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Old 04-23-2020, 01:17 PM   #1
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Solar Panel Mounting Ideas - Feedback?

I'm ordering three 100 watt panels to put on the roof of our Collins, and I'm thinking of how to mount them. I've seen a lot of people use "Z brackets" bolted directly to the roof. However, I would like the holes through the roof to be permanent, meaning if we add more panels or replace panels in the future, we don't change the roof, put more holes in, etc. Also, I'm somewhat leery of the strength of those aluminum Z brackets at highway speeds, not to mention they may likely not land on roof ribs.

Therefore I'm planning to run a pair of Unistrut channels down the length of the bus as my starting point, bolted through each rib along its path with 1/2" hardware. I plan to use washers and nylocks to hold them fast from above. I'm also considering putting a rubber-backed washer (maybe with a second standard washer) between the roof steel and the Unistrut to both pad a little and give some room for water to run off under the rail. My first question is whether I should go with basic grade 8 bolts with washers, or if grade 5 zinc carriage bolts would be sufficient? The carriage bolts would save headroom on the inside below each rib and leave at least some room for a little insulation, as the ceiling will be attached about 1/2" below the ribs.

Up from the Unistrut rails, I plan to use 90-degree Unistrut brackets (https://www.lowes.com/pd/Superstrut-...racket/3534516), along with 1/2" bolts. Next question - do you use lock washers when using spring nuts in Unistrut rails? Also, is one bolt per angle strong enough? They do make angle brackets with room for two bolts per side.

Next, I plan to run angle iron from one rail across to the other, bolted at the 90-degree uprights with 1/2" grade 8 bolts and nylocks. There would be two angle irons per solar panel. (I assume that bolting the angle iron directly to the Unistrut rails wouldn't work due to the pitch change of the roof, though if that would work, I'd be happy to get rid of the uprights! Thoughts on that as well?)

Finally, I plan to bolt each panel to each pair of angle irons. This would allow me to use more than just 4 bolts directly on each panel, since that would seem to be the weak part of the system (aluminum that can tear out more easily under the winds at highway speeds). In addition, I can put the angled part of the angle iron on top of the panel instead of below to help clamp the panel in place (realizing I can't shade any of the cells).

However, this also means there are realistically only 4 bolts holding each panel to the bus/Unistrut rails and brackets (two through each piece of angle iron into the 90-degree brackets). If I use 1/2" grade 8 hardware, can anyone see any issue with strength to hold down the panels at highway speeds? I'm pretty sure the angle iron won't fail, so it really leaves the bolts from the Unistrut to the angle iron as the weak point. Thoughts?

Thanks in advance as always!!

Chris
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Old 04-23-2020, 01:46 PM   #2
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Seems like you’re planning on bolting through the side of the panel? Who’s panel? Renogy says you need to use their holes or you void the warranty. Also they have certified for Cat 4 hurricane so I wouldn’t worry about tearing the frame apart. Like you, I was skeptical of the aluminum frame and Z brackets, but after setting it up, I’m not now. I do agree though, that screwing directly to the roof isn’t strong enough and would probably leak over time.

What I did was to drill through the hat channel and install a 1/4-20 stainless carriage bolt from the inside. From the outside I applied sikaflex UV550, a neoprene-backed stainless washer, a lock washer and a stainless nylock nut. Then I installed the unistrut on top of that with a double-thick 1/4” fender washer that just fit inside the channel.

To install the panels, for each Z bracket I used two 1/4” strut nuts and two saddle washers.

The saddle washers and the stainless neoprene washers were from McMaster-Carr.
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Old 04-23-2020, 03:42 PM   #3
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"Up from the Unistrut rails, I plan to use 90-degree Unistrut brackets (https://www.lowes.com/pd/Superstrut-...racket/3534516), along with 1/2" bolts. Next question - do you use lock washers when using spring nuts in Unistrut rails? Also, is one bolt per angle strong enough? They do make angle brackets with room for two bolts per side."


Well, I follow this part but got lost in your description, too many angles for my ol brain.



So yes, definitely use lock washers on 2"square washers when using strut nuts.


I'd use unistrut bolts also of 1/2" variety, can't go wrong there.


