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Looking for a more effective way to get power out of PV system on three roofs

  • 05-01-2023 1:34pm
    Registered Users Posts: 38

    Hello all -

    At the end of last summer, I got a 6.5kW PV system installed across three roof surfaces - front and back of the house (E-W), and on a (mostly) flat-roofed N-S facing extension.

    There's 5 panels on each side of the main roof, and 8 on the extension. These all feed into a Solis Hybrid Inverter which currently has a 3.5kWh battery.

    This inverter can only take two strings, so the 8 panels on the flat roof are configured as east-west "tents" - every two panels are propped up so they match the orientation of the main E-W roof.

    Based on four months of data, we're heading towards an annual output of around 3,700kWh - so approx half of what the 18 panels could deliver if they were facing due south in a single array.

    I new at the start that this installation was never going to score highly in terms of efficiency, given the mixed orientation and shading. As it was part of a one-stop-shop retrofit project that covered a lot of trades, there wasn't a huge amount of time to tailor the Solar PV to make the most of our complex setting. I was happy to get the system up and running, and to work to improve it over time.

    I'm now looking to see if I can do anything to increase the output of the system - I'm open to getting a different inverter, and to increase and reorient the panels on the flat roof so they get more south-facing time. I'm also going to increase the battery storage to 10 or 12kW so I can better match our daily use with battery storage.

    Our original installer doesn't have the time to come back out to us - they're neck-deep in new installs - and I've no complaints about that. So I'm looking for advice on an installer who will take a fresh look at our install, as well as any real-word tips on how to optimise three string installations. Happy to pay for expert advice - it seems thin on the ground at the moment!

    Ideally I would love to get my hands on a three-string hybrid inverter… but I'm not sure if there is one out there for single-phase domestic use. Or is it possible to add a second inverter that just handles the flat roof panels?

    Any and all suggestions welcome! Thanks…


  • Moderators, Sports Moderators Posts: 17,888 Mod ✭✭✭✭slave1

    Any installer will take the same stance as your one, they are too busy with new installs at high margin to come out and look at someone elses work to tweak.

    For you, sounds like a few micro-inverters would do the job

  • Registered Users Posts: 476 ✭✭idc

    Other option I've read about is to put your east/west roof in parallel on one string and then put all the flat roof panels south facing.

  • Registered Users Posts: 2,226 ✭✭✭bullit_dodger

    I'd echo in behind what slave mentions above, I've used a few micro-inverters for a 6 panel secondary system, they work well. However, I'd probably hold off for a bit. You mention that you got your system in 4 months ago (end of Aug?) so therefore you've only seen it operate in the darker months where you could have all manner of shading issues going on that wouldn't be applicable in (say) may where the sun is high in the sky and beating down on your panels.

    I'd be inclinded to leave it as is until you see what's what (run until summer solice at any rate) and then decide what you should do based on that data. You might otherwise be trying to fix a problem which doesn't really exist in Apri-Aug

  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 62,707 CMod ✭✭✭✭unkel

    Be careful with that though. It's possible that the paralleled output exceeds the max amp the inverter can handle. I can well imagine this could happen if the panels are relatively flat, which is quite usual for those "tent" setups. If they are at a typical house roof angle, he'd probably be ok, just beware of the risk.