Maximum usage size of panel for touring caravan

Hi all am a new member and looking for a little advice. Been a lurker and soon to take the plunge in removing the existing 100w panel fitted as standard to my caravan.
Reading the great advice here I’ve its better to have a higher voltage system if possible, especially if you live in an area of cloudy conditions which I do. Rather than using 12v style panels, I’ve looking at used panels that presumably have been removed from residential roofs that could fit my caravan roof space. These vary from 250w-400w. They are all in the region of 1.7M X 1M. This looks to be a standard size?

I would be using mounts like below that are then bonded to the roof. Is this to large, would the wind lift the panel whilst travelling ?

Thank you in advance
C

How will your mounts be "bonded to the roof"? Here's a thread you may find helpful: Large solar panel install

sunshine_eggo said:

What’s the largest panel I can safely fit to caravan roof?

Hi all am a new member and looking for a little advice. Been a lurker and soon to take the plunge in removing the existing 100w panel fitted as standard to my caravan. Reading the great advice here I’ve its better to have a higher voltage system if possible, especially if you live in an area of...

diysolarforum.com

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Got it. Thanks!

Is your roof flat or does it have a curve?
Those mounts are a problem on a curved roof

If you have a rubber roof you shouldn't be using adhesive to hold the panel/mount to the roof.

AmyG said:

How will your mounts be "bonded to the roof"? Here's a thread you may find helpful: Large solar panel install

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The roof is flat, and grp construction. European touring caravans use these mounts and an adhesive such as sikaflex 522 or dekalin ms-2

The plastic mounts have been known to fail and panels becoming detected. This is due to the release agent used in the manufacturing process of the mounts compromising the bond of the sealent adhesive used. In addition UV degrading and localised stress cracks around any fixing can cause issues.
Note with some caravan roofs the GRP skin is 'floating' to allow for thermal expansion/contraction.
Metal mounting brackets, through bolted and bonded to the roof, offer secure fixing, either DIY from alloy L section or ready made,


Mike

mikefitz said:

The plastic mounts have been known to fail and panels becoming detected. This is due to the release agent used in the manufacturing process of the mounts compromising the bond of the sealent adhesive used. In addition UV degrading and localised stress cracks around any fixing can cause issues.
Note with some caravan roofs the GRP skin is 'floating' to allow for thermal expansion/contraction.
Metal mounting brackets, through bolted and bonded to the roof, offer secure fixing, either DIY from alloy L section or ready made,

https://www.amazon.co.uk/Renogy-Brackets-Mounting-Motorhome-Installation/dp/B09WRL362S/ref=asc_df_B09WRL362S/?tag=googshopuk-21&linkCode=df0&hvadid=570361926612&hvpos=&hvnetw=g&hvrand=7423627344101948889&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1006988&hvtargid=pla-1676246262171&th=1

Fatal accident caused by loose panel on road

Just seen a post on another forum about a fatal road accident in Tasmania, Australia police believe was caused by a solar panel on the toad that had fallen from a caravan roof Here is a news article about the accident...

diysolarforum.com

Mike

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Thing is there isn’t anywhere to make these fixings

1crb1 said:

Thing is there isn’t anywhere to make these fixings

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Does that mean there is also no place to attach a tether? Sorry I am not familiar with GRP-skinned caravan roof structures, but there has to be some kind of frame somewhere, right? Hopefully someone with direct experience will chime in.

Personally I wouldn't want any size panels on my trailer roof that can't be attached via bracket to a metal frame under the roof, but if I had no choice, I'd at least want to use small panels that are tethered.

AmyG said:

Does that mean there is also no place to attach a tether? Sorry I am not familiar with GRP-skinned caravan roof structures, but there has to be some kind of frame somewhere, right? Hopefully someone with direct experience will chime in.

Personally I wouldn't want any size panels on my trailer roof that can't be attached via bracket to a metal frame under the roof, but if I had no choice, I'd at least want to use small panels that are tethered.

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It’s basically a foam sandwich panel that may or may not have some bracing but where the bracing is would be impossible to find. No tethering points either

I'm half inclined to say that if you don't have a walk-on roof, then you shouldn't be installing traditional solar panels on it. Flexible panels might be a better fit since they can't catch any wind if they're attached to the roof with no raised brackets.

The roof is walkable and strong.

thanks for all your thoughts, I’m swaying towards 2 smaller (and unfortunately more expensive) panels or semi flexible

1crb1 said:

The roof is walkable and strong.

thanks for all your thoughts, I’m swaying towards 2 smaller (and unfortunately more expensive) panels or semi flexible

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Hi mate I have mounted a few of those 250w (1.7m/1m) panels to caravan / camper roofs here in the UK

The last one I did , I literally glued it on with stixall , flat to the roof, 3 tubes of gobbo . It stayed up their years no probs. (I think you'd probably have a bit of a job trying to get the thing off to replace it lol but they have a 25yr life span so shouldn't be an issue)




Another good option is to drill the panel frames, bolt on right angle brackets , then bolt right through the foam sandwich roof and use big plate washers on the inside (not the prettiest solution but again very effective)

Seal the holes in the roof with stixall you're good to go

Brackets bolted to panel frames

plenty of people have reported good results using tape and long rails to spread the load of the panels over more roof area

attach it with the 3M tape .... all along the rail so you get maximum hold down
add some screws into the roof for added protection (optional)

if you want to you could over-drill the drill holes
pull out any foam and use epoxy to fill the voids then screw into the epoxy after it is cured

I put solar panels on conversion vans in California, so similar but not identical.

It is pretty important to have an air gap between the panel and the roof for cooling - at least in hotter climates. Not sure about London as that is quite a bit cooler. A typical panel produces ~ 500 watts of heat for every 100 watts of electricity, and that heat has to go "somewhere". If it is bonded to the roof, then it will try to conduct into the roof. If it is trapped, then it will over time destroy the cells.

For vehicles that spend a lot of time along the Pacific Coast up to Washington, I like to use poly panels as they typically have a much wider acceptance angle, diffused light, and are often built to work better with a red shifted spectrum like you have vs a blue shifted spectrum in for instance N Africa.

The largest panel that I will personally put on a vehicle is ~ 26 x 62 inches. ( ~ 700mm x 1600mm). This is partly driven by:
- My ability to physically put it up there carefully with a helper
- It takes just a tiny bit of wind to pull a large solar panel out of your hands and when on a ladder it can be dangerous
- Large area solar panels can sometimes start "drumming" from wind and unstable air flow over a vehicle. This sound is very annoying and can result in a broken panel.
- The wind speeds on a vehicle roof can be pretty high. It is a combination of the speed of the vehicle and the wind speed.

What I do is first mount an aluminum extrusion rail to the vehicle roof, and then mount the panels to this rail.

I will try to find an example photo. It isn't the only way - just one way to do it.

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Ok - this one was a test fit for a customer who wanted to absolutely max out the amount of solar. In testing, this solar panel was too far forward and was getting bounced around by the wind. Eventually it was moved back to be just behind that front mounting point.

The rail shown is a type of 8020 or T slot called "1515" that is 1.5 x 1.5 inches. Probably locally you can find a similar 30 x 30 or 45 x 45 mm size.

1crb1 said:

would the wind lift the panel whilst travelling

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Probably not right away but I would not attempt it. Risk of killing someone is too high.
Solid mounts for me, please. Hold the majic-mayo.