Question s regarding mounting panels on a curved roof?

[Kbarb]

The Unistrut will work fine - it's quite strong, way stronger than you actually need.. You could also go to a steel & metals supplier and buy any dimension aluminum bar or square tubing to accomplish the same thing, only lighter.

If you have to bolt it through just the sheet metal, use washers on the other side to distribute the load over the sheet metal. 15ga is pretty heavy stuff. Or use a small piece of flat aluminum or steel bar, or multiply plywood for that.
Or go through the 24" o.c. ribbing as planned (best). If you're worried about galvanic action, epoxy coat them or use rubber in between dissimilar metals.

For the panels . . . in that photo on the first page it's hard to tell, but it looks like there could be a cross-wise aluminum bar, and perhaps similar bars along the perimeter length of the panels. If not, you could likewise though, add a lengthwise aluminum bar underneath the panels, parallel and next to the unistrut, and bolt those together.
Screw from those additional aluminum bars, whatever, to the panels, or use clips, stock or homemade.

I don't really see the wind being an insurmountable hurdle, as long as everything is bolted down tight. The panels are for the most part going to slice through the wind. The problems happen when you have a large surface area facing the wind, or mattress like, a moderate area initially facing the wind, but then getting pushed up by the wind to the point that it acts as a sail. You don't have that situation. There will be a small differential uplift because the air flow over the top will be faster than the flow below, but probably not enough to get either the panels or the bus airborne (or even close).
You could always attach the Unistrut, whatever, then attach a similarly sized piece of plywood up there, then drive at 100mph or so to test see how it goes.

You could even attach some temporary plywood with short pieces of wire or string, drive your 100mph, and have someone drive next to you and report back how much lift the plywood seemed to experience.

[Ampster]

My question is still: How shall I mount them securely?

I have seen answers that vary from zip ties & L brackets to Solar rails and several ideas in between. Are you still looking for answers after 4 pages? No one is going to guaranty one of the many approaches. Even of they did, it is an anonymous recommendation.

[PNW_Steve]

Hmmmm.....

I appreciate the recommendations but I still cannot charge a 24v battery bank from a 12v alternator..

While some may think that mobile solar cannot be done I have seen enough successful installs on RV's and boats that I am willing to try.

My question is still: How shall I mount them securely?

[J.P.M.]

also, as a side note about motorhomes and roof panels - motorhomes don't use their solar panels while traveling since the Alternator is providing charging to the house battery bank, the solar is only needed when parked. Motorhomes also typically use the roof for solar since it's out of convenience - being mobile and traveling frequently tends to lean most owners toward the ease--of-use of the roof area for their panel placement. But, that's also why motorhomes and RVs don't get the most out of solar - the panels are hardly ever tilted in the 'best' direction. These same concerns come up all over the RV forums, and everyone decides what's best for their situation. Sometimes RVrs even realize that the investment into solar has no great impact, at least financially, over the long term. They already have a generator, for instant power whenever they need it, and most are 'normally' plugged-in to power when they arrive at their rv park or campground.
There are a few of us who might go several days 'off-grid', but the vast majority don't ever do more than an overnight without being plugged in. The few that are very serious about off-gridding for the long term certainly have more interest in solar, but the reality is that is doesn't provide for air conditioning, in most situations, without a huge financial investment, without many hours of true sun-hours, and with a BIG increase in battery storage over the typical RV or motorhome.

Thank you for the reality check. FWIW, makes sense to me.

