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Some questions before I get some quotes for PV and battery

  • 02-12-2022 2:51pm
    Registered Users Posts: 133 ✭✭


    I am thinking about getting solar PV and battery and want to make sure before I get quotes that I know what system to look for and to have my homework done. I will then need to convince my better half about the investment.

    We are a 6 person household incl 4 young adults.

    Electric showers, not interested in Eddi at the moment.

    EV charging - 2015 Nissan Leaf (24kw)

    Annual electricity usage: 11,000 kWh.

    I have smart meter but still on non-smart plan with Electric Ireland.

    Roof: Front-East and Back is West facing

    I work from home most days but car is sometimes used by kids so not at home all the time so was thinking of getting a battery.

    If charging battery on night rate - would it be able to handle an electric shower or 2 in the morning - 5 minutes each? ~7.5 kw

    Kids generally shower in the evening after sports etc

    What should I consider for electric shower on battery or direct from solar? Can solar or battery sustain the high level of power needed for an electric shower?

    What size system would make sense?

    What size battery and inverter should I be looking at? Average daily usage = 25kwh, sometimes up to 40kwh.

    My car charger is the standard one ESB installed back in 2015. I suppose I would need a Zappi or similar?

    Picture below is a standard electricity usage pattern in our house - EV charging for an hour or 2 over night, washing machine timed to finish by morning time, shower in the morning then in evening dinner, showers etc.

    Thanks in advance


  • Registered Users Posts: 4,858 ✭✭✭paulbok

    Your system choice will be driven more by the amount of panels you can fit on your roof, with your usage the more you can get up there the better.

    Panels are roughly 2m x 1m and you need to allow 300m from the edges. Can you work out how many you can fit? bear in mind roof obstructions e,g, vents, may limit the no of panels. Also, is there any shading on the roof from chimneys/ trees etc? A pic will also help.

    The number of panels and the kWh potential they will provide, will help those with better knowledge of PV to advise on your queries.

    Inverters & batteries can only push out a certain kWh at a time, so for a 7kWh shower, they will only provide, an example 2.5kWh each (depending on the system) towards the entire house demand, so it's unlikely you'll be able to run the showers in entirety, esp with just the batteries in the morning, though I am well open to correction on this.

    If you are working from home every day, and with FIT, a battery would probably be only use to you for night time charging, so may not make financial sense.

    However, getting solar PV installed, does make absolute financial sense. Payback will likely take 5-8 years depending on the size installed, and while there is a hefty initial outlay, you are unlikely to see any return on investment like it in the current economic climate.

  • Moderators, Sports Moderators Posts: 24,261 Mod ✭✭✭✭CramCycle

    Getting a system installed myself in 2 months and had thought about getting a battery but looking at the outlay vs cost, not convinced its worth it anymore, would love someone to convince me otherwise.

    We use around 6000 per year 3 adults, 2 children. Getting 20 panels with an expected output of 7250 per year. Same as the OP, roof is east west, we are putting 10 panels each side, diverter to hot water and then back to the grid with the remainder. Hoping the rebate of units back to the grid (will put a dent for our winter bills) but back of the envelope calculations (at current prices, excluding inflation which will make it quicker) had pay back in 5 years.

  • Registered Users Posts: 1,374 ✭✭✭DC999

    Echoing what @paulbok said above, go as large as you can fit on the roof. You're using 11,000 kWh a year so largest will be best for you.

    Sizing: If it came down to spending money on panels or battery, for me it’s panel, panels, panels… FIT means the ‘saving’ from a battery is reduced really – it’s the cost of a unit you buy less the credit for FIT for units you don’t consume. You wouldn’t generally charge the car from a small house battery (small battery feeding a larger one means you’ve a load of electrical loses, and more wear on house battery).

    Try use flat roofs / any spare roofs to fit the max. Take any South orientation you can get too. South will provide more than E / W, and much more in Winter. I’ve an E/W split but also a small South roof and helps a lot. I’ve a 5kWp system (max I can fit) and I’d get more tomorrow if I had space. So max it out on day 1.

    Some here have gone for 9kWp of panels on a 6kWh inverter. On an E/W split that oversizing is fine as they won’t be both in sun at same time. Installers will tell you the max panes / size the inverter can handle.


    If that cheap rate is lower than the FIT of 15c+ per 1kWh (depending on the provider), then it’s cheaper to charge the car at night. But means it won’t be able to charge during the day, which is the only advantage of a Zappi over a non solar aware charger.

    On the car charger, you can leave it as is and change to a day / night meter or smart EV tariff on smart meter and charge the car on that. Factor about 1.5k for supply and fit of the Zappi. You won’t get the grant afaik if got it before (worth 600 quid). But you could sell the old charger. There’s a forum here for selling solar stuff. So that change could always happen at a later stage. 

