43 replies to this topic

[steve whiteside]

Gents, I looked at the lay out of my roof given the vents and the installed Yakama tracks.  I think I can get 4 of these (100w Newpowa flexible) panels up there between the obstructions.  Reading  this forum is seems like it is not advised to glue directly to roof since the heat from the panel has no where to go and then the panel gets very hot. The heat can damage the panel. I saw where some guy (Tito?) put a thin, channeled/ribbed piece of plastic between the panel and the roof to provide an insulate barrier.  

 

First off, That thin insulating barrier may protect the roof from heat but I don't see how it is helping the panel off-load heat.  Am I missing something?  Isn't the idea to provide some means for the panel to transfer heat not insulate the roof??  

 

It seems like many people build a bracket and then thy have big air gap to allow the heat to dissipate.  The downside to this is the air drag 24/7 as you drive down the road.  

 

I wonder about industrial double sticky foam tape fully across the top, the middle and the bottom?  Get the kind that is 1/8" thick with foam to provide some air gap.  I would probably also tape the leading edge for pealing tendencies from the wind.

 

thoughts?

 

Steve

[Jack]

Before I mounted my panels, I talked with RK Pawley, who does camper mods in Reno and is well spoken of. He's not a fan of flexible panels, primarily for reliability, but has mounted flexible panels on a few campers/vans with velcro and not had any problems.

I put my panels down with 2" high strength velcro. A strip in the front, the center and on each side. This leaves an air gap under the panel of about 1/4". There are gaps in the front and sides for airflow. I also put tape on the front edge with a gap in the center.

 

That was this past fall and we have not been out of the PNW so we have not been in high sun and high temperatures. I have a small battery operated temperature logger that so far has shown little temperature rise. The panels have stayed put.

 

When we are able to travel into high sun and temperature I will track the panel temperatures closely. If I do see a temperature problem, my plan is to double up the velcro to lift the panels up to a bit less than 1/2" off the roof.

 

I stayed away from a polycarbonate layer. It may protect the roof by insulating it, but what you really want is airflow to remove the heat so that the panels are more efficient.

 

 

[steve whiteside]

Before I mounted my panels, I talked with RK Pawley, who does camper mods in Reno and is well spoken of. He's not a fan of flexible panels, primarily for reliability, but has mounted flexible panels on a few campers/vans with velcro and not had any problems.

I put my panels down with 2" high strength velcro. A strip in the front, the center and on each side. This leaves an air gap under the panel of about 1/4". There are gaps in the front and sides for airflow. I also put tape on the front edge with a gap in the center.

 

That was this past fall and we have not been out of the PNW so we have not been in high sun and high temperatures. I have a small battery operated temperature logger that so far has shown little temperature rise. The panels have stayed put.

 

When we are able to travel into high sun and temperature I will track the panel temperatures closely. If I do see a temperature problem, my plan is to double up the velcro to lift the panels up to a bit less than 1/2" off the roof.

 

I stayed away from a polycarbonate layer. It may protect the roof by insulating it, but what you really want is airflow to remove the heat so that the panels are more efficient.

Jack, thanks for the info.  I like your solution and it is in line with what I have been thinking.  steve

[lostcreek]

Couple of thoughts, based on my own experience and others':

 

- 3M VHB is very sticky and reliable for lightweight flexible panels, as long as your roof is suitable & clean (mine is bare aluminum).

There are a number of varieties of VHB, research and find the appropriate one for your materials.  The one I use was pretty easy to remove after 3 years.

 

- Flexible solar panels seem to generally get a bad rap on nearly all internet discussion boards, but many people do not seem to realize that 1) brands differ, there are some high-quality ones that reliably work well and for a long time.  You get what you pay for.   2) some of us need light panels because we have pop-up roofs that will not work well if overloaded.  I happen to have 3 flexible panels - two excellent quality (expensive) and one average quality (cheap).  All use adhesive of one sort or another and are very securely mounted.  This also avoids unnecessary holes & brackets in & on the roof.

