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Would a Solar PV system make sense here?

  • 14-04-2022 11:17am
    Registered Users Posts: 21,418 ✭✭✭✭

    So, have been thinking of getting a Solar PV system for a while now, but am wondering if it makes sense for me.

    Situation is as follows ...

    Semi-D bungalow with south facing roof, fairly "flat" angle, certainly not 45 degrees. Some slight tree shading in summer (silver birch). Other available roof area is east facing, so probably no use. Might fit 8 panels on at a pinch?

    Me retired, wife working mainly from home. According to my Efergy energy monitor, the background consumption during day approx. 0.3-0.4 kW with odd peaks for kettle/coffee machine/toaster etc. Occasional washing machine run also. Main consumption is in early evening - cooking and dishwasher. "Normal" daily consumption (excluding car charging) is around 11 kWh.

    Have a PHEV at the moment which is charged up 1-2 times per week, usually takes somewhere between 7 - 9 kWh for a full charge. May upgrade to a full EV at some time in the near future but won't be doing any more mileage than I am currently.

    According to my energy supplier I'm averaging 15kWh per day which seems about right, i.e. about 5,500 kWh per year.

    Have a pretty new gas combi boiler and no hot water tank any more, so no possibility for dumping excess PV production into water heating.

    Any insights here? My uninformed thinking is that on an average day, solar would cover my background usage hopefully with some to spare, and a 5kWh battery would both absorb any small spikes during the day, and hopefully mostly cover the early evening peak usage. On a good day though I'd imagine I'd have a good bit of excess, so would end up exporting it and be dependent on what I'd get as a feed in tariff which as I understand it is still a bit of an unknown.


  • Registered Users Posts: 2,419 ✭✭✭bullit_dodger

    These mails are great as it's clear that you've already given it a bit of thought and not just randomly posted "help me" :-)

    So your consumption Alun is a little above average. Most houses in Ireland average about 4000-4500 a year. Typical installation size for that is 5Kwp in panels and 5Kwhr in battery. I wouldn't go above that in battery size unless you have some extensive analysis as you have a PHEV to soak up additional excess. Bad news is as you noted you woun't be able to get solar to heat the water via an Eddi or some other diverter. They all work on the old "immersion" type resistive heating elements and with no hot water tank because of the combi boiler, you won't be able to do that.

    In some respects that's ok, you still have a significant "dump area" with a battery and PHEV.

    East facing roof isn't a bad shout out. What the installer would probably do is install 2 banks of panels. The bulk of them on your south facing roof and then some other panels on your east one. You'll probably be looking at 14 panels (5Kwp-5.5Kwp). The south facing roof may need optimisers if you have significant shading. remember if one panel is partially shaded, it drags down EVERY panel in the array to that level unless you have optimisers (about €80-100 per panel).

    Depends on the level of shading, which only you'd know. For example, while you might have shading, that might only be from late oct-feb, in the afternoons from 3-5pm and you might decide that the loss isn't worth the extra expense. Your installer should help you here.

    Overall, I'd say your in a good place for solar. You've good usage, PHEV helps so that you'll be driving mostly for 5-6 months a year for nought.

  • Registered Users Posts: 21,418 ✭✭✭✭Alun

    Thanks for that, very useful info for if I ever talk to a potential installer.

  • Moderators, Sports Moderators Posts: 18,652 Mod ✭✭✭✭slave1

    Optimisers are just over €40 each, EEL, Boucher Road Belfast

  • Registered Users Posts: 2,419 ✭✭✭bullit_dodger

    Good shout mate - I see midsummer have them for €46 (ex vat) Midsummer Renewables

    They aren't error prone, but if you can avoid them, I would. Not only would it be cheaper, but it's just one less thing to have on your roof.

  • Registered Users Posts: 6,177 ✭✭✭Ubbquittious

    What is in one of those? Just a buck converter?

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  • Registered Users Posts: 2,419 ✭✭✭bullit_dodger

    Not sure Ubbquittious. I'm familiar with a buck converter (vaguely), but as i understand it if you have a panel that is shaded, the internal resistance on that panel increases and that has a knock on effect on all the panels as they are connected in series. This effectively gives an alternative pathway bypassing the panel itself. You sort of lose the panel effectively, but without killing the array.

    I'm not knowledgeable enough about it to speak beyond that. (I don't need them myself - so I never looked far into them)