Cheap "Popcorn Ball" Solar Cells Set Efficiency Record
April 13, 2008 2:00 PM
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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
building massive new plants
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,
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 ...
4/14/2008 8:55:31 PM
Of course there are ways of storing energy (the grid itself acts as a "battery" on it's own in a round-about sort of way), however there are no real large-scale "battery" technologies on the market currently available that are cost-effective ways of storing all that energy.
Sure, Ontario currently uses a peak of about 18,000MW during the day, and about 14000MW at night. Nothing currently can come CLOSE to storing 14,000MW. How many solar plants will have the sole purpose of simply charging batteries (or other such energy storing methods such as you put out) to be able to have that available? (1)
Quick maths (bad maths too):
12 hours daily of sunlight (sun at 100% power)
12 hours of night time (sun at 0% power)
Assuming no other energy creation methods are being used.
Looking at the graphs, there is approx. 12 hours of 18000MW, and 12hrs 14000MW (it's really more usage than that, but this makes the math easy).
12*14000 = 168,000MW
12*18000 = 216,000MW
Total power used daily:
384,000MW Total power used.
Therefore, the amount of power needed to be generated during the day, from solar (alone) is:
384,000/12 = 32,000MW per hour.
A lithium ion cell the power/weight ratio of: 1800W/kg. (2)
32,000MW = 32000000000 Watts.
32000000000 / 1800 = 17777777.7 KG
That's 17,777 TONS of lithium ion cells.
The cost of 1watt of lithium ion power is: 2.8W/US$ (2)
32000000000 / 2.8 = $11,428,571,428.57
11 TRILLION DOLLARS for Ontario ALONE. This is a bad example of course (there would be better methods of storing power other than chemical), but the cost to do so, is so huge, there's no point. It would bankrupt the province to do that with conventional chemical power. Plus, after 1000 days, you would need to spend 11 TRILLION dollars AGAIN to last another 3 years. It's not sustainable.
There are better methods of storing such large quantities of energy, but the best battery cells we have can't do it. The other things you mentioned, nothing practical about them so far.
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