  • Registered Users Posts: 2,727 ✭✭✭yankinlk

    Panels will help reduce bills but changing habits will save just as much money...try load shifting to use the cheapest electricity... Self use sunshine, then night rate if you can.

    My family have all been a huge help on switching OFF the electric shower and only using the normal one. I still need to heat the water of course, between timed Eddi and oil heating I have constant hot water.

    The temptation to have 30-45 minute showers by kids is why I got them to stop using the electric shower. It will heat water on demand ... Forever. At least the tank empties on the non-electric shower limiting how long they can run it.

  • Registered Users Posts: 133 ✭✭Trojan00

    Thanks for your comments. I would say that I could get something around 16-20 panels split between front and back. I have a wooden shed with a metal roof facing south. Its about 4 meters from the back of the house. Not sure if its allowed to run cables along garden wall?

    I hadn't thought about FIT at all. I need to do some sums here.

    Unfortunately, we don't have a normal shower. We have 2 electric showers with a priority switch. Our immersion is on ground floor level and we tried in the past to get pumps to pump the hot water upstairs but it never worked out well. We gave up and now have all electric. We have started to reduce our shower usage. Some of the kids used to take forever now they are starting to reduce to 5-10 minutes.

    Thankd for all your help here. Plenty to think about.

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  • Registered Users Posts: 2,727 ✭✭✭yankinlk

    If it helps, I reckon using an electric shower for short quick showers is cheaper than my method of heating on a tank to use later... But it's key to know that 2.5kwh limit is probably all you will get any solar PV system to supply.

    So think about other things that draw power... And try not to use them all at same time. Electric cooking? That will use 2.5 easy. Washer and dryer? If they aren't modern efficient then they might pull that much and so can dishwasher!

    Think about panels as covering just base draw not peak power. The battery if you get one CAN add additional power to supplement solar... But that's only really middle of the day stuff. On summer you will be running around at midday trying to run everything electric!

  • Registered Users Posts: 1,229 ✭✭✭Galego

    Why would it not be worthy? Do you mean because you get paid FIT for whatever you export?

    Without doing any maths in ROI are choosing between certainty, using what you generate, versus uncertainty, whatever companies wanna pay you (if even they pay you at the end - I am yet to see any fit money myself).

    If you research about fit in other countries where fit was introduced before Ireland, rates went down (quite a bit), after first few years. Use UK as example where things are a bit ahead than here.

  • Registered Users Posts: 145 ✭✭johndoe11

    Just wondering how you get the east/west and some south as well? I have an East/west install in Feb and I asked if I could add 2 panels on a made up frame for a South facing gable. He said all inverters only take 2 strings and I would need three string for this. I would like to have some South production to help in winter. Thanks.

  • Registered Users Posts: 1,374 ✭✭✭DC999

    First off, I had to push to get all roofs covered. Some installers wanted an easy life. But it's my electricity for 25 years.

    I have 2 inverters so could have 4 strings. Only use 3 strings.

    Or can put E and W on one string but need optimisers on all panels and same of panels afaik. Or @bullit_dodger has a way to do the same but without optinisers.

    Or you could get a micro inverter for South if only a small number of panels. That is DIY able. @bullit_dodger and others did that on flat roofs themselves.

  • Moderators, Sports Moderators Posts: 24,261 Mod ✭✭✭✭CramCycle

    Not what I meant, more the increase in outlay cost isn't justifiable for me at the minute. The set up will lower bills to the point that it just won't be necessary. This said the option is there in the future and the installer said it won't be any cheaper to get it done now compared to the future (bar increase in the battery cost itself). In my old home our solar system reduced our bills to 15% of what they were. This is a different house with different costs but I'm happy that in my situation the battery isn't worth it right now. This said, I'll give it a year after install, and if a battery makes sense then after a year to review I will get one.

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  • Registered Users Posts: 2,727 ✭✭✭yankinlk

    I agree. Getting solar to cover half of your bill is easy enough. Trying to get solar to cover the remainder... trying to get the bill to zero... May cost more than it saves.

    I am glad I got a battery... And I haven't seen dime one of fit yet. In a year I might feel different, especially if prices settle down.

  • Registered Users Posts: 890 ✭✭✭Ultimanemo

    I tried the same, when I got quotes and googled how much the hardware they installing will cost, I put it on the shelf.

    They are charging insane prices for labour cost, if it wasn't insurance issues, I would have done it myself on the ground "I have space"

  • Moderators, Sports Moderators Posts: 24,261 Mod ✭✭✭✭CramCycle

    Suppose that's the benefit of the latest install. Install price is agreed, if supply prices increase, payback is quicker, if they slow or stop, then a return of 20% a year on any investment, that, at the very least will provide that for another 5 after its recouped is a nice investment. Now when you add up interest rates, costs etc. The truth is, in an utterly worst case scenario, it costs me nothing.