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Flexible panels direct mount to the roof.


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#11 ntsqd

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Posted 12 February 2021 - 03:16 AM

Not too sure about the 3M adhesive being a thermal conductor. If it is not then you won't have gained much for your trouble.


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#12 searching for nowhere

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Posted 12 February 2021 - 04:11 PM

I ran across these flexible panels on the web.  They claim to not have the heat problem.  Anybody know anything about these panels?

 

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#13 ri-f

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Posted 12 February 2021 - 07:55 PM

I ran across these flexible panels on the web.  They claim to not have the heat problem

All Solar PV Modules will have a parameter indicated by the manufacturer called the “temperature coefficient”. The temperature coefficient represents the percentage at which the panel efficiency reduces at each increase in degree Celsius (°C). Unless a manufacturer has managed to defy the laws of thermodynamics, loss of efficiency will occur in any panel that does not provide for dissapation. Even with a low temperature coeffient there will be efficiency losses that add up. The higher the temperature, the greater the loss. Any air gap <= 4 inches will help improve panel efficiency. While you might, according to a manufacturer's marketing brochure, safely be able to mount a low-temperature coefficient solar panel without any air gap, with only an adhesive backing on the panel's underside, that in itself does not mean it will perform optimally when exposed to strong direct sun. There are other reasons besides solar efficiency for leaving an air gap, too. But, more to the point, If you are willing to accept the tradeoff of efficiency degradation through heat buildup, then maybe direct surface-to-surface mounting is an option you can consider.

 

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#14 searching for nowhere

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Posted 13 February 2021 - 12:24 AM

Thanks for the explanation.  No magic. 


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#15 ntsqd

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Posted 13 February 2021 - 01:06 AM

Marketing trumps physics every time!


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#16 JHanson

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Posted 13 February 2021 - 03:52 AM

I'm not sure we're not worrying too much about this. We had semi-flexible panels mounted directly to the roof of our FWC in 2012; when we sold the camper last year they were still functioning perfectly. I glued two Renogy panels directly to the roof of the pop top of our Land Cruiser Troop Carrier last year. Short of mounting rigid panels an inch or more above the roof, I don't believe there will be much difference between different mounting strategies in terms of reducing the heat issue. The temperature under the roof skin directly under the panels should be lower than the top of the panels with any mounting system, if it's a differential you want to achieve. An air gap that doesn't allow free air flow wouldn't do much if anything to reduce temperatures.

 

It's well-known that PV panels produce more power in colder weather. We simply take this into account in Arizona when figuring the wattage we need. 

 

For me the benefits of having the panels adhered directly to the roof (lower profile to avoid snagging overhanging vegetation and for "aerodynamics," invisibility to passersby), outweighs any disadvantages. FWC and Troopy below.

 

8267748122_c5e8e29091_z.jpg

 

50937682981_e6747ec73a_z.jpg


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#17 steve whiteside

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Posted 13 February 2021 - 03:58 AM

I'm not sure we're not worrying too much about this. We had semi-flexible panels mounted directly to the roof of our FWC in 2012; when we sold the camper last year they were still functioning perfectly. I glued two Renogy panels directly to the roof of the pop top of our Land Cruiser Troop Carrier last year. Short of mounting rigid panels an inch or more above the roof, I don't believe there will be much difference between different mounting strategies in terms of reducing the heat issue. The temperature under the roof skin directly under the panels should be lower than the top of the panels with any mounting system, if it's a differential you want to achieve. An air gap that doesn't allow free air flow wouldn't do much if anything to reduce temperatures.

 

It's well-known that PV panels produce more power in colder weather. We simply take this into account in Arizona when figuring the wattage we need. 

 

For me the benefits of having the panels adhered directly to the roof (lower profile to avoid snagging overhanging vegetation and for "aerodynamics," invisibility to passersby), outweighs any disadvantages. FWC and Troopy below.

 

8267748122_c5e8e29091_z.jpg

 

50937682981_e6747ec73a_z.jpg

Good input from someone that has actual experience!  :-).   Also thanks for the pics those look like clean set ups!   Steve


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#18 ri-f

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Posted 13 February 2021 - 07:48 AM

Short of mounting rigid panels an inch or more above the roof, I don't believe there will be much difference between different mounting strategies in terms of reducing the heat issue. The temperature under the roof skin directly under the panels should be lower than the top of the panels with any mounting system, if it's a differential you want to achieve. An air gap that doesn't allow free air flow wouldn't do much if anything to reduce temperatures.

 

Yes.that is correct, and thanks for pointing that out in case anyone is confused about that, but we're talking about a free flowing air gap. Not sure why anyone would create an air gap under a PV panel, specifically for dissapation of heat, and then enclose that gap and trap the heat. Seems like circular logic.


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#19 rando

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Posted 13 February 2021 - 02:48 PM

I have had two sets of semi-flexible panels on the roof of campers, unfortunately both have failed (3 panels in total).   The first panel was an earlier and expensive panel VHB taped to the top of the my old pop-top landcruiser.    It failed for no apparent reason.  This was an aluminium backed panel mounted to an aluminium roof, so about as good as it gets for heat dissipation.   This was a major pain to remove due to the VHB tape and absolutely destroyed the panel in the process, so no chance for a post mortem.

 

The second set failed in a hail storm (2 panels, both failed).   I had at least learned from the first failure and had VHB's some 1"x1/8" aluminium bars to the roof with studs to mount the panels to, so removal was easy.  Unfortunately the panel sizes changed slightly over the years and I couldn't find a new panel with the same mounting holes.   So yes failures happen, and you want to be aware of that.

 

As to heat dissipation - when we want to get heat out of an electrical component, we strap it to a heat sink or radiator.  The aluminium roof of the FWC is a pretty decent radiator being a large sheet of thermally conductive Aluminium, painted white.   My feeling is that bonding it to the aluminium roof is probably better than leaving an air gap, at least thermally.   Now if you were mounting these to a black asphalt roof (normal application) then an airgap would completely make sense.


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#20 steve whiteside

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Posted 13 February 2021 - 04:06 PM

I have had two sets of semi-flexible panels on the roof of campers, unfortunately both have failed (3 panels in total).   The first panel was an earlier and expensive panel VHB taped to the top of the my old pop-top landcruiser.    It failed for no apparent reason.  This was an aluminium backed panel mounted to an aluminium roof, so about as good as it gets for heat dissipation.   This was a major pain to remove due to the VHB tape and absolutely destroyed the panel in the process, so no chance for a post mortem.

 

The second set failed in a hail storm (2 panels, both failed).   I had at least learned from the first failure and had VHB's some 1"x1/8" aluminium bars to the roof with studs to mount the panels to, so removal was easy.  Unfortunately the panel sizes changed slightly over the years and I couldn't find a new panel with the same mounting holes.   So yes failures happen, and you want to be aware of that.

 

As to heat dissipation - when we want to get heat out of an electrical component, we strap it to a heat sink or radiator.  The aluminium roof of the FWC is a pretty decent radiator being a large sheet of thermally conductive Aluminium, painted white.   My feeling is that bonding it to the aluminium roof is probably better than leaving an air gap, at least thermally.   Now if you were mounting these to a black asphalt roof (normal application) then an airgap would completely make sense.

 

 

Your post kind of lends credence to the industrial velcro...You make an excellent point about the conductivity of the Aluminum roof.  Steve


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