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Doubling my panels -- is it worth it?

  • 04-09-2022 12:16pm
    Registered Users Posts: 152 ✭✭

    My latest question to self is, if I doubled my panels (maxing out the 5kW inverter capacity) with a second string facing SW (to complement the SE array) would I save money. At todays prices, I do. About €300 annually after tax -- reduction comes mostly(2/3) from FIT. So I would be a solar 'farmer'. That leaves me at risk of market fluctuations.

    I do not think that unit rates and FIT will continue to be 'excessively' high for the ~10 years of repayment window (removing gas as backstop; increased wind generation; additional grid storage). I have assumed ~€3500 to ground mount and install 12/13 panels about 30m from the inverter.

    So I will stick with what I have unless my self usage increases -- say the EV or a heat pump.

    and after doubling down on panels

    Adding a 2nd battery (5.7 kWh -> 10.3kWh) does not help me either.

    So basically I'm telling myself to suck it up for a few years. Am I mad? Have I missed something?

    Remember/Disclaimer this is my situation and my data, and not general advice. You need to run your own figures, to inform your own decisions.

    🌞4.55 kWp, azimuth 136°, slope 24°, 5kW, 🛢️10.9kWh, Roscommon


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

    I think ~€3500 for installing 12/13 panels is optimistic on a ground mount. They are currently going for about €200-250 a panel on midsummer. So call it 12x panels at €225 = €2700 (delivery not included). That might go down a little in the short term if they finally get rid of VAT on renewables.

    So then assuming we take the €2700 for the moment, do you think you could get a ground mount done for €800? Dunno myself. Partially depends on what you have going for you already. For example are you mounting next to a wall or something. Certainly doable, but if you are buying a lot of 2x4, brackets, cabling, cement to anchor it, etc etc it mounts up.

    Not sure where you get ~€300 in savings though. According to PVGIS that 12x400w panels would generate 3995Kwhr in a SE configuration. Call it 4Mwhr. Assuming that a unit you generate on your new panels would either

    a) be consumed by your house at the equivalent day rate (what's that €0.30 or something at the moment?)

    b) if not consumed by your house, you'd export it and you would reap FIT rate. (€0.14)

    Since b) is less than a) , let's take b) as the rate to use. So then it's 4000x€0.14 = €560. Not sure where €300 comes in from your spreadsheet. I couldn't follow it. That's not to say it's wrong, only I couldn't follow it.

    Course, you'd only be allowed €200 tax free, so then there's the tax you have to pay on

    (€560-€200)= €360 (taxable),

    so you would probably come out ~ €400-450/year, after tax I reckon. Could me more as using b) for every unit is pessimistic. You will probably beat that as you will use some of those extra units you generate yourself not at the FIT rate but at €0.30, but I wanted worst case.

    So maybe €500-550?

    Post edited by bullit_dodger on

  • Registered Users Posts: 152 ✭✭curioustony

    @bullit_dodger I'll definitely accept my back of envelope for the ground mount is well out. I recently did a costing for a second wood (fuel) shed. Madness.

    The tables are output from a simulator. Nett = bought - (sold+bonus) + standing. It uses the hourly PVGIS data for my location (2020), and the 15m data from the standard load profile for the second table. The first uses data from my inverter. They are pretty close. Good enough for this type of comparison.

    I have 5kW inverter with a 5.7kWh battery. So that actually caps what gets exported too. I do seasonal load shifting. The 2nd battery had marginal savings. The increase in units used is a result of the load shifting.

    On the flogas rows I ignored the bonus as it is for one year only. I also used 325kWp panels as they are what I have. Probably cannot get them anymore so working towards 400 is a good idea. That would help for sure, but I would still be selling the bulk of the extra, so even more dependent on the market to repay. I do not trust the market to stay this dysfunctional. My consumption will be steady at least untill the ICE dies and an EV replaces it.

    I really thought this would help more in winter. Last year I manage almost 10% of load in dec/Jan. I should no I should compare just those two months, with a better winter slope maybe.

    Anyway, thanks for the very detailed answer. I will update the figures when I get the chance.

    Unless the kWh bought goes down, I am unlikely to invest.

    🌞4.55 kWp, azimuth 136°, slope 24°, 5kW, 🛢️10.9kWh, Roscommon

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

    It’s doable, I have installed 455w panels at €160 each on clearance, I put in a 3.7m ground mount too (galvanised tubular steel with Renusol mounting) and would assume yours is less in height, all in for less than €3.5k

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

    No bother - always interesting to crunch the numbers. Although I think your perhaps going off on a tangent with factoring in suppliers when you start doing things like "(sold+bonus)" etc. The suppliers doesn't really factor in here all you care about is the number of units. Ultimately your panels will generate electricity and those units will either be consumed by the house at the higher day rate, or exported in which case you'll get the lower FIT rate. Yeah the rates do matter, but just pick an average of whats out there on the market. Most FIT's are in about €0.14, so use that.....even though others like Energia are €0.18.

    Using those two values, you now have a range. Probably about €450 (total FIT consumption) -> €650 (total self-use consumption). Your actual yield will be somewhere in there. Maybe as I said €550 or something.

    The 5Kw inverter isn't as much of an issue as you might think. Yes, it will "clip" your output, but your talking about installing the new panels in a different aspect than the current ones, so when your getting full power in the morning on the SE array the SW one has yet to take off. In summer with the sun more overhead then this is more of an issue, but for 8-9 months of the may only see minor clipping and at that, only for 1-2 hrs, where you lose a few %. I figure maybe 5% drop overall at a guess.