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Old 11-17-2019, 10:25 AM   #1
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Questions on Installing Unistrut for Solar Panels

The roof on my bus is curved so I figure the unistrut will have to be installed longitudinally (pointing front to back). I will be able to fasten it at the seams in the roof panels under which the roof structural member is located. What is an acceptable method for fastening the unistrut to the roof? Obviously, bolts with washers and nuts on the inside of the roof would be best. Is there any suitable alternative that would not require me to open up the ceiling in the interior?
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Old 11-17-2019, 10:28 AM   #2
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The roof on my bus is curved so I figure the unistrut will have to be installed longitudinally (pointing front to back). I will be able to fasten it at the seams in the roof panels under which the roof structural member is located. What is an acceptable method for fastening the unistrut to the roof? Obviously, bolts with washers and nuts on the inside of the roof would be best. Is there any suitable alternative that would not require me to open up the ceiling in the interior?
Rivnuts will work. A lot of people use them for this purpose.
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Old 11-17-2019, 10:42 AM   #3
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We used Blind Bolts to fasten L brackets to the roof through the ribs, then attached angle iron to the brackets. You'll need to factor in the angle of the roof. I bent the L brackets to the correct angle to allow the angle iron (unistrut in your case) to be level so the panels could mount to it.
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Old 11-23-2019, 07:28 AM   #4
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We used Blind Bolts to fasten L brackets to the roof through the ribs, then attached angle iron to the brackets. You'll need to factor in the angle of the roof. I bent the L brackets to the correct angle to allow the angle iron (unistrut in your case) to be level so the panels could mount to it.
Those blind bolts look interesting. Did you use the ones where the bolt in the center is driven by the hex socket? I am ordering a rivnut setting tool that is like a big blind riveter, but I will check out these bolts as well. Whichever one has the better grip on the reverse side of the panel will get my final vote.
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Old 11-23-2019, 08:27 AM   #5
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Those blind bolts look interesting. Did you use the ones were the bolt in the center is driven by the hex socket?I am ordering a rivnut setting tool that is like a big blind riveter, but I will check out these bolts as well. Whichever one has the better grip on the reverse side of the panel will get my final vote.
Yikes, $2 to $10 ea. for the blind bolts, and it looks like they're not really meant to be removed once they're driven. Neither is necessarily bad for a roof rack, of course. It certainly looks like the blind bolts would have a stronger grip than rivnuts of the same thread diameter.
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Old 11-23-2019, 08:39 AM   #6
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Just noticed these,Looks like just the ticket for installing rooftop solar panels on the sheet metal roof of a bus. I just need to contact somebody to confirm which tool is used to install them.

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Old 11-23-2019, 08:50 AM   #7
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Just noticed these,Looks like just the ticket for installing rooftop solar panels on the sheet metal roof of a bus. I just need to contact somebody to confirm which tool is used to install them.
You should be able to use any rivnut setting tool with the correct bit. Or you can always use a wrench (the irony!) and a long-ish piece of metal with a hole in one end.
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Old 11-23-2019, 08:56 AM   #8
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It looks like you can get these plusnuts for around $.75 apiece, but the largest size seems to be for 5/16 inche thread. Is that adequate for the task? I was planning to use 3/8 inch hardware.

