Solar Panel Mounts

[Chram]

Hey everyone, long post ahead. If you feel like you can contribute on solar mounts, I, and anyone reading this later, would be very grateful!

We have 6 320w Renogy panels. They aren’t particular light, or small. About 40lbs each, and 40”x66”.
Fitting them on our roof will be a tight squeeze, but should work in theory. I am however terrified of these things blowing off and hitting someone on the highway, so any wisdom here would be wonderful.

Things we’re working around:
Stationary sky light at front, max fan over kitchen (middle), sky light / emergency hatch in the back along with a smaller 7x8 deck.
We also did a roof raise, so we have a transitional panel raising about 16” over 2’ at the ribs right behind the front door. I could theoretically place a panel on this transition at a somewhat weird angle (see just another skoolie), or in front of the transition on the very front of the bus.

I have some z brackets, and will be using them where I can, but given the curve of the bus, I will have to improvise on the sides where I have as much as a 5” drop.

I have seen some use heavy duty galvanized gate hinges for drops like this - is that actually safe? I’m sure they won’t hurt, but I’m not sure I would count on them without some verification that it’s a legit bracket alternative.

If I did install some struts bolted down to the ribs, how could I secure them without having the end of the bolt sticking through the ceiling? (Ceiling framing is placed on the sides of ribs to save space, so the bottom of the metal rib will essentially touch my tongue and groove ceiling)
Would a unistrut system significantly add to the structural integrity of the rig?

Would a slight forward angle on each panel help aerodynamics? Without a wind tunnel, it’s hard to know exactly how the wind will be hitting these things. I want to avoid them acting like a sail as much as I can.
Has anyone here build a wind shield? If so, how? Is it necessary?

Would a panel at the very front of the bus catch too much wind coming over the top?

Would an awkwardly mounted panel at the transition be helpful as a wind break, or a hazard? I’d also be concerned that it would not be as efficient if it’s at a different angle than it’s series partner.

Thanks for any and all input!

 

[Iceni John]

Your primary consideration should be to maximize solar harvest; there's little point in having PV panels if they can't produce almost their rated power year-round. Attaching the panels to the bus is best done with an over-engineered system that's specific to your bus, using mounts that allow for the very curved bus roof. Z-mounts may be OK for a house, but I think they're too flimsy for any moving vehicle: driving at 60-plus MPH causes a hurricane-force wind to flow over the panels, so you'd better be 100% confident in how they're mounted!

I first made a walkway on my roof between my two roof hatches, then hinged my eight panels to the walkway so one array can be raised up for optimum insolation in the winter or in northern latitudes. The walkway itself is through-bolted to the roof ribs with thirty-six 3/8" stainless bolts and nylok nuts, and the panels' lift struts are similarly attached with thirty six 5/16" bolts, i.e. it ain't going anywhere! Sure, it's complete overkill, but on a moving vehicle one can't be too thorough; besides, I like making things that last!

Having a walkway on the roof makes it very easy and totally safe to wash down the panels when (not if) they get dirty: I have two quick-connect water outlets on the walkway that I just plug a washdown brush into, and all the dirty water flows down away from me. Easy!

There have been some PV panel "installations" (I use that word reservedly) on van and ambulance conversions that have resulted in panels flying off while driving. No bueno. Hint: double-sided sticky tape is not the way to go for that...

John

 

[TheHubbardBus]

You ask great questions. And I appreciate your desire to avoid causing other people harm or damage with hardware that could fly off your roof. Wish more people had those same concerns.

I can't speak from experience (yet). But part of our plan was to avoid having a large expanse of unbroken panels that could form a large airfoil. Then again, I see some with solar farms on top that don't seem to have an issue, so they're probably better equipped to comment. Personally, I want a gap between our panels to prevent creating a big wing.

Angle of attack is also something I considered. In our case, our bus is short and heavily sprung. So if we mount our panels flat, unless heavily loaded, they're still likely to be pointed a hair nose-down in relation to airflow.

Brackets need to be strong, of course. But no stronger than the aluminum comprising the panel frame. I feel a larger quanitity of adequately strong brackets per panel is better than 2 or 4 uber-strong brackets that may still be attached to the roof when the panel rips away from them.

That's a lot of words to say "I don't really know". But like I said you ask great questions. I'll be as interested in the answers of smarter / more experienced folks in this regard as you are.

 

[Iceni John]

Brackets need to be strong, of course. But no stronger than the aluminum comprising the panel frame. I feel a larger quanitity of adequately strong brackets per panel is better than 2 or 4 uber-strong brackets that may still be attached to the roof when the panel rips away from them.

Thank you for mentioning that very important factor. For this exact reason I made support frames for each panel that take most of the load off the panel's own frame, also hopefully eliminating the possibility of glass cracking due to panel flexing. Each frame is made from a 16' length of 1.75" x 1.75" x 1/8" 6063 angle, with a 24" piece to rivet the two ends together at the hinge edge. The panel simply sits inside this frame, held in place by four 5/16" stainless bolts, and it could be easily replaced in a few minutes if needed. The hinges between the support frame and walkway are heavy stainless piano hinge, and each frame's two stainless telescoping support struts hinge, pivot and slide to eliminate any loads except pure compression or tension. When the panels are stowed down against the roof for travel, they are positively locked in place by simple over-locking clamps that prevent any chance of movement. So far, so good!

I realize that most folk won't/cannot/can't be bothered to make their PV system like I've made mine, but if anyone here wants to incorporate elements of mine into their own system then it may result in a slightly easier job for them, and (I hope) maybe a more reliable and safer system.

John

 

[magnakansas]

Aerodynamics

This is something I know about…. Do not use any angle of attack. If you can leave no space under the panel or a couple of inches. That zone of zero to two inches will add drag. Figure a panel about 30” by 60”. Can develop 400 lbs of lift in the right kind of conditions. Also think about “flutter”. A condition where the whole panel lifts up and then down, like a vibration. At 400 lbs up then 400 lbs down. Your mounts should put up with that kind of abuse. These kind of force numbers are not that difficult to do. Think of some of the conditions of 60 mph road speed, 30 mph head wind passing another semi truck going in the opposite direction on a two lane highway right as you go under a bridge for a county line road…. Or when you are parked and you get one of those Oklahoma summer thunderstorms that result in tornadic winds.

William

 

[David from Ontario]

. I have a 2004 Thomas built dog nose bus. I just finished removing the ceiling panels and insulation. The next step is to attach fasteners to the roof to secure solar panels. I want the fasteners to be securely attached so there is no risk of panels blowing off. I'm thinking of using 3/8" grade 8 nuts and bolts.

In the attached picture you see one of the ribs running across the ceiling.

Q: Where do I drill bolt holes in the roof in relation to these ribs? Just close to them? Do I use 3" long bolts and drill right through the ribs? Or is that overkill?