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A close up of a single ball, 300 nm across. The ball is made up of 15 nm grains.  (Source: University of Washington)

Millions of the balls compose a layer of the solar cell.  (Source: University of Washington)

The thin light-absorbing zinc oxide surface, pictured here in a picture from a scanning electron microscope, is about 10 um thick, and composed of the popcorn ball like structures.  (Source: University of Washington)
While not very tasty, these balls are extra efficient

With gas prices going up, refining capacity stretched to its max, and the reality that fossil fuels will eventually be depleted settling in, interest in alternative energy solutions of various types is at an all time high.  Among these is renewed vigor in the solar power industry.  From building massive new plants to new ground breaking research, the rather old field of solar power, is adapting quickly to the latest tech.

The University of Washington just made another breakthrough in solar power, that while humorous sounding, certainly offers serious gains.  Researchers at the university studying solar cell configurations discovered that by implementing a popcorn ball design -- tiny spheres clumped into bigger porous spheres -- efficiency in cheap solar cells was near doubled.

The dramatic improvement was included in findings presented at the national meeting of the American Chemical Society in New Orleans.  Lead author Guozhong Cao, a UW professor of materials science and engineering, states, "We think this can lead to a significant breakthrough in dye-sensitized solar cells."

Dye-sensitive cells have been in vogue since early pioneering research in 1991.  The cells have the advantage of being flexible, cheaper, and easier to manufacture than brittle silicon solar cells.  Rough surfaces have been a focus in the dye-sensitive field's research, with researchers reach efficiencies of approximately 10 percent capture of the suns energy absorbed.  This efficiency is only about half that of traditional silicon solar cells found on roof tops and calculators but with the lower price its is enough to stay competitive with the silicon cells.

The University of Washington researchers looked to compare homogeneous rough surfaces with various clumped designs, instead of trying to maximize the efficiency of the well researched homogeneous rough surface.  One dilemma that researchers faced was the size of the grains used.  Bigger grains, closer to the visible wave length of light cause the light to bounce around inside the thin-light absorbing surface, increasing the probability that it will be absorbed.  On the other hand, small grains have a bigger surface area per volume, increasing absorbtion.

Explains Cao, "You want to have a larger surface area by making the grains smaller.  But if you let the light bounce back and forth several times, then you have more chances of capturing the energy."

Other researchers have tried unsuccessfully to improve efficiency by mixing small and large grains.  The UW researchers instead took tiny 15 nm grains and clumped them together into 300 nm agglomerations, essentially making large grains composed of small grains, an approach that resembles macroscopic scale popcorn balls.

Each gram of the material has an incredible surface area of 1,000 square feet per gram covered in light absorbing pigment.  Thanks to the complex design light also gets trapped inside the larger balls, increasing absorption remarkably.  The researchers were surprised at their success, saying it surpassed even their best hopes.  Says Cao, "We did not expect the doubling.  It was a happy surprise."

The overall efficiency was 2.4 percent for small grains only, the current highest efficiency achieved for the material (there are higher efficiency materials, hence the 10 percent in commercial designs).  The popcorn-ball design showed an overall efficiency of 6.2 percent, a 258 percent increase in efficiency.  Cao states, "The most significant finding is the amount of increase using this unique approach."

The research used the pigment zinc oxide, which is of lower efficiency than the commercially used titanium oxide, but easier to work with during experiments.  Titanium oxide layers are expected to show similar gains.  Cao gives an update on this explaining, "We first wanted to prove the concept in an easier material. Now we are working on transferring this concept to titanium oxide."

While titanium oxide cells currently have a record efficiency of 11 percent, the researchers hope that by using the new method they can by far surpass this old record, possibly even surpassing silicon cell efficiencies.  Such progress could make silicon cells, used for decades, obsolete, replaced by cheaper, more efficient, flexible cells.

The research was funded by the National Science Foundation, the Department of Energy, Washington Technology Center and the Air Force Office of Scientific Research.  The postdoctoral research was co-authored by Qifeng Zhang, research associate Tammy Chou and graduate student Bryan Russo all in the UW material sciences department, and Samson Jenekhe, a UW professor of chemical engineering.

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RE: Encouraging But ...
By indiana56637 on 4/14/2008 8:53:17 AM , Rating: 2
Absolutely, I am not sure what sparked this debate, but it is almost irrelevent. Current advances in battery technology will allow the storage of much of the energy required for use overnight. This is far more efficient than transmission allong inter-continental lines. However, the main problem with these solar cells is the low efficiency. The only way to make a real difference is to make it mandatory that all new houses have these or similar on the roof, and to offer significant tax benefits or grants to allow current home owners to upgrade.

Either that or cover an area of the Sahara the size of Germany with light concentrating solar power stations, as this would be enough to power all of the EU (personally Im up for this ;D although there may be some political implications to all of europe relying upon Libia for energy)

RE: Encouraging But ...
By spluurfg on 4/14/2008 9:48:02 AM , Rating: 2
Yeah... transmission and storage is the obvious answer. How exactly to do it is subject to debate (just like generation is still debated), but to simply rule out wind and solar because they have variable output... well... I think you could have thought a bit more about it...

There are some discussions of mechanical storage (i.e. wind farms are used to power a pump to fill a reservoir, etc) and also long distance transmission is much more practical if using direct current (and appropriate transformers).

RE: Encouraging But ...
By masher2 on 4/14/2008 9:48:23 AM , Rating: 2
> "advances in battery technology will allow the storage of much of the energy required for use overnight..."

Perhaps one day, but its not feasible any time in the near future. Current plans for solar installations which can store power don't even use batteries, but rather thermal-based solutions like molten salt storage.

RE: Encouraging But ...
By Earl E on 4/14/2008 2:26:16 PM , Rating: 2
People who use solar produce more energy than they consume at their homes in some cases.
What you might be saying is that it costs more money than you are willing to spend with all the other things money can buy.
So as the dollar devalues, the installed solar base becomes more valuable. Its nice to know that as the cost of utilities goes up and the value of the dollar declines, that your alternative energy systems payback period shortens.

"What would I do? I'd shut it down and give the money back to the shareholders." -- Michael Dell, after being asked what to do with Apple Computer in 1997

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