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I am designing a FPC for heating water. I was wondering about the feasibility of replacing the usual Low-iron tempered glass with Cast Acrylic sheets [owing to non-availability of the former where Im from]. I am concerned however, about its structural integrity under thermal loads. Will its optical performance remain satisfactory at the higher temperatures expected during service, or would it deform, or even melt. If it would melt, I was considering adding 5mm ordinary glass glazing above the Absorber plate, and then add the acrylic after an air gap for protection, and added insulation. However this arrangement would lead to added costs and reduced transmittivity [and thus efficiency]. I'd appreciate any input regarding the problem, and suggestions regarding the design.

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  • $\begingroup$ If you have more specific details about the material, try Matweb , then look for service temperature spec $\endgroup$
    – Pete W
    Feb 24 at 17:19
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Been done with a polycarbonate type sheet.

Actually I bought a solar collector with this type of cover. The sheet was formed with “pillow” type bulges to prevent sagging. About 5mm thick and strong enough to withstand hail etc as well as the high temperature from a panel heated when it has no water in it.

Btw, don’t need the ordinary glass that is just a further loss.

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  • $\begingroup$ As per a research paper I read, ''The infrared light transmissivity in PC sheet is roughly 40% of that in glass in 2-5 μm wave range.... PC sheet is not as good as glass for greenhouse glazing material in light transmittance, but it is excellent in insulation.'' Also, ''Solar radiation from the infrared spectrum [with a wavelength of >700 nm] provides 49.4% of solar energy''. So, as per these statements, I would be losing almost half of the incident solar radiation by using PC instead of glass, right? $\endgroup$ Feb 25 at 5:25
  • $\begingroup$ The panel I used was also used by others and with some example systems - the stored water got just as hot. If you are so wortied about those losses, do the obvious and increase absorber areea. If you really want to delve into all the parameters then read Solar Thermal Engineering by Duffie and Beckman - so much more thorough than a single research paper. And you can loose, or gain, much more energy by how you place the panel anyway. But you should be aware of that. I answered your original question sufficiently and correctly. $\endgroup$
    – Solar Mike
    Feb 25 at 6:13

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