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Solar on Flat Roof - to tilt or not to tilt

  • 14-11-2024 05:57PM
    #1
    Registered Users, Registered Users 2 Posts: 2


    Hi Everyone.

    I will soon be getting solar installed on my home office roof. It is almost flat, metal corrugated sheeting on timber roof deck. The solar installer plans to install the panels flat on rails on the deck. I had expected them to be tilted, perhaps not to the optimum ~30 degrees, but at least a little to get a better yield. They are proposing the Van Der Valk ValkPitched system but that looks to me to be for a pitched roof, which I don't have.

    Roof.jpg

    Apart from cleaning the gutter and removing the leaves, should I push the installer for a tilted system (ballast or similar) or just go with the proposal and accept the reduced yield?

    Thank you.



Comments

  • Registered Users, Registered Users 2 Posts: 791 ✭✭✭conor_mc


    Optimising for yield is different to optimising for consumption, so it depends on what you are targeting. First question, are you putting in a battery? Second question, if so do you intend to charge it up on night rate or just let solar charge it? With an uncharged battery you should optimise for yield, but otherwise I’m not sure it’s worth the hassle tbh.

    Not tilting will give you a wider spread of generation across summer days which may help self-consumption rate, at the cost of a) lower peak generation mid-day, and b) slightly lower generation in winter months (15 degrees vs flat are almost equally poor in deepest winter).



  • Registered Users, Registered Users 2 Posts: 2,646 ✭✭✭SD_DRACULA


    Forget about the ballast/plastic bins, you need at least 50cm if not more gap between so they don't shade each other so you'd get maybe about 9 panels up there if you do that and over 1 tone of stone to keep them down, plus I'm sure that doesn't work on that metal roof anyway (without modifications)



  • Moderators, Sports Moderators Posts: 18,289 Mod ✭✭✭✭slave1


    Tilt, will improve gain and help avoid scum buildup

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  • Registered Users, Registered Users 2 Posts: 1,592 ✭✭✭DC999


    I've a flatish roof with 5 panels on it. Maybe 15 degree angle. They work fine. Use the angle you have and fill the roof.



  • Registered Users, Registered Users 2 Posts: 2 XC7469


    Firstly, apologies for the delayed response. I didn't have notifications set up and thought my post had been lost to the ether. Thank you all for your responses.

    @conor_mc Yes, I plan on installing batteries, 10kWh, and yes, I plan to charge by night to take advantage of cheap night rate. I am hoping that in brighter months I may not need to charge to 100% at night but I will have to wait and see.

    @SD_DRACULA thanks for the sanity check on the bins. The amount of additional weight would seem to be huge. It is metal on a ply deck on 9 inch joists, but even at that I would be slow to add that much weight. With the required gap between the rows of panels, whatever I gain by tilting I will probably lose by having to install fewer panels.

    @slave1 , the build up is probably one of my biggest concerns, I don't want to have to climb up there regularly to clear them off.

    @DC999 , I think that is what I will do, fill the roof with as many panels as can be made to fit.

    Thank you all for your insight.



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  • Registered Users, Registered Users 2 Posts: 2,646 ✭✭✭SD_DRACULA


    Yes I agree when they are flat they do get dirty (won't really affect production) but then again even the 15 degree tilt ones on my shed get dirty and I clean them from time to time anyway.

    I found these things to be amazing for draining the water off the flat ones though: https://midsummer.ie/buy/mounting-accessories/D_PanelDrain30



  • Registered Users, Registered Users 2 Posts: 791 ✭✭✭conor_mc


    how do they work, hard to make out from the link?



  • Moderators, Home & Garden Moderators Posts: 7,102 Mod ✭✭✭✭graememk


    Must be some sort of siphon. Like a Pythagoras greedy cup.



  • Registered Users, Registered Users 2 Posts: 2,646 ✭✭✭SD_DRACULA


    You clip them to the side of the panel and then water drips down below them, surprisingly it works!



  • Registered Users, Registered Users 2 Posts: 3,136 ✭✭✭Buffman


    I'd never put in a flat system, I've had a flat roof shed system similar looking size to yours and built a basic frame to give them some tilt. (I actually made it adjustable tilt but rarely bothered moving it)

    You'd be amazed at the amount of dirt that builds up in urban areas, at least with tilted you get a bit of cleaning with heavy rain but with flat panels it won't go anywhere. You'll get puddles of water forming which will start growing green algae/scum. Instead of an annual clean on tilted panels, you'll be up and down like a yo-yo cleaning them.

    It can have a substantial effect on production, after a recent powerwash on one of my roofs during the summer, I was down 20-30% until I cleaned the crud I'd created off the panels properly. (I had to wash them manually in the end as the powerwasher wouldn't lift the crud at the safe settings I was using.)

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