Paper-Thin
Plastic Film Soaks Up Sun to Create Solar Energy
Environmental and Agricultural Resources
Originating Technology/NASA Contribution
A solar cell is a semiconductor device that converts photons,
or light, into electricity. The most widely used solar
cells today are made from wafers of mono- or poly-crystalline
silicon.
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Thin
film solar cells derived from amorphous silicon,
pictured here, are gaining more and more attention
in a market otherwise dominated by mono- and poly-crystalline
silicon solar cells. |
Mono-crystalline silicon, or single-crystal silicon, is
produced by growing a large pure crystal of silicon in
a furnace. The pure crystal is then sawed into wafers and
assembled in an array. The resulting silicon is highly
efficient, but expensive and time-consuming to mass-produce.
Further, because the silicon has to be cut prior to assembly,
approximately 50 percent of material goes unused, and is
therefore wasted.
Poly-crystalline silicon, or multi-crystal silicon, is
created by casting molten silicon in blocks. While this
process is a little less expensive and faster than the
process used for growing a single crystal, the resulting
multi-crystal silicon is less efficient than its single-crystal
counterpart.
Although less commonly used, a third type of solar cell,
called a thin film solar cell, can counterbalance many
of the disadvantages associated with mono- and poly-crystalline
silicon manufacturing by using only a fraction of pure
silicon. Thin film solar cells are made by depositing a
very thin layer of silicon (or another semiconductor substance,
depending upon the application) on a very thin supporting
material, such as glass, plastic, or metal foil. This process
is known as chemical vapor deposition.
A non-crystallized silicon known as amorphous silicon is
the semiconductor material most frequently chosen for deposition,
because it is a strong absorber of light. According to
the U.S. Department of Energy, amorphous silicon absorbs
solar radiation 40 times more efficiently than single-crystal
silicon, and a thin film only about 1-micrometer (one one-millionth
of a meter) thick containing amorphous silicon can absorb
90 percent of the usable light energy shining on it. Peak
efficiency and significant reduction in the use of semiconductor
and thin film materials translate directly into time and
money savings for manufacturers.
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PowerFilm
Solar manufactures thin, flexible solar panels
by way of a proprietary, low-cost, “roll-to-roll”
process. The rollable solar panels are monolithically
integrated, which eliminates the need for damage-prone
manual connections of individual solar cells. |
Thanks in part to NASA, thin film solar cells derived from
amorphous silicon are gaining more and more attention in
a market that has otherwise been dominated by mono- and
poly-crystalline silicon cells for years. At Glenn
Research Center, the Photovoltaic & Space Environments Branch conducts research focused on developing this type of thin
film solar cell for space applications. Placing solar cells
on thin film materials provides NASA with an attractively
priced solution to fabricating other types of solar cells,
given that thin film solar cells require significantly
less semiconductor material to generate power. Using the
super-lightweight solar materials also affords NASA the
opportunity to cut down on payload weight during vehicle
launches, as well as the weight of spacecraft being sent
into orbit.
Iowa Thin Film Technologies, Inc., of Boone, Iowa, worked
closely with the Photovoltaic & Space Environments
Branch so that both parties could broaden their understanding
of thin film solar cells made from amorphous silicon. The
commercial payoff of this alliance has now been realized,
with terrestrial trickle-downs coming in the forms of solar-powered
headset radios for recreational use and battery chargers
and solar tents for military operations.
Partnership
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The
Soltronix HR-1 solar-rechargeable AM/FM Headphone
Radio eliminates the cost and inconvenience of
replacing batteries. The portable and powerful
system automatically recharges itself when in sunlight,
even while listening. |
In November 1989, Glenn awarded Iowa Thin Film Technologies
with a $50,000 Phase I Small
Business Innovation Research (SBIR) contract to research the potential for a lightweight
and flexible thin film solar cell that uses amorphous silicon
as a semiconductor source, for air and space applications.
With this initial-phase funding, Iowa Thin Film Technologies
demonstrated that development of the solar technology was
viable and, thus, was awarded a $500,000 Phase II contract
to move ahead with the manufacturing process, which then
occurred over the course of 2 years. Funding from Glenn
supported the research and development programs of Iowa
Thin Film Technologies in the early years of the company
and helped improve the company’s process for depositing
solar cells on rolls of thin, flexible plastic substrate.
Iowa Thin Film Technologies also received funding for this
project from several other government agencies, as well
as from private resources. The private investments provided
the financing necessary for the company to build a complete
production facility. In addition to expanding its workspace,
the company expanded its workforce, growing from just a
few employees to 12 full-time and 8 part-time employees.
Because of the NASA SBIR support that led to new technology
and helped create new jobs, the company today shines as
a leading producer of thin film photovoltaics.
