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diy solar

Mounting panels to metal roof

JoeyJibJab

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Nov 13, 2020
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19
Location
Tasmania, Australia
Hi guys, Ive begun mounting my solar panels to my car port roof. I'm a little unsure about grounding the system. I'm fastening the panels with L brackets, secured directly onto the metal roofing. My question is, isn't that basically grounding my system to the metal roof and thus the steel supports holding the roof up?

Should I be insuring that the panels aren't making direct contact to the metal roof and then grounding the system with grounding cable? Hope that makes sense. Thanks

I've attached some photos to make it more clear IMG20210731105345.jpg

IMG20210731105345.jpgIMG20210731105416.jpg
 
A diligent code inspector would not accept that as grounding unless you used something like a WEEB washer to ensure electical contact. Even then, I don't know what rules might be in place to ensure good electrical contact between the coated metal roof sheeting and earth ground.

Note: See this resource for more on WEEB washers:
 
You might want to check out S-5 direct-attach solar brackets. I'm sure they've taken that concern into consideration.
 
Typically metal panel roofs have poor and/or inconsistent conductivity between panels due to paint, corrosion over time etc.

Folks in radio who use them as a ground plane for vertical antennas often bond each panel to the next one with wire but this is not a high current carrying application.

I would want properly bonded rails with a 6 or 8 AWG ground wire.

Without a rail you can put a WEEB clamp on each panel and terminate the ground wire at an 8 ft ground rod.

One example here :

 
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For a metal roof, such panels are ideal. I have several of the same brand, and they work perfectly. No complaints. I think it would be much more convenient to use shorter and gentler screws for this roofing material because the panels are very delicate about it. If you snag the main part by accident, you'll have to invest quite a bit in fixing this breakage. Don't install them close to the gutters, or you might crash. These panels don't like moisture. Keep that in mind.
 
Folks in radio who use them as a ground plane for vertical antennas often bond each panel to the next one with wire but this is not a high current carrying application.
…and I’m not certain that for radio they wouldn’t work acceptably well anyways, without daisy chain grounding. Maybe a ham guy will confirm.
 
Maybe someone that reads this can chip in.

I put solar panels on metal roof 11 years ago. Where the panel frame drips onto the sloped roof it is rusting like crazy. No rust anywhere but along that drip zone. What is anyone doing about this ?
 

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My metal roof has rust spots too.
I wire brush the rust off cold_galvanize.pngand apply this stuff.
Lasts a few years, then repeat.
 
I've done the Ospho in a spray bottle, brush, repeat, brush, and paint with Elastomeric from Rust-oleum. Comes with 10 year warranty from walmart. Too soon to tell if effective. Too bad salesman 11 years ago didn't warn me. If I painted that drip area at the outset, there shouldn't have been any rust.
 
I think it’s a bitter family disagreement between AlO2 and Zn
I’d go one step further than galv paint and use 2 coats rustoleum paint over the galv paint. It’s amazing to look at my boat trailer I painted off-white rustoleum in ~2001
 
Maybe someone that reads this can chip in.

I put solar panels on metal roof 11 years ago. Where the panel frame drips onto the sloped roof it is rusting like crazy. No rust anywhere but along that drip zone. What is anyone doing about this ?
Of course it rusts at the runoff point from the panels. Heavy water flow washes away the zinc.
 
Heavy water flow washes away the zinc.
WARNING: Wild speculation follows

I wonder if it is more than 'washing away' the zinc..?? If the rain is hard enough, there could be a stream of water between the panel and the roof. With all the different metals of the panel and racking system, could there be a small battery formed with the rain being the electrolyte? The current would circle through the roof to the panels and back to the roof through the water. This would tend to eat away at the zinc in the roof coating faster than the other metals involved. Once the zinc is destroyed, the underlying steel will start to rust. (On boats they put sacrificial chunks of zinc on the hull so the zink will corrode away rather than the hull.)
 
