Mounting panels on galvanized steel structure

[PRTransplant]

I'll try to make this as brief as possible. I have a galvanized steel rack on my roof, specifically designed to have solar panels mounted directly to it. It is already sloped correctly and has "rails" in place for mounting panels to. The person who built it had intended to simply use a bolt, nut, and couple of washers, drilled through the galvanized steel rails, to make his own mid clamps. While I have no doubt this would work, I do have questions. I don't intend on scrapping the rack - It's in perfectly fine shape and should last for many years. I just want to utilize what we have while ensuring that we limit the potential damage to the panels as much as possible.

1. Since the panels are anodized, they should be good to sit directly on the galvanized steel rails, so long as we don't scrape off the coating where it contacts the galvanized, right?

2. Are there any mid/end clamps that I can use in this fashion? Most require them to be slotted into the aluminum rail channel, but I don't have that here. I need something that I can drill the hole through my galvanized rail, and tighten down the nut to attach. I can make my own using the bolts and washers of course, but I'd prefer to have something specialized to the task.

3. Regardless of whether I make my own or buy an off the shelf product, what material should the clamp and bolt be made out of in order to limit the galvanic reaction between the materials? I was thinking galvanized hardware would be the way to go, but not entirely sure on this one.

[Ampster]

I spent a lot of time living near the ocean and have two properties with solar only a quarter mile from the ocean. I would recommend stainless fasteners with an antisieze compound.
I presume the panels would have to be grounded per code. That may present challenges if the rail has to be grounded as well. I know from experience that two dissimilar metals will expand and contract differently and that may present challenges to not wear off the protective anodization.

What does the cross section of your galvanized rails look like? Is it a right angle, T shape or U channel?

[PRTransplant]

We're well away from the ocean, up in the mountains. Plenty of rain, no salt.

Stainless fasteners, so do you mean stainless bolts, washers, and nuts, and just make my own clamps? Or do you mean an off the shelf clamp and replace their T bolts with my own bolt and nut?

I intended to run the ground to each panel AND through the structure, tying everything together. Would that not work OK?

The rails (And dang near the entire structure, aside from bracing) is made from Galvanized Rectangular tubing. To attach anything to it, I'll have to drill through it I think.

[Ampster]

We're well away from the ocean, up in the mountains. Plenty of rain, no salt.

Stainless fasteners, so do you mean stainless bolts, washers, and nuts, and just make my own clamps? Or do you mean an off the shelf clamp and replace their T bolts with my own bolt and nut?

Either way would work. The holes would have to be drilled more precisely than sliding t bolts in aluminum rails. I have seen fender washers substituted for brackets. The real issue is reaching under the panel to get a wrench on the nut so you can tighten the bolt.

I intended to run the ground to each panel AND through the structure, tying everything together. Would that not work OK?

It should work okay as far as lightening protection. I would watch for galvanic corrosion between the two dissimilar metals. There was another thread on this forum that discussed using galvanized Unistrut.

[J.P.M.]

Metallurgical considerations aside for a moment, are building codes for things like wind design a consideration in any of this ?

As for galvanic corrosion, keep the steel and aluminum out of contact with one another to lower the corrosion potential. Stainless or al-bronze bolting will not corrode, but won't do much for galvanic corrosion if the steel and aluminum get to form a galvanic cell. As others write, if you do use stainless bolting, be sure to avoid galling the st. stl. threads w/anti-galling goop.

[PRTransplant]

Either way would work. The holes would have to be drilled more precisely than sliding t bolts in aluminum rails. I have seen fender washers substituted for brackets. The real issue is reaching under the panel to get a wrench on the nut so you can tighten the bolt.

Yeah the holes will have to be fairly precise but that shouldn't be an issue. Getting under the panel is easy - The rack is raised off the ground more than 1' at its lowest point. At it's highest, it's almost 5' off the ground, so plenty of room to get under and work.

It should work okay as far as lightening protection. I would watch for galvanic corrosion between the two dissimilar metals. There was another thread on this forum that discussed using galvanized Unistrut.

The Corrosion is what I'm worried about. I wonder if I could/should insulate them some how, like with a piece of material running down the length of my galvanized rail, or if there is a better way perhaps.

Metallurgical considerations aside for a moment, are building codes for things like wind design a consideration in any of this ?

No, not even a little bit. The installation is very well protected and sees minimal wind and there are no building inspectors to speak of here.

As for galvanic corrosion, keep the steel and aluminum out of contact with one another to lower the corrosion potential. Stainless or al-bronze bolting will not corrode, but won't do much for galvanic corrosion if the steel and aluminum get to form a galvanic cell. As others write, if you do use stainless bolting, be sure to avoid galling the st. stl. threads w/anti-galling goop.

Any ideas for insulating the aluminum from the steel structure? I basically have 4 very long rails that the panels will be mounted on. 2 columns, 2 rails per column.

[emartin00]

Don't worry about the modules being on the galvanized rail. There are many Gigawatts of utility scale solar farms built exactly like this. Modules are bolted directly to galvanized steel rails every day.
For hardware, use stainless steel, and apply anti-seize to the threads. I would suggest using an off the shelf clamp rather than a washer. These clamps have been tested to withstand the wind loads a solar array will see. A washer hasn't.
For grounding, make sure you use a tin plated copper ground lug such as a WEEB-LUG or CL501TN. These are designed to be used on either galvanized rails or aluminum module frames.

[PRTransplant]

Don't worry about the modules being on the galvanized rail. There are many Gigawatts of utility scale solar farms built exactly like this. Modules are bolted directly to galvanized steel rails every day.
For hardware, use stainless steel, and apply anti-seize to the threads. I would suggest using an off the shelf clamp rather than a washer. These clamps have been tested to withstand the wind loads a solar array will see. A washer hasn't.
For grounding, make sure you use a tin plated copper ground lug such as a WEEB-LUG or CL501TN. These are designed to be used on either galvanized rails or aluminum module frames.

Thank you for the advice!

For the off the shelf clamp, do you have one that you'd recommend specifically? Since they're all designed to slide into that channel on the rail, I'm hesitant to buy one without somebody explicitly telling me, yeah you can through-bolt that to your galvanized rail.

I have a ton of WEEB-LUGs added to my online shopping cart already, but wasn't sure if they could be used on the galvanized rail. Glad to hear that they can be. Just to clarify, I'll want one lug per panel and then one per rack as well, right? (I have two individual racks sitting right next to each other)

[J.P.M.]

Any ideas for insulating the aluminum from the steel structure? I basically have 4 very long rails that the panels will be mounted on. 2 columns, 2 rails per column.

I'd not worry a lot about it. Galvanized steel and aluminum are close in galvanic potential. The galvanized steel being a bit more cathodic will corrode a bit less than the aluminum, but given their closeness in a galvenic series table for most environments, the rate of corrosion will be rather slow. Google "galvavic corrosion".