Harvesting energy from gym users

HONG KONG -- A health club here is hoping that a car
battery, some StairMasters and dozens of gym rats can help ease the
world's energy problems.

Rita Wong is doing her part. One evening recently, the
fit 27-year-old, dressed in black spandex, pedaled furiously on an
elliptical machine at the California Fitness health club. As she worked
up a sweat to a Madonna song blasting on the gym's sound system, the
energy she created was transformed into electricity and stored in a
battery that powers some of the gym's lights.

"It's very good motivation," Ms. Wong said, pointing
at the fluorescent bulb above her head. "You can watch yourself burning
fat to turn on that light."

This virtuous cycle is just one of a wave of projects
on the fringes of the renewable-energy movement that are trying, in
small ways, to tap the power of the human body.

Experiments range from a dance floor that generates
electricity from the vibrations of the dancers to energy-harvesting
shoes that convert motion from walking into electricity. One shoe
prototype can generate about six watts, more than enough to power a
cellphone.

Like many of these projects, the California Fitness
setup isn't going to light up the Hong Kong skyline or even power the
club's own air conditioning. The gym chain has rigged up 13 machines at
one of its clubs here. When all of them are in use, the power generated
amounts to about 300 watts, roughly enough to run three 27-inch
television sets, five 60-watt light bulbs or several hundred video
iPods. If all the exercise machines were in use 10 hours a day for a
year, the gym could generate roughly $183 worth of electricity. At that
rate, it would take about 82 years to pay off the initial $15,000
investment.

Converting elbow grease into electricity has a long,
odd history. The first telephones, in the 1800s, had hand cranks that
generated an electrical signal to alert the operator when one wanted to
make a call. Hand-crank flashlights have long been available. So have
hand-crank portable radios.

But unlike these predecessors, many of the new
projects focus on capturing energy that is a byproduct of casual human
activities, such as walking or exercising. Scientists call such devices
"parasitic" generators. Many of the most futuristic projects focus on
harvesting the energy of crowds.

Enviu, a Dutch environmental group, is building a
nightclub in Rotterdam that will have a dance floor that converts
vibrations from all those feet into electricity. One potential design
for the floor involves piezoelectric crystals, which generate a small
electric current when compressed. But Enviu's 20-by-20-foot floor cost
$260,000 and will generate only enough power to run some lights
embedded in it.