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DISCOVER 43
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millimeters up to a meter; the “nano”
refers to the scale of the charges. Since
then, Wang’s lab has designed and tested
dozens of potential applications for these
energy-harvesting devices. He’s also moti-
vated multiple groups and thousands of
researchers around the world to build
their own applications. Ideas for work-
able TENGs range from paper-based
audio speakers that charge while folded
up and tucked in a shoe, to generators that
convert the mechanical rise and fall of a
breath to power a pacemaker. (See “The
Triboelectric Wave,” page 44.)
A TENG relies on the same principle
as static electricity: When two different
materials come into contact, electric
charges can accumulate on one, leaving
the other with the opposite charge. In the
case of that plastic sphere in Wang’s hand,
charges accumulate when the interior and
exterior balls touch and separate, over and
over. Attach electrodes and wires to the
oppositely charged materials, and current
flows to correct the imbalance. It won’t be
a big current, but many applications don’t
need much.
Most researchers agree that triboelec-
tric generators have the most potential
when it comes to powering small devices,
like phones and watches, but Wang
wants to go big. His team recently took
a few dozen of those plastic spheres to a
neighborhood swimming pool — after
hours — and set them loose to oscillate
in the ripples. Even the slightest bob-
bing produced enough energy to power
small lights or devices. Their calculations
suggest that a grid of 1,000 spheres, float-
ing freely in the ocean, should generate
enough power for a standard lightbulb. A
grid measuring about a third of a square
mile could power a small town.
Wang doesn’t want to stop there; he
sees the potential for a wealth of untested
possibilities. Imagine a matrix of these
spheres covering an area of the ocean
equal to the state of Georgia and extend-
ing about 30 feet down. That’s about a
quadrillion spheres.
“If we use this,” he says, in his demand-
ing, fierce whisper, “the power generated
is for the whole world.”
FUTURE SHOCK
Triboelectricity suggests a clear way to
solve existing energy challenges with
ROCK AND ROLL ENERGY
TENGs can already harness static electricity to power small
devices, but perhaps one day they could do more. These
ball-shaped TENGs, designed in Wang’s lab, generate
electricity by rolling a silicone rubber ball along the inside
of a plastic shell. The rubbing of different materials creates
a charge imbalance within them; attaching electrodes to the
different sides allows current to flow from one to the other,
balancing their charges.
How it works
Inner rolling ball
Rocking sphere
A single ball doesn’t produce too much power, but a network of them, powered by the
gentle swells of ocean waves, could theoretically power cities.
Moving ball causes
charge imbalance
Further movement
restarts cycle
Charge imbalance causes
current flow, to re-balance
Cycle
repeats as
ball rolls back
and forth