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Solar roof install on already busy roof

  • 24-10-2022 11:16am
    Registered Users Posts: 132 ✭✭

    Hi all.

    I'm looking at installing Solar PV on south facing roof.

    Roof already has Solar Thermal installed (came with new build house 5 years ago), and it is about to get 2 large and one small Velux windows as part of attic conversion.

    My rough calculations suggest there will be approx 15m2 of relatively open roof space remaining, not including fiddly bits between windows etc.

    My question... is it likely that installation cost will be increased by virtue of not having one large free space to install on, by having to fit panels in 3 or 4 separate open spaces on roof?



  • Registered Users Posts: 1,234 ✭✭✭DC999


    Rails are metal so cost a bit at the moment I expect. But installer only needs more rails. And there will be a cable run from each rail so you’ll see more cables. And a little more time needed on the roof (assuming all the panels are on the same roof).

    Panels are about 1m wide, 1.7m in length. Can't go right to the edge due to regs for the SEAI grant.

    Unlike solar thermals, shade kills the output of PV – even a tiny bit kills it for all the panels on the string. And you’ll have 1-2 strings in total. So a very small bit of shade will drag down the overall production hugely. Unless you get optimisers on every panel that gets shade. Maybe 100 supply and fit (just a rough ball park). PV panels are low to the roof – only a few inches above the roof. So the solar thermals could cause shade. Better to remove the chance of shading where possible.

    Wanna add some pics that show the roof and shade and time of day and the compass direction of the roof?

    But….would you consider moving the solar thermals so you could max out the roof on PV? If the installer could do it, the cost mightn’t be so much. PV gives you all the electricity and if you have an EV (or will) you can charge for free a lot of the months of the year. Gas boilers are going end of life in the not to distant future, so will heat from electricity. And electricity prices are only rising IMO. Ministry of the obvious - solar thermals only gives water in the HWT (but are hugely more efficient at heating water than PV, so don't get rid of them if ye use a lot of hot water). And you get ~15c ‘FIT’ payment on solar units you don’t use now. So you can actually use that to pay back the cost of the install.

    Others here have thermals and PV. I’ve only solar panels (PV). 

  • Registered Users Posts: 63,649 ✭✭✭✭unkel

    I'm the same as you, @ohlordy

    Small 3 bed semi-D house in Dublin area estate. Already had attic converted with 2 very large and 1 smaller Velux window and already had 40 solar thermal tubes all south facing. Got 5 PV panels fitted (but possibly could have got 7), but these were older standard size of 165*99cm, most current panels are bigger

    Don't forget that even if the other side of the roof might be north facing, it could still be worth your while. On my north facing empty roof I could possibly install 15 of those panels, and even with their output only half of what a south facing panel outputs, the whole array would actually give 50% more output, but obviously initial outlay would be higher. That said it is super easy to fill an empty roof with panels from a labour point of view

    That's my own next project anyway, panels on my north facing roof!