourself converting those calories to light, and helping the club out with its electricity bill.

The California Fitness club in Hong Kong is among the first to jump on the green energy treadmill — stairmaster and cross-training machines at the gym have been wired up to the building's lighting system. If other gyms follow suit, it could kick off a new motivational craze, in which sweat equals glow.

The idea of gaining light from pedal power is not exactly new — kids have been riding bikes with dynamo-powered lights for years, and you can buy watches that never stop working as long as you remember to move your arm. But the Hong Kong scheme is one of a new wave of 'energy recapture' ideas aimed at harnessing the surplus power of casual activities, to generate electrical power that would otherwise come from the national grid.

Other recapture ideas include using the energy of footfalls to light up pedestrian tunnels, and military backpacks that use the wearer's movements to refrigerate the medical supplies inside. And a Dutch nightclub has even installed a dance floor that lights up when tiny 'piezoelectric' crystals inside it are deformed by the dancers' feet.

Slow burn

Power companies aren't fretting yet, however. When all 13 machines at the Hong Kong gym are being furiously pedalled, the energy output is only enough to power five 60-watt bulbs. And even if they were used for 10 hours a day, it would take the club 82 years to pay off its US$15,000 investment.

This would put energy more 'in their face'.
Graeme Bathurst, TNEI
But members clearly find it a good source of motivation — the gym is emblazoned with signs saying "Powered by YOU".

What's more, the scheme will encourage power users to think about where their energy comes from, says Graeme Bathurst, an energy consultant based in Manchester, UK. "People are very detached from where their energy comes from. This would put energy more 'in their face'," he says. Or their legs, presumably.

Nevertheless, energy recapture schemes are a long way from being economically worthwhile, Bathurst says. "I'm not sure how much pure commercial value there will be," he says. "It's simple back-of-the-envelope economics."

No free lunch

The so-called 'free energy' that comes from local generators, such as the on-site wind turbines installed by many businesses and homeowners, isn't really free. Bathurst notes that the often-high cost of installing the equipment means that many such schemes tend to function more as gimmicks or 'green PR', rather than a genuine cost-saving measure.

The Dutch dancefloor, for example, cost a staggering US$260,000 — far more than the club can expect to save on its lighting bill (although they should get more business from the gimmick). Micro wind turbines on city homes can likewise not make enough energy to economically justify their installation cost. "Cities are not that windy, so you never get the payback," says Bathurst.

So where does this leave Hong Kong's gym bunnies, running on their hamster-wheels, acting as guinea pigs for energy recapture? Nowhere near the commercial market. "Until someone invests heavily in it, it's too expensive," says Bathurst. "It's a nice idea and very entertaining but it's more of a distraction at this stage."


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