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Hi all.

Simply question really. Assuming a wooden frame, eg pergola, designed to create a pent south facing roof with space for a 3x4 array of panels (ie three colums of four panels, landscape arrangement), with 2 rafters per column. What would be the best and/or simplist way to attach the panels to the rafters? And more pertinently, would the rafters need to be perfectly alligned for the specific solar panel, or could there be leeway with the fitting? Would some sort of rail system be best?

To be clear, currently designing the structure and step by step construction and additional timber ordering timeframes. There are follow up questions with DC/DC coupling versus inverters for different strings, plus best ways to keep the wiring tidy, etc but I have to get this structure up first. There could be pictures if people want that...

Advice is much aprpeciated.

“Washer head screws” work well. Make sure to avoid the panels contacting anything steel that isn’t galvanised, eg stainless steel fixings.

When I did this I used a rail system and its associated panel clamps. The rails themselves I fixed to the timbers by simply drilling the rails at a 45 deg angle and driving woodscrews through.

Hi Krill,

I've just done exactly what you are thinking of doing, I have a 4x4 grid (approx 3.6m x 7m) I just have the edge of the panels on the main front to rear beams held down by 120mm coated external coach screws, while fitting I realised I needed washers but only had some brackets from rail fixings and as they were aluminium there was no issue just don't look great. I will add some brackets under the joists at some point but everything is solid and stable

dlw wrote: ↑Sun Nov 06, 2022 7:48 am Hi Krill,

I've just done exactly what you are thinking of doing, I have a 4x4 grid (approx 3.6m x 7m) I just have the edge of the panels on the main front to rear beams held down by 120mm coated external coach screws, while fitting I realised I needed washers but only had some brackets from rail fixings and as they were aluminium there was no issue just don't look great. I will add some brackets under the joists at some point but everything is solid and stable

Thanks for the pictures dlw, this looks to be essentially what I'm doing. What size are the rafters,150*50? And the panels are 20kg each assuming those dimensions? I might be over engineering mine (looking at three joists and two rafters per column, but you look to have shared a rafter between columns?) Also that looks to be about 3m tall at the back, any issues with neighbours?

And the panels just screw into the wood?

I just used 75mm M10 coach screws plus 50mm square washers.
The washers were the perfect size to clamp down on the panel edges without shading any cells.
Bolts are shared between panels so there's a 10 - 12mm gap between panels.

Works well, inexpensive and quite inconspicuous.

Krill wrote: ↑Sun Nov 06, 2022 8:22 am
Thanks for the pictures dlw, this looks to be essentially what I'm doing. What size are the rafters,150*50? And the panels are 20kg each assuming those dimensions? I might be over engineering mine (looking at three joists and two rafters per column, but you look to have shared a rafter between columns?) Also that looks to be about 3m tall at the back, any issues with neighbours?

And the panels just screw into the wood?

Yeah one rafter on each side of the panel shared between 2, before I built this I did a test with 8 panels on some old roof trusses and they were in the garden for a long time not being used but stood up to all weathers so I just went with the same, 150x50 joists 3.6m long from a local Travis Perkins. The rear is 3m and the front is 2m so not ideal angle especially for winter and my rear neighbours house is side facing so they don't look directly at anything but I was going to go 4m but while building I met the neighbour and he asked if they would be at the height I had the posts, 3m is within regs for a pergola as long as 2m inside the boundary (I'm 1.7m my tape measure was broken )
Panels were about 20kgs, I have thought about putting some wood across the panel length to support them but will see how it goes, I have decking under the panels so its a very good multi use space. Will be adding some pictures of my setup probably next week when I get back to the UK.

Cool piccys, hmm you've got me wondering if I could use the pergola as well..............while Mrs Desp is not looking??

I am planning something similar on the woodstore roof and also on top of the loft conversion, what I would say with pressure treated timber is that if you can cut it all to length and then immerse the ends in a bucket of Cuprinol 5 star or similar it will help keep the rot at bay, and whatever you do dont stick wood in the ground.

Desp

spread-tee wrote: ↑Sun Nov 06, 2022 10:26 am I am planning something similar on the woodstore roof and also on top of the loft conversion, what I would say with pressure treated timber is that if you can cut it all to length and then immerse the ends in a bucket of Cuprinol 5 star or similar it will help keep the rot at bay, and whatever you do dont stick wood in the ground.

From expensive past experience I now use Met Posts either driven in or bolt down onto concrete. They mean you can replace the post if and when it does rot a lot easier and cheaper.

spread-tee wrote: ↑Sun Nov 06, 2022 10:26 am Cool piccys, hmm you've got me wondering if I could use the pergola as well..............while Mrs Desp is not looking??

I am planning something similar on the woodstore roof and also on top of the loft conversion, what I would say with pressure treated timber is that if you can cut it all to length and then immerse the ends in a bucket of Cuprinol 5 star or similar it will help keep the rot at bay, and whatever you do dont stick wood in the ground.

Desp

Get it done

I need to add some treatment to the ends of the wood.

I've buried my 100x100 posts 800mm, I doubt they will rot in the ground more likely just above ground similar to my fence posts I've just had to replace