Solar Panels How many panels on this space?

r8sso80 · Mar 20, 2022

So I've looked at the dimensions of certain panels and they vary depending on cells but whenever I speak to a company about how many panels I can fit on my roof they always reduce it down to the point where I'm wondering is there some sort of rule about how close to the edge of your roof or ridge line you can go?

So I have a garage roof which is 3400mm x 3520mm and a main roof which is 5700mm x 3510 (or 4000 as I had to estimate based on tile length)

What do you think I could squeeze on that space?

SparkyChick · Mar 20, 2022

Personally, not an expert, but I would be more interested in the type of roof construction you have and the size and materials of the various roof members involved, since I would consider those to be the limiting factor (the weight bearing capacity of the roof itself) rather than the surface area available.

There may be other rules as well, as you suggest, but I suspect they are erring on the side of caution as it sounds like they've not actually been out and looked at it.

r8sso80 · Mar 20, 2022

SparkyChick said:
Personally, not an expert, but I would be more interested in the type of roof construction you have and the size and materials of the various roof members involved, since I would consider those to be the limiting factor (the weight bearing capacity of the roof itself) rather than the surface area available.

There may be other rules as well, as you suggest, but I suspect they are erring on the side of caution as it sounds like they've not actually been out and looked at it.

It's a fairly new house, 2018, and has your standard sort of W joist setup in the loft. I've been working on the fact that new properties have over engineered roofs with structural timber so panel weight shouldn't be an issue. Older houses in the street have 16 panels on one roof so that's more then I'll need as I'm going across two roofs.

snowhead · Mar 20, 2022

r8sso80 said:
the fact that new properties have over engineered roofs with structural timber so panel weight shouldn't be an issue.

SHOULDN'T BE is not good enough, the additional weight of P.V panels and support framing on the roof has to be calculated and be within the max design loading for the roof structure.
Plus there's the DNO export limit to take into account, which may limit the total number of panels.
Permttied development rules mean the panels can't stick up over the existing roof line.

The only people than can say how many panels can be fitted on any particular roof are the people who design and fit the panels for a living

littlespark · Mar 21, 2022

16 panels is standard, as the domestic limit for export is around 4kW. (250W per panel)
There may be panels that can generate more, so less panels needed, but I don’t know.
I’m an end user, not an installer, and I’ve got 16 panels that just about fill my south facing roof.

There may be local council building regs that limit the area covered if your roof faces the public street as it looks like yours does.

r8sso80 · Mar 21, 2022

littlespark said:
16 panels is standard, as the domestic limit for export is around 4kW. (250W per panel)
There may be panels that can generate more, so less panels needed, but I don’t know.
I’m an end user, not an installer, and I’ve got 16 panels that just about fill my south facing roof.

There may be local council building regs that limit the area covered if your roof faces the public street as it looks like yours does.

Thank you. There's no way I have space on my roof for 16 panels so it's good to know weight will unlikely be an issue. Seems to be a lot of concern about it 'maybe' being an issue.

I hadn't actually considered the 4kW export limit yet, I'm still trying to work out how many SSW panels I can fit on the 3400mm x 3520mm space available. You can get 455W panels but they are 2120mm in length so with the space I have I'm looking at a comfortable 3 panels at best.

If I drop the panels down to 400W, they are 1722mm in length which potentially allows me to stack two vertical panels together at 3444mm... it's just whether it's possible for the fitters to do that with 3520mm of tiles (exc ridge line tile). I think if I went for a smaller W panel I can shave even more off the size of the panels. At best I think 6 panels (6*380W) is the most I could get.