My plan now is to run the 14 gauge strut longitudinally on the roof of the bus, attaching it through the ribs and the roof. Then run more struts on top of those, perpendicular (at a 90 angle to the struts beneath). These struts will be bent to accommodate the shape of the roof with flat sections to accommodate each panel. This will stand my panels about 2 inches off the roof, which will allow good air circulation and room for wiring connections, and at the same time allow for the whole installation to conform to the curvature of the roof to the greatest degree possible.
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Old 11-23-2019, 10:05 AM   #9
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Quote:
Originally Posted by wrenchtech View Post
Those blind bolts look interesting. Did you use the ones where the bolt in the center is driven by the hex socket? I am ordering a rivnut setting tool that is like a big blind riveter, but I will check out these bolts as well. Whichever one has the better grip on the reverse side of the panel will get my final vote.
I used the ones with the phillips head, but I've bought some more with the hex head to have on hand if anything pops up and I need them sometime. I stripped the phillips head on 2 of them when I was putting in the solar rack (luckily I always order a few extra of stuff like that), which is why I ordered the hex head ones the next time.
They're a bit pricey, I think I paid around $2.25 apiece for them, but I think I only needed 16 total so it wasn't a big expenditure or anything (I spent much more on beer during the buildout).
I don't know the specs on the Plusnuts, but I would think 5/16 would be plenty strong. That's the size I used. I like your plans for the Unistrut, should be plenty solid the way you're laying it out with crossmembers.
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Old 11-23-2019, 10:39 AM   #10
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Ive been thinking about this. I think the easiest thing to do is to drill a hole straight through the hat channel and install a carriage bolt with a washer and nut on the outside with some RTV to make a seal.
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Old 11-23-2019, 10:40 AM   #11
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My eight panels are hinged to a walkway I built between the two roof hatches, and I bolted the walkway and the panels' outer strut rails through the roof ribs using 5/16" and 3/8" stainless socket-head bolts going through from underneath, then Nylok nuts on the outside. To prevent leaks the walkway and strut rails are sealed against the roof with EPDM rubber washers, and after several winters there are still no water leaks anywhere there. This method is completely secure and strong, but drilling all the holes through the roof in exactly the correct locations wasn't fun! The holes now in my ceiling will be covered by whatever thin insulation and ceiling covering I choose to install later.

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Old 11-23-2019, 11:06 AM   #12
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Ive been thinking about this. I think the easiest thing to do is to drill a hole straight through the hat channel and install a carriage bolt with a washer and nut on the outside with some RTV to make a seal.
Use a nylon lock nut, those vibrations are something else. We're constantly finding loose screws!
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Old 11-23-2019, 11:51 AM   #13
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And would it be wrong to just drill and tap the roof panel and rib for 1/2" strut nuts with a flat square unistrut washer with a lock washer?

Pretty sure nothing is stronger.


You have to drill holes anyway, just space them to fall on the rib lines.
Waterproof to best of your ability when turning bolt into the tapped hole.


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Old 11-23-2019, 12:09 PM   #14
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And would it be wrong to just drill and tap the roof panel and rib for 1/2" strut nuts with a flat square unistrut washer with a lock washer?

Pretty sure nothing is stronger.


You have to drill holes anyway, just space them to fall on the rib lines.
Waterproof to best of your ability when turning bolt into the tapped hole.


John
" drill and tap the roof panel and rib"
This implies (to me...) you mean threading the hole in the drilled sheet metal panel and rib...? That doesn't sound any stronger than using self-tapping screws...

I'm guessing I mis-understand...
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Old 11-23-2019, 04:35 PM   #15
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" drill and tap the roof panel and rib"
This implies (to me...) you mean threading the hole in the drilled sheet metal panel and rib...? That doesn't sound any stronger than using self-tapping screws...

I'm guessing I mis-understand...



Yup, right thru the skin and rib. That's enough thickness I think for a good tap, but don't strip it.


If it strips you still have the nut option inside in the rib. Best not to though.


Let the washers do their work and you'll know when they are all pretty close for tightness. You are using unistrut square washers and locks?


However many you need down each side, run or whatever will certainly entertain more physical stresses than an equal amount of self tappers.


Not sure if stress levels on highway speed panels on buses has been discussed but they must be incredible numbers and differ with each individual build on here.


So, not sure if you misunderstand, thought I was clear but glad you asked. Just my thoughts,



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Old 11-25-2019, 12:46 AM   #16
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Quote:
Originally Posted by wrenchtech View Post
It looks like you can get these plusnuts for around $.75 apiece, but the largest size seems to be for 5/16 inche thread. Is that adequate for the task? I was planning to use 3/8 inch hardware.

