Sciencemadness Discussion Board

Crazy Idea - What do you think?

ssdd - 23-6-2007 at 17:32

I was having an interesting conversation the other day and I came up with a neat idea.

Most modern solar cells are made from materials that convert light at one peak color of light. If these panels were able to pick up light over a larger range of colors more light could be converted to electricity thus having a higher efficiency rate. (I was searching for the frequency of light that most cells peak out at but had some problems finding it, if anyone knows please inform me.)

Now I was thinking this: Our eyes absorb light on all visible frequencies. (Actually a combination of blue, green, and red.) Now If the chemicals from our eyes (or other animals) could we perhaps use them as a type of solar cell which should have a greater efficiency level.

From what I can gather these chemicals would need to be regenerated over time and replaced. (This is far fetched but you could have bacteria generate the chemicals much as we use bacteria to generate insulin.)

I have a copy of Gray's Anatomy sitting next to me and I'm reading more about the eye to see what I can gather up, but I was just wondering how crazy you guys would think I am. ;)


-ssdd

12AX7 - 23-6-2007 at 17:48

Eyes contain photosensitive chemicals, but as far as I know, they are NOT of interest in transferring the energy.

Do read up on plants, however. They're quite good at it -- they've been going strong for the last two billion years or so (dating back to seas of cyanobacteria).

Tim

not_important - 23-6-2007 at 18:45

It's being handled by making the PV cells responsive to more wavelengths

http://www.google.com/search?hl=en&safe=off&q=multib...

Another approach is to use other power conversion methods instead of photovoltaics, such as thermal driven generators of one sort or another. More efficient thermoelectric materials would really help with this.

And Tim is correct, the photochemistry of eyes is neither good at transforming light to useful power, nor is it easy to maintain outside of a living animal.

If you look at the response curves, both the scoptic and photopic response curves of the human eye aren't hat wide, both are only about 100 nm wide at the 50% point and roughly 150 nm at the 25% points. Modern solar cells have a wider response curve than that.

cool_arrow - 24-6-2007 at 01:40

take a look at this link:

http://www.prismsolar.com/index.html

ssdd - 24-6-2007 at 03:28

Yea after sitting and reading a bit more last night I see that as everyone pointed out this wouldn't work all to well. (Not to mention cost effectiveness!)

Now the thing with plants is that they seem to not absorb green light. If I recall correctly green is the peak emission color of the sun. (Plants do most of their light conversions on violet and red.)
Off topic but why would they not use green?

Thanks for the links they turned up some cool results and cool_arrow that site was pretty neat.

-ssdd

12AX7 - 24-6-2007 at 05:57

That's something that's always stumped me a little. There are dark plants, but I don't know that they perform any photosynthesis on the green that's absorbed (i.e. it's just pigmentation).

Probably, they have never had an incentive to do so. CO2 is relatively scarce in the atmosphere. Wind blowing through a forest doesn't carry too much CO2 (currently, 0.04%), and after a few miles, it contains even less (though I don't know how much less; CO2 absorbtion is probably a slow and self-limiting thing with plants).

Now, if we blew coal burning exhaust into miles of greenhouses, maybe some plants would develop the heat resistance and efficiency to maximize growth. The problem is that Darwin is slow.

Tim

Eclectic - 24-6-2007 at 06:03

I read, or heard on one of the Discovery channels, that the green of chlorophyll may just be an evolutionary accident. Apparently there are, or have been, other photosynthetic pigments that are red, purple, and other "odd" colors. Chlorophyll may just have an evolutionary edge regarding efficiency or availability of required trace elements.

Twospoons - 24-6-2007 at 15:57

There's as much energy in the IR as there is in the visible.
Green doesn't make up that much of the total energy output.

[Edited on 25-6-2007 by Twospoons]

spectrum.png - 38kB

indigofuzzy - 24-6-2007 at 23:13

Since silicon's bandgap is around 1100 nm, and there are transparent semiconductors with larger bandgaps, couldn't a double layered solar cell produce more efficiency? Put the transparent semiconductor on top, and silicon on the bottom.

<pre>
-----------------------------
| SiC P-doped layer |
----------------------------- SiC -- frequently used in Blue LEDs,
| SiC N-doped layer | bandgap should be aroun 470nm.
----------------------------- <--- conductive SnO<sub>2</sub> or similar
----------------------------- (this layer avoids a P-N junction being formed
| Si P-doped layer | between dissimilar semiconductors.)
-----------------------------
| Si N-doped layer |
-----------------------------
| Metal substrate |
-----------------------------
</pre>

not_important - 24-6-2007 at 23:35

Quote:
Originally posted by indigofuzzy
Since silicon's bandgap is around 1100 nm, and there are transparent semiconductors with larger bandgaps, couldn't a double layered solar cell produce more efficiency? Put the transparent semiconductor on top, and silicon on the bottom.
...


Done there, been that:

single junction multigap
http://emat-solar.lbl.gov/research/Multiband.html
http://www.trnmag.com/Stories/2004/042104/Material_grabs_mor...

decent overview of multijunction and multigap research
http://gcep.stanford.edu/pdfs/solar_workshop_10_04/SolarWalu...

YT2095 - 25-6-2007 at 03:09

I could be wrong, but I know with Laser power testing it`s common to use LEDs and a current meter, Phosphide and arsenide green and red LEDs respectively for the laser beam color, so green LED is used for a green laser etc...
now this May or Maynot have anything to do with anything, but when you think of how White LEDs work, perhaps it may be possible to incorporate another Layer that absorbs and re-emits at a frequency the panel is more responsive to.
turning some of this wasted UV into visible light.

just a thought :)

cool_arrow - 25-6-2007 at 10:37

I've often wondered why so much emphasis is put on the efficiency of PV's when when the cost has to be just as big an issue. What if the the efficiency stayed at their current levels but costs were dramatically reduced? If a company announced that they had figured out how to manufacture these things at a fraction of what the currently cost I think that would be big news. Perhaps there are some limits to how cheap the materials to mfr. can be sold?

YT2095 - 25-6-2007 at 12:20

well I currently produce (no pun intended) 12v at 5 amps with the combined power of my PV panels, so I`de welcome ANYTHING that could lower the price for the same product!

Twospoons - 25-6-2007 at 14:37

The emphasis on efficiency is relevant to cells intended for space use, where reductions in launch weight are really important.

For terrestrial use, where there is plenty of room (like on a roof), then cost really is the critical factor. Or, more correctly, $ per watt over lifetime. No good having a cheap cell that only lasts a week!

The other factor is we really need a manufacturing process that consumes much less energy than the cells can produce over their life, otherwise we are wasting our time.