Solar Panel Mounting Ideas - Feedback?

[lebusmagique]

I've skipped through this thread a bit, but here's my very overbuilt superstut roof rack system with solar installed. Deck coming this week. 40 3/8" bolts through modified skoolie.com adjustable roof rack feet, as well as riveted supports down the middle.

[Danjo]

Originally Posted by lebusmagique

I've skipped through this thread a bit, but here's my very overbuilt superstut roof rack system with solar installed. Deck coming this week. 40 3/8" bolts through modified skoolie.com adjustable roof rack feet, as well as riveted supports down the middle.

Attachment 44058

Attachment 44059

I can’t really see the attachment to the roof on my small screen. Got a closeup?

Have you ripped down the freeway at 80 yet?

[sepudo]

Originally Posted by Danjo

Here’s a picture of those rails. You’re right, they are structural.



It looks like the roof sheet abuts this and then it’s capped with trim. I don’t think that’s going to hold a thread. It looks like that if you drill it, then you’d have a hole to the inside?

I can't be certain but it looks like your photo shows inner roof rails.

As I understand the order of build is
Structure rails running side to side (upside down U shaped)
Then inner rails connected to those running front to back
Then the outer skin
Then on top of all that the outer rails *that I'm talking about*...
Which leads me to believe if I only make holes in those rails I wouldn't be making any holes into the actual roof

Thoughts?

[Jolly Roger bus 223]

alright?
everyone look at the shear strength of a single 3/8 inch bolt before you comment about multiples in a unistrut configuration.
yes the entire system configuration can be engineered but how many here are engineers?
its not hard to find bolt strength or the strut strut strength on the WWW ?
we all have opinions and ideas but we all ask how did you do it questions
that i like alot better than having to deal with them at my actual job
kinda nice to be able to come home and make what i want instead of something someone dreamed up on a computer?
sorry?
i can and will help and i live in the 28584 area code

[lebusmagique]

Originally Posted by Jolly Roger bus 223

alright?
everyone look at the shear strength of a single 3/8 inch bolt before you comment about multiples in a unistrut configuration.
yes the entire system configuration can be engineered but how many here are engineers?
its not hard to find bolt strength or the strut strut strength on the WWW ?
we all have opinions and ideas but we all ask how did you do it questions
that i like alot better than having to deal with them at my actual job
kinda nice to be able to come home and make what i want instead of something someone dreamed up on a computer?
sorry?
i can and will help and i live in the 28584 area code

I have literally no idea what point you're trying to drive home here.

[Danjo]

Originally Posted by sepudo

I can't be certain but it looks like your photo shows inner roof rails.

As I understand the order of build is
Structure rails running side to side (upside down U shaped)
Then inner rails connected to those running front to back
Then the outer skin
Then on top of all that the outer rails *that I'm talking about*...
Which leads me to believe if I only make holes in those rails I wouldn't be making any holes into the actual roof

Thoughts?

IDK about build order. I wish there were more detailed photos from Thomas. I chased and chased structural photos for the Minatour to try to answer questions about whether the frame that the AC condenser hangs from is structural.

That’s a screenshot of a Thomas bus factory video. That looks like the rails, right?

[lebusmagique]

Originally Posted by Danjo

I can’t really see the attachment to the roof on my small screen. Got a closeup?

Have you ripped down the freeway at 80 yet?

Sure.




And no, but with it being bolted into the channel at 40 points, and riveted at over 20, and the panels both clamped and bolted in place, I don't think anything is going anywhere.

[Danjo]

Originally Posted by lebusmagique

Sure.

Attachment 44100


And no, but with it being bolted into the channel at 40 points, and riveted at over 20, and the panels both clamped and bolted in place, I don't think anything is going anywhere.

Someone should sell those

[lebusmagique]

Originally Posted by Danjo

Someone should sell those

They do.

https://www.skoolie.com/products1

Pretty easy to fabricate though if you know how.

[kidharris]

Originally Posted by musigenesis

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.

First of all, Godzilla doesn't dare come into Kongs territory. That over grown lizard knows to stay in Asia and out of Kongs space.


Why is everybody using the word "hat channel" to describe Unistrut "C" channel.


As far as the bolt size goes, The only advantage that I can see to using the oversized bolts is that the bigger area of the bolt heads will help keep it from pulling thru the sheet metal roof, which is the weak link in the strength department here. Big thick washers epoxied to the inside ribs with the carriage bolts epoxied to the washers would be more to my liking (be like studs sticking out of the roof). A good polyurethane caulk around the bolt penetrating the roof and a rubber spacer to hold the unistrut off the roof for drainage.


A aluminum "z" the length of the panels, bolted to the Unistrut (with stainless bots and a thin rubber separator to stop galvanic corrosion of the aluminum where it contacts the Unistrut and/or bolts) could be used to provide more holding power on the panels.


But the panel manufacturer probably has hardware that is engineered for the 90 mph winds? Wind warranty is probably void if you don't follow their instructions?

[kidharris]

Originally Posted by farok

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

I always followed the boat builders advice, especially since it was often speced that way on the blueprints specs. Aluminum can be in contact with galvanized as long as it doesn't get wet, maybe. At least I have seen some aluminum fastened with galvanized screws that didn't blow away. I always followed the specs and used stainless fasteners because I liked getting paid. You have to be really careful with aluminum in contact with stucco or concrete.. not really a problem for schoolies



here is a search page if you are really interested. Have fun...


https://duckduckgo.com/?t=ffnt&q=gal...=v190-1&ia=web

[TomA]

Boatbuilders are obsessed with metallurgy because the electrolysis in a boat will corrode the most oxygen reactive metal away regardless where it is in relation to the other metals. All the metal in the boat is electrically connected and reactive through electrolysis.

