Mounting Solar Panels on GRP Roof?

efunc · 8 Sep 2020

Hi all,

any advice on the best way to proceed with this? I've bought a couple of LED wall lights which come with a separate solar panel, about the size of an iPad. These have a mounting bracket designed to be screwed to a fence with a couple of screws. I would like to keep these out of view though and the best location is the roof deck of my now completed garden room. These pictures are from during the build:

It's now completed and the GRP has been finished in topcoat. Had I planed for this I might have mounted some threaded bar into the OSB before applying GRP matting and resin, however at this stage I don't really want to drill into it. Is there any other solution to mount the two panels? They are small and probably only weight 200g each, so hardly demanding, but I don't want them blowing away.

Currently I'm considering using something like 3M VHB Double-Sided Adhesive Pads to stick them down. Alternatively some velcro strips, if the adhesive was waterproof. Other options might just be ballast to weigh them down. 1 or 2kg ought to be sufficient.

How is this normally done?

big-all · 8 Sep 2020

simply do not under any circumstances pierce the roof
a small probably fairly useless solar panel will be more off a novelty rather than useful so not worth damaging a roof
take the maximum rated output off the panel then take the time you need it most and call that winter when the output will be perhaps 3-5% off maximum on average for perhaps 6-8 hours so a gimmick pure and simple

efunc · 8 Sep 2020

So..... to get this back on topic..

Anyone have any thoughts on the options listed above?

1 3M VHB
2 Velcro
3 Ballast
4 Other

big-all · 8 Sep 2020

Apologies if you think my input is frivolous the light will be close to not worth attaching to not worth attaching but off course if you wish to spend time i wish you luck and please enjoy the light from the lamps

mattylad · 8 Sep 2020

Have you done the roof yourself?
If you have any stuff left can you grp it to the roof?
Add a little box shape to fit it?

But as big-all says - the output may not be good enough, it is also likely that the panel will fail, then you will need to replace it.

Harry Bloomfield · 8 Sep 2020

Glue each panel to a brick (Gorilla glue) and simply sit both on the finished roof. I agree that solar lights are at best a novelty, if you want something permanently useful, use mains powered lighting.

efunc · 8 Sep 2020

Harry Bloomfield said:
Glue each panel to a brick (Gorilla glue) and simply sit both on the finished roof. I agree that solar lights are at best a novelty, if you want something permanently useful, use mains powered lighting.

Thank you, I hadn't considered using the ballast as a base instead of a weight. But it's even simpler - I can use the mounting screws to just screw it to a brick, or to a piece of one of my limestone slabs. That won't be going anywhere. Rubber Butyl tape is also a great option for waterproof bonding. My main concern with positioning a block or brick was just that I'd be creating a small moisture trap there that could allow the build up of water or mould, algae, moss growth. But I suppose regular inspection/cleaning will keep things in check. I could also raise the brick up slightly on spacers to allow water to run under it. Thanks for the advice all.

Notch7 · 8 Sep 2020

Easy -just silicone a lump of timber to the roof and screw into that....or an offcut of composite decking board for longevity

you can pull silicone off too if you decide to remove it -which is why I would recommend it over CT1 or similar.

efunc · 8 Sep 2020

Notch7 said:
Easy -just silicone a lump of timber to the roof and screw into that....or an offcut of composite decking board for longevity

you can pull silicone off too if you decide to remove it -which is why I would recommend it over CT1 or similar.

Thanks for that idea too. Is it the silicone that would hold it down, or the weight of the timber?

big-all · 8 Sep 2020

you need to place the panel at an angle so as the sun passes overhead it at 90 degrees to the suns arch across the sky so as said above silicon to a slab and perhaps a brick or two to give adjustment

datarebal · 8 Sep 2020

Ballast is fairly common.
Maybe you could contact your grp installer and glass the brackets to the existing roof

Harry Bloomfield · 8 Sep 2020

datarebal said:
Ballast is fairly common.
Maybe you could contact your grp installer and glass the brackets to the existing roof

They will be steel, the steel will rust out and burst the glass. I would not make them a permanent fixture.

Notch7 · 8 Sep 2020

efunc said:
Thanks for that idea too. Is it the silicone that would hold it down, or the weight of the timber?

The timber will be stuck to the roof by the silicon. When cured you can screw your panels to the timber.

motorbiking · 8 Sep 2020

Not sure what type of panels you are installing.. But you could probably attach a frame to the back wall, given they need to be at an angle anyway. 200g Panels? I'm assuming this isn't a FIT system?

Mr Chibs · 8 Sep 2020

You could glue down with something like puraflex from toolstation around £5 tube, it's frequently used by motorhome and boaty folk for gluing skylight frames, solar panels etc.

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Mounting Solar Panels on GRP Roof?

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