Power harnessed one step at a time
Engineers call it 'crowd farming.' If it works, you could help power city
lights just by taking a stroll.
By Chris Gaylord | Staff writer of The Christian Science Monitor
26 September 2007
In the push to harvest alternative energy, scientists have tapped a
number of novel sources: the sun, corn, old cooking oil. But
how about the simple act of walking?
For two architecture students at the Massachusetts Institute of
Technology in Cambridge, Mass., the sound of footsteps is an echo of
energy gone to waste. They figure that the stomp of every footfall
gives off enough power to light two 60-watt bulbs for one second.
"Now imagine how many people walk through a train station each
morning, or walk down the street in Hong Kong," says James Graham,
who, with fellow MIT graduate student Thaddeus Jusczyk, is helping to
develop the growing field of "crowd farming."
They devised a special floor of sliding blocks that can turn motion
energy (such as from a footstep) into electrical energy. As commuters
march across the floor, it would collect tiny flickers of power from
each stride and channel that energy.
According to their design - which this summer won a prestigious award
from the Holcim Foundation for Sustainable Construction in Zurich,
Switzerland - 28,527 footsteps could power a train for one second -
84,162,203 paces could launch a space shuttle.
The problem with their plan: Right now, it only exists on paper. But
others have developed real-world examples of plugging into people
power. Over the past few years there's been a boom in technology that
harnesses piezoelectricity - the science of drawing power from
mechanical stress, including motion. While the crowd-farming push has
its critics, the discipline is growing, and businesses are signing on.
[Editor's note: The original version's definition of piezoelectricity
needed clarification.]
"This is a really exciting time because there's been a lot of growth
all of a sudden," says Steve Anton, whose review article on recent
piezoelectric advances ran in the June issue of the journal Smart
Materials and Structures. "For a long time the research was confined
to the lab, but a number of real applications have started coming
out."
Take POWERLeap. This project, built by sustainable designer Elizabeth
Redmond of Chicago, is a scaled-down, but glammed-up, version of Mr.
Graham's scheme. When pedestrians trot across one of the flooring
system's four decorated glass tiles, LED lights flicker to life
underneath their feet.
"I installed it on a sidewalk in Ann Arbor [Mich.] and people were
really surprised and excited by the lights glowing from the street,"
says Ms. Redmond. "When people find out that they were powering the
lights, and there were no batteries involved, you get a whole other
wave of wows."
Redmond is now crafting a new design for POWERLeap, thanks to a
$10,000 grant from flooring giant Mohawk Industries of Calhoun, Ga.
Graham says the two of them have been e-mailing about combining their
interests.
Power-generating backpack
Human energy can also be harnessed to power a cellphone or charge a
battery. Henry Sodano, an engineering professor at Arizona State
University in Tempe, Ariz., has developed a backpack that serves as a
portable, wearable way to keep gadgets juiced.
His team created piezoelectric straps that draw power from the bag's
natural bounce. At a normal stride, the stress on the bands can pull
in 45.6 milliwatts (mW) - just shy of what's needed to perpetually
power an iPod nano MP3 player, and more than enough to keep a Motorola
Razr mobile phone charged.
"We could power a Razr in standby using 9mW of power and store the
remaining 36.6mW of power, allowing us to talk for one minute for
every 10 minutes walked," he says. "Or you could charge an LED
headlamp while you walk in the day and use it at night while you
camp."
The catch: for the straps to collect the full 45.6mW, they need to
support a 100-pound knapsack. "That's a lot," Mr. Sodano admits with a
laugh. But he designed the straps for the US military to use. Since
soldiers are used to encumbering loads, the special straps in their
packs will capture practically free energy, he says.
Finding a balance of how much to leech off a person's movement is the
most difficult problem for human-powered technology. All energy has to
come from somewhere. So if you're the one charging the device, then,
to some extent, you're the one feeling the drain.
Self-winding watches work well because they are so light to begin with
that the added weight of the self-winding mechanism is almost
unnoticeable. But watches also require barely any power.
"To get anything substantial out of these devices, they would have to
weigh a ton, and that's something few consumers will agree to," says
Peter Glaskowsky, a technology analyst for Envisioneering, a
market-research firm, in Seaford, N.Y. "The energy you're saving by
not using batteries is actually coming from you, and therefore its
coming from food. If you add up the energy used to grow, package,
ship, and eat, food is an extremely inefficient energy source."
Many plans for battery-charging shoes have been abandoned because
walking in them was too taxing, says Mr. Glaskowsky. Most models so
far have relied on an extra thick sole that depresses and generates
electricity with each step - like a mini version of POWERLeap built
into the boot. "A lot of people complain that it feels tiring after a
while, like walking in sand," says Glaskowsky.
(Mr. Anton, a graduate student at Virginia Tech, plans to unveil a new
shoe design in October that places a piezoelectric charger in a box
above the heel. This would add weight, he says, but eliminate the
deflating feel of the sole-based style.)
Similarly, the One Laptop per Child foundation ditched their plan to
attach an auxiliary hand crank to the side of its "$100 laptops,"
deciding the strain was not worth what little power it provided. The
group then signed on for a "yo-yo" pull-cord charger, but are now
leaning toward using simple solar panels.
Simple movements may soon extend battery life
Some piezoelectric engineers have found successful, subtle ways to
feed off human motion. A consortium of mostly British companies is on
track to release by the end of the year an in-body microgenerator that
will convert energy from joint movements, heartbeats, and breathing,
says manager Martin McHugh of Zarlink Semiconductors. The tiny device
will help both decrease the size and extend the life of batteries
attached to pacemakers and other medical instruments, saving patients
from costly, surgical replacements.
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