Best way to secure Unistrut to roof for panels

[Pigeoneer]

What’s the general consensus on the best way to secure unistrut (or any support system) to the roof, with regards to:
-Anchoring points (ie Rivnuts vs bolts through hat channels)
-Sealing (butyl tape/sikaflex 221 etc)
-Vibration isolation (is it necessary? Hockey puck method?)
-dealing with the curve on the edges

I’m leaning towards the hockey puck method with unistrut to support 8x panels running perpendicular to the bus, down the length of the bus.

What I’m specifically interested is how to get the bolt perpendicular to the hat channel, while still ending up with a flat level run of unistrut (two rows down the length of the bus). Basically ensuring the bolt clamping forces are all in line/parallel.

I’ve seen brackets custom fab’d but that seems excessive to get the angle right and the repeatability.

The width if the unistrut runs would preferably be wide enough to capture a good amount of width of the panel, but that puts you out on the curve. If the runs are narrow (ie in the flat section of the roof), then the two clamping forces on the panel are pretty close in the middle and leave a good amount of overhang (basically unsupported/cantilevered sections of the panel, which at driving speed would not be ideal).

 

[Timeline]

I used a chalk line inside and made a jig out of 2 small wood blocks screws together to transfer that line down to where the hat channel meets the skin.

The panel manufacturer will have fact sheet that tells you the safe range on where the panels should be clamped.

I used 3M 5200 sealant and 1/4" bolts and none leaked.

I did not use slotted unistrut thinking it would whistle going down the road, and I found ironridge solar rails locally for a similar price.

 

[desrtdog]

I used 8020 extruded aluminum to fabricate a custom roof rack that is 6’ wide. Used their 90 degree brackets attached to the roof with 3/8” SS bolts and fender washers / nylock nuts, and pivots to get the rack flat across the top…chalk line to get the line down the roof and a temp jig for position across the top…

Sealed with 3M dynatron under the brackets and a bead of silicone caulk around them…

 

[Pigeoneer]

I used a chalk line inside and made a jig out of 2 small wood blocks screws together to transfer that line down to where the hat channel meets the skin.

The panel manufacturer will have fact sheet that tells you the safe range on where the panels should be clamped.

I used 3M 5200 sealant and 1/4" bolts and none leaked.

I did not use slotted unistrut thinking it would whistle going down the road, and I found ironridge solar rails locally for a similar price.

View attachment 1335554

Nice, thanks for the input!

I'm a Sikaflex kinda guy but I'll definitely be smothering everything in it.

Did you bend those L brackets to match the curvature of the roof to get the top of the ironridge mounting level/square?

 

[Pigeoneer]

I used 8020 extruded aluminum to fabricate a custom roof rack that is 6’ wide. Used their 90 degree brackets attached to the roof with 3/8” SS bolts and fender washers / nylock nuts, and pivots to get the rack flat across the top…chalk line to get the line down the roof and a temp jig for position across the top…

Sealed with 3M dynatron under the brackets and a bead of silicone caulk around them…

Just checked out the pivots for 8020 and that's exactly what I'm looking for. Too bad I already bought the unistrut. I'll have to investigate if they make a similar application for unistrut that would be suitable for 100mph winds.

Regarding wind speeds, I'm trying to find something compliant, or at least designed, with Miami-Dade county building code for High-velocity hurricane zone. This seems to be a pretty solid standard for ensuring I won't have a panel fly off while driving.

https://www.miamidade.gov/building/library/presentations/pv-solar-workshop-presentation.pdf

 

[Timeline]

Yes, found the correct angle and fine tuned them all in a vice, tapped them with a big hammer.

 

[Timeline]

I used 8020 extruded aluminum to fabricate a custom roof rack that is 6’ wide. Used their 90 degree brackets attached to the roof with 3/8” SS bolts and fender washers / nylock nuts, and pivots to get the rack flat across the top…chalk line to get the line down the roof and a temp jig for position across the top…

Sealed with 3M dynatron under the brackets and a bead of silicone caulk around them…

Wow that is awesome, well done!

