How to mount some old panels on trapezoidal (corrugated) roof?

[julianf]

I have a number of these -

https://www.solartradesales.co.uk/Cache ... BMC-39.pdf

The 355w panels, IIRC (they're in my friends barn at present). Datasheet says they're 35mm thick and 21kg in weight.

And id like to mount them on this type of roof -


Trapezoidal box section or something?

Anyway, what's the sensible way to do this? The pitch of the roof is minimal. 12.5 degrees ish. OSB and purlins under the metal.

Thank you.


ps. first post here on the new forum, many posts on the old forum... : )

[Stinsy]

There are “systems” designed especially for there roofs but they can be expensive. Most installations I’ve seen secure the rails directly to the “ridges” of the metal roof with self tapping screws.

[Stan]

Fundamentally it’s going to be aero loads that you are reacting with the fasteners, when a storm arrives. That load will be reacted by whatever clamping arrangement you use and then by those little roofing screws seen in you corrugation photo. I’m less than impressed by using self tappers through the ridges.
If you can see the underside of the sheets then you can drill and fit butch bolts and washers.


The attached photo shows my experiment attaching a scrap panel. It needs bigger washers on top. Drawbacks are accuracy needed on length of spacer tube around bolt and on positioning of holes.

[Andy]

This is a well timed post. I was looking at the same myself. I was wondering what happens when you have dissimilar metals next to each other. The roof is steel and the rails/panels aluminium. Will something rust badly in that scenario?

I saw some 3M glue strips https://voltaconsolar.com/solar-panel/p ... nting.html
and rails with screws https://voltaconsolar.com/solar-panel/p ... nting.html.

The glue strips I hesitate with. I read that who knows how strong the plastic coating is as it is now the weak link. In the demo video it looks like they are bonding to bare metal. Also in 25 years will the bonds still retain their strength. These are questions I have been unable to find an answer to.

[Stinsy]

I was wondering what happens when you have dissimilar metals next to each other.

Zinc or Copper will cause Aluminium to corrode galvanically, steel has the same effect to a lesser degree. Frankly I'd only worry about the Steel-Aluminium galvanic corrosion if I was on the coast. The simplest way to avoid galvanic corrosion in this situation is to electrically isolate the two metals, eg with rubber tape between the panels and fixing or a grommet in the steel roof.

[julianf]

I do not have access to the underside of the roof. Not without taking out the insulation anyway.

I was hoping for a mount that would fit in the gullies of the corrugation, so as I could screw through into the perlins, but evreything ive seen just seems to sit on the ridges.

There's no end of fittings for t-slot alluminium extrusion -

I assumed there would be a good off the shelf solution that I could just throw money at, but, if there isn't, maybe buying some 40x40 extrusion would suit?

But... If I were to do that, I guess the panels would only be able to be clamped at top and bottom, as the edges would be very unlikely to specifically line up with the gullies on the corrugation.

Are top and bottom only fittings acceptable? I have no idea at all. We are not talking side of a mountain, but things do blow over in storms.

[Mr Gus]

Some years ago "elsewhere" I popped up this link with a map of cold dip galv steel area by area uk, it is now more advanced but still mapped based (as it must be a decade later)

https://www.galvanizing.org.uk/corrosion-map/

In the highlands by the sea our old stone croft houses were often clad in corrugated galv which would then be over-painted, they were very durable.

I'd maybe ask a local council (Western highlands, Ross & Cromarty) for leads with regards to solar mounting as this sort of croft still exists after all, so likely someone in planning will know via experience what you are after.

(As i'm sure will the galvanisers association who have a decent technical helpline, it might be worth mentioning that you are ok with a protective contact strip from the outset)

https://www.galvanizing.org.uk/galvaniz ... o-for-you/

I'd be interested in the results too.

[julianf]

I'm not too fussed about corrosion.

The roof is on s single story building that's entirely accessible and it's not s high value roof. Sure, I don't want it to rust out, but, at the same time, I don't want to procrastinate for ever whilst the panels could be generating power.

I have a landrover or two. The dissimilar metals thing is an issue but (in my personal experience) we are talking decades rather than months.

[Stan]

This is how the mcs people attached the array on my stable. Long stainless screws with a threaded stud on the head go into a wooden purlin.
PS just like the next post.

[Fintray]

I was hoping for a mount that would fit in the gullies of the corrugation, so as I could screw through into the perlins, but evreything ive seen just seems to sit on the ridges.
I assumed there would be a good off the shelf solution that I could just throw money at, but, if there isn't, maybe buying some 40x40 extrusion would suit?
But... If I were to do that, I guess the panels would only be able to be clamped at top and bottom, as the edges would be very unlikely to specifically line up with the gullies on the corrugation.

You could use these to screw through the gullies and into wooden purlins:

Screenshot 2021-10-11 104609.jpg (8.63 KiB) Viewed 3851 times

Beaten to it by Stan!

For a strong and relatively cheap mounting rail use hot dip galvanised Unistrut, my panels have been on my garage roof for 11.5 years in rural NE Scotland and only secured at the edges not the top and bottom as well.