Product Outcome
PowerFilm Solar, the solar division of PowerFilm,
Inc. (the company previously known
as Iowa Thin Film Technologies), manufactures and markets
a differentiated line of next-generation, amorphous silicon,
thin film solar panels that can easily and economically
be integrated with consumer and military products. The
amount of amorphous silicon used in the panels is as low
as 1 percent of the amount used in traditional crystalline
silicon solar panels, according to PowerFilm Solar.
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The
PowerFilm AA Foldable Solar Charger provides portable
power for charging AA rechargeable batteries. The
charger automatically begins charging once unfolded,
and a light informs the user when the batteries
are fully charged. |
These thin film solar panels, branded as PowerFilm solar
panels, are constructed using a process called monolithic
integration, which is the automatic, built-in connection
of individual solar cells. According to the company, monolithic
integration improves durability and reduces cost by eliminating
the need for expensive and failure-prone manual collection
of individual solar cells. It further noted that it is
the first and only company in the world to manufacture
and sell monolithically integrated semiconductors on a
flexible polymer substrate. During the manufacturing process,
PowerFilm Solar uses its proprietary “roll-to-roll” manufacturing
technology platform. (Roll-to-roll processing is the action
of creating electronic devices on a roll of flexible plastic
or metal foil.)
“Imagine taking paper-thin plastic film and making it generate
power again and again. That’s what PowerFilm is and does,”
claimed Michael Coon, the company’s chief operating officer.
“This is not your father’s solar technology from the ’70s.
PowerFilm’s durable plastic base is superior to fragile
glass or corrosive metal,” he added.
Available in a variety of standard and custom configurations
to meet specific voltage, current, and environmental needs,
the rollable PowerFilm products boast a durable and aesthetically
pleasing design, and are quickly adaptable within their
intended market, be it commercial or military. Moreover,
they are not hazardous to human health, since amorphous
silicon is completely free of cadmium (a naturally occuring
metallic element known
to produce toxic effects in humans), unlike many other
solar technologies.
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The
PowerFilm 60-Watt Foldable Solar Charger, the largest
in PowerFilm, Inc.’s line of foldable solar chargers,
is very lightweight (2.6 pounds), considering the
amount of power it produces (3.6 amps at 15.4 volts). |
Across the board, PowerFilm Solar’s PowerFilm commercial
products are experiencing very strong sales. One of the
company’s first offerings sprung from its research partnership
with NASA was the HR-1 Soltronix Solar Rechargeable AM/FM
Headphone Radio. Featuring a breakthrough combination of
PowerFilm solar technology and premium sound, the HR-1
headphone radio automatically recharges itself when in
sunlight, even while the user is listening to it. (One
hour of charging in full sunlight provides 1 to 3 hours
of listening.) It will even recharge under interior house
lighting or on cloudy or rainy days, albeit at much slower
rates. When fully charged, the headphone set will play
for more than 20 hours, even in the dark.
Other features include an internal antenna for powerful
reception, a dual headband for added comfort, all-weather
durability (Some users have remarked on the usefulness
of the headset while walking/jogging in the rain or while
boating.), and an extended bass range for setting graphic
equalization to a listener’s liking.
The sophisticated solar cells also serve as precision chargers
for AA batteries. In 2005, PowerFilm Solar launched the
PowerFilm Foldable Solar Charger that can recharge up to
four AA batteries at a time, to optimum level, without
inducing damage associated with overcharging. “Unlike other
solar chargers for AA batteries, this new charging circuit
does not get confused from variations in current typically
seen from a solar panel,” noted Frank Jeffrey, PowerFilm’s
chairman.
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The
flexible, thin film solar cell can be a source
of power for laptops, MP3 players, portable televisions,
and other items that might be used during outdoor
recreational activities. |
The technology, comprised of a rugged fabric that houses
the lightweight, flexible solar panels, is being marketed
in partnership with Johnson Outdoors, Inc., a recreational
product manufacturer. In addition to this commercial version,
PowerFilm Solar has introduced a military version that
is ideal for soldiers in the field, especially in remote
locations.
Also in 2005, PowerFilm Solar teamed up with the U.S. Army
to supply PowerFilm-equipped tents. The largest tent ordered
by the Army is a canopy that can provide up to 2 kilowatts
of power. “This is enough energy to power up to 66 laptop
computers or 260 cell or satellite phones [when the sun
is shining],” said Steve Martens, the president of PowerFilm.
“A second, smaller model can produce enough power for 5
laptop computers or 24 cell or satellite phones,” he added.
The power generated by each tent is stored in a bank of
batteries.
The solar tents help meet the Army’s growing demand
for rapid-response rates and portable, remote power,
and eliminate the need for noisy generators, spare batteries,
and excessive fuel storage.
PowerFilm® and Soltronix HR-1® are
registered trademarks of PowerFilm, Inc.
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