 

- It is not necessarily so that flexible panels generate extra heat on their back (bottom) sides.  There is some info out there that these release all or most of their heat from the top, but I have not yet been able to satisfactorily verify that.  In any case, my next cheap 100W flexible panel will be mounted with a layer of plastic corrugated board between roof and panel.

[ntsqd]

All panels are facing a heat source, admittedly one a long ways away, but it's pretty effective even at that distance. For a panel to radiate out heat out of the top face it has to drive backwards against that heat source. Clearly this works, but I have to wonder what doing so costs us?

 

I believe that I was the first to post about the need for the backside of a panel to be able to operate at a lower temp than the top surface. I suspect that my comments were taken to mean that the roof needed to be insulated from this heat. I never intended that conclusion. The roof would be facing the sun if the panel were not there. I doubt that any panel would act to make that temperature even greater than direct exposure. What I was getting after is, that I was told by a friend in the power generating industry, who deals with PV farms semi-regularly, that the cooler the backside can be made to operate directly increases the panel's efficiency. Said differently, the larger the temperature difference between the top and bottom surfaces of the panel, the better it will work. There are practical limits to this, and since I don't see the PV's in those farms fitted with actual heat-sinks on their backsides I wouldn't get too crazy going down that particular path. I'm pretty sure that if there was a long term performance gain to be had that was economically viable then those farms could justify several miles of extruded aluminum heat-sinks.

 

IF (big word) I were to use a flexible panel in a fixed installation I would use a thermally conductive adhesive to bond it to a thin sheet of aluminum. That sheet would then be mounted in such a way as to promote airflow between it and the camper roof.

[steve whiteside]

All panels are facing a heat source, admittedly one a long ways away, but it's pretty effective even at that distance. For a panel to radiate out heat out of the top face it has to drive backwards against that heat source. Clearly this works, but I have to wonder what doing so costs us?

 

I believe that I was the first to post about the need for the backside of a panel to be able to operate at a lower temp than the top surface. I suspect that my comments were taken to mean that the roof needed to be insulated from this heat. I never intended that conclusion. The roof would be facing the sun if the panel were not there. I doubt that any panel would act to make that temperature even greater than direct exposure. What I was getting after is, that I was told by a friend in the power generating industry, who deals with PV farms semi-regularly, that the cooler the backside can be made to operate directly increases the panel's efficiency. Said differently, the larger the temperature difference between the top and bottom surfaces of the panel, the better it will work. There are practical limits to this, and since I don't see the PV's in those farms fitted with actual heat-sinks on their backsides I wouldn't get too crazy going down that particular path. I'm pretty sure that if there was a long term performance gain to be had that was economically viable then those farms could justify several miles of extruded aluminum heat-sinks.

 

IF (big word) I were to use a flexible panel in a fixed installation I would use a thermally conductive adhesive to bond it to a thin sheet of aluminum. That sheet would then be mounted in such a way as to promote airflow between it and the camper roof.

 

So, what you are getting at is the backing material should be conductive to offload heat not insulating such as the plastic corrugated material.  In fact, to insulate behind the panel works against you vs just an air gap that allows some convection.  I agree with you that some sort of thin sheet of metal the conducts heat would be perfect.  I used to have this roll of thin copper that had adhesive back on one side.  I twas like super heavy duty tin foil.  It was 24" wide.  Im thinking it would have been perfect backing material to the solar panel. Then install the panel with an air gap- allowing the air to flow over the copper backing.  

 

Steve

[steve whiteside]

You know what might be an easy solution.  Use some of that 3M adhesive spray with some heavy duty aluminum foil.  Coat the back of the panel with aluminum foil and then install with a small air gap (like with the heavy duty velcro).  Aluminum is a pretty good conductor of heat and that 3M spray is pretty good stuff.  

 

Steve

[ri-f]

You know what might be an easy solution.  Use some of that 3M adhesive spray with some heavy duty aluminum foil.  Coat the back of the panel with aluminum foil and then install with a small air gap (like with the heavy duty velcro).  Aluminum is a pretty good conductor of heat and that 3M spray is pretty good stuff.  

