Purple Pokeberries hold secret to affordable solar power worldwide

April 29, 2010

the weeds that children smash to stain their cheeks purple-red and that Civil War soldiers used to write letters home - could be the key to spreading solar power across the globe, according to researchers at Wake Forest University's Center for Nanotechnology and Molecular Materials.

Nanotech Center scientists have used the red dye made from pokeberries to coat their efficient and inexpensive fiber-based solar cells. The dye acts as an absorber, helping the cell's tiny fibers trap more sunlight to convert into power.

Pokeberries proliferate even during drought and in rocky, infertile soil. That means residents of rural Africa, for instance, could raise the plants for pennies. Then they could make the dye absorber for the extremely efficient and provide energy where power lines don't run, said David Carroll, Ph.D., the center's director.

"They're weeds," Carroll said. "They grow on every continent but Antarctica."

Wake Forest University holds the first patent for fiber-based photovoltaic, or solar, cells, granted by the European Patent Office in November. A spinoff company called FiberCell Inc. has received the license to develop manufacturing methods for the new solar cell.

The fiber cells can produce as much as twice the power that current flat-cell technology can produce. That's because they are composed of millions of tiny, plastic "cans" that trap light until most of it is absorbed. Since the fibers create much more surface area, the fiber can collect light at any angle - from the time the sun rises until it sets.

To make the cells, the plastic fibers are stamped onto plastic sheets, with the same technology used to attach the tops of soft-drink cans. The absorber - either a polymer or a less-expensive dye - is sprayed on. The plastic makes the cells lightweight and flexible, so a manufacturer could roll them up and ship them cheaply to developing countries - to power a medical clinic, for instance.

Once the primary manufacturer ships the cells, workers at local plants would spray them with the dye and prepare them for installation. Carroll estimates it would cost about $5 million to set up a finishing plant - about $15 million less than it could cost to set up a similar plant for flat cells.

"We could provide the substrate," he said. "If Africa grows the pokeberries, they could take it home.

"It's a low-cost solar cell that can be made to work with local, low-cost agricultural crops like pokeberries and with a means of production that emerging economies can afford."

Explore further: Wake Forest earns patent for efficient, inexpensive fiber-based solar cells

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5 / 5 (2) Apr 29, 2010
That means residents of rural Africa, for instance, could raise the plants for pennies.

Once a patch gets started, they'll be able to raise them forever for nothing. They can have all they want from my backyard.
5 / 5 (2) Apr 29, 2010
once again the lack of hard figures -- doubling the power output seems like you are making solar cells twice as effecient in one step... well at least give me the base line effeciency ... was it 13% or 25% .. heck give me watts per cm^2 or any type of measurement

Anyone got a link to the site or the paper??
5 / 5 (1) Apr 29, 2010
According to the following at :
the Fibercells are about 6% efficient.
4 / 5 (1) Apr 29, 2010
How long can pokeberry colour last? I am sure it would fade away in the sun in less than one year.
3 / 5 (1) Apr 29, 2010
The fiber cells can produce as much as twice the power that current flat-cell technology can produce.

This does not gel with the figures provided so kindly by Bradfield above. It seems to me that is good news that they are talking about cheaper solar panels but to say they are more efficient is a flat out lie.
5 / 5 (3) Apr 30, 2010
--Low light operation and high performance at oblique illumination--

"During a day, FiberCell can generate up to twice the power of a traditional flat panel device of the same effeciency (sic) rating"

This is from the Fibercell website. They are referring to the amount of total power generated over a typical day, from sunrise to sunset. Because of the cell's ability to more efficiently harness light from oblique angles, they are claiming that they can produce twice as much power as a flat cell when accumulated over that period of time. Possible, I guess...
5 / 5 (1) Apr 30, 2010
--Low light operation and high performance at oblique illumination--

"During a day, FiberCell can generate up to twice the power of a traditional flat panel device of the same effeciency (sic) rating"

It would be possible if they figure out a way how to
coat them with efficient solar light adsorbed and current collectors. What is missed for the discussion
that you need a sandwich of multiple materials to make
good solar cell. Typically it is underlying conductor,
actual semiconductor to adsorb light (typically itself is 2-3 layers), and another transparent conductor on the other side.
Are efficient adsorbing materials deposition (typically high temperature process) compatible with their polymer
fibers is the key question.
3.5 / 5 (2) Apr 30, 2010
So the improvement in this panel is that it is less temperamental to be operated in its optimum environment? The 6% efficiency quoted is about half that of a typical polycrystalline panel. (Sharp for example quotes just under 14%.) As with many of these canned press releases, it is big on promises and short on specifics that allow one to identify the appropriate disclaimers. It gets almost as bad as a political campaign. :-)

How efficiency is measured makes a huge difference. How close to optimum does the panel have to be operated to achieve this in real operation? How long does the panel last? Organic dyes like this often degrade quickly as was pointed out above.

Inattention to detail can make an installation half as effective as planned, especially over time. What happens when this fibrous panel gets dirty?
Solar still has a long way to go to be economically viable compared to existing modern electric infrastructure, but certain remote applications make sense.
2.3 / 5 (3) Apr 30, 2010
What happens when this fibrous panel gets dirty?

They're machine washable darling, that's a new feature.
3 / 5 (1) Apr 30, 2010
Is this like putting a rug on your roof, then dying it purple? Doesn't sound like it would last very long, but I live in Minnesota, not Africa....
5 / 5 (1) Apr 30, 2010
A key to the lower efficiency yet higher yield may certainly be due to the fact that cu^3 (in some areas up to 15kwh peaks at some geographic locations) of sunlight is much higher then one would expect vs cu^2 due to all the extra light refracted from the surrounding land and through atmospheric lensing. It states in the article that these do not require a heliostat, an array of fibers could very well tap into light hitting from many reflected/refracted sources while a flat panel is just going to bounce them off. I mean if you stand in the shade of a tree- does the casual observer see a silhouette or maybe a 30% reduction in visible light reflecting off you.

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