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Bifacial solar panels have a glass backplane instead of the usual aluminum and are designed to absorb and convert to electricity light incident on either face. Many manufacturers claim that their bifacial panels operate at lower temperature than normal (monofacial) panels because bifacial panels transmit the 20% of the solar spectrum that is too low-energy to be absorbed by silicon. See for example this manufacturer's datasheet. Meanwhile, the only reputable study I could find (apologies for the paywall) was of a lab-scale cell and not a commercial module. That study argues that convection is the dominant heat transfer mechanism and so the differences in optical absorption and emission aren't relevant. However, temperature differences of a few degrees centigrade can have a noticeable impact on solar cell efficiency and useful life. Anybody have a compelling argument or know of other relevant experimental work on this topic?

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    $\begingroup$ The idea that "convection is the dominant heat transfer mechanism and so the differences in optical absorption and emission aren't relevant" sounds a bit weird to me: convection may be the dominant thing removing heat from the cell, but it's absorption of thermal radiation that's putting the heat there in the first place. The less optical radiation you absorb, the less convection has to carry away. At least, that's how it seems to me without knowing much about the specifics of the cells you're talking about. $\endgroup$ – Nathaniel Aug 27 '13 at 7:37
  • $\begingroup$ Granted the input heat is from radiation, but convection could be strong enough to set the cell's boundary temperature to ambient even if the radiation intensity is increased by 20%. Conduction is likely the dominant heat transfer mechanism within the cell and could also potentially fully compensate for the increased radiation if convection made the cell surface a good enough heat sink. I'm not saying that the above is happening, just that it's hard to rule out. $\endgroup$ – sevenofdiamonds Aug 29 '13 at 7:10
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A typical bifacial module will transmit energy that passes through the silicon as well as the energy that passes around the edges of the cells which would otherwise be absorbed in a typical monofacial module design, around 3% of the total. Using the 20% energy transmission value quoted above, a bifacial solar module will absorb ~23% less energy than a monofacial module. Other considerations to be taken into account would be thermal transmissivity from the back of the cell to the glass (or in the case of monofacial modules, aluminum) and differences in mounting the module. Bifacial modules are often edge-mounted without a frame, whereas monofacial modules are typically framed. I would expect the framed design to allow for less efficient convection. Of course, the bifacial module is designed to allow energy reflected from the surface over which it is mounted to be absorbed by the cells, so the spectral characteristics of the background play into the result.

As a former engineer in a bifacial module supplier, it was our experience that we showed lower temperatures than those claimed by monofacial manufacturers, but true comparative studies were expensive.

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  • $\begingroup$ Does this imply that the temperature difference was almost too small to be noticeable? $\endgroup$ – user6972 Sep 5 '13 at 4:23
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For what it's worth, lg310's seem to run a little cooler than gxb300's, at least on my roof.

See also http://dx.doi.org/10.1016/j.egypro.2014.02.148 but read Table 4 carefully. The differences seem to be small.

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  • $\begingroup$ Welcome to PSE. To make a comment please write it in comment box. Please explain your link thoroughly, because links get rot. Providing a link is not an answer , unless it is self contained in answer. $\endgroup$ – Anubhav Goel Apr 25 '16 at 3:26
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    $\begingroup$ While I agree that it would be best to just copy out (with attribution) the most important values and explain them, I think that "link-rot" is not a problem here - the DOI is made to prevent that. $\endgroup$ – Martin Apr 25 '16 at 9:18

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