John
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Old 04-23-2020, 04:26 PM   #4
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if I were to use something other than my intent method of just welding brackets on the roof, I'd do it like Danjo. that's clean!
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Old 04-23-2020, 05:08 PM   #5
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if I were to use something other than my intent method of just welding brackets on the roof, I'd do it like Danjo. that's clean!
I was going down that road, but I thought it was getting too expensive and heavy. That being said, I consider this install version 1.0 with the possibility to change to an articulated rack-like setup if I donít pull the Watts I hope for (I over-paneled by 20% to account for the sub-optimal angles). The weight of the setup with 6 strut and 6 panels is just under 200 pounds.
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Old 04-23-2020, 06:38 PM   #6
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if I were to use something other than my intent method of just welding brackets on the roof, I'd do it like Danjo. that's clean!
How are you going to weld them to the roof?
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Old 04-23-2020, 06:41 PM   #7
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How are you going to weld them to the roof?
Just weld 2 steel door hinges straight to the roof and attach the panel to the other end of the hinge. The other 2 sides have steel angle iron with a cotter pin so they can be tilted.
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Old 04-23-2020, 08:15 PM   #8
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FYI, I first made a walkway from 6061 angle and diamond-plate aluminum that runs the 26 feet between my two roof hatches. I attached it to every roof rib (spaced every 19") with stainless 3/8 socket-head bolts through the flanges of each rib from underneath, using a pair of EPDM washers against stainless washers to seal the holes in the roof; the bolts are secured with stainless NyLok nuts on the diamond-plate walkway. To this walkway I hinged my eight panels: they are all at 21 degrees down when stowed for travel, and either side can be raised to 21, 33 or 45 degrees up depending on season. They are supported by stainless telescoping struts that attach to 6061 angle running the length of the roof a few inches above the drip rail, again secured with stainless SH bolts from underneath, 5/16" this time. There are a total of 72 bolts holding everything securely, and the EPDM washers absolutely prevent any water ingress even during heavy winter storms here. So far, so good. With the ability to raise half my panels to the optimum angle and the other half at 21 degrees, I lose very little power throughout the year, and I can maximize harvest even during winter. I also built in two quick-connect water outlets under the walkway that I can plug my washdown brush into to easily and safely clean the panels, and I have additional hot and cold water lines to/from the roof for my two eventual solar water heating panels that will also raise like the PV panels.

I gotta catch all those little photons!

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Old 04-23-2020, 09:05 PM   #9
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If you use the 7/8 or 13/16 strut don’t get the spring nuts. They just barely fit and had to be crammed. I did three that way and then cut the springs off the rest. And if they don’t have springs you can slide the panel up and down the rail to adjust its position
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Old 04-23-2020, 09:06 PM   #10
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Seems like youíre planning on bolting through the side of the panel? Whoís panel? Renogy says you need to use their holes or you void the warranty. Also they have certified for Cat 4 hurricane so I wouldnít worry about tearing the frame apart. Like you, I was skeptical of the aluminum frame and Z brackets, but after setting it up, Iím not now. I do agree though, that screwing directly to the roof isnít strong enough and would probably leak over time.

What I did was to drill through the hat channel and install a 1/4-20 stainless carriage bolt from the inside. From the outside I applied sikaflex UV550, a neoprene-backed stainless washer, a lock washer and a stainless nylock nut. Then I installed the unistrut on top of that with a double-thick 1/4Ē fender washer that just fit inside the channel.

To install the panels, for each Z bracket I used two 1/4Ē strut nuts and two saddle washers.

The saddle washers and the stainless neoprene washers were from McMaster-Carr.
Danjo - Thanks for the input! I'd love to see a picture of the fasteners for the hat channel (more outside than inside), if you have any. Seems like a reasonable solution! Sounds like my 1/2" is overkill, and 3/8" or even 5/16" would be fine, especially if you're good with 1/4". No disrespect to your setup, but I'd rather over-build for my personal peace of mind.

My panels are HQST Polycrystalline, and I originally planned to install them down the center of the bus, so 26" long, and 36" wide across the roof curve, roughly. I don't know if I'd void the warranty by drilling separate mounting holes, but I think I'll take my chances to make them a bit more secure. In any case, the panels are under $80 a piece, and I suspect they'll continue to drop in price over time.

Your plan honestly looks good, though I'm somewhat leery of taking the mounting hardware to more than 1/2 it's rated capacity, since Cat 4 hurricanes are up to 156mph (I suspect 90mph, maybe more, if driving into a headwind, which it seems like we always are ). I think I'm still going to bolt the panels to angle iron, and just need to determine how best to attach that to the Unistrut.

Quote:
Originally Posted by BlackJohn View Post
"Up from the Unistrut rails, I plan to use 90-degree Unistrut brackets (https://www.lowes.com/pd/Superstrut-...racket/3534516), along with 1/2" bolts. Next question - do you use lock washers when using spring nuts in Unistrut rails? Also, is one bolt per angle strong enough? They do make angle brackets with room for two bolts per side."

Well, I follow this part but got lost in your description, too many angles for my ol brain.

So yes, definitely use lock washers on 2"square washers when using strut nuts.

I'd use unistrut bolts also of 1/2" variety, can't go wrong there.
Thanks! I will definitely check out the Unistrut variety as well. Sorry to lose you - I think I over-complicated the design for a roof without much curvature.

The more I think about it, the more I think it makes sense to future-proof by having two rows of strut rails, rather than the one down the middle like I was originally planning. The Unistrut is 10' long, and I can get three panels longwise on each set of rails, giving me the ability to expand to 6 panels if we think we ever need it.

