Using unistrut for panel mounting

I’m collecting brackets and rails to mount 5 regular sized panels on a tiled roof.
Unistrut appears to be the most common rail wrt availability but are there complications when trying to attach the extruded aluminium panel brackets?

Do yourself a favour and just get some proper Renusol rails and clamps. It is not that expensive, looks so much better, lasts a long time, easy to remove panels if you need to, and saves you a lot of time on the roof.

There was a time I welded my own steel frames because the mounting hardware was as much as the panels (I remember the hardware around at the time was Schletter). This has improved so much that there really isn’t an excuse for DIY’ing it anymore. Not for your standard stuff.

Geewiz is not a bad shop to get it from. A couple of generic roof hooks. Mid clamps are around R40 a piece and end clamps around R80, if you shop around.

Although, I must admit now that I do the math, just the rails and the brackets puts you around the price of an extra panel :slight_smile: Still, I don’t like unistrut. It’s galvanised steel. It is not going to be as long lasting as the aluminium railing nor will it look as good.


The Renusol rails with hardware works out to roughly half the price of the panels, but they are much better. One of the biggest downsides of the Unistrut is that you cannot cut them (if you do, they will have an ungalvanized end that will rust).


I used Unistrut, had no choice in the matter, it was that or no panels. I had to cut them. Use Zinc spray to protect the cut areas, and reapply yearly or when required. It works a treat, bot the Unistrut and spray on Zinc.


I wonder how well that would work at the coast? Yearly maintenance sounds like a nightmare to me, but I suppose it’s worth the savings to some.

I’m not even sure Unistrut (assuming it is not your only option of course) is really that big a cost saving. Unistrut works out around R65/meter, Renusol “Variosole” is around R100/meter. If the “Standard sized” panel is about 1 meter wide (they used to be 1m x 2m for a long time), we’re talking a little over R80 per panel extra, which for 5 panels is not going to break the bank.

I do see mid/end clips coming in as cheap as R15 a piece. Anyone know if this is any good? It looks pretty similar to some early stuff I used, with a rectangular “nut”, shaped to turn only in one direction, that sits in the rail.

I’ve also mounted a few panels with just big stainless steel washers as mid clamps :slight_smile:

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I would rather go with a reputable brand - lifespan and insurance are factors for me… I’m at the coast.


I am inland, and I have used unistrut on an IBR roof.
The way I did it was:
Initially lengths from apex to eave, these lengths were sensibly spaced apart and secured with 3m VHB tape. (galvo-cleaned before taping).

On top of these vertically sloping lengths, I secured horizontal lengths of unistrut spaced to make the fixtures relative to the top and bottom of a panel in portrait.
The panels are attached to the horizontals of the lattice. Now that it is two unistrut widths above the high part of the IBR there is the ideal gap underneath for airflow.
Unistrut makes a simple slide-in fitting to extend lengths.
As far as I can remember the end of the panel row needed a proper aluminium panel fitting, but between panels in the row unistrut makes a fitting that clamps two panels down.
I think it was considerably cheaper than the proper solar rails. I can’t remember but it was a lot, a big saving on those midspan fittings as well.

Now, it isn’t all beer and skittles, galvanic corrosion is not addressed, as well as rust where cut.
Although there wasn’t a whole lot of cutting. In mitigation, I am not at the coast and galvanic corrosion happens in the presence of moisture and panels dry out pdq. Zinc and aluminium are also not very reactive together.

This setup has grown and withstood the elements, with the oldest panels being around a decade old. I think it’ll see another decade easily. I must have over 20kWp of panels fitted this way. I would use unistrut again in an inland situation.

Using the tape is optional, I think I’d use a connection that would penetrate the IBR in future. I did this job for my late father and his stipulation that he didn’t want any holes in his roof.

Edit: there is a unistrut fitting for endspan of solar row now.

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I’ve used Cabstrut on three installs and no regrets. First one, eight years ago, I bolted the panels down to the strut using short 8mm bolts into spring nuts. Quick and easy enough also not obvious to thieves how to remove. Last two I used anti-theft clips and mounting took a few seconds. All three installs could be described as ground mounts (think Gazebo or Carport with the panels replacing roof sheets) so access underneath is good.

Was this leak free? If so how did you seal between the panels?

Yes, I butted the panels hard up against each other and ran a bead of neutral cure silicone along the joints from the top.

I’d like to see the fittings that allow for the panels to be butted up against one another, if you have a photo, please?


My only 2 concerns with Unistrut if its galvanized. Dissimilar metals don’t do well in coastal areas. Galvanic corrosion proves to be problematic as quick as 6 months in, causing you to lose earthing properties real fast. Using unistrut will require that you earth each panel separately or bond them all together as earthing the rails alone as with Alu to Alu, won’t work in this case. Installers in PE area refuse to use Unistrut/cabstrut as they tend to bend open under wind pressure, sending your panels to the neighbours back stoep.

There is a lot of conflicting ideas, but the general feeling is to stay way clear of using them as a mounting structure. Even in your bigger Solar farm installations, Alu rails are used on top of Galv frames and all the cabling runs in Cab/Uni strut.


I cant find it now, but there is a rubber profile that you can use in between panels that makes it “water tight” allowing you to build a veranda or carport with panels.

Wait, Here it is.

I bond PE panel to panel regardless of mounting structure as I understand it is the correct method. It’s not difficult.

This panel was bolted to the strut with an 8mm bolt into a spring nut 8 years ago. No obvious corrosion that I can see. I’m a few minutes from the sea. The wasps are anti-theft devices.

SANS only require you to bond all the rails together, this is the same method used in PV farms. You then use bonding/earthing clips under the end or mid clamps or mid and end clamps that puncture the coating on the panels and rails to ensure proper earthing.

Just imagine earthing hundreds or even thousands of panels individually.

Richard, about two years ago we inspected a system just across the river from your place. We could see your house from the roof we were on. The original installation were done with Unistrut and about a year old. The corrosion has creeped into everything, even seemed to attack the Stainless bolts used to hold the mid and end clamps down. There was holes right through the Unis struds. I need to look for the pictures to show you.

We had to replace the rails with Alu rails.

A good panel will have a coting that acts as a “Gasket” and will prevent corrosion. If that coting breaks down, or the grade of the unistrut is low, it can cause havoc.

I will link a post about it from another site. Not all sites shows signs, but we have seen some serious cases where the clients were not as fortunate as yourself.

A good read Here.

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To be fair towards a owner installer that wants to save a few rand, it remains his choice to use Cabstrut or not. Its remains his choice and his risk. As an installer with a couple hundred installs country wide, I will not take that risk, I have just seen too many sites that used it giving issues. I can not afford going back to all my installations to fix problems at my expense.

@warwickchapman has some good reasons not to use it. Maybe he sees this post and have the time to share his views with us as well.