[NCmountainsOffgrid]

also, as a side note about motorhomes and roof panels - motorhomes don't use their solar panels while traveling since the Alternator is providing charging to the house battery bank, the solar is only needed when parked. Motorhomes also typically use the roof for solar since it's out of convenience - being mobile and traveling frequently tends to lean most owners toward the ease--of-use of the roof area for their panel placement. But, that's also why motorhomes and RVs don't get the most out of solar - the panels are hardly ever tilted in the 'best' direction. These same concerns come up all over the RV forums, and everyone decides what's best for their situation. Sometimes RVrs even realize that the investment into solar has no great impact, at least financially, over the long term. They already have a generator, for instant power whenever they need it, and most are 'normally' plugged-in to power when they arrive at their rv park or campground.
There are a few of us who might go several days 'off-grid', but the vast majority don't ever do more than an overnight without being plugged in. The few that are very serious about off-gridding for the long term certainly have more interest in solar, but the reality is that is doesn't provide for air conditioning, in most situations, without a huge financial investment, without many hours of true sun-hours, and with a BIG increase in battery storage over the typical RV or motorhome.

[NCmountainsOffgrid]

as a Motorhome/motorcoach owner, a diesel pusher, with over 92,000 miles all over this country, including Alaska, and most all of Canada, my two 100w HQST panels, mounted simply on the roof, have never had any issue with wind, rain, or even hail... and that's including two hail events this week, and driving typical 65mph highway speeds, even with high cross winds. The panels seem to handle it very easily as they allow the wind to move thru and around them.
I used the typical 'L' aluminum bracket that came with them, and while I used simple short screws into my roof, which is a rubber membrane over a 1/4" luan wood 'base', the panels are actually only zip-tied to these brackets.

As for the 'tilt' angle of permanently mounted panels on a 'mobile' roof, you have to realize that you are going to only have the sun's rays directly on the panels at certain times of the day, usually the very middle of the day between 11 and 2... before and after you are going to see much less amperage because of the angle of the rays. Some motorhome owners have built tiltable systems, but the reality is that unless your rig is going to be parked for extensive 'off-grid' days, such an investment might not be worth it. Some owners decide to leave their panels 'portable', bringing them out of storage and finding the best place for them once they've arrived and parked, also certainly allowing for more tilt options since they are now on the ground.
I myself built a 'portable' panel hitch-based tiltable travel system when we decided to venture to Alaska, using an unused 4-bike tiltable carrier to hold my two panels. It worked very well, and kept the panels close to the ground for me to tilt them when we arrived, and also off the roof so that managing them was easier - they rode on the hitch just like my bikes would have. I also towed my car behind.

While I understand that the 'unused' roof footprint is a great place to mount solar panels, a more 'mobile' system might be best for you - but your travel and parking style are going to weigh heavily into that decision - If I were to be very mobile, then the roof is probably a good option, but if travel was infrequent, and 'parked' was more the norm, then it seems the roof may not be the best - on the ground where they can be managed and tilted would be. Or, you could use a combination of both ideas - some panels on the roof that are always available, even while traveling, and some that are solely for the ground, when parked. You'd have to work out the wiring scheme for this, but it's certainly an idea.

[J.P.M.]

How would you recommend that I deal with this?

Thanks

As I wrote, I don't have much in the way of solutions here. I wish I could be more encouraging, but what you have is a bunch of equipment whose original design intent and application was in a stationary position. Now, you're subjecting it to off design conditions such as a lot of shock and vibration over extended periods on a regular basis. Without a lot more information and time, my suggestions are one of two: Abandon the idea of rooftop panels altogether, or put them on shock absorbers and fit them with a removeable, rigid and opaque wind protection system when moving. Neither option is probably what you want to read.

I'm aware that RV/bus conversion rooftop PV systems exist, but I'm not in the business of designing them or making recommendations as to the design considerations necessary for a safe design. With more information I could, but not for what someone would be willing to spend.

Others more informed and/or less ignorant than I may be of more help.

[foo1bar]

I am confident in my ability to attach the Unistrut to the roof securely.

You need to both have sufficient attachment of unistrut to roof - and sufficient attachment of panels to unistrut.
Also I wouldn't be confident in my ability to attach the unistrut to the roof...
Those modules give a LOT of surface area for air to push on.

My biggest concern is that I support the panels adequately.

