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If you knew then what you know now. Looking for a steer in the right direction.

  • 20-03-2022 2:08am
    Registered Users Posts: 2 Qwerty1971

    Breaking ground on a new build in North Galway in the next month or two and my head's wrecked with all the new technologies.

    We did a self build in 2005 and just sold last year so we're trying again but ideally without a mortgage this time.

    We're building ICF, 2 storey with a flat roof (roof area will be about 100 sqm)

    Initially we were going A2W with UFH but with energy prices the way they are we're starting to re-evaluate.

    Could we go UFH with Solar only (and Electricity of course) or would that be possible?

    I've checked the Solar Data site and it says you'll get approx 1kwh average/day in Dec/Jan but as much as 3/4kwh from Apr to Aug (when you need it least)

    What I was thinking (from my unlimited reading but limited understanding of this forum) was approx 30 panels on the roof plus 10kw battery with the night rate electricity filling the battery during the months where the PV performance is minimal.

    As I work from home I'd also like the option of switching to battery if there's a power outage and adding an EV in the next year or two (so will probably need something that's scalable as our usage grows).

    Getting on now so I'm happy to invest in Solar what I would have previously invested in A2W and a generator backup for power outages.

    Am I being realistic?

    Planning that the house will be A1 or 2 rated with MVHR.

    Money is an consideration of course but I'm not too worried about getting an 8-10 year payback moreso looking for something that's clean, works well and keeps bills under control as we head towards retirement.

    Any advice would be gratefully received.

    Thanks in advance.


  • Registered Users Posts: 3,138 ✭✭✭ con747

    You need to read some of the threads here I installed a 4.1kw system on 22/2/22 and have generated 277kw since then and mine is a small system compared to some on

  • Registered Users Posts: 8,699 ✭✭✭ the_amazing_raisin

    Personally I'd just use the whole roof space for solar panels and go with an ASHP. Makes more space for electricity generation and keeps the plumbing down at ground level where it's easy to access if things go wrong

    I think you're on the right track generally, maybe aim for a bigger battery to cover heat pump usage

  • Registered Users Posts: 2,124 ✭✭✭ bullit_dodger

    You'll struggle to get 30 panels on there with standard hardware. Most inverters will handle 24 panels. It's a question of voltage where they max out at 600V and with each panel in a string being 40-45volts, you'll get 12 (maybe 13 at a push) on there before you hit that 600v limit. 12 is the realistic limit per string as it's also temperature dependent and you might get a voltage spike if the sun comes out from behind the cloud and the panels are cooler, so you need a little buffer. Hence why 12 is the realistic limit.

    That said, 12 panels x 2 strings x 380 watts ~ 9Kwp in panels. That's a very tidy system that which is on the top end of what many would have here. (My own is 5.3Kwp) Now you can go higher, but that involves 3 phase into the house, which you can get put in from the get go, but generally if you are at the retirement stage of life, 3 phase is (probably) overkill.

    Very little point in getting that amount in panels without a battery. Without an EV I'd be going large'ish (8-10Kwhr), with an EV you could consider lowering that to 5Kwhr, but one thing you didn't mention is your actual consumption today (in your existing house). While the general advice is to "go large or go home" on the panels, you can over spec the arrays too if you don't actually use them. Ballpark €15K as you won't get the grant (will you?)

    The question of heat pump I know less of myself (I don't have one). One thing I do know though is that a ground sourced heat pump is generally more efficient (and expensive) over an air sourced one. Efficiency is better, it can be quieter, on colder days runs nearly as well as average days while the ASHP drops off a little, and if you are planning a new build, you might have the opportunity now to put in a ground sourced one. Worth considering.

  • Registered Users Posts: 418 ✭✭ CtrlAltDelete

    Hi Qwerty1971, Just wondering how your project has progressed since? I have planning permission myself and looking at our options. I am feeling the way you described in your original post. So many options.

  • Registered Users Posts: 3,930 ✭✭✭ graememk

    When you say UFH with electric are you talking about the pure electric stuff?

    Like a heating mat in the floor?

    I'm sure the biggest cost of the heatpump is the actual underfloor pipes not the heatpump itself

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  • Registered Users Posts: 5,665 ✭✭✭ zg3409

    Ideally you need a heat pump with enough power to warm house overnight and top up at peak of day.

    A battery generates zero energy and it's energy you need to warm house in winter.

    First 3 things are insulate, insulate, insulate. Air changes should be minimal.

    You don't mention cooking but if that's electric that will need to be allowed for in consumption.

    A heat pump is theoretically 4 times more efficient than electric heating. So air to water powered by solar is equivalent to 4 times the solar compared to non heat pump type.

    Ideally you should design your house as a passive House, which is specifically designed to use little heating. You could design your house to heat in winter using the sun through windows rather than sun->PV>inverter>heat pump >underfloor heating.

    If using the sun directly to warm house you need a method to not overheat in summer, either passive blinds or shapes, or active opening windows or opening awnings etc.

    Ideally a good architect who has built passive houses should design house if possible and specify house that does not cost a lot to heat.