Have a look at Renusol part 420131 which their rails fasten to. I don't know if gaps are necessary but it's standard practice. Ask the panel manufacturer??

If you use standard rails and mid clamps then yes a circa 25mm gap is needed for the clamp to fit between panels. That's not the case for a gap left between rows where there's no clamp but a gap always seems to be left. Maybe it's for aesthetics so there's a uniform gap all round the panel??

We have a ground array on a wooden frame where the panels are clamped to the wood with stainless wood screws and large washers bearing on the panel frame so the gap there is 6mm ish. If you bolt panels in place using the mounting holes on the backs of the frames then you could have no gap. Whether you need a gap I guess would be for the manufacturer to say??

Aluminium coefficient of expansion is 23E-6/degC, wood is around 4E-6/degC. So if a 1m wide panel heats up by 100C maximum from winter to summer, it needs a 2mm expansion gap I think, to avoid stress.

My ground array is on an Renusol aluminium frame. The brackets holding down the panels comprise of a sprung "nut" which fits in the frame verticals, and a capping bracket which is rebated and fits over the adjacent panels, the rebates maintain a distance of 23 mm between panels. A bolt goes through the cap and is torqued up to the specified amount and as it tightens it pulls the bracket containing the nut tight into the verticals of the frame and clamps down the frame of the panel. What is often missed as far as I can make out is that the frame needs grounding with a ground earth rod and to ensure good contact throughout the entire array a special thin SS rectangular U shaped flat plate with slight barbs on it is fitted between the panel frame and aluminium frame which bite through the powder coating to make the contact. The panel earth must not be connected to the inverter/house earth.

Those interested will find a drawing in this guide.

https://www.renusol.com/files/content/Downloads/Zubeh%C3%B6r/20210915_All_Languages_P-Clip_InstallationGuide.pdf

I had a look at the rear frame fixing holes on our ground array panels and the holes are only 300mm in from the ends so easily reachable for a single row of roof mounted panels if you wanted to do away with the clamps to close up the gaps. 2 or more rows of panels would be a challenge to get the fourth bolt in, but maybe doable with sliding channel nuts in unistrut and a long reach spanner??

Posted By: revorI am truly stuck cannot start new thread as says am not signed in when I am so cannot post.

I just used Firefox to start a new discussion for you without any problem. I'd recommend changing your browser.

@revor, how are the rails attached to the roof itself?

Posted By: ComeOnPilgrim@revor, how are the rails attached to the roof itself?

I'm not revor. But you said at the start that your roof used S-5-E clamps? How the rails are attached to the roof depends entirely on what brand/type of standing seam roof you have. You might want to ask the manufacturer if you're not sure. It will affect their warranty.

@revor, thanks! I think the L-bracket and clip shown in the photo here is what I need: https://www.renusol.com/en/solar-panel-mounting/metal-roof/standing-seam-connections/