Photovoltaic solar panels?

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solar panels Question by bryant m: why are photovoltaic solar panels “relatively inefficient”?
Does it have to do with a “small” number of photons striking the panel relative to the size of the panel (i.e. panel would have to be huge) – or the inability of the cells to utilize all of the photons striking the panel (i.e. more photons bouncing off than utilized) or something completely different.

Best answer:

Answer by Frank N
The wavelength of light needs to be closely matched to the bandgap of the semiconductor material. Some newer, multilayer photovoltaic cells are more efficient because each layer absorbs photons of a different wavelength. They already use antilreflective coatings to reduce reflected light.

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This entry was posted on Tuesday, April 24th, 2012 at 8:29 am and is filed under Solar panels. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

 

2 Responses to “Photovoltaic solar panels?”

  1. Santa Claus Says:

    Typical photovoltaics only use somewhere around 15% of the light energy that strikes them. More efficient cells are being developed but they are costly and most are only prototypes.

  2. amansscientiae Says:

    The first answer got it right: photons with energies below the bandgap of the semiconductor material can not separate electrons and holes. Any photon energy significantly above the bandgap is lost as heat. This limits the max. efficiency of a singly type of material for the solar spectrum to approx. 25%. Silicon is actually pretty close to that theoretical limit. With two bandgaps optimized for the right wavelengths in the solar spectrum over 30% efficiency is possible. Three bandgaps can reach 40% in parctice (and this has been achieved quite some time ago) and cell structures with four bandgaps and more are in development. Ultimately 60% efficient solar cells are certainly possible and there are also ways to convert one photon into two with longer wavelengths that are better suited for cheap semiconductor materials , which would remove the cost disadvantage of multilayer cells. In the end its all about lowering cost. At some point optimizing cell efficiency is a lost cause. I would venture to guess that 60% is an economic limit.

    The thermodynamic limit, by the way, is given by the temperature of solar radiation and the temperature of the solar cells. It can be estimated by an ideal Carnot process to be less than (5600K-300K)/5600K=94.6%. Concentrating solar thermal plants can easily do 40% today and will probably do close to 60% a few decades from now.

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