cracking solar panel mounts

tanuki.himself

Active member
Its 4 months since I mounted my solar panels and almost all the mounts have cracked

IMG_20201031_163424179.jpg

IMG_20201031_163431210.jpg

The questions now are why and what to do about it.

The mounts were supplied by a solar panels supply company listed as specifically for motorhomes and caravans and so far their response is "its the screws you have used" which is pretty lame and unhelpful.

The screws are actually 4mm stainless bolts through the mounting and panel aluminium frame with a washer, nut and threadlock on the back. I fitted the mounts to the panels on the bench so they are a flush fit but i don't think overtightened, then i glued the whole thing to the roof with Sikaflex 252 - it was easier to put the glue on the bottoms of the mounting and then let gravity and the weight of the panels bed them down onto the fibreglass roof.

Panels were mounted one evening in the summer with a reasonably high ambient temperature but not direct sunlight, so one possibility is thermal expansion/contraction of the panels in direct sun or overnight cold. Should i have left some sort of gap/padding between panel and mount to allow some amount of movement?

Its only been driven a few KMs at low speed so far but with a lot of swaying and bouncing, so whilst it could be movement and flexing of the whole setup , its not likely to be wind load - but obviously that would become an issue at high speeds.

Its now extremely difficult for me to reach the panel mounts in the centre line of the roof as its high up and i have limited reach on my stepladders. I'd also be concerned about trying to cut through the adhesive and doing damage to the fibreglass roof to remove the mountings, so my inclination is to leave them in place to support the weight of the panels, as long as they are not going to damage or crack the panels by constraining them round the edges and corners, and to tie the panels down to the roof with some more angle brackets, possibly aluminium angle, probably made from woven fibreglass tape which is strong in tension and would probably give a better bond onto the roof using the same Sikaflex 252 - my understanding of aluminium is that even with intensive cleaning its still a bugger to glue reliably.

Thoughts and suggestions please...
 

Joe917

Explorer
You need to add some aluminium mounts. Forget the solar panel company ,or better yet, give them a terrible online review(accurate). I would be very cautious driving with those mounts in that condition, a failure could kill someone.
 

tanuki.himself

Active member
Maybe you over-torqued the screws? Flat washers may have helped too.

the screws were little more than finger tight as there should be no tensile load on them, but i was also thinking that maybe a large penny washer or flange head screw would have reduced the point stress from the relatively small screw head on the plastic, especially if it was able to move vertically in the hole as the panel moved up and down.
 

Kmrtnsn

Explorer
Question; how big were the screw holes for those (10/32?) screws and was there any kind of expansion gap between the bracket and the panel?
 

Kmrtnsn

Explorer
It looks like the brackets cracked from lift. I'd go with a metal bracket.

By the looks of it from that angle there was a significant amount of tension between the the screw and the mount. I’m betting there‘s indications on the brackets underneath the panels of vibration from air flow/air pressure under the panels while driving. I wonder too in there’s curve to the roof. Regardless, I’d expect better from a mount after only four months.

what is the make/model, and can you post a front view of the van?
 
Last edited:

tanuki.himself

Active member
screws are 4mm in a 4.5mm hole, so slight clearance. I fitted the brackets to the panels with no packing pieces or clearance and then glued the whole assembly to the roof, so there was probably no scope for movement/expansion - the intention was that the screws should just have been in shear whereas a clearance would allow more leverage on the screw. They were just hand tightened - no power drivers or anything - again because they should only have been in shear. Roof is completely flat - that's a whole different design issue for drainage, but was what i could get manufactured at the time.

There was no branding on the brackets or the packaging - they were supplied by a solar retailer who does sell renology panels and the design looks identical to stuff on the renology web site, but could be third party clones/ripoffs

the rig has only been driven at low speeds for a couple of KMs since the panels were fitted - thankfully or I'm guessing they would have flown off.

