Solar Panels taking flight - Disaster

[aandncaravan]

This thread - https://www.motorhomefun.co.uk/forum/threads/solar-panel-blown-off-roof.186806/page-7#post-3089561 documents someone losing a Solar panel while driving.

With bigger Solar panels making it onto Caravan/Motorhome roofs there is potential for serious injury.

 

We have heard other stories about them working loose, but not actually detaching.

It is clear from the thread that unsuitable materials are being used, one owner admits to using Sikaflex 512 which is a primarily a Sealant based adhesive, not a proper Structural adhesive.

 

In the absence of any other solid advice, and because the Solar web pages get so many hits anyway, we have created a web page on attaching a Solar panel to the roof of a motorhome or Caravan. This new web page includes the advice of Sikaflex experts.

 

 

It is still a work in progress, it should be completed by the end of next week, but we would welcome any feedback, hints and tips, etc.

http://www.aandncaravanservices.co.uk/solar-panels.php

 

Thank you.

 

Anyone know where a source of these Solar panel 'spoiler' fixing brackets can be found in the photo below?

 

 

 

 

[colin]

I've seen many a post recommending just sticking down with Silkaflex, I'm not a fan of this method and glue and screw.

[weldted]

Hi Alan, I have used Sikaflex structural adesive scoring the area first to help adhesion, I have also a forward facing down angle on the panels only slight but to improve the downward pressure when driving, with a small deflector about 150 mm in front of them, it allows the rain to run off and would appear the aid cooling as the slope possibly creates a slight thermal draught when parked up level. Hope you are doing ok Ted

[Paul-]

One of the common problems is through poor preparation particularly with the plastic feet (mounting brackets), the feet moulds have silicon release agent added and if not removed from the mounting brackets before fitting the glue can't stick as it should, the feet should be well cleaned to remove any silicon excess and ruffed up with 80 to 40 grit production paper, the roof should also be well cleaned and abraded where they're going to fit.

Another problem is through not using the correct thickness of adhesive, small pads are advisable to give the recommended thickness.

If using Sika adhesive use a sika cleaner, likewise if using 3m adhesive use a 3m cleaner.

[BruceM]

An authoritative source of information on solar panel fixing will be useful.

 

I’ve read on forums people recommending the use of the marine grade Silkaflex 291i which is an adhesive sealant (recommended for general sealing), when in actual fact Silkaflex 292i is the required marine grade structural adhesive.

 

Personally, I check the stability of my panels every time I go up on the roof to clean them – which is too often at this time of the year.

 

 

[aandncaravan]

Paul, We think the biggest issue is that these adhesives are not suitable for all plastics, even those which have 'good bonding'.

Both the Sikaflex expert, and the documentation, says that the adhesive can't be used with plastics under stress that might then be prone to stress cracks.

That probably rules out almost all the Plastic brackets currently on sale, as it will be pretty much impossible to identify the actual plastic used and if a solar panel generates 'stress'.

 

The new web page combines the Sikaflex Technicians advice, and our own, presenting potential solutions, including how to use the technicians experience in reducing 'tearing' of the adhesive, which is it's greatest weakness, even on Sikaflex 292.

 

I have completed the first draft of the web page : http://www.aandncaravanservices.co.uk/solar-panels.php

 

I will now wait for Sikaflex to see it and then update as necessary.

 

 

Bruce, I am not sure about authoritative, but if enough experts supply info it could be.

 

I have never fitted a solar panel to a PVC, always flat roofed motorhomes, so comments from someone who has done this and can maybe contribute to the flutes/curve aspect of having front and rear mounting brackets would be useful?.

 

 

[weldted]

I made my own fixing brackets using 40 x 60 mm alumium 80 mm long with 3, 10 mm holes drilled in the base so the adesive comes up through the holes to give extra grip, with the side that fixes to the panel itself having 10 mm rubber strip inserted to allow for some movement in the frame of the panels. I have probably fitted over 40 panels to other Motorhomes over the years and to my last three. My previous van covered over 76,000 miles with no problems, and our current van now six and a half years old has had them from new. But are still checked periodically

[spirou]

We mounted the panel to our PVC using custom made roof bars. We took alu extrusion profiles, rounded front bar for some (imagined?) downforce, others square. We also used locking glue on the screws to possibly prevent them unscrewing under dynamic stress.