They actually take advantage of this, and put a sacrificial zinc anode somewhere in the boat to protect everything else. They also use top quality corrosion-resistant metals like silicon bronze and monel stainless where it counts. On a land vehicle this is far less important, as atmospheric electrolysis is orders of magnitude less than on a boat.

Most of the electrolytic corrosion you'd be expecting on a bus is at the interface layer where dissimilar metals are actually fastened together. This becomes a major headache where, for example, steel bolts are torqued down into aluminum cylinder heads and blocks. Anti-sieze compound is a layer of a third, soft metal (usually zinc or copper alloys) between the dissimilar parts that will shear first, allowing the corroded together dissimilar metal interface to come apart without damage to the harder base metals.

It really isn't going to be that big of a problem on a solar rack. Aluminum rivets into steel ribs, galvanized steel bolts into aluminum channel, tek screws into steel- its all going to be pretty much OK from a corrosion standpoint so long as you can keep it reasonably dry. Put another way, if the corrosion you'll likely encounter threatens to weaken your parts or fasteners to the point of failure of your structure, then your engineering has too little margin of safety to begin with. Most home built non-engineered structures don't have that problem.

The more common problem is poor deployment of structural elements and fasteners (using bolts and rivets in tension, not in sheer, lack of structural integrity, not managing forces across the design, undersizing components, failing to resist vibration, thermal cycling, etc.) Better off spending your time making your structure strong, and focusing on other more pressing issues (lighting strike protection, vibration control, leaks and mold, etc.)

Just my $.02...

[kidharris]

Originally Posted by TomA

Boatbuilders are obsessed with metallurgy because the electrolysis in a boat will corrode the most oxygen reactive metal away regardless where it is in relation to the other metals. All the metal in the boat is electrically connected and reactive through electrolysis.

They actually take advantage of this, and put a sacrificial zinc anode somewhere in the boat to protect everything else. They also use top quality corrosion-resistant metals like silicon bronze and monel stainless where it counts. On a land vehicle this is far less important, as atmospheric electrolysis is orders of magnitude less than on a boat.

Most of the electrolytic corrosion you'd be expecting on a bus is at the interface layer where dissimilar metals are actually fastened together. This becomes a major headache where, for example, steel bolts are torqued down into aluminum cylinder heads and blocks. Anti-sieze compound is a layer of a third, soft metal (usually zinc or copper alloys) between the dissimilar parts that will shear first, allowing the corroded together dissimilar metal interface to come apart without damage to the harder base metals.

It really isn't going to be that big of a problem on a solar rack. Aluminum rivets into steel ribs, galvanized steel bolts into aluminum channel, tek screws into steel- its all going to be pretty much OK from a corrosion standpoint so long as you can keep it reasonably dry. Put another way, if the corrosion you'll likely encounter threatens to weaken your parts or fasteners to the point of failure of your structure, then your engineering has too little margin of safety to begin with. Most home built non-engineered structures don't have that problem.

The more common problem is poor deployment of structural elements and fasteners (using bolts and rivets in tension, not in sheer, lack of structural integrity, not managing forces across the design, undersizing components, failing to resist vibration, thermal cycling, etc.) Better off spending your time making your structure strong, and focusing on other more pressing issues (lighting strike protection, vibration control, leaks and mold, etc.)

Just my $.02...

There is a lot here that I would argue with, but I don't have the time, so I will try to stick to one point.


The whole problem with galvanic corrosion and fasteners, especially screws, is that the corrosion makes the hole in the aluminum a little bigger and All "holding power" is lost, thin materials are affected worse than thick materials. With tight bolts and nuts some "holding power" is retained longer because of the clamping action between the bolt and nut, at least until enough aluminum has corroded so that you are just trying to clamp air.


In the case of your steel head bolts and aluminum heads galvanic corrosion is not the only factor at play. The different materials, steel and aluminum, have different coefficents/rates of thermal expansion and high temperatures which complicates things tremendously. OK, that's 2 points, sorry.



Just my $.02...


BTW, I would suggest if anyone is concerned with a particular fastener and aluminum, look for signs of a white crust or powder. With screws, try lightly turning the screw with a screwdriver, if it turns easily then you have problems.

[firebuild]

Originally Posted by farok

I 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.

Just to put it out there.... I just drove cross country and back at top highway speeds, and then down the east coast and back up, and my z brackets held up just fine. However they really HAVE to go into the roof ribs, in my opinion.

[kazetsukai]

Originally Posted by lebusmagique

I've skipped through this thread a bit, but here's my very overbuilt superstut roof rack system with solar installed. Deck coming this week. 40 3/8" bolts through modified skoolie.com adjustable roof rack feet, as well as riveted supports down the middle.

Wow, this is the first system I've seen that is similar to my own.

[mrpincher]

Guys, Thanks for sharing all the ideas here. I'm about 1 1/2 years into my build and have just ordered 6 300W panels for the roof. I WILL be following good advice given on this thread. Thanks to all.



MIke