Breakthrough - Spray-On Nanotech Solar Power Cells
By Stefan Lovgren - National Geographic News - 17 January 2005
Scientists have invented a plastic solar cell that can turn the
sun's power into electrical energy, even on a cloudy day.
The plastic material uses nanotechnology and contains the first
solar cells able to harness the sun's invisible, infrared rays.
The breakthrough has led theorists to predict that plastic solar
cells could one day become five times more efficient than current
solar cell technology.
Like paint, the composite can be sprayed onto other materials and
used as portable electricity. A sweater coated in the material could
power a cell phone or other wireless devices. A hydrogen-powered
car painted with the film could potentially convert enough energy
into electricity to continually recharge the car's battery.
The researchers envision that one day "solar farms" consisting
of the plastic material could be rolled across deserts to generate
enough clean energy to supply the entire planet's power needs.
"The sun that reaches the Earth's surface delivers 10,000 times
more energy than we consume," said Ted Sargent, an electrical
and computer engineering professor at the University of Toronto.
Sargent is one of the inventors of the new plastic material.
"If we could cover 0.1 percent of the Earth's surface with
[very efficient] large-area solar cells," he said, "we
could in principle replace all of our energy habits with a source
of power which is clean and renewable."
Infrared Power
Plastic solar cells are not new. But existing materials are only
able to harness the sun's visible light. While half of the sun's
power lies in the visible spectrum, the other half lies in the infrared
spectrum.
The new material is the first plastic composite that is able to
harness the infrared portion.
"Everything that's warm gives off some heat. Even people and
animals give off heat," Sargent said. "So there actually
is some power remaining in the infrared [spectrum], even when it
appears to us to be dark outside."
The researchers combined specially designed nano particles called
quantum dots with a polymer to make the plastic that can detect
energy in the infrared.
With further advances, the new plastic "could allow up to 30
percent of the sun's radiant energy to be harnessed, compared to
6 percent in today's best plastic solar cells," said Peter
Peumans, a Stanford University electrical engineering professor,
who studied the work.
Electrical Sweaters
The new material could make technology truly wireless.
"We have this expectation that we don't have to plug into a
phone jack anymore to talk on the phone, but we're resigned to the
fact that we have to plug into an electrical outlet to recharge
the batteries," Sargent said. "That's only communications
wireless, not power wireless."
He said the plastic coating could be woven into a shirt or sweater
and used to charge an item like a cell phone.
"A sweater is already absorbing all sorts of light both in
the infrared and the visible," said Sargent. "Instead
of just turning that into heat, as it currently does, imagine if
it were to turn that into electricity."
Other possibilities include energy-saving plastic sheeting that
could be unfurled onto a rooftop to supply heating needs, or solar
cell window coating that could let in enough infrared light to power
home appliances.
Cost-Effectiveness
Ultimately, a large amount of the sun's energy could be harnessed
through "solar farms" and used to power all our energy
needs, the researchers predict.
"This could potentially displace other sources of electrical
production that produce greenhouse gases, such as coal," Sargent
said.
In Japan, the world's largest solar-power market, the government
expects that 50 percent of residential power supply will come from
solar power by 2030, up from a fraction of a percent today.
The biggest hurdle facing solar power is cost-effectiveness.
At a current cost of 25 to 50 cents per kilowatt-hour, solar power
is significantly more expensive than conventional electrical power
for residences. Average U.S. residential power prices are less than
ten cents per kilowatt-hour, according to experts.
But that could change with the new material.
"Flexible, roller-processed solar cells have the potential
to turn the sun's power into a clean, green, convenient source of
energy," said John Wolfe, a nanotechnology venture capital
investor at Lux Capital in New York City."
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