Of course it rusts at the runoff point from the panels. Heavy water flow washes away the zinc.
So you are saying it is the intensity of the rain flow that triggers the rust ? Cause the rest of the roof panel is fine. I think others suggested the aluminum oxide present at these locations.
 
I *believe* I read in the code just recently that an all metal building could be used as ground for PV panels. I *think* there was verbiage how the structure needed to be grounded as well, ie a rod, wire to the rod etc.

There are several specialty products out there that I have been looking at for direct mounting of panels to metal roofing. They are far more robust than the OP's "L" brackets. His roof is a little sketch too -- loose screws in the picture. The specialty mounts tend to involve using the ridges. Do a search. I don't have any personal experience, but there a lot of metal roofs out there.
 
So you are saying it is the intensity of the rain flow that triggers the rust ? Cause the rest of the roof panel is fine. I think others suggested the aluminum oxide present at these locations.
I am getting way out of my area of expertise, but I think you are right. It is probably more than just erosion from the water. Between the panels, racks, clamps, roof, and grounding there are several different kinds of metals present so some kind of electro-chemical process seems likely. Whether it is aluminum oxide dripping off the panels and interacting with the roof or some kind of circuit between the aluminum and steel through the water, I can't say. It would be interesting to know.
 
So you are saying it is the intensity of the rain flow that triggers the rust ? Cause the rest of the roof panel is fine. I think others suggested the aluminum oxide present at these locations.
Any time there is a concentration of water flows over a zinc coating, the normal zinc wash off is exponentially increased.
Ya see it anyplace there is a runoff area on a metal roof.
It’s why zinc plating doesn’t last many years in rain. And ALL zinc plated roofing eventually turns to a rusty mess that leaks.

Sure, it’s possible there is some electrochemical action from the assortment of materials and PV… but even if it was a wood plate concentrating the washout it would do the same… to stop it, ya need an aluminum sheet where the water hits the roof.

Think about why it doesn’t seem to happen on the uncovered part of the roof… the zinc from above runs down and is deposited by the light wash off above.
 
I am getting way out of my area of expertise, but I think you are right. It is probably more than just erosion from the water. Between the panels, racks, clamps, roof, and grounding there are several different kinds of metals present so some kind of electro-chemical process seems likely. Whether it is aluminum oxide dripping off the panels and interacting with the roof or some kind of circuit between the aluminum and steel through the water, I can't say. It would be interesting to know.
Having been involved in building materials sales off-and-on and a lot of ag in my region I’ve been exposed to a lot of information over the years. Some masonry chimneys, aluminum plumbing vent boot bases, certain non-ferrous brackets for electrical ice-belt cables, etc… they all react with unpainted galvanized metal roofing creating a wash pattern where the water flow is. Paint solves it, just needs a barrier.
While the concentration of water flow is a factor to consider- it’s a real thing- if that were a primary factor then steel roofing would rust below every screw, no? For most areas in the northeast one screw per square foot installed on the flat is the general guidance by several manufacturers- so there’s 1500-2000 opportunities to create water flow diversion on an average-ish ranch house. Yet this is not typically where steel roofing fails.

The mix of the pH of rain, organic deposition, and galvanic potential of metals are the subtle participants of wash-rust on unpainted galvanized roofing.

Aluminum is a funny thing. Even marking/writing on it with a pencil (graphite) can cause it to fail in that area, and the mental exercise of envisioning zincs on boats being sacrificial anodes for aluminum, ferrous, and bronze components is a good visual of aluminum versus galvanized steel (zinc bath plating).
 
Why would a screw be a factor?
A row of panels dumps the rainwater from the entire surface of the array onto a single spot on the roof dumping thousands of times the volume of water the surface would normally see from rain...
A screw just diverts the runoff slightly around it...
 
 
I actually don’t recall ever seeing that in writing before. Although I’ve been bashed occasionally in the last 30? years when I’ve offered that explanation.
 
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