 

[nikitis]

Is your uni strut good enough for that deck? Holding up well? I'd think it'd be fine for just solar panels but roof decking the mounts seem light to me.

 

[Timeline]

For starters that deck is not uni strut.
Really man quit with the wild guessing..

 

[desrtdog]

Here are are the supports (brackets) I used for mounting the deck to the roof... total weight of the rack is somewhere around 110 lbs...dimensions are 17' long by 6' wide...solar panels weigh about 50 lbs...deck boards are cedar, which weighs approximately 1.5 lb/ft; total linear feet: 101, so deck weighs no more than 160 lbs...rack is supported every 28"-35" (varies with windows), with a total 7 supports on the left side / 6 on the right (due to cutout for shower), PLUS support blocks down the middle.

...Am I concerned about the mounts being too light or not enough of them? Nope.

...and yes, as noted above, it is not unistrut, but 8020 aluminum extrusion...

 

[nikitis]

For starters that deck is not uni strut.
Really man quit with the wild guessing..

First off, chill out with that tone @Timeline There's no guesswork about it. I'm calling it what the guys above called it. If it's not uni strut yell at them as that's what the OP called it. I have no idea about brands etc. I've yet to do this myself.

However I do have a good understanding about tolerances, weights, and galvanic corrosion that can occur for using the wrong metals on the bus roof. And the type of rails being used don't look like it could support long term a deck with people on it well which is why I'm asking the question of how it's holding up for him. I'm in the market soon for a good setup, or a custom built one that I'll build myself. The very fact I'm asking the question automatically means I don't know everything so I'm approaching this from a humble perspective.

The weight of a couple of human bodies looks like it could easily bend one of those brackets eventually. So I'll ask @desrtdog how's the brackets holding up on yours holding up? Any issues with brackets bending at all? How long have you had it and do you use the deck often? If it's holding up well I may consider a similar setup.

 

[desrtdog]

So I'll ask @desrtdog how's the brackets holding up on yours holding up? Any issues with brackets bending at all? How long have you had it and do you use the deck often? If it's holding up well I may consider a similar setup.

Brackets are holding up fine. Deck has been mounted for over 2 years. Minimal use,but absolutely no movement or flex when I am up there.

As to the brackets, the link I posted above is the specific part. They are pretty stout, with thickness of the long end being 5/16”…if you’re curious about their durability, I guess you could always buy a couple for testing.

 

[nikitis]

Ah ok, good to know.

 

[jbeech]

This is a fantastic thread, glad I clicked on it. Pal has panels on the roof of a 16' utility trailer and along with one pack out of a Mach-E (they have several, maybe 6-8 of them?) he runs a small minisplit 24/7/365 here in Florida to keep it at 72°. He's pretty much persuaded me into doing similar with the 24' box on my rig so I'm all ears about these installations. I won't need to divert around any hardware on the roof so I'll be going for maximum panels. Anyway, thanks for sharing.

 

[Tejon7]

I used closed end rivet nuts through every rib flange (every 18" or so on my bus). Finding the closed end ones with the right grip range was difficult. Put them in "wet" with your favorite sealant. Rivnuts can supposedly loosen up over time, so I check mine before every major trip. About 10k miles now and no issues.

Looking back, I think I'd be tempted to do plus nuts or blind bolts for more pull-out resistance. Back then I was more worried with waterproofness, now I think I lean a little more toward bombproofness.

 

[Mercuric Mind]

I used 8020 extruded aluminum to fabricate a custom roof rack that is 6’ wide. Used their 90 degree brackets attached to the roof with 3/8” SS bolts and fender washers / nylock nuts, and pivots to get the rack flat across the top…chalk line to get the line down the roof and a temp jig for position across the top…

Sealed with 3M dynatron under the brackets and a bead of silicone caulk around them…

This is basically the same method I used to mount my panels, with the exception that I have them mounted lengthwise down the roof on slight angle to stay as close to the roof as possible.
I made frames out of 8020 for each panel and mounted them using the 8020 pivot fittings. The panels are then clamped in between using aluminium tabs with 1/4-20 bolts with locking nuts. The frames can be unbolted from the pivot and tilted up to access the wiring or the roof. The pivots are mounted to the roof with 4 bolts going through the hat channels with locking nuts and bedded in 3m 5200 marine adhesive. Four years in, No leaks so far.