 

We got the standard aero alu mouting profiles with the panel but having to mount it across, the irregular roof shape and little confidence in glue together with hesitation of drilling yet another hole in the roof, we thought another solution would be better. Added bonus with the roof bars is the ability to have a ski rack and something to hold on to when climbing up. The negative is slight problems with clearing snow off the roof. :-D

[Deneb]

Allan, I don't know where the brackets in your image can be sourced as standalone items, but they appear to be the brackets incorporated in the frames of NDS Aero solar panels, for whom Road Pro are the UK distributor.

 

https://www.roadpro.co.uk/catalogue/02h09-nds-aero-solar-panel-kits

 

I have one of these 100W panels fitted as standard on the roof of my Vantage PVC. The panel is however mounted with its length across the roof, with the brackets situated towards the edges of the van roof. They sit over the wide raised areas of the Ducato van roof (which also incorporates the built in fixing lugs for roof bars, also used by Fiamma etc for the fitting brackets of their roll out awnings).

 

The panel is fixed by what I assume (since I didn't fit it myself) is a sealant adhesive, with the addition of two screws each side through the outer flat edge of the brackets into the roof.

 

I have since fitted a second identical NDS panel further back on the roof, in the same orientation. I used a layer of Dekasyl MS-2 polymer adhesive sealant under each bracket, with a minimum thickness of 2mm as indicated in the technical data sheet for the sealant. The bed of sealant is thicker towards the outer edges, due to the slight curvature of the van roof profile. Prior to fixing the panel I abraded the underside of the brackets and the roof panel to roughen both surfaces and cleaned them thoroughly with acetone. Both are also additionally secured with screws through the roof as with the original panel.

 

I don't have any photos of my roof, but the edge of a similar NDS bracket can just be seen in the attached image of another Vantage van (not mine).

 

[thebishbus]

Another thing to remember, if just using adhesive, it may be sticking just to a layer of paint.

Brian B.

[pepe63xnotuse]

aandncaravan - 2018-11-18 9:35 PM

 

We think the biggest issue is that these adhesives are not suitable for all plastics, even those which have 'good bonding'.

 

Yes agree, different I know but I tried using Sika' 512 to stick/seal a pair of small mushroom vents onto the roof of our Toyota festival-van (having used it before, with success, I thought it do the job).

 

However, they soon leaked and when removing them, it was clear that the Sika' just hadn't adhered to the cleaned and prep'd "plastic" at all.

I trialled it again on the bench, by sticking a piece of offcut from the roof skin, to the vent flange...but no joy.

(So the vents ended up just getting bedded onto the non-setting type of sealant, and being retained by being sandwiched by the inner trim portion).

 

I think that it's maybe just too simplistic, to expect to be "specify" any one sure-fire type/brand of adhesive, as there will far to many *variables, and what may work fine on one van may fail miserably on another.

(*roof materials, roof rigidity, suitability of brackets, "footprint" of brackets , airflow over roof, competancy of the person doing the installing etc etc..)

 

Having said that, if something like a 3' x 2' panel is getting buffeted at speed and wants to let go, I doubt a few no6 self-tappers through the roof skin are going to stop it for long. :-S

 

Sorry Brian B , missed your post

Agree, any adhesive is only ever going to be as good as the surface it's sticking (or not!) to.

[Tall_Mike]

Absolute nightmare, damage to the van and worse a huge potential of causing fatalities, heaven help a biker hitting the thing in the road or being hit by it.

 

I've never heard of this happening before so hopefully it's a very rare occurrence, saying that, once is too many times,

 

From my point of view I rely on the installer doing his job properly - it's one of those trust things.

 

When I clean the roof of the van I do check that everything is secure up there, - Skylights, Solar Panel and TV Ariel. - We do have roof bars, - Very unlikely to come loose but check them as well.

[aandncaravan]

Deneb - 2018-11-19 9:07 AM

 

Allan, I don't know where the brackets in your image can be sourced as standalone items.

 

I have since fitted a second identical NDS panel further back on the roof, in the same orientation. I used a layer of Dekasyl MS-2 polymer adhesive sealant under each bracket, with a minimum thickness of 2mm as indicated in the technical data sheet for the sealant. The bed of sealant is thicker towards the outer edges, due to the slight curvature of the van roof profile. Prior to fixing the panel I abraded the underside of the brackets and the roof panel to roughen both surfaces and cleaned them thoroughly with acetone. Both are also additionally secured with screws through the roof as with the original panel.

