Flexible Solar Panel mounting - Magnets?

[@Michael]

I bought four neodymium magnets that come with a 6mm bolt & rubber coating and used them to hold down the four corners of a flexible solar panel. No adhesive, No holes in the roof. I'm spacing the panel off the roof with a bit of foam weatherstripping, partially for airflow, and partially to keep the panel from damaging the paint.

The magnets have about 26lbs force each. I could add a couple more or buy stronger ones if necessary.

Has anyone tried this before? Any reason why this won't work?

Should I run 'er up to a 'hunnerd and see if anything fly's off?

[GeorgeRa]

Originally Posted by @Michael

I bought four neodymium magnets that come with a 6mm bolt & rubber coating and used them to hold down the four corners of a flexible solar panel. No adhesive, No holes in the roof. I'm spacing the panel off the roof with a bit of foam weatherstripping, partially for airflow, and partially to keep the panel from damaging the paint.

The magnets have about 26lbs force each. I could add a couple more or buy stronger ones if necessary.

Has anyone tried this before? Any reason why this won't work?

Should I run 'er up to a 'hunnerd and see if anything fly's off?

Any shade could block harvesting, your AC blocks 6 cells, it could cause problems.

[@Michael]

Originally Posted by GeorgeRa

Any shade could block harvesting, your AC blocks 6 cells, it could cause problems.

Yep. But when this panel is shaded, the others are not - and vice versa. The way they are arranged, no matter where the sun is, I'll have two of three unshaded.

[GeorgeRa]

Originally Posted by @Michael

Yep. But when this panel is shaded, the others are not - and vice versa. The way they are arranged, no matter where the sun is, I'll have two of three unshaded.

Good strategy, with limited available space it is tough to eliminate shade. I assume panels are connected in parallel.

Good idea with magnets. You could add a strip of EPDM tape on the leading edges but I doubt it will be necessary.

[Davydd]

There is a lot of forces on solar panels. I lost a flexible panel that was mechanically fastened down on the side rails. You probably need a faring on the lead panel which might impede low sun. I would think there will be more forces that those magnets can overcome.

[GeorgeRa]

Originally Posted by Davydd

There is a lot of forces on solar panels. I lost a flexible panel that was mechanically fastened down on the side rails. You probably need a faring on the lead panel which might impede low sun. I would think there will be more forces that those magnets can overcome.

Was it a panel spanning across the roof attached to roof rail, there could be a lot of panel oscillation and lifting. But, I agree, there is some risk.

Sealing a front panels gaps would likely solve a problem.

My preference is rigid panel with rigid mounts.

[markopolo]

If lower on the vehicle I'd expect you'd see iron debris accumulating and rusting. Roof might be different, you'll have to report back on that to let us know. Also, I have some plated neodymium magnets that rusted pretty quickly so hopefully your rubber coated ones will fair better.

[Davydd]

Exterior magnets attract a lot of iron debris. We had magnet closures in our last van for the nerf bar storage that Advanced RV later eliminated. They don’t use any magnets now on the exterior but we have a lot of magnets inside the van mostly for hanging curtains and night closer curtains and the bathroom door stays open if there is any unlevelness that could cause it to swing back.

[avanti]

Anyone who has ever carried a mattress on their car's roof at speed understands how easy it is to build an airfoil with very powerful lift. IMO, using magnets for this purpose is asking for trouble. If you don't want to drill holes, 3M VHB adhesive tapes (the strong ones) will do the job, if properly installed.

[mkguitar]

I like magnets , but that thing needs a mechanical fixture to keep it from killing the guy behind you.


"it's only air"




yes air:

[booster]

Wind forces are huge in some cases, think wings a spoilers on vehicles to hold them down as the driving wind can severely reduce the weight on the tires and make the car float.


Static force is bad, but conditions can also make flexible stuff flutter and that is way, way, worse for making things break or come off.