 

Steve

I don't see any advantage in gluing down a solar panel to your roof, especially since you said that you've already got Yakima tracks up there. Since you have those, why not use them? You can avoid drilling any holes in your roof, you can avoid mucking up your roof with messy dried up glue, you can easily remove or eventually swap out your panels with no residual clean up to mess with, and with a frame, such as a z-bar aluminum frame, your're panels will sit 1 1/2 - 2 inches off the roof and provide air flow - they will also sit behind and at the same level as the roof vents and not significantly increase your air flow turbulence to the point that you will be stoppiing to fuel up with greater frequency. You can also run your wires under the panels to a large extent and increase protection from the sun and elements. With flexible panels you can easily build a z-bar frame and attach to the Yakima tracks you already have in place. With rigid aluminum frame panels you can attach little L-bracket legs to them and easily attach them to the Yakima tracks, too. Excess heat will absolutely drop the efficiency of a solar panel. Solar efficiency is higher in cool weather. Anything you can do to increase your panels efficiency will only help you. Leaving two inches under the panels for dissapation is a no brainer and a perfect use of your Yakima tracks.

 

Rich

[steve whiteside]

I don't see any advantage in gluing down a solar panel to your roof, especially since you said that you've already got Yakima tracks up there. Since you have those, why not use them? You can avoid drilling any holes in your roof, you can avoid mucking up your roof with messy dried up glue, you can easily remove or eventually swap out your panels with no residual clean up to mess with, and with a frame, such as a z-bar aluminum frame, your're panels will sit 1 1/2 - 2 inches off the roof and provide air flow - they will also sit behind and at the same level as the roof vents and not significantly increase your air flow turbulence to the point that you will be stoppiing to fuel up with greater frequency. You can also run your wires under the panels to a large extent and increase protection from the sun and elements. With flexible panels you can easily build a z-bar frame and attach to the Yakima tracks you already have in place. With rigid aluminum frame panels you can attach little L-bracket legs to them and easily attach them to the Yakima tracks, too. Excess heat will absolutely drop the efficiency of a solar panel. Solar efficiency is higher in cool weather. Anything you can do to increase your panels efficiency will only help you. Leaving two inches under the panels for dissapation is a no brainer and a perfect use of your Yakima tracks.

 

Rich

Hi Rich, yes, all good points and I agree with your analysis.  What you don't know is that I like to put longboard surfboards up on my yakima racks. When Im not actively using the surfboards I like to leave them on the racks for theft prevention.  Between the 2 roof vents and the surfboards I have very little space left for solar panels If I want to use the Yakima tracks for mounting.  So, anyway that is why I am looking at using the roof directly.  Steve

[ri-f]

Hey Steve, I get that. Yes that is a more complex arrangement. I can see why you're looking for an alternative without too much compromise in panel efficiency. One thing I did once, on a sailboat, was mount thin semi-flexible panels directly to the curved deck using some Dri-Deck. Dri-Deck will provide a buffer with air flow under the panels. I screwed into the deck for that install and sealed the screws with Sikaflex 291 (you could also use 3m 4200). Since your camper has a flat roof you could use rigid panels if you prefer. If you don't want to screw into the roof, you could perhaps use some adhesive (again,3m 4200 or Sikaflex 291 are a couple good ones) to secure some z-bar aluminum directly to the roof and then bolt your panels to the z-bar instead of screwing into the roof or trusting a sticky tape for long-term performance. Just saying. I  wouldn't normally recommend screwing into the roof or using a permanent bonding adhesive unless you have no other options. Could you possibly use the jack brackets and adapt a locking bracket to hold and secure the long board to the side of the camper instead of putting it on the roof. That might not work if its a 10 ft. longboard. I guess it depends on whether you have a long bed and extended cab. Too many variables without knowing how your rig is setup. One last thought is regarding all that weight up top. I'd be concerned that  lifting and lowering the roof might require quite an effort, even with heavier duty struts installed. Anyway, good luck, i'd be interested to hear what solution you eventually come up with.

 

Rich

Edited by ri-f, 12 February 2021 - 01:08 AM.