Therefore, I think I'll revise my plans to simply bolt the angle iron to the long sides of each panel, and then directly bolt the angle to the strut channel. The curve on the Collins roof is very slight, so I think this'll work without issue.

Also, I think I can get away with the half-height strut channel, so that'll be my plan!

Any other ideas to consider?

Thanks all!
Chris

PS - Welding is not currently in my skillset...
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Old 04-23-2020, 09:32 PM   #11
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I like overbuilding. Just to put it into perspective for the 1/4” carriage bolts I used, the tensile strength of a 18-8 series stainless 1/4-20 bolt is nearly 3000 pounds. For each pair of rails totaling 12 sq ft there are 8 bolts, so that’s loosely, about 20,000 pounds of collective tensile strength holding 2 panels to the roof.

Don’t make me worry
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Old 04-23-2020, 11:13 PM   #12
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Quote:
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Just weld 2 steel door hinges straight to the roof
You're going to weld the door hinges to the 20 ga sheet metal on your roof?
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Old 04-24-2020, 06:34 AM   #13
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I like overbuilding. Just to put it into perspective for the 1/4Ē carriage bolts I used, the tensile strength of a 18-8 series stainless 1/4-20 bolt is nearly 3000 pounds. For each pair of rails totaling 12 sq ft there are 8 bolts, so thatís loosely, about 20,000 pounds of collective tensile strength holding 2 panels to the roof.

Donít make me worry
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Old 04-24-2020, 09:03 AM   #14
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I like overbuilding. Just to put it into perspective for the 1/4Ē carriage bolts I used, the tensile strength of a 18-8 series stainless 1/4-20 bolt is nearly 3000 pounds. For each pair of rails totaling 12 sq ft there are 8 bolts, so thatís loosely, about 20,000 pounds of collective tensile strength holding 2 panels to the roof.

Donít make me worry
FWIW the tensile strength of a pretensioned bolt is probably its least relevant property for a structure like this (unless Godzilla is trying to pull the solar panels off your roof). Bolts primarily prevent two pieces from slipping relative to each other through the frictional force they generate; when that frictional force is overcome, the bolts are exposed to shear forces rather than tension.

This is a good writeup about it: Bolt Mechanics.
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Old 04-25-2020, 05:16 PM   #15
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Stainless or Galvanized Fasteners?

Thanks again all for the feedback!

OK, so the next question is what kind of bolts to join the strut channel to the roof, and again what kind of bolts to attach the brackets (plated steel) to the aluminum solar panel frames?

My understanding is that stainless will corrode the steel that it's exposed to, and so galvanized may be a better choice to mount the strut channel to the roof. It's about as strong, and if it doesn't corrode the bus steel, it's far cheaper than stainless.

For the panels, I've understood that stainless and aluminum definitely don't mix, especially when wet, and so I would assume galvanized for this connection as well.

This WAS my understanding until a boat builder said that they always use stainless, NOT galvanized, for aluminum boat hulls (which contradicts the aviation industry, it seems).

What am I missing here?

Chris
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Old 04-25-2020, 06:07 PM   #16
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FWIW, Renogy supplied stainless HW with their aluminum brackets/panels.

My bus has an aluminum skin affixed to steel channel with what looks to be electrogalvanized screws. It’s going on 14 years without significant signs of galvanic reaction. It’s in a dry environment though, so...

IDK at that point what it matters if I throw some stainless at it.
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Old 04-25-2020, 06:59 PM   #17
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Good info. For the time we'll be in these vehicles, it may very well not matter, as you say.

Anyone else with experience in this area? Can we get a good heated debate and confuse me even more?

Thanks,
Chris
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Old 04-25-2020, 09:36 PM   #18
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On my PV installation which is entirely stainless and aluminum (no galvanized/ZP hardware or mild steel anywhere), I have a small amount of surface oxidation where the SS washers touch aluminum, but it's not got worse and it seems to be only superficial. I'm not going to worry about it at this stage. If I were somewhere very humid and salty, like Hilo HI or Veracruz MX, maybe it could be a problem, but for mostly-dry Southern California I'm going to just live with it. I haven't noticed much corrosion difference between 6061 and 6063, and I'm using just normal hardware-grade SS, not the more expensive marine grades.

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Old 04-30-2020, 07:16 AM   #19
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Oddly enough the 100w panel is the perfect width with the brackets to line up with the ribs on my Thomas. Those aluminum brackets are going to bend before they snap, but I may leash each panel in case they do. Added two 1.25 inch wide rubber washers between the panel and the bracket so I could get it flush on the roof. I used self drilling screws with neoprene washers, putting the washer under the bracket so the rubber would be directly covering the hole. I yanked up on it really hard and it's not moving. I have a picture but not sure how to attach it
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Old 04-30-2020, 10:33 AM   #20
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Because of my disability and I can't get on the roof to keep them clean I am mounting mine on the driver side of the bus on a hing so I can lift them out and put a pole underneath them I will be able to do the different angles for the sun. Any ideas on on how to hang it please let me know. Thanks
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