Personally, I wouldn't consider that setup safe and as Avanti mentioned, if it comes off and causes an accident lots of bad things could happen.

[mkguitar]

mounting panels on the roof requires you park in the sun.


consider carrying your panels inside the vehicle


parking in a shady spot


and then setting up your panels where the sun is better, moving them to take best advantage through the day



you just need 20' of wire


mike

[@Michael]

Originally Posted by avanti

3M VHB adhesive tapes (the strong ones) will do the job, if properly installed.

VHB is an option, but VHB has a disadvantage of being really hard to remove and clean off the roof when I need to replace the panel. I already have two factory panels that are held down with some kind of adhesive (Sika 221 or Manus-bond??), which seems to be impossible to peel off the roof without damage.

Originally Posted by booster

Wind forces are huge in some cases, think wings a spoilers on vehicles to hold them down as the driving wind can severely reduce the weight on the tires and make the car float.

Static force is bad, but conditions can also make flexible stuff flutter and that is way, way, worse for making things break or come off.

I hear you. The question is 'how much is enough' when it comes to resisting the dynamic forces from wind under the panel.

It seems like a few square inches of VHB will hold a rigid panel in place. I.E AMSolar says two 1" x 5" strips of VHB are enough to hold a rigid panel in place. This implies that 10 sq. in. of VHB at 22lbs/sq. in. peel adhesion strength is enough.

Originally Posted by mkguitar

consider carrying your panels inside the vehicle
... and then setting up your panels where the sun is better, moving them to take best advantage through the day

Been there. Done that. Storing 2' x 4' panels inside the van is a genuine PITA, and the portable panels are only useful when one is sitting in one spot & can leave them unattended without worrying about theft or damage.

The fold-up panels store easier, but are more expensive less inefficient.

[Bud]

Originally Posted by @Michael

VHB is an option, but VHB has a disadvantage of being really hard to remove and clean off the roof when I need to replace the panel. I already have two factory panels that are held down with some kind of adhesive (Sika 221 or Manus-bond??), which seems to be impossible to peel off the roof without damage.



I hear you. The question is 'how much is enough' when it comes to resisting the dynamic forces from wind under the panel.

It seems like a few square inches of VHB will hold a rigid panel in place. I.E AMSolar says two 1" x 5" strips of VHB are enough to hold a rigid panel in place. This implies that 10 sq. in. of VHB at 22lbs/sq. in. peel adhesion strength is enough.



Been there. Done that. Storing 2' x 4' panels inside the van is a genuine PITA, and the portable panels are only useful when one is sitting in one spot & can leave them unattended without worrying about theft or damage.

The fold-up panels store easier, but are more expensive less inefficient.

Very Interesting Michael, would also be interesting to 'see' what's happening up there with a video camera?

I'm not placing any bets yet, but I'm going with just maybe you're ok. Problem is without a camera, maybe not a good bet to make. But heck if I know.

Fun project though. Have fun.

Bud

[GeorgeRa]

Originally Posted by @Michael

VHB is an option, but VHB has a disadvantage of being really hard to remove and clean off the roof when I need to replace the panel. I already have two factory panels that are held down with some kind of adhesive (Sika 221 or Manus-bond??), which seems to be impossible to peel off the roof without damage.
……………..

VHB uses acrylic adhesives vs Sika 221 (or 3M 4XXX or 5XXX) which is polyurethane. VHB, once separated, can be removed with solvents like WD40 or GooGone. Polyurethane can be removed with Aqua Regia, unfortunately it would make a hole in the roof. Best way to cut through polyurethane is a piano wire, for example windshields replacements.

Sealing the leading-edge gap between the solar panel on the roof would prevent potentially harmful harmonic oscillation. Butyl tape could be used, it stays flexible and can easily be removed.

[booster]

I think tight to the roof and sealed front edge is totally different than standing proud on the magnets. You still get the upward pull on the panel is tight down and retained on edges, though, depending on roof shape and attack angle of the wind to the roof. Of course the right roof shape could help hold it down also.


