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The science is rather sound on this; melanin has been shown to produce a photosynthesis effect with ionizing radiation. Incidentally, this likely means the sola

The science is rather sound on this; melanin has been shown to produce a photosynthesis effect with ionizing radiation. Incidentally, this likely means the solar panels would actually be able to work at near maximum efficiency on partially cloudy days, even on a lightly clouded day it should still work well. It generally takes much less water to deflect visible light and reduce the efficiency of a silicon solar panel than it takes to absorb the UV that is producing power through the melanin. What I believe is important here is the melanin. If an efficient and stable way is found to manufacture a melanin-based solar panel, it could be used in a wider range than many traditional solar panels. I suppose the ideal would be to produce a traditional solar panel that is transparent to UV, allowing it to be caught in a melanin-based solar panel. In theory you could double the power output of a solar panel and extend its power production into cloudier periods.

physcab 17y ago
"It generally takes much less water to deflect visible light and reduce the efficiency of a silicon solar panel than it takes to absorb the UV that is producing power through the melanin." I'm confused by this statement. I'll try to clarify. Melanin's absorption spectrum can be found here: http://www.cl.cam.ac.uk/~jgd1000/melanin.html http://www.cl.cam.ac.uk/~jgd1000/melanin.html As you can see, it has high absorption from 300nm-700nm which is in the UV-Vis range. Similarly, silicon's absorption spectrum is here: http://www.wsi.tum.de/Research/StutzmanngroupE25/Research/Photovoltaics/tabid/220/Default.aspx http://www.wsi.tum.de/Research/StutzmanngroupE25/Research/Ph... So it absorbs much more in those wavelengths so that's why you're bound to get higher efficiencies. Alternatively, water's absorption spectrum can be found here: http://en.wikipedia.org/wiki/File:Water_absorption_spectrum.png http://en.wikipedia.org/wiki/File:Water_absorption_spectrum.... Water does not have a high absorption in this region. So clouds will not absorb wavelengths in this region. And sorry to nitpick, but nothing deflects light. Light is absorbed, transmitted, and emitted. If it is emitted in the direction from which it came, its called reflectance.
- madh 17y ago
  What about refraction?
  - physcab 17y ago
    It's similar phenomena. When light impinges on a material it is absorbed. Electrons in the ground state are lifted into a higher state, and after a very short time (nanoseconds) they relax, re-emitting that light. That light goes in every direction possible, but the light that you perceive is that fraction of the light that is emitted back in your direction...or in a refracted direction.
    - kragen 17y ago
      I do not believe that this is how refraction works. It would imply that light of frequencies other than those corresponding to the bandgap energies of the material would proceed unrefracted, or be absorbed. Furthermore, it would render coherent light incoherent, since nanoseconds are very large compared to the frequencies involved in visible light, and this incoherence would result in the light being re-emitted in every direction, not a particular refracted direction. In short, although the phenomenon you are describing is real, it is very different from refraction. It is phosphorescence and fluorescence. Refraction works because the permittivity of the transparent material is different from the permittivity of vacuum. See http://en.wikipedia.org/wiki/Permittivity http://en.wikipedia.org/wiki/Permittivity.
- lutorm 17y ago
  Light can scatter (Rayleigh scattering, Thompson scattering), which does not involve an absorption/emission event (unless you are talking about resonant scattering for example in the Lyman Alpha line). That's how clouds work. The albedo of clouds is very high, so little is absorbed. Nevertheless, the small water drops scatter the light.
  - physcab 17y ago
    Sure. I was thinking more from the material perspective, but yes there are other phenomena to consider.
- ilitirit 17y ago
  > And sorry to nitpick, but nothing deflects light. Light is absorbed, transmitted, and emitted. If it is emitted in the direction from which it came, its called reflectance. Sorry to nitpick even further, but IIUC the angle (not the direction) of reflection equals the angle (not direction) of incidence.
lutorm 17y ago
I have no idea of how melanin works as a photovoltaic, but if it indeed only converts UV light then the power output will be severely limited compared to visible-light cells, because the Sun only emits a very small part of its luminosity in the UV.
FooBarWidget 17y ago
I'm a little skeptical. How come my hair doesn't cause my head to burn on a lightly clouded day? I have a lot more hair than that device has.
- physcab 17y ago
  Every material has optical and electrical properties. Light is always interacting with materials. The difference is that you're not applying a load. Or maybe you are and its just small...I'm not too familiar with biological materials. Either way, you need to complete the circuit and channel the electron flow.
  - jacquesm 17y ago
    The circuit is normally completed at a scale where you can't use the electricity generated by the photo-electric effect. To make is useable you have to somehow collect the electrons before they fall back to their base state. For that you need a semiconductor, which effectively creates a barrier across which the electrons can not travel back. The little metal wires that are silk screened on to solar panels collect these free electrons and transport them to the edge of a photocell, where they can be used to drive a load on their way back to the substrate from which they've been liberated.

