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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 Some1ne on 4/13/2008 9:44:24 PM , Rating: 4
quote:
because the sun is only out for 12 hours a day


No, the sun is out 24 hours a day. Just not 24 hours in any single spot on the planet's surface. Even discounting that, the duration of sunlight that a given spot recieves in a single day is not 12 hours, it's a variable duration depending upon time of year and latitude, and may be anywhere from 0 to 24 hours of sinlight in a day. The point being that the fact that a given spot on the earth's surface will not ever be in perpetual sunlight is not a valid reason to decry solar power. If it's dark where you are, it's light where someone else is, and it's entirely feasible to send the power out from where they are to where you are, negating the need for 24/7 generation in your locality (or anyone else's, for that matter). It would probably require a massive overhaul of the existing power distribution infrastructure, and international cooperation on a massive scale, but it's theoretically possible.


RE: Encouraging But ...
By masher2 (blog) on 4/13/2008 11:22:23 PM , Rating: 4
It's not even possible in theory at present. Most power generated today is consumed within a couple hundred miles of where it's produced, and even still we waste some 7% in transmission. Piping power halfway around the globe would require major scientific advances in superconducting power transmission, followed by the rebuilding of the world power grid from the ground up.

And even still, I don't see it being feasible to run gigawatt-capacity superconducting lines under the ocean. We don't even run super high-voltage lines underground at present...putting them in storm-ridden highly-conductive saltwater would be a challenge, to say the least.

I'm sure we'll be able to do it one day. But not in the next 50 years.


RE: Encouraging But ...
By dug777 on 4/14/2008 12:21:30 AM , Rating: 2
That's not true even now, masher.

HVDC is used under the ocean quite regularly, and is capable of transferring significant amounts of power.

The Basslink is just one example:

http://www.pti-us.com/pti/company/eNewsletter/2004...

Some further info on others (yeah it's wikipedia, get over it, you can follow all the links if you're concerned that it's all a pack of lies):

http://en.wikipedia.org/wiki/Submarine_power_cable


RE: Encouraging But ...
By masher2 (blog) on 4/14/2008 2:39:32 AM , Rating: 4
> "HVDC is used under the ocean quite regularly, and is capable of transferring significant amounts of power."

True, but it's still very far from a solution for intercontinental power transfer. If you notice, all the existing links are in the 250km or less range. Why?

HVDC loses roughly 10% every 1000km, plus an additional 1.5% fixed from conversion overhead. That means powering the nightime US from the daytime in Asia or Eastern Europe would waste more than 60% of the total power generated. Put another way, you'd have to generate 2.5X as much just to break even.

And then there's the cost. Massive capital costs for the converters at each end, plus the costs of the cable itself.

According to the figures in your link, an 8GW 40 km link between the UK and France would cost in the range of $2B dollars. Even assuming costs are linear with distance (they're not -- they rise faster), a trans-global cable capable of powering the US would cost in the realm of $20 trillion dollars. That's 150X the cost of the Apollo program. Plus annual maintenance of nearly $1T/year

And that's just to transport the electricity...not to generate it. And that assumes demand doesn't rise. If we start replacing petroleum with electric or hydrogen-powered cars, electric demand will rise dramatically.


RE: Encouraging But ...
By dug777 on 4/14/2008 3:15:13 AM , Rating: 2
That's a bit of a straw man and you know it ;)

I was simply rebutting your assertion that it was unfeasible or unlikely to ever work under the ocean:

I don't see it being feasible to run gigawatt-capacity superconducting lines under the ocean. We don't even run super high-voltage lines underground at present...putting them in storm-ridden highly-conductive saltwater would be a challenge, to say the least.

FWIW, I'm in general agreement with everything you said in your reply to me :)


RE: Encouraging But ...
By masher2 (blog) on 4/14/2008 9:37:55 AM , Rating: 2
> "I was simply rebutting your assertion that it was unfeasible or unlikely to ever work under the ocean"

Ah, point taken. However, I didn't say it would never work, just that it was unfeasible at least for the next 50 years.

By 2100 or so, though, who knows?


RE: Encouraging But ...
By mattclary on 4/14/2008 10:51:32 AM , Rating: 3
I think you need to brush up on what "Straw Man" means. He countered your point, deal with it.

http://www-personal.umich.edu/~lilyth/strawman.htm...


RE: Encouraging But ...
By dug777 on 4/14/2008 8:12:32 PM , Rating: 3
Fair enough.

I was labouring under a misapprehension that the concept of a straw man extended to countering someone's correction of your factual error with an argument that certainly didn't address any of the points you made, or were trying to make.

I simply felt that a statement masher made was inaccurate.

I provided a correction to that inaccuracy. I made no attempt to discuss the economics of the technology, merely pointed out that submarine HVDC power transfer was quite feasible with current technology.

Masher then proceeded to 'counter' my feasibility comment with a brief economic analysis of the situation, extrapolated to larger and longer examples, which I generally agree with. However it's not something I had initially suggested was economically feasible in longer and larger examples. His point did not counter anything I had said, hence my apparently erronous reference to a straw man.

I'm not quite sure as to what I need to 'deal with' here, and it's that kind of mindless angst and aggression that drives people away from posting on DT.

I also struggle to understand why I've been downrated, I've been perfectly civil throughout, and I don't actually disagree with anything masher is saying at this stage.


RE: Encouraging But ...
By mattclary on 4/15/2008 12:50:45 PM , Rating: 2
My apologies for the "deal with it" comment. Wanted to delete that after I posted it... I have been seeing a lot people cry "straw man!" at the drop of a hat (and in error) on every forum I visit, I think I was being overly pissy about it. ;)


RE: Encouraging But ...
By dug777 on 4/15/2008 7:55:58 PM , Rating: 2
Thankyou, much appreciated.

I've learnt something into the bargain :)


RE: Encouraging But ...
By andrinoaa on 4/14/08, Rating: 0
RE: Encouraging But ...
By Chernobyl68 on 4/24/2008 1:33:11 PM , Rating: 2
some designs of breeder reactors gereate waste with a relatively short half life. We're simply not building them. Japan does though...


RE: Encouraging But ...
By Paratus on 4/14/2008 12:33:38 AM , Rating: 3
While that is in theory true, time in insolation is only part of the equation. You also have the efficiency of the cells , which this article addressed, how good your tracking is as power falls off with the cosine of the solar vector, and how much of the incidence solar radiation is reflected off the atmosphere.

In earth orbit you get a maximum of~1300 W/m^2. With all the above factors your lucky to get above 100-200W/m^2. You'll need ALOT of popcorn balls to replace any significant amount of dirty power.

To put it another way if you wanted to replace all the ICE vehicles on the road with solar powered electric vehicles you would need a strip of solar collectors (panels, etc) 10 miles wide by 3000 miles long........

Solar makes a lot more sense in a distributed environment. Where these flexible cells are installed on roof tops all over the country. Just think your electric bill would drop, you could charge your plug-in vehicle, and when the grid went down due to a failure, weather or homeland security scare of the day you would still have a working refrigerator for medicine, food, etc.


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