Question s regarding mounting panels on a curved roof?

[jflorey2]

Where is the source of the galvanic corrosion?

Steel fasteners on aluminum panels.

[PNW_Steve]

Following up on an earlier post :

One poster was very concerned about galvanic corrosion. I don't see it being an issue. With steel fasters attaching steel Unistrut to the steel roof.

Where is the source of the galvanic corrosion?

Am I missing something?

[PNW_Steve]

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.

I use solar to charge my house batteries while traveling. Unless I can find a mount that will accommodate a second alternator I won't be able to charge my house batteries from an alternator.

I think that we hang out with different crowds of RVers. The folks I hang out with like to spend weeks at a time off grid. A few of them spend months at a time off grid. I will be as well. Plans are to sell the house in the Spring of 2022 and go back on the road again. I lived in my first bus for 7+ years. Six years of that was spent bouncing around the country. I managed to visit 44 states, 4 Canadian provinces and 2 Mexican states. I put almost 250k miles on it during my travels.

Perhaps that will give a more accurate picture of what I am doing.

[zamboni]

I'm late to this party but I do have another suggestion for mounting to a curved roof.

I used aluminum tube and joined it into a frame using "handrail" connectors. The frame is anchored at the edges of the roof (where there is actually more than 1/4" of wood) -- and i also added some 2x6 blocking within the roof to anchor to (i was redoing the roof before installing solar). The frame sits level, with 2-3 inches clearance to the roof at the edges, and the cross-members just kiss the crown of the roof at the center, where i have another bracket anchoring each down. The panels are then bolted to the frame. You can get these nifty nylon washers that are flat on one side and concave on the other, for bolting a flat thing to a round tube.

I know that description isn't very good...if you're interested i can probably dig up some better pics but for now the best ones i have are about halfway down in this blog post:

http://www.livesmallridefree.com/blog/off-gridable-electrical-design-part-1-solar

The resulting frame is pretty light for it's strength. I got the tubing from a local fab shop at a decent price; the "handrail" connectors were kinda pricey though. As you can see in the pics, the frame is pretty tall and presents a nontrivial "lip" to the wind, but i have not detected any issues with it in 4 years of driving, including the famously rough roads of Yukon territory and Dempster highway. I actually had a friend follow me on the interstate and film the trailer to see if there was any buffeting, bouncing, or scary harmonic vibration in the array; it appeared very solid. Will the panels last 10 years this way? 15? Maybe not. But they paid for themselves in campground fees 3 years ago...

- Jerud
------------------------------------------------------------
1220W array / 1000Ah LFP house bank
MidniteSolar Classic 150, Magnum MS2812
ME-RC, Trimetric, and JLD404
Full-time 100% electric boondocking (no propane, no genny) since 2015
2001 Fleetwood Prowler 5th wheel 25 foot, self-rebuilt
www.livesmallridefree.com

[SunEagle]

I see a lot of RV's with solar and have not heard of folks having issues.

I guess we'll find out.

I actually met someone representing a company called TinCanSolar at an RV rally a couple of weeks ago. The hardware is all made in the US and is very sturdy to handle RV roof mounting.

They cater to RV owners throughout the US and seem to make some pretty nice hardware although it is a little expensive compared to what you can find on the web but it is very heavy duty stuff.

[PNW_Steve]

I see a lot of RV's with solar and have not heard of folks having issues.

I guess we'll find out.

[J.P.M.]

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.

I bet the service life and output of the panels may very well be shortened from microcracks that develop in the cells from the vehicle/road vibration and impact/shock loading of the type, intensity and duration not usually experienced by stationary 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.)

[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.

[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.

[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.

[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.

[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..

[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" ....

[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