Its going to be too difficult to replace these so I will leave them in place for now to allow them to take the static weight of the panels, and i'm going to make and fit some additional woven fibreglass tape ones alongside them at the front and back of the panels , and in the long term i may make a complete new roof with more contours for drainage, upstands for better waterproofing of vents and supports for the solar panels - that would give a smoother, more level upper surface for wind resistance and allow a deeper cross section to take the weight of the panels better. But this one will do for a couple of years....IMG_20200810_175106734_HDR (1).jpg
 

Kmrtnsn

Explorer
screws are 4mm in a 4.5mm hole, so slight clearance. I fitted the brackets to the panels with no packing pieces or clearance and then glued the whole assembly to the roof, so there was probably no scope for movement/expansion - the intention was that the screws should just have been in shear whereas a clearance would allow more leverage on the screw. They were just hand tightened - no power drivers or anything - again because they should only have been in shear. Roof is completely flat - that's a whole different design issue for drainage, but was what i could get manufactured at the time.

There was no branding on the brackets or the packaging - they were supplied by a solar retailer who does sell renology panels and the design looks identical to stuff on the renology web site, but could be third party clones/ripoffs

the rig has only been driven at low speeds for a couple of KMs since the panels were fitted - thankfully or I'm guessing they would have flown off.

Its going to be too difficult to replace these so I will leave them in place for now to allow them to take the static weight of the panels, and i'm going to make and fit some additional woven fibreglass tape ones alongside them at the front and back of the panels , and in the long term i may make a complete new roof with more contours for drainage, upstands for better waterproofing of vents and supports for the solar panels - that would give a smoother, more level upper surface for wind resistance and allow a deeper cross section to take the weight of the panels better. But this one will do for a couple of years....View attachment 625869

Thanks for the picture, it helps for my visualizing the issue and helps dispel some thoughts I had on the cracking. The roof is quite flat so bridging between mounts from a curved roof isn’t an issue. Nor should thermal changes in dimensions causing stress be an issue unless those panels were wedged in tight but your explanation of the mounting and hardware dispel that notion too. I’m left with two things. There’s a hell of a lot of vibration caused by airflow under the panels and/or there’s a lot of flex in those panels (I don’t see how, those frames look substantial and rigid) causing vibration from the road. Is it possible for someone to drive on the road and for you to feel the ceiling/roof by the vent? If it’s an NVH issue from either the road or aerodynamics then you should be able to feel the vibrations in that area.
 

tanuki.himself

Active member
Thanks for the picture, it helps for my visualizing the issue and helps dispel some thoughts I had on the cracking. The roof is quite flat so bridging between mounts from a curved roof isn’t an issue. Nor should thermal changes in dimensions causing stress be an issue unless those panels were wedged in tight but your explanation of the mounting and hardware dispel that notion too. I’m left with two things. There’s a hell of a lot of vibration caused by airflow under the panels and/or there’s a lot of flex in those panels (I don’t see how, those frames look substantial and rigid) causing vibration from the road. Is it possible for someone to drive on the road and for you to feel the ceiling/roof by the vent? If it’s an NVH issue from either the road or aerodynamics then you should be able to feel the vibrations in that area.

I hoped the mid-panel mounts would have damped any tendency to vibration, but i'll definitely give your suggestion a go - won't be until xmas when a friend hopefully visits as the wife won't drive the truck with the camper on, and its not road legal at the moment anyway as i have suspended the UK road tax while its not being used.

If it is air vibration what is the cure? some kind of air dam/spoiler on the roof in front of the panels? I had thought of putting the panels at a slight angle with the rears higher so that airflow whilst driving would apply a light downward pressure on the panels. but again that would require taking the panels off which gives me the two problems of reaching the centres now they are mounted up high, and trying to remove the damaged brackets from the glue may cause damage to the roof, which i'm not in a position to replace yet - that will have to wait until I can rent another place with more flat ground to work on and rig some kind of scaffolding....
 

Kmrtnsn

Explorer
If it is an an airflow issue, it becomes a matter of tuning that flow. Sometimes it is as easy as a crude air damn in front. Years ago I was assigned a new patrol vehicle. When driven at highway speed the light bar would generate all Kinds of noise against the thin roof from the airflow. In the end moving a couple of inches was all it took to make the problem go away. Since it sounds like Winter is taking you off the road for the season, is it possible to pull one corner and one center mount and make them into molds to recreate the mounts in stronger fiberglass?
 

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