Mounting flexible solar panel with insulation

[Zirdu]

I am thinking of attaching semi-flexible solar panels (Suaoki, 100 W see: https://www.amazon.com/SunPower-Flexible-Connector-Charging-Compatibility/dp/B01DXYNGA0/ref=cm_cd_al_qh_dp_t) via tape to roof of new Four Wheel Camper. I live in Southwest and am concerned about heat degrading performance of the unit. Do you think it would help or hurt to put thin (1/4 inch) insulation between the panel and the roof, using tape on the edges to attach?

 

[DesertDave]

I think the heat concern is best mitigated by air space under the panel itself, to help reduce the temperature of the panel. My brain says that putting the insulation board under the panel probably won't help heat leave the panel, but it might help contain it more.

 

[ntsqd]

If anything I'd be looking for a bulk buy on thermally conducting grease to spread inside the adhesive border. Try to use the roof skin (if metal) as a heat-sink.

 

[fuzzymarindave]

How about a sheet of 3D open cell mat between the panel and the roof to allow airflow?

 

[Zirdu]

Thanks for the replies. I have read all the posts about the failures of the tape or glue on flexible panels. Some seem to work, some not. Not sure of the reasons. But I suspect the failures are mostly due to heat. It gets very hot in the SW, and the aluminum roofs get hotter. So I am thinking that the flexible panel in contact with the aluminum roof actually gains heat in the hot sun from being in contact with the roof. Maybe the successes are people who live and camp in more northerly climates?

But I love the idea of the light weight and simplicity of the flexible panels. Now I am thinking of mounting Suaoki panels on a polycarbonate 8mm twin wall sheet (https://www.amazon.com/Easy-Ship-clear-Twinwall-Polycarbonate/dp/B013XIVX0Q/ref=sr_1_1?ie=UTF8&qid=1471804296&sr=8-1&keywords=twinwall+polycarbonate). These panels are designed for outdoor use and are very strong. VHB tape the twin-wall to the roof, and VHB the panel to the twin-wall. Leave a 5 inch gap in the middle of the panel for more ventilation. That would give some air flow under the panel, and it would not pick up heat from contact with the hot aluminum roof.

The Suaoki panels claim that they have a "Working Temperature" of -40 to +185 degrees. I doubt it would get that hot even 5/16 inch off a hot aluminum roof in Death Valley in the summer? And I don't plan to camp anywhere in the summer in much over 100 degrees!

I ordered a new Grandby, so I have a few months to decide. Maybe something better will come along in the meantime.

 

[Zirdu]

I measured the temperature of the roof and solar panel on my current camper during the day yesterday:

Location St. George, UT
August 23, 2016
Partly cloudy, though every temperature reading was done in full sun, except for the first in the garage.
1999 Eagle camper, with Solar Cynergy 120 Watt solar panel, mounted on 6 Z feet.
I had the Fantastic Fan on low and the Engle Fridge operating on high, for a load.
Lower edge of aluminum panel frame sits 3/4 to 1 3/16 inch off the roof, and panel thickness was 1.3 inches.
I used a handheld infrared thermometer to measure surface temperature. Roof is aluminum painted white (a bit dirty).

Time Outside Roof Panel
8 AM 76 81 81 (inside garage in shade)
9 AM 76 79 76
10 AM 78 102 106
11 AM 81 107 109-118
12 AM 85 109 114-122
1 PM 88 114 128
2 PM 91 117 124-129
3 PM 92 116 122-128
4 PM 94 120 125-130
5 PM 96 108 105-109
6 PM 97 98 93

The panel had different temperature readings depending on the particular cell measured. Sometimes I gave the range, other times just the average. When operating in full sun toward noon, the panel was hotter than the roof. During the morning and afternoon, the panel was actually cooler than the roof.

When working, the solar cell must be taking a certain amount of the incident solar energy and removing it, through the wires, to be changed into heat in operating the fan, fridge, charging the battery inside the camper. That would explain why the dark panel would actually read a cooler temp than the white roof at times.

I am surprised at how hot the panels do get at times, even in what is a somewhat moderate summer day in St. George, UT. Dring the heat of mid day, with air temps 91 to 94, I was pushing 130 degrees for surface temp in some solar cells.

For my next test, I may put insulation under half of the panel, and take the temperatures of both sides, to see if the air circulation under the panel makes a big difference. If it works, I am including a picture of my panel and roof.

 

[Zirdu]

Today I stuffed fiberglass insulation under one end of my 120 Watt solar panel. Mounted as stated in post above.

Put out in sun at 3 PM, turned on the Engle fridge, and turned the Fantastic Fan on high. Ambient temperature is 90 degrees, with a very slight breeze. No clouds between sun and me.

At 3:40 PM: Temp of uninsulated side: average of 108 degrees. Temp of insulated side: average of 121 degrees. Again 3 or 4 degree variance in temperature depending on the solar cell measured.

Conclusion: Air space under fixed panel of about one inch, vs. fiberglass insulation under panel, makes for about a 13 degree difference in temperature in solar cell temperature, when panel is under load.

 

[Vic Harder]

great data! I too would like to go flexible vs big and beefy rigid panels, but am concerned about reliability. Leaning towards big and beefy right now

 

[Zirdu]

I don't know that the flexible panels are inherently any less reliable than the old rigid panels with glass, frames, etc. I suspect the problems people have had with them are because of higher operating temperature from being glued directly to the camper roof. As my experiment showed, lack of air circulation causes higher solar cell operating temperatures.

I am now thinking of using VHB tape to attach a light weight 1 inch square aluminum channel to the roof, then attach the flexible panels to the square channel. Maybe drill holes in the channel for additional air circulation. That way I get the best of both worlds: Light weight and small air resistance of the flexible panels, and some air circulation under the panel for cooling.

You apparently don't need much of that 3M VHB tape for a solid connection. I see that AM Solar sells "sticky feet" mounts that come with the VHB tape already on the bottom of each mount. Four mounts per rigid panel. Total square inch of VHB tape to mount a rigid, heavy panel is only 10 square inches, 2.5 sq inch per foot. They say this is more than sufficient to hold a heavy, rigid and 1.5 inch thick panel on your RV going down the highway at high speed! It seems it would take even less adhesive to securely attach the thin, light, flexible panels. I don't see why anyone drills into their roof anymore. If I am not mistaken, FWC uses adhesive to attach the roof of our FWC campers to the support ribs.