My plan now is to run the 14 gauge strut longitudinally on the roof of the bus, attaching it through the ribs and the roof. Then run more struts on top of those, perpendicular (at a 90 angle to the struts beneath). These struts will be bent to accommodate the shape of the roof with flat sections to accommodate each panel. This will stand my panels about 2 inches off the roof, which will allow good air circulation and room for wiring connections, and at the same time allow for the whole installation to conform to the curvature of the roof to the greatest degree possible.
This unistrut plan is how I covered my old Motorhome roof from front to back with 2500 watts of solar. After I stripped the old AC units, antennas, vents, TV antenna, etc. I used the 1.5 unistrut longitudinally and the thinner 3/4 Unistrut perpendicular to save weight, money, and keep the height down.
One consideration is this gives some clearance for air flow underneath and also to clean out any stuff, leaves, etc. Also I heard rodents running on my roof so I looked and didnt see any nests under my panels.
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Old 11-25-2019, 05:22 AM   #17
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The roof on my bus is curved so I figure the unistrut will have to be installed longitudinally (pointing front to back). I will be able to fasten it at the seams in the roof panels under which the roof structural member is located. What is an acceptable method for fastening the unistrut to the roof? Obviously, bolts with washers and nuts on the inside of the roof would be best. Is there any suitable alternative that would not require me to open up the ceiling in the interior?
I figured you may have already seen this but just in case...

I used bolts, washers and stop nuts to attach the unistrut, but my bus has tubular roof supports whereas I understand that some (many, most?) buses have U-channel roof supports? More info here. Rivetboy had some good input on potential alternate fasteners...

This pic was before doing the final cleaning and painting of the roof...


Although not complete yet (like everything else on my bus) here is the roof with the panels and decking (mostly) installed.
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Old 11-25-2019, 10:34 AM   #18
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@ComfortEagle,


Sometimes the simple answers escape you. Or, at least me. I've been struggling for days trying to figure out how to get a similar system using unistrut to level on a curved roof. Shims make perfect sense! Me ->

Q: Did you set the shims individually, or figure out where to drill for one set & duplicate for the rest?
Q: What size is the unistrut down the center compared to the two outside runs?
Q: Are there non-visible fasteners securing the panels (like from underneath), or are they secured entirely by the hold-down tabs you can see from your pics?

Everything you do rocks. Your build has & continues to be such an inspiration for us.
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Old 11-25-2019, 11:13 AM   #19
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Q: Did you set the shims individually, or figure out where to drill for one set & duplicate for the rest?
I drilled all the shims at once, but oversized the holes to allow a bit of adjustability
Quote:
Originally Posted by TheHubbardBus View Post
Q: What size is the unistrut down the center compared to the two outside runs?
The outer sections are 1 5/8 and the center section is 13/16.
Quote:
Originally Posted by TheHubbardBus View Post
Q: Are there non-visible fasteners securing the panels (like from underneath), or are they secured entirely by the hold-down tabs you can see from your pics?
Panels are fastened to the unistrut with the bolted square tab washers, and to each other with panel to panel bolts/stop nuts near the outer edges.

For in between panels:


For end panels:


Additional bolts thru the panels near the edges to tie the panels together:
Side view (nuts between panels are spacers...):


Additional bolts thru the panels near the edges to tie the panels together:
Underneath view:


And thank you for the kind words; think I could get you to call my wife and let let know how inspirational I am...?
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Old 11-25-2019, 12:36 PM   #20
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And thank you for the kind words; think I could get you to call my wife and let let know how inspirational I am...?

Considering the detail you just provided, I'd deliver the message via singing telegram if I lived in your area. But unless AZ just got one heck of a lot greener, I doubt that's the case



THANK YOU
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