 

 

 

 

There is a supplier on ebay that used to list the brackets, but they currently only list them as in stock in 'Black' and they are plastic. Currentlly out of stock of the Aluminium Spoiler brackets, but have convention 'L' shaped Ali ones which will work if you use enough ; - https://www.ebay.co.uk/itm/Solar-Panel-Mounting-Bracket-Sets-Caravan-Boat-Corner-side-spolier-Plastic-ABS/122311434322?hash=item1c7a546052:m:mDGg2g83pLGBh1kmfq0A7hw:rk:6:pf:1&var=422800522764&frcectupt=true

 

 

 

Thank you for this, your time and effort is appreciated. Your installation is clearly a good, safe one.

 

It is interesting that you used Dekasyl MS-2 and I hope you won't mind me using this adhesive as an example of one NOT to use on a Motorhome with Plastic solar panel fitting brackets?.

 

Last night I got an email from someone accusing me of making 'guesses' without any information to back that up, so using the Dekasyl documentation, I can point them to what a manufacturer is saying about the issues here?.

 

 

In the case of PVC's with a steel roof, the screws will attach a Solar Panel very firmly, so the Adhesive is less important.

So the below observations do not apply in the case of a Steel Roofed van, but I am going to use the MS-2 adhesive as an example to show how inappropriate some adhesives can be.

 

 

Dekasil MS-2 is a good adhesive/sealant, but it's tensile strength is not as good as Sikaflex 292 and it's strength deteriorates in wet conditions.

It doesn't work so well in it's basic form with ordinary rain, let alone Salt Water, clearly a weakness when it come to a motorhome roof?.

 

The manual for the adhesive also states it isn't great with Plastics, see this extract below from the documentation -.

 

"In general, Dekasyl MS-2 adheres well without primer on clean, dry, dust- and grease free substrates of aluminium, stainless steel, galvanised steel, zinc, copper, brass, powder coated metal, most lacquered metal surfaces, glass, PVC, polyester (GRP), painted and lacquered wood, etc.

No adhesion on untreated polyethylene, polypropylene and teflon.

In those cases where due to great thermal or physical loads, especially under wet conditions or high adhesion demands are needed, the use of an adhesion promotor is recommended.

For not mentioned substrates and additional information consult Dekalin".

 

 

You will note that only 'Plastic' suitable for bonding is PVC. It also lists two very common Plastics as having 'No adhesion', hence our advice to play safe and avoid Plastic brackets and go for Aluminium.

 

Regardless of it's 'adhesion', remember some Plastics deteriorate in bright sun, not a characteristic that is perfect for a motorhome solar panel bracket?

 

 

The above limitations are not unique to Dekasyl MS 2, it applies to many of the products being 'recommended' on the forums, etc.

 

Our recommended Sikaflex 292 is specifically designed for Salt water environments, so won't weaken when wet. It has one of the highest tensile strength of any similar adhesive and is specifically designed for high structural loads. It's tear resistance is also higher than most.

 

But also very important to most motorhome owners, Sikaflex 292 doesn't shrink leaving gaps for water to penetrate the roof. It's shrinkage is just 2% and three times better than the 'best of the rest'.

One of the things that is important on a boat is an adhesive that doesn't shrink leaving gaps for water to get in, obviously, so attention to detail in a marine product is better than the usual adhesive/sealers.

 

Sikaflex 292 is specifically designed for the Marine/motorhome environment, it isn't cheap, but we think is the best on so many levels. Try 'UKSsealants' at £15 a tube.

 

 

The web page is now complete, but developing, may we suggest everyone reads it if they have a solar panel that wasn't fitted by us - http://www.aandncaravanservices.co.uk/solar-panels.php

 

It also contains tips on how to reinforce an existing Solar panel that may not be secure.

 

 

Note that we no longer do Solar, so this isn't an attempt to bring in work, which most will know from my battle with Cancer I physically can't do anyway.

 

 

 

Pepe63, the web pages show how, with the right technique, you can make a self taper in a thin aluminium skin work in your favour to get a very strong fix, almost as good as Steel.

 

 

[spirou]

I've read on some other forum Sikaflex 252 deteriorates under UV so might not be ideal for the roof? Same source claims 52x series might be better.