I know the panels I dealt with had specific instructions on where they expected to be suppported/clamped (at least XX milimeters from the edge and not more than YY milimiters from the edge.)
It had two specificiations - one for traversing the the short dimension of the module (the "width") and another for if you're traversing the long dimension of the module (the "length").

In your case, I'd probably use the built-in bolt holes that the modules have.
For example - here's the instructions with the bolt hole spacing, etc for one brand/model (LG MonoX): https://www.lg.com/us/commercial/doc...ion-Manual.pdf

I don't know how you tell whether a set of 4 M6 bolts is suffiicient to hold down a module like that on a vehicle moving at 65mph+. Especially when you start adding wind from mother nature (and "wind" from passing trucks, etc)

[SunEagle]

How would you recommend that I deal with this?

Thanks

I would talk to other RV owner's and see what panels they mounted and how they are working out. Since most rigid panels were not really designed for a mobile application I would say vibration could be a factor but there are a lot of them out there mounted to RV's and trucks.

[PNW_Steve]

Possibly, but beyond fixation of the frames to resist wind loadings, I'd be more concerned about vibration of the body of the panels (the cells) than the fixation of the frames. I don't have much in the way of solutions here, but the panel faces will have a lot of reason to rattle from vehicle motion/road vibration as well as wing induced flow vibration. Most arrays don't see high winds that often. Chances are yours will see close(r) to wind design loads every time you get on the open highway, and for longer periods more than a usual design consideration.

How would you recommend that I deal with this?

Thanks

[J.P.M.]

Thanks for the recommendation.

I had already planned to bolt through the frame members..

My biggest concern is the well being of the panels.

As I ponder this I am considering one run of Unistrut down the centerline of the roof and support each end with two "L" brackets.

Possibly, but beyond fixation of the frames to resist wind loadings, I'd be more concerned about vibration of the body of the panels (the cells) than the fixation of the frames. I don't have much in the way of solutions here, but the panel faces will have a lot of reason to rattle from vehicle motion/road vibration as well as wing induced flow vibration. Most arrays don't see high winds that often. Chances are yours will see close(r) to wind design loads every time you get on the open highway, and for longer periods more than a usual design consideration.

[PNW_Steve]

If you are not doing so already, I'd respectfully suggest you consider bolting through to the 24" O.C. framing and not simply the sheet metal.

I once had a newly minted and young BSME engineer that reported to me design a pressure vessel lug for a 9,000 lbm lift. The lug was fine and calc'ed out OK, as did the attachment welds, but it was welded to 3/16 " thick vessel wall that would have failed with that loading. It's more than just the lug strength alone.

Thanks for the recommendation.

I had already planned to bolt through the frame members..

My biggest concern is the well being of the panels.

As I ponder this I am considering one run of Unistrut down the centerline of the roof and support each end with two "L" brackets.

[J.P.M.]

I have the space.

I am confident in my ability to attach the Unistrut to the roof securely.

The roof consists of steel frame members about 24" O.C. covered with 15 gauge steel that is riveted to each frame member.

My biggest concern is that I support the panels adequately.

An option that I am contemplating is to follow the example in the picture and add 2 "L" brackets at each end of the panels.

If you are not doing so already, I'd respectfully suggest you consider bolting through to the 24" O.C. framing and not simply the sheet metal.

I once had a newly minted and young BSME engineer that reported to me design a pressure vessel lug for a 9,000 lbm lift. The lug was fine and calc'ed out OK, as did the attachment welds, but it was welded to 3/16 " thick vessel wall that would have failed with that loading. It's more than just the lug strength alone.

[PNW_Steve]

I posted some where on this thread about some $10 brackets (set of 4) but it must have got deleted. I did a google search and some Amazon parts came up. I have actually seen them on flat roofed RVs.

Thank you.

All of the factory made brackets that I have found so far are too short to mount to the ends of the panels. If I use something like that I will probably have to make them myself.

I am contemplating "L" brackets made from 1/8"x1" steel.

[PNW_Steve]

Here are a couple of pics of the rig that I am mounting them on: