Question s regarding mounting panels on a curved roof?

[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.

[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.

[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.

[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.

[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?

[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.

[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.

[GodsPyro]

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?

You may be over thinking this, I was questioning the same thing and was also overthinking it, I'll try to break down the concerns and my thoughts.

1: Wind speed when driving. The Peimar panels I am looking at are rated for 5400 Pa, https://www.cactus2000.de/uk/unit/masswsp.php says that is equal to wind speed of over 200 mph, https://www.solarpowerworldonline.co...-solar-panels/ says that a pa of 5000 simulates the stress of the strongest possible typhoon for 200 cycles,
keep in mind also that many solar arrays look like a giant wind sail and don't fall apart in the wind, I'm pretty sure the bus doesn't go much more than 70 and the panels would be cutting the wind, not catching it.

2: Bumps in the road. like you mentioned, youtube is full examples where people mounted the panels (even house panels) to their stick and staples roof, if you are looking at anchoring into steel supports and not just the skin I don't see how you would have a concern, I do like J.P.Ms idea about shock absorbers but it may be a bit of overkill.

3: Curved roof. could be mounted just like flat roofs but with taller L brackets, or Z brackets, https://www.youtube.com/watch?v=2Cy4dnPtw4A these guys have a curved roof although I think you have a BB so have a bit more curve then theirs, or my Prevost.

4: Heat. Really? All these huge installs on black roofs that work, and you putting a couple on a white bus roof with way better airflow is a problem?

5: Is not enough power to make a difference. a little battery power is precious on an RV and not needing to break out the generator to keep the lights on is priceless.

Final thoughts, my only concern with the channel you are considering is the potential for dirt/water to build up behind it.
Would love to see your build if you bring it around Spokane.

Edit: you could add a 24v alternator if you wanted charging on the road, $200 buys you 100 amp at 24v, I have 24v coach system and may be getting a second alternator for charging/ running AC

[Yet another Yeti]

Curved roof ?

Something like a "Barrel Roof" ( Ton Roof ) ?

Wikipedia :
https://en.m.wikipedia.org/wiki/Barrel_roof


These barrel roofs had been a little bit "popular" in Germany in the 1950s for refugees ...



But you seem to talk about "mobile devices" ....

[Ampster]

Curved roof ?

Something like a "Barrel Roof" ( Ton Roof ) ?

Wikipedia :
https://en.m.wikipedia.org/wiki/Barrel_roof


These barrel roofs had been a little bit "popular" in Germany in the 1950s for refugees ...



But you seem to talk about "mobile devices" ....

Curved roofs are still popular for buses.Based on the photo posted earlier in the thread that is the "mobile device" that the Original Poster has been talking about..

[PNW_Steve]

You may be over thinking this, I was questioning the same thing and was also overthinking it, I'll try to break down the concerns and my thoughts.

1: Wind speed when driving. The Peimar panels I am looking at are rated for 5400 Pa, https://www.cactus2000.de/uk/unit/masswsp.php says that is equal to wind speed of over 200 mph, https://www.solarpowerworldonline.co...-solar-panels/ says that a pa of 5000 simulates the stress of the strongest possible typhoon for 200 cycles,
keep in mind also that many solar arrays look like a giant wind sail and don't fall apart in the wind, I'm pretty sure the bus doesn't go much more than 70 and the panels would be cutting the wind, not catching it.

2: Bumps in the road. like you mentioned, youtube is full examples where people mounted the panels (even house panels) to their stick and staples roof, if you are looking at anchoring into steel supports and not just the skin I don't see how you would have a concern, I do like J.P.Ms idea about shock absorbers but it may be a bit of overkill.

3: Curved roof. could be mounted just like flat roofs but with taller L brackets, or Z brackets, https://www.youtube.com/watch?v=2Cy4dnPtw4A these guys have a curved roof although I think you have a BB so have a bit more curve then theirs, or my Prevost.

4: Heat. Really? All these huge installs on black roofs that work, and you putting a couple on a white bus roof with way better airflow is a problem?

5: Is not enough power to make a difference. a little battery power is precious on an RV and not needing to break out the generator to keep the lights on is priceless.

Final thoughts, my only concern with the channel you are considering is the potential for dirt/water to build up behind it.
Would love to see your build if you bring it around Spokane.

Edit: you could add a 24v alternator if you wanted charging on the road, $200 buys you 100 amp at 24v, I have 24v coach system and may be getting a second alternator for charging/ running AC

THANK YOU!

1- That's good to know. I had no idea what kind of wind they can tolerate.

2- I will be bolting to the roof frame, not just the sheet metal.

3- I haven't been able to find "L" brackets that are long enough. Perhaps I could bend some up out of 1/8" x 3/4" flat stock?

4- My understanding is that inadequate air space behind the panel will cause the panel to run warmer. I just don't know what is "adequate".

Regarding the 24v alternator, 24v alternators are plentiful but I have no place to mount it. I have searched high and low for a bracket to accommodate a second alternator and have not found one.

I found a variety of brackets to fit a. Range of applications but not one for an 8.3 Cummins.

[Kbarb]

For the L brackets you might have to get a bit creative. Perhaps check out adapting a construction L available at a hardware store or lumber yard. Simpson brand and the like have a myriad varieties and versions. Some of the smaller hardware stores, even Home Depot, only carry a small inventory of what's available. But a real full service construction business will have closer to a full line. Simpson has their catalog available online, although it can be a bit daunting.

[BoloMKXXVIII]

If you are worried about vibration damage to panels you might consider using thick rubber washers when bolting down the panels.
i.e.: on threaded rod - nylock nut, metal washer, rubber washer, solar panel frame, rubber washer, metal washer, uni-strut, bus roof, frame member, metal washer, nylock nut.

[PNW_Steve]

Thanks for the suggestions.

I am thinking this to death. I have about decided to duplicate what the gent in the picture did and then add L brackets on the ends of the panels.

[jflorey2]

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

There are plenty of 12V/24V converters that work quite well. (And many of them are bidirectional, giving you an additional option if you kill your starter battery.)