physcab 17y ago

"It generally takes much less water to deflect visible light and reduce the efficiency of a silicon solar panel than it takes to absorb the UV that is producing power through the melanin." I'm confused by this statement. I'll try to clarify. Melanin's absorption spectrum can be found here: http://www.cl.cam.ac.uk/~jgd1000/melanin.html http://www.cl.cam.ac.uk/~jgd1000/melanin.html As you can see, it has high absorption from 300nm-700nm which is in the UV-Vis range. Similarly, silicon's absorption spectrum is here: http://www.wsi.tum.de/Research/StutzmanngroupE25/Research/Photovoltaics/tabid/220/Default.aspx http://www.wsi.tum.de/Research/StutzmanngroupE25/Research/Ph... So it absorbs much more in those wavelengths so that's why you're bound to get higher efficiencies. Alternatively, water's absorption spectrum can be found here: http://en.wikipedia.org/wiki/File:Water_absorption_spectrum.png http://en.wikipedia.org/wiki/File:Water_absorption_spectrum.... Water does not have a high absorption in this region. So clouds will not absorb wavelengths in this region. And sorry to nitpick, but nothing deflects light. Light is absorbed, transmitted, and emitted. If it is emitted in the direction from which it came, its called reflectance.

madh 17y ago
What about refraction?
- physcab 17y ago
  It's similar phenomena. When light impinges on a material it is absorbed. Electrons in the ground state are lifted into a higher state, and after a very short time (nanoseconds) they relax, re-emitting that light. That light goes in every direction possible, but the light that you perceive is that fraction of the light that is emitted back in your direction...or in a refracted direction.
  - kragen 17y ago
    I do not believe that this is how refraction works. It would imply that light of frequencies other than those corresponding to the bandgap energies of the material would proceed unrefracted, or be absorbed. Furthermore, it would render coherent light incoherent, since nanoseconds are very large compared to the frequencies involved in visible light, and this incoherence would result in the light being re-emitted in every direction, not a particular refracted direction. In short, although the phenomenon you are describing is real, it is very different from refraction. It is phosphorescence and fluorescence. Refraction works because the permittivity of the transparent material is different from the permittivity of vacuum. See http://en.wikipedia.org/wiki/Permittivity http://en.wikipedia.org/wiki/Permittivity.
lutorm 17y ago
Light can scatter (Rayleigh scattering, Thompson scattering), which does not involve an absorption/emission event (unless you are talking about resonant scattering for example in the Lyman Alpha line). That's how clouds work. The albedo of clouds is very high, so little is absorbed. Nevertheless, the small water drops scatter the light.
- physcab 17y ago
  Sure. I was thinking more from the material perspective, but yes there are other phenomena to consider.
ilitirit 17y ago
> And sorry to nitpick, but nothing deflects light. Light is absorbed, transmitted, and emitted. If it is emitted in the direction from which it came, its called reflectance. Sorry to nitpick even further, but IIUC the angle (not the direction) of reflection equals the angle (not direction) of incidence.

lutorm 17y ago

I have no idea of how melanin works as a photovoltaic, but if it indeed only converts UV light then the power output will be severely limited compared to visible-light cells, because the Sun only emits a very small part of its luminosity in the UV.

FooBarWidget 17y ago

I'm a little skeptical. How come my hair doesn't cause my head to burn on a lightly clouded day? I have a lot more hair than that device has.

physcab 17y ago
Every material has optical and electrical properties. Light is always interacting with materials. The difference is that you're not applying a load. Or maybe you are and its just small...I'm not too familiar with biological materials. Either way, you need to complete the circuit and channel the electron flow.
- jacquesm 17y ago
  The circuit is normally completed at a scale where you can't use the electricity generated by the photo-electric effect. To make is useable you have to somehow collect the electrons before they fall back to their base state. For that you need a semiconductor, which effectively creates a barrier across which the electrons can not travel back. The little metal wires that are silk screened on to solar panels collect these free electrons and transport them to the edge of a photocell, where they can be used to drive a load on their way back to the substrate from which they've been liberated.