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Solar PV and Battery Payback

  • 09-11-2021 1:00am
    Registered Users Posts: 57 ✭✭

    Hi Folks,

    Ahead of the unknown tarriffs coming in January for PV, im looking to get 4kw of solar and a battery installed in my house as an investment opportunity. To the best of my knowledge, the 4kw panels and battery is the max that is covered by grants for this system, €2400 for the 4kw, €600 for the battery.

    From an investment perspective, im wondering what would the expected payback be for this if we were to base the payback on just exporting, not self consumption (Im usnure will electricity providers take produced units off bills first, or will they just charge for the full amount consumed, and home owners get payed the tariff for the whole amount of kwhs produced which could potentially be 1/2 what the providers charge)

    For calcuating this number, I dont have the below info if someone could give me broad estimates:

    -How many kwhs a typical 4kw array produces in Ireland a year on a South West Facing roof

    -Contractor costs to purchase and implement the 4kw of panels and a battery

    -Governments tariff rate, I know this isnt announced yet, i seen France is 9c so I might use that to make a calculation

    -Is there any further grants for people not on any welfare for solar?


  • Registered Users Posts: 2,269 ✭✭✭bullit_dodger

    The amount that you typically will save it quite dependant on a number of factors - but a decent enough (rough) estimate is

    Solar Electricity Calculator (

    9C for feed-in-tariff would be.....optimistic, for Ireland. Most people are thinking 4-5C.

  • Registered Users Posts: 63,599 ✭✭✭✭unkel

    A 4kwp SW system in a good area of Ireland will generate about 3000kWh per year

    So if you exported it all and the FIT is 5c / kWh, you would make the princely sum of €150 per year 😂

  • Registered Users Posts: 57 ✭✭

    5c per kwh, thats desperate! Any idea on contractor costs? Im sure they will be a few grand dearer than the €3k of grants I mentioned above! Looking at well over 20 years to payback the contractor costs and the panels/battery might need replacing by then, hardly seems worth it?

  • Registered Users Posts: 2,269 ✭✭✭bullit_dodger

    Depends really on what your looking for. If your thinking of a small'ish installation say 2-3Kwp, then Solar as a Service is probably the way to go, even now after them raising their prices a little.

    Ultimately though, every household is a little different. When in the day your usage is, how much are you using, etc. The goal of most of us here on the forums would be to have as high a "self-consumption" rate as possible. Sure, Feed-in-tariffs (FIT) is a nice bonus that we don't have today, but it's in all honesty going to give solar owners 100 maybe 200 euros a year. Sure, i won't say no, but in terms of payback, it doesn't substantially move the needle.

    The main benifit of solar is in avoiding as much of the high "daytime" units that you utilize. For example putting on the washing machine in the middle of the day when it's sunny etc.

    Your typical household though should be looking at 7-9 years or there abouts to completely payback the system (ballpark)

  • Moderators, Sports Moderators Posts: 18,126 Mod ✭✭✭✭slave1

    Keep below €1k /kWp install costs and you are looking circa 9/10 years payback

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  • Registered Users Posts: 63,599 ✭✭✭✭unkel

    7-10 years payback on a battery system, even if you got the full subsidy and you got the best deal going and we are getting a 5c FIT for every unit we export, is still very optimistic at today's electricity prices

    It would require lots of micro management like above, putting on machines during the sunny hours and a bit of cheating like counting that as full day rate savings (whereas those machines could have run at the cheap night rate)

    Realistically it's more in the 15 year ballpark range. And approaching the never range if you overpay by a grand or two compared with the best quotes possible that some people on here got

    That said, it is very likely electricity prices are going up (and possible that night rate prices are going down), this could well decrease the payback time considerably

  • Registered Users Posts: 2,269 ✭✭✭bullit_dodger

    I think the original question was more around the complete solar installation (incl battery) rather than a battery specifically.

    The math on the batteries in isolation is highly variable. My own case I reckon I'll have the battery paid for in 7-9 years, but I do tend to burn through the units (30+ units/day) so all of the 8.2Khw that I store currently are consumed at day rate prices - that naturally helps reduce payback time in these dark months. Battery was depleted at 5pm yesterday for example from 8.05am start. Course in the brighter days (i.e. not november) the battery would last longer and longer into the evening, so I won't consume all the units at day rate, but right now that's how it's earning it's keep.

    It's also hard to factor in math like "sunny in the morning, dull for 2-3 hrs and then sunny again" so your battery could even cycle during a day - (I ignored that scenario although it's potentially one I'll avail of a little as I've 1.4 Kwp east facing and 3.8 Kwp West facing.

    Gut feeling tells me it probably lower than 15 years and in about the 10-11 year mark assuming that the battery they buy is fit-for-purpose and they didn't pay completely over the odds - but again, it's highly dependent on the user profile. As your mentioned, I'm certain that there's people out there unkel on 15-20 year payback with poorly quoted costs and not fit to purpose installations.

    Overall though to the original question on solar installations as a complete package, 8-10 years seems to be the general payback timeline. Course keeping Gretta happy has it's own rewards in itself :-)

  • Moderators, Sports Moderators Posts: 18,126 Mod ✭✭✭✭slave1

    If you want to max the financials, get a 6kWp system with minimum sized battery for grant. Sell the battery and DIY battery setup yourself like DrPhil/Garo/myself whenever I get around to it.

  • Registered Users Posts: 2,269 ✭✭✭bullit_dodger

    +1 on that slave1, but to be fair......out of 1,000 users reading this I'd say there's probably less than 10-20 users that have the skills and/or inclination to do a DIY battery build. In fact I'd go as far to say that I know people (we all do) that they should be kept well away from said devices :-)

    5-6Kwp and a 5Kwhr battery should see (I guess) 80% of households in Ireland generally sorted with the quickest payback.

  • Registered Users Posts: 11,985 ✭✭✭✭DrPhilG just make sure you price around big time on the install. Some absolute savages in the industry are ripping people off left, right and centre with colossal install costs and BS generation & payback estimates.

    The solar quotes thread on this forum is a national treasure.

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  • Registered Users Posts: 57 ✭✭

    Thanks folks for the feedback.

    Just so I fully understand how the utility providers sort the bills:

    Am I right in saying utility providers dont do two seperate sums of produced and used kwhs at the end of each bill cycle, and pay/charge you for both seperatley? So youd be earning approx 5c for all your produced units, and paying approx 20c for all your used units on daytime hours?

    Its more a case of live data, what kwhs you produce on a particular day is taken off your bill ONLY if your using those kwhs in your house at the same time of day, resulting in you not having to pay the utility provider the dearer approx 20c units they charge on daytime hours?

    And only surplus kwhs you produce on that day is exported at the approx 5c rate?

  • Registered Users Posts: 2,717 ✭✭✭yankinlk

    Think about it like a hybrid electric car. U only pay for fuel u use in the tank.... if you use electric instead u don't use fuel.

    The provider has no idea of the units produced that you Self consume in the house. They just see you draw down less power from the grid.

    Right now they don't pay anyone for the electricity that you over produce and give back to the grid... and if they ever do its unlikely to be worth much anyways.