 

I have no experience whatsoever with either, just relaying potentially useful/less info

[Paul-]

aandncaravan - 2018-11-18 9:35 PMPaul, We think the biggest issue is that these adhesives are not suitable for all plastics, even those which have 'good bonding'. Both the Sikaflex expert, and the documentation, says that the adhesive can't be used with plastics under stress that might then be prone to stress cracks. That probably rules out almost all the Plastic brackets currently on sale, as it will be pretty much impossible to identify the actual plastic used and if a solar panel generates 'stress'.The new web page combines the Sikaflex Technicians advice, and our own, presenting potential solutions, including how to use the technicians experience in reducing 'tearing' of the adhesive, which is it's greatest weakness, even on Sikaflex 292.I have completed the first draft of the web page : http://www.aandncaravanservices.co.uk/solar-panels.phpI will now wait for Sikaflex to see it and then update as necessary.Bruce, I am not sure about authoritative, but if enough experts supply info it could be.I have never fitted a solar panel to a PVC, always flat roofed motorhomes, so comments from someone who has done this and can maybe contribute to the flutes/curve aspect of having front and rear mounting brackets would be useful?.

I appreciate what you say about sika adhesive and can't comment on the worthiness as a adhesive for the plastic solar panel brackets, however we used Hodgson's and haven't had any problems.

However I would be warry of using any adhesive to aluminum brackets unless it was anodised aluminum. 

[aandncaravan]

spirou - 2018-11-19 1:47 PM

 

I've read on some other forum Sikaflex 252 deteriorates under UV so might not be ideal for the roof? Same source claims 52x series might be better.

 

I have no experience whatsoever with either, just relaying potentially useful/less info

 

 

 

Spirou, There are no references in the manuals for the 252 to say it isn't resistant, nor is there anything in the 52x manual to say it is especially resistant so I wonder where that has come from?

 

I know the 512 suffers on the very edge of it's exposed 'skin', but the sealant inside the joint is unaffected.

 

 

In any case our web page suggested method of fitting won't leave key structural fitting points open to UV light.

The Adhesive plays a big part but it is the screws into the soft Aluminium roof skin that are the primary structural tie. You need to read the web page to see why.

 

 

 

Paul, For both 252 and 292, Sikaflex quote -

"Sikaflex® 292 is suitable for structural joints that will be subjected to dynamic stresses. Suitable substrates include wood, metals, particularly aluminium".

 

Note the word 'particularly'.

 

But in any case, as we mention above, it is the screws that are key. With our suggested fitting, the Adhesive plays a might lighter secondary role.

 

 

[Deneb]

aandncaravan - 2018-11-19 11:25 AM

 

It is interesting that you used Dekasyl MS-2 and I hope you won't mind me using this adhesive as an example of one NOT to use on a Motorhome with Plastic solar panel fitting brackets?.

 

Hi Allan,

 

Do whatever you wish with it as far as I'm concerned :-)

 

Where my panels are mounted, they bond to the high points of the Ducato's ribbed steel roof, so I reasoned that the adhesive was never going to be under water or that wet for any length of time, and rain flows into the troughs and runs off the back of the van when driving, or off the front when parked on the slight slope of my driveway.

 

I note that the Sika product you mention has a higher tensile strength according to its data sheet, but the shear strengths are virtually identical for both products. I can't remember the exact area of roof that each panel is bonded to, and I'm not going to climb up to the roof to find out now, but it was over 500 cm2 for each panel, and I reasoned that the quoted tensile stress of Dekalin at slightly more than 17 kgf/cm2 should be more than adequate. That didn't convince me to not bother with screws as well though!

[globebuster]

Using a generic term - some 'plastics' could be an equal source of potential weakness or failure, because simply put - they're not capable of withstanding degradation from exposure to the elements or even being weakened by the sealant used in installation.

 

However, what is often omitted when installing or adhering using PU sealants [to many substrates] is the appropriate primer or, what I'd term the correct bed thickness.

 

In my industry using Sika, Bostik or any other PU or Hybrid adhesive without the recommended and appropriate cleaning and priming regime would be unacceptable, and in some cases dangerous.

 

At the risk of sounding confrontational - some appear to be doing half a job

 

 

 

[Robbo]

Congratulations Allan for setting the ball rolling on this one. There are a lot of confusing/conflicting vews on the subject. A specific motorhome related definitive user guide is well overdue IMO to avoid the possible freak incident reported in MHFun (one flying solar panel is one too many).

 

I've just got a few suggestions on your draft document:

 

1) When doing the dry fitting, mark the outline of the feet (as suggested). Then with the panel removed, apply drafting tape around the outline BUT 3mm further out. You then have an area to prepare without damage to the adjacent areas of the roof. Also, after the adhesive has been applied, removal of the drafting tape will remove any excess adhesive that may have squeezed out.