 

[nikitis]

My 2 cents.

If you are going to have 2 different angles like the images in @Mercuric Mind 's post, have 2 banks, All panels on left in one bank, and all panels on right in one bank because they are at two different angles. Solar operates on voltage generation per the weakest link so if say ALL the panels were on one bank, (left and right side) and sun is best angled for the right side, the left side wouldn't get as much sun and bring down the energy generation of those on the right and vice versa.

But if separated left and right side by banks, you could get good generation on the left in the morning, not as good on the right but not bring down the left side, and at the evening better generation on the right, but not as much on the left and not bring down the right, if the two sides were separated.

If you had angled them straight horizontally at the same angle they'd all get the same angle and always generate the same energy. It doesn't look as pretty when the panels don't follow the roof curve, but it works slightly better, and we need all the watts we can get on our buses.

If you want the best of both, panels aligned with the curve of the roof and better generation, then separate left and right banks electrically.

 

[Mercuric Mind]

My 2 cents.

If you are going to have 2 different angles like the images in @Mercuric Mind 's post, have 2 banks, All panels on left in one bank, and all panels on right in one bank because they are at two different angles. Solar operates on voltage generation per the weakest link so if say ALL the panels were on one bank, (left and right side) and sun is best angled for the right side, the left side wouldn't get as much sun and bring down the energy generation of those on the right and vice versa.

But if separated left and right side by banks, you could get good generation on the left in the morning, not as good on the right but not bring down the left side, and at the evening better generation on the right, but not as much on the left and not bring down the right, if the two sides were separated.

If you had angled them straight horizontally at the same angle they'd all get the same angle and always generate the same energy. It doesn't look as pretty when the panels don't follow the roof curve, but it works slightly better, and we need all the watts we can get on our buses.

If you want the best of both, panels aligned with the curve of the roof and better generation, then separate left and right banks electrically.

Yes, that is true, and a very good point that I left out in my previous comment. I have each side on a separate controller. I had initially planned to have a linear actuator raise and lower a side to gain efficiency by tracking the sun angle but time money and motivation were lacking. I just wanted to be done and use the bus. As it turns out, in the current configuration, I have plenty of solar power for my needs and as a bonus the angled panels shed rain and snow better. When it rains the water tends to wash off the dirt.

 

[nikitis]

Good point about the snow load. I'm in a climate where it doesn't snow much so didn't think of that

 

[LargeMarge-TC]

Does this look like a DIY job for a part-time inexperienced amateur engineer with a mail-order degree from H-1b University?
.
Formula:
Maximum traveling wind speed [80mph/130kph], multiply by maximum wind gusts from multiple angles simultaneously [100mph/160kph], multiply by torsion forces from road imperfections and pot-holes and topès (Mexican speed-bumps, colloquially known as 'dead cops').
.
.. Multiply that number by decades of vibrational flexing and metal fatigue inside the foundational structure.
.. Multiply that by unknown-content brackets from a minimum-wage manufacturer.
.. Multiply that by tin-foil bolts from the grocery store.
.. Multiply that by temperature fatigue.
.
If intended for human occupancy:
Multiply that by intoxicated stompers.
.
Divide by the amount of decapitated by-standers.
.
.
If I was me, I would hire a competent certified welder-fabricator company with insurance and a bond.
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I am old-fashioned.
For my peace of mind, I want each individual involved in the entire process to be Heritage American, and I need all my components to be Made In America by Heritage Americans.
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[edited to add]
Do an image search for 'roof rack failure'.