New panels and inverter ordered!

[Oldgreybeard]

You've got some serious structural integrity in a small package there.

Indeed, that's one of the really great benefits of using these profiles, they are very stiff, not just in bending but also in torsion. There's a whole range of standard fixings and brackets for the stuff, that make it very easy to build strong and neat structures. The fixings use semi-captive nuts or bolts that fit in the same way as for strut, they go down the slot and turn 90° to lock in place, or you can get sliding T nuts that just feed into a slot from one end.

The rack that holds the six Pylontechs we have was built using 3030 profile and an assortment of brackets. Works a treat, even carrying around 192kg of batteries.

[openspaceman]

Indeed, that's one of the really great benefits of using these profiles, they are very stiff, not just in bending but also in torsion. There's a whole range of standard fixings and brackets for the stuff, that make it very easy to build strong and neat structures. The fixings use semi-captive nuts or bolts that fit in the same way as for strut, they go down the slot and turn 90° to lock in place, or you can get sliding T nuts that just feed into a slot from one end.

What are the semi-captive bolts made of? In general what are the rules for avoiding electrolytic corrosion when attaching the aluminium PV panel frames to galvanised steel?

Also I see you intend to clamp between the panels why not clamp at top and bottom, which is what I plan, and slide the panels in from the side, one by one?

[Oldgreybeard]

Indeed, that's one of the really great benefits of using these profiles, they are very stiff, not just in bending but also in torsion. There's a whole range of standard fixings and brackets for the stuff, that make it very easy to build strong and neat structures. The fixings use semi-captive nuts or bolts that fit in the same way as for strut, they go down the slot and turn 90° to lock in place, or you can get sliding T nuts that just feed into a slot from one end.

What are the semi-captive bolts made of? In general what are the rules for avoiding electrolytic corrosion when attaching the aluminium PV panel frames to galvanised steel?

Also I see you intend to clamp between the panels why not clamp at top and bottom, which is what I plan, and slide the panels in from the side, one by one?

They are galvanised steel, I think. The clamps that are holding the panels are standard anodised aluminium ones, so there is no contact between galvanised or stainless steel fasteners and the panels. The galvanised captive nuts seem to be fine for use with the anodised rails, as the system has been around for many years now. Where I have stainless screws going down through aluminium panel clamps I'll be using nylon top hat washers anyway, no idea if this is what installers do but I have a stock of top hats left over from when I had a boat and often had to fit stainless bolts through aluminium parts.

There's no way to clamp at the top and bottom as the top is against the wall and the bottom has to run off into the gutter. I'm running the rails at the Airy points of the longest axis of the panels which will also be far better in terms of transmitting the load from the panels plus any live loads to the structure. I would be wary of top and bottom supports as that will put a fairly hefty bending stress into the panels, far better to try to use supports evenly spaced so as to minimise the bending stress.

[openspaceman]

Where I have stainless screws going down through aluminium panel clamps I'll be using nylon top hat washers anyway, no idea if this is what installers do but I have a stock of top hats left over from when I had a boat and often had to fit stainless bolts through aluminium parts.

Have you a link to those top hat washers? I need to isolate the scaffold tube fixings from the aluminium extrusions I intend to use. I was thinking of using tyre rubber between the tube and extrusion.

My panels will be slid in so no clamping force and I hope the two extruded aluminium beams under each panels will provide enough stiffness.

[Oldgreybeard]

Have you a link to those top hat washers? I need to isolate the scaffold tube fixings from the aluminium extrusions I intend to use. I was thinking of using tyre rubber between the tube and extrusion.

There are lots of suppliers on places like eBay, search either for top hat washers or flanged washers. The ones I will be using for the panel clamps will be 8mm OD, 6mm ID, like these, as the clamps I've bought have roughly 8mm diameter holes: https://www.ebay.co.uk/itm/400481731718

My panels will be slid in so no clamping force and I hope the two extruded aluminium beams under each panels will provide enough stiffness.

The clamping force isn't the issue, as that's neutral and imposes no stress in the panel. It's the dead and live loads that will create bending stresses in the panels as those loads react through the panel fastening points. The best location for clamps is at points 25% of the panel linear dimension on the fixing side in from each end. This assumes that the panel live and dead loads will be evenly distributed, which is probably very close to reality. If supported only at the ends then the bending stress in the panel will be a great deal higher, both under the dead load imposed by the panel mass and by live loads such as wind and snow.

[Oldgreybeard]

Just taken some photos of panel clamp, showing the top hat washer:

Panel clamp 1.jpg (53.17 KiB) Viewed 1093 times

Panel clamp 2.jpg (79.59 KiB) Viewed 1093 times

[Mart]

I think I've come up with a way of keeping the worst of the rain out of the gaps between the panels, needs a bit more research as the idea came to me as I was nodding off last night (as the best ideas often seem to).

Hiya OGB, I may be too late, had a quick skim of the posts, but I have a couple of panels that replaced an old canopy over the back door. My simple and cheap solution to the gap between the panels was to buy a roll of clear tape, I think it was called/classed as greenhouse glass tape, for going over cracks. It's pretty tough, reminds me of sticky back plastic (that takes me back). It lasts about 5yrs, before the sun wears it out, then I replace. Still got the original roll, which is excellent for tough jobs where you want it to remain clear.

[Oldgreybeard]

I think I've come up with a way of keeping the worst of the rain out of the gaps between the panels, needs a bit more research as the idea came to me as I was nodding off last night (as the best ideas often seem to).

Hiya OGB, I may be too late, had a quick skim of the posts, but I have a couple of panels that replaced an old canopy over the back door. My simple and cheap solution to the gap between the panels was to buy a roll of clear tape, I think it was called/classed as greenhouse glass tape, for going over cracks. It's pretty tough, reminds me of sticky back plastic (that takes me back). It lasts about 5yrs, before the sun wears it out, then I replace. Still got the original roll, which is excellent for tough jobs where you want it to remain clear.

Thanks, that's a great idea, and I think I know of a very weather resistant tape that would probably last a lot longer, "helicopter tape", as used to protect the leading edge of propellers and helicopter blades. I think I know where I could get some of that for free - I shall ask around and see what I can find. I know the stuff is very expensive to buy, it'd cost around £75 at these prices: https://cpc.farnell.com/premiumshield/h ... dp/SA03255

[openspaceman]

Just taken some photos of panel clamp, showing the top hat washer:

Thanks for the information and pictures, I'll get there slowly.

[Oldgreybeard]

I've just sketched up a rough drawing showing the bending stress issue, and why end supports aren't a great idea. The live load goes up and down, relative to the panel face, due to wind loading, and the red dashed lines in this sketch show roughly what the deflection looks like for both end constraints and constraints at the Airy points:

Airy point stress distribution.JPG (22.7 KiB) Viewed 1072 times