 

2) Application of a fat bead of adhesive several millimetres within the original outline may not ensure 100% coverage of the mating surfaces. To ensure full coverage, a simply test rig can be used. Mark out the outline on a piece of glass, apply the bead of adhesive (as you describe), press down the support bracket to the 3mm spacer units. Observe coverage through the glass. Repeat as necessary using fatter/smaller beads and additional intermediate beads, if required.

 

3) Manhandling a large panel on the roof probably needs 2 pairs of hands. To overcome this, perhaps fabricate a temporary wooden frame (same outside dimensions as the panel) to set the position of the mounting brackets. Once the adhesive has cured (say 2 days) remove wooden frame and support the solar panel on 25mm spacers. Using the pre-drilled holes in the support brackets, drill holes in the solar panel surround to connect using self-tapping screws.

 

4) I'm not a great fan of securing the brackets to the roof using additional self-tapping screws, except for perhaps PVC steel roofs. Providing preparation of the mating surfaces is carried out in accordance with the manufacturers recommendations, security should be assured !!! An areofoil type design on the leading edge of the solar panel is certainly worth considering (if an aluminium type can be sourced).

 

Just my thoughts. Keep up the good work Allan, while you're able.

[aandncaravan]

Robbo, thank you.

I like some of those ideas so will try and include them.

 

Thanks.

[aandncaravan]

This company - https://www.ebay.co.uk/itm/Solar-Panel-Mounting-Bracket-Sets-Caravan-Boat-Corner-side-spolier-Plastic-ABS/122311434322?hash=item1c7a546052:m:mDGg2g83pLGBh1kmfq0A7hw:rk:6:pf:1&var=422800522764&frcectupt=true

 

Intend to have stock of the Spoiler Aluminium mounting brackets by next week.

 

 

The web page page on fitting a Solar panel, suggests 'special' screws that include an EDPM seal and load spreading washer (the advantages of which are mentioned on the web page) are used to fit them. Plus it suggests using 3mm Tile spacers to stop the Solar panel pulling right down onto the roof, leaving too thin a film of adhesive to be effective.

The Adhesive manufacturer species a minimum 3mm adhesive bead should remain between the bracket and roof after the Solar panel is fully screwed in place.

 

While the screws and Tile spacers are not expensive you generally have to buy them in 1,000's. We are therefore hoping that the supplier of the Aluminium brackets will also stock the screws and spacers. So please will anyone buying their brackets ask for the screws and spacers. If they think demand is there they will then stock the items for sale in reasonable low cost quantities.

 

Please may we ask that anyone who uses our guide to fit a solar panel gives feedback so we can improve it?

 

 

[Paul-]

I find that the foam transit pads that window people use are ideal spacers when cut into 1/8" strips, any window fitter will have them and in different thicknesses  This sort of thing in the link

https://www.wholesaleglasscompany.co.uk/acatalog/Glass-Transit-Pads.html

[monique.hubrechtsgm]

There are two things who are very bad explored on RV vehicles, and that is the roof of all what is sitting there on the roof substrate. The second is the under-body. Take picture of it at first owner. Record their thickness and material. In case your screws are too long. Seal off any drilling. Clean the roof regularly. to avoid Airborne of solar, And do some pull off stress tests on all apertures on the roof, being a lot of them. My present pop- up van has a ultra flat solar sheet by adhesive. The under-body is even important how it looks like on a RV.

[BKen1]

If you are going to screw the panel for extra security make sure the screws are good quality Stainless Steel ..mine where glued and screwed one of the screws turned out to be normal steel and rusted away over the years causing water to ingress fortunetley it was in a cupboard so just a small pin size rust stain on the ceiling ....All roof panel must experience the same dynamics as an aircraft wing ( as attachment ) the faster you go the greater the lift so screwing and gluing is for me .

[laimeduck]

BKen1 - 2018-11-21 12:02 PM

 

All roof panel must experience the same dynamics as an aircraft wing ( as attachment ) the faster you go the greater the lift so screwing and gluing is for me .

 

 

A solar panel is symetrical, basically a rectangle in profile. The only way that will act as an aerofoil is if you alter the angle of attack eg lift the leading edge. Even then it is not a true aerofoil, more of a control surface generating drag - like the elevator on an aeroplane..

It therefore means it would be sensible that you mount the panel parallel to the roof surface or airflow.

 

Trouble is that the airflow over the van roof will be turbulent due to roof lights etc so who knows whether it will be up or down pressure on the panel?

If I were fitting I think I would put some sort of baffle along the leading edge between the panel and the roof to deflect the air up.