The roof of our Chevy Roadtrek slopes down to the rear and is crowned a bit side to side, so our rigid panels are mounted stair step style on angled mounts, with the panel orientation carefully matched to be parallel to the ground to minimize lift or push down on them. I intentionally did not seal the front edge except for the no choice area where the air is blocked by the ceiling vent fan cover as that in itself will create more air pressure on the panels. We have had no issues with it affecting the van handling or with looseness, but our brackets are on with rivet nuts with bolts and urethane caulking/adhesive so very secure. The crown on the roof makes the thicker, stronger, adhesive necessary. Tape would only contact about 20% of our bracket area in this case unless the brackets were bent to exactly the same curvature.

[GeorgeRa]

Originally Posted by booster

I think tight to the roof and sealed front edge is totally different than standing proud on the magnets. You still get the upward pull on the panel is tight down and retained on edges, though, depending on roof shape and attack angle of the wind to the roof. Of course the right roof shape could help hold it down also.


The roof of our Chevy Roadtrek slopes down to the rear and is crowned a bit side to side, so our rigid panels are mounted stair step style on angled mounts, with the panel orientation carefully matched to be parallel to the ground to minimize lift or push down on them. I intentionally did not seal the front edge except for the no choice area where the air is blocked by the ceiling vent fan cover as that in itself will create more air pressure on the panels. We have had no issues with it affecting the van handling or with looseness, but our brackets are on with rivet nuts with bolts and urethane caulking/adhesive so very secure. The crown on the roof makes the thicker, stronger, adhesive necessary. Tape would only contact about 20% of our bracket area in this case unless the brackets were bent to exactly the same curvature.

I think, if the front gap between the panel and the roof is completely sealed with a butyl tape as thick as rubber magnets it will prevent front edge from oscillation and variable vortex. A 3-4 inches wide butyl tape could form a wind deflector as well. There still going to be some lift on the panel but likely insufficient to rip the panel off the roof.

I still prefer rigid panels:
1. No issue with potential flying frisbees
2. Air gap will allow cooling airflow under panels
3. A "Double Roof" will keep van cooler in sunny days.

[@Michael]

Originally Posted by GeorgeRa

VHB uses acrylic adhesives vs Sika 221 (or 3M 4XXX or 5XXX) which is polyurethane. VHB, once separated, can be removed with solvents like WD40 or GooGone. Polyurethane can be removed with Aqua Regia, unfortunately it would make a hole in the roof. Best way to cut through polyurethane is a piano wire, for example windshields replacements.

Sealing the leading-edge gap between the solar panel on the roof would prevent potentially harmful harmonic oscillation. Butyl tape could be used, it stays flexible and can easily be removed.

Good info. Thanks.

Originally Posted by GeorgeRa

I think, if the front gap between the panel and the roof is completely sealed with a butyl tape as thick as rubber magnets it will prevent front edge from oscillation and variable vortex.

That would be easy to do.

Originally Posted by Bud

Very Interesting Michael, would also be interesting to 'see' what's happening up there with a video camera?

Good idea. A perfect excuse to buy a GoPro.

[markopolo]

Originally Posted by booster

................if it comes off and causes an accident lots of bad things could happen..........

Yes, really bad such as this: ( https://www.abc.net.au/news/2020-10-...-ross/12726538 )

Police believe the crash occurred after a southbound vehicle, a red Toyota Celica, lost control after trying to avoid hitting a solar panel that dislodged from a caravan, then colliding with a northbound vehicle.
The driver of the southbound vehicle, a 48-year-old man from Launceston, his 15-year-old daughter and 71-year-old aunt died at the scene.

Here's a video of a non-related incident that gives an idea of what any of us might encounter at any time when following an RV.

https://www.youtube.com/watch?v=-X8BF8HrhaI

[Boxster1971]

My only thought - Yikes!!