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etmax
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Gold
Re: Natural fit
etmax   7/12/2013 11:33:41 AM
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Thanks Karl, points well made but I think if you used the measure of how much of the solar radiation is a lattice match for Silicon (very narrow view) we would see higher numbers from silicon too up to 86% (although not as high as just the thylakoids). There's an IEEE article that suggests that quantum efficiencies of solar cells can exceed unity as sometimes two electrons are released for one photon. That's why I see narrowing the field of view to one thing only and not stating that is somewhat misleading. I'm not saying they are deliberately misleading us, more likely is a reporter left all of the stuff out he didn't understand resulting in the article.

karl
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Silver
Re: Natural fit
karl   7/12/2013 11:08:16 AM
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The efficiency discussed in the Wikipedia article is for the conversion of sunlight into biomass. The starting point, 100%, is for the conversion of the entire bandwidth of sunlight that falls on the leaf into biomass. The calculation of inefficiencies begins with subtracting all bandwidth that is not bioavailable, then all that is reflected from the surface of the leaf, and all photons that strike components other than cloroplasts. Energy used to make sugar, and energy used to keep the plant alive in the dark or to maintian roots are also deducted. This is therefore a measure only of what ends up as new growth, or biomass (while from the "plant's point of view" the goal is survival as a whole, and job well done!)


The scientists in the article are likely referring to the efficiency of the thylakoids, starting with 100% of bioavailable wavelengths that actually strike the cloroplast, and at only the conversion to electrons after splitting the water molecule. In fact, I think they are referring to the efficiency of the thylakoid for conversion of light to electrons.

There is one other inneficiency cited in the Wiki article that may affect the accuracy of the claim by the scientists:

"24% of the absorbed photon energy is lost due to degrading short wavelength photons to the 700 nm energy level"

If this loss is after absorption by the cloroplast but before the conversion by the thylakoids, then the scientists may be referring only to the efficiency of the thylakoids.

If the resulting solor cell technology they create uses the modified thylakoids to directly convert sunlight into electrons then the only loss when measured as other solar cells are measured would be the 47% of non-bioavailable soar bandwidth, leaving at least 50% for conversion. That's quite a good conversion, and double current technology.

 

etmax
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Gold
Re: Natural fit
etmax   7/12/2013 9:34:11 AM
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Thanks for posting, it's interesting stuff. I was however puzzled at the claim of 100% efficiency in plants (or for photosynthesis, so I googled it and got this from Wikipedia: "which results in an overall photosynthetic efficiency of 3 to 6% of total solar radiation". Sugarcane is the exception achieving up to 8% This is a far cry from the 24% achieved in labs for silicon photocells. Wikipedia talks about the theoretical maximum being ~40% for the wavelengths that plants utilise but a lot of real world stuff gets in the way. This match more closely what I remember.

Here's the link for those interested:

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


I think maybe the boon here would be that they are sooo cheap that maybe acres could be covered for a few dollars (metaphorically)

vimalkumarp
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Gold
Re: Natural fit
vimalkumarp   7/12/2013 1:18:28 AM
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This is Biomimetics at its best...!

Ann R. Thryft
User Rank
Blogger
Re: Natural fit
Ann R. Thryft   7/11/2013 6:46:54 PM
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This does seem intuitively obvious in a hindsight kind of way, doesn't it? Thanks for reporting these results.

Elizabeth M
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Blogger
Natural fit
Elizabeth M   7/11/2013 7:07:00 AM
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It makes perfect sense to use plants to harvest solar energy in solar panels or cells, as they're nature's original solar-energy harvesters. I am only surprised this type of research hasn't been going on longer. I think if there can be a way to use this method commercially, it could be a real breakthrough in solar energy cell development and certainly make the cells more environmentally friendly.

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