Solar Collectors

Why are plants green, while solar panels are black?

Ever touched a solar panel that has been out in the sun for a while? It's pretty hot. Too hot for the cells of a plant to function.

Plants is using chlorophyll in a photo-chemical process.
Solar cells are using a heat carrier in a thermo-dynamic process.
Two different processes.

Originally posted by AThousandYoung
Why are plants green, while solar panels are black?

a solar panel is a device which uses the sun's energy to heats up water. black attracts heat, and thus is rather useful here.

not sure why solar cells are black though (they provide electricity). it may be the same reason, although it may just be because of the materials they are built from.

*shrugs*

Originally posted by genius
a solar panel is a device which uses the sun's energy to heats up water. black attracts heat, and thus is rather useful here.

not sure why solar cells are black though (they provide electricity). it may be the same reason, although it may just be because of the materials they are built from.

*shrugs*

Actually, a "solar" (or photovoltaic) cell converts light directly to electricity. The black surface is an anti-reflective coating applied to minimize the amount of light energy that bounces off.

See http://science.nasa.gov/headlines/y2002/solarcells.htm or
http://www.howstuffworks.com/solar-cell.htm

Originally posted by genius
a solar panel is a device which uses the sun's energy to heats up water. black attracts heat, and thus is rather useful here.

not sure why solar cells are black though (they provide electricity). it may be the same reason, although it may just be because of the materials they are built from.

*shrugs*

The answers have already been given.

Solar panels work better the hotter they get, and black things heat up quicker than non-black things. (Actually I'm talking about the sort of solar panel we are used to, e.g. on the roofs of houses, rather than solar cells which use light to create electricity).

Plants rely on light, not heat, for photosynthesis. They evolved the molecule chlorophyll to extract out the energy from light, and it just so happens that chlorophyll is green.

This means that if a plant which uses photosynthesis wants to be any colour other than green, its going to have to produce the colour itself, so it better have a good reason for doing so.

They evolved the molecule chlorophyll to extract out the energy from light, and it just so happens that chlorophyll is green.

This means that if a plant which uses photosynthesis wants to be any colour other than green, its going to have to produce the colour itself, so it better have a good reason for doing so.[/b]

well, not quite.

Chlorophyll is a complex biomolecule which contains magnesium. These molecules contains specialized ring shaped structures that capture preferred wavelengths of light. Green is not a preferred wavelength so it is not "captured" by the Chlorophyll and therefore is reflected back to our eye.

You're making it sound more complicated than it is. Anything which is green reflects green light. That's what " is green" means.

So why is it that the molecule that evolved to do photosynthesis was green? Perhaps it has something to do with the wavelengths of light from the sun. Does the sun emit more of one wavelength of light than another? Was chlorophyl the molecule that evolved because it is good at absorbing the most abundant wavelengths of light and it just happens to reflect green light that the sun does not produce much of?

Originally posted by Fat Lady
The answers have already been given.

Solar panels work better the hotter they get, and black things heat up quicker than non-black things. (Actually I'm talking about the sort of solar panel we are used to, e.g. on the roofs of houses, rather than solar cells which use light to create electricity).

Plants rely on light, not heat, for photosynthesis. T ...[text shortened]... , its going to have to produce the colour itself, so it better have a good reason for doing so.

i was just making it clear that there was a difference between solar cells and solar panels.

Originally posted by smomofo
So why is it that the molecule that evolved to do photosynthesis was green? Perhaps it has something to do with the wavelengths of light from the sun. Does the sun emit more of one wavelength of light than another? Was chlorophyl the molecule that evolved because it is good at absorbing the most abundant wavelengths of light and it just happens to reflect green light that the sun does not produce much of?

"Does the sun emit more of one wavelength of light than another?"

Yes, that's true. One wavelength is at maximum and this is yellow. If you mix all wavelengths of the sun you get pure white.

"Was chlorophyll the molecule that evolved because it is good at absorbing the most abundant wavelengths of light and it just happens to reflect green light that the sun does not produce much of?"

The green color of chlorophyll is not optimized of Mother Nature for the photo-chemical process. It just happened and it was god enough. Scientists are trying to mimic the chlorophyll but are using other atom than magnesium to enhance the effect. Man beats nature, so to say. The result might very well be a low-cost, effective photo synthesis.

Originally posted by Fat Lady
The answers have already been given.

Solar panels work better the hotter they get, and black things heat up quicker than non-black things. (Actually I'm talking about the sort of solar panel we are used to, e.g. on the roofs of houses, rather than solar cells which use light to create electricity).

Plants rely on light, not heat, for photosynthesis. T ...[text shortened]... , its going to have to produce the colour itself, so it better have a good reason for doing so.

Seems like there's an extremely good reason; there's a whole lot of green light out there that isn't being used by any other plant!

Solar cells have wavelength bands of maximum energy transfer. Most cells have a response to wavelengths, called the photonic bandgap, that specifies the wavelength (color) of the light that will produce usable electricity. Most cells today have single bandgap materials, say a 2 ev (electron volt) bandgap, somewhere in the vicinity of green.
Now the sun produces usable energy in the 0.4 ev to 4 ev, infrared to ultraviolet and no single bandgap material will get more than about 30% efficiency as a result. The sun deposits about 1 KW per meter ^2, on top of the atmosphere. The amount that gets to the ground may be only one tenth of that or half at best so suppose we get 500 watts per square meter and the cell is only 30% efficient, the cell will give out 150 watts if it is one square meter in area. Recently there have been discovered what is called multiple photonic bandgap material, it means the cell will respond to a wider range of colors than before and may lead to cells over 50 % efficient. Here is a link to a 50 cent tour of the concept:
http://www.lbl.gov/~msd/PIs/Walukiewicz/02/02_8Walukiewicz_InN.pdf#search=%22photovoltaic%20bandgaps%22

Originally posted by AThousandYoung
Seems like there's an extremely good reason; there's a whole lot of green light out there that isn't being used by any other plant!

I find it ironic that when people tell you to think of nature and be friendly to the environment they tell you to "THINK GREEN" when in fact, nature doesn't like green at all for the most part, and bounces the green wave-length of light away.

Nature hates green yet we're told to think green. Crazy

Originally posted by uzless
I find it ironic that when people tell you to think of nature and be friendly to the environment they tell you to "THINK GREEN" when in fact, nature doesn't like green at all for the most part, and bounces the green wave-length of light away.

Nature hates green yet we're told to think green. Crazy

In solar energy, think black! The photons check in but they don't check out! Like the roach hotel! 'They' are also working on materials that produce a chain of electrons, say 3 or 4 electrons for each impinging photon. I think in another 5 or 10 years we will see 60 to 70% efficiency ratings. Of course they may be more expensive also.
There is also work going on on solar converting polymers, polymers doped with a molecule that conducts electricity and others that promote conversion of light to electrons. It would be not as efficient as silicon cells but so much cheaper that even if it was only 8 or 10% efficient, they could be 100 times cheaper and therefore take up more surface area but a lot less expensive than silicon or Gallium Arsenide or other semiconductor material.