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How to size and configure domestic solar PV system

  • 25-10-2020 6:14pm
    #1
    Registered Users Posts: 199 ✭✭ minnow


    Hi

    Are there any resources to design and size a solar PV system? There are so many options out there (diverter, battery, future proof for expansion for future EV car etc). I'm reluctant to ask installers as most will tell me I need whatever they want to sell.

    My preference would be to split over a South facing roof and a West facing garage. However the garage is a separate building so not sure would that have a big cost impact?

    Ideally I'd like to have a few options suitable to my particular situation that I could get priced by installers.

    Any thoughts would be appreciated.


Comments

  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 58,868 CMod ✭✭✭✭ unkel


    South and west is fine, even on different buildings. I'd generally recommend to go big, it doesn't cost an awful lot more to have a 6kW system compared to say a 3kW system. For prices of systems, have a look in the quotes thread. It's quite likely we will get a feed in tariff (where you get paid if you produce more electricity than you consume) and if we do a big system will pay for itself very quickly

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Registered Users Posts: 76 ✭✭ Energy1


    I am the same, I have asked for quotes and this industry seems to be all over the place in terms of quotes, products, batteries. I mean, its very difficult to get like for like quotes, most companies are quoting different brands


  • Registered Users Posts: 199 ✭✭ minnow


    Energy1 wrote: »
    I am the same, I have asked for quotes and this industry seems to be all over the place in terms of quotes, products, batteries. I mean, its very difficult to get like for like quotes, most companies are quoting different brands

    Hi, for that reason I think a lot of people would be interested in a service which provides a short study outlining the technical options for your particular house, orientation, energy use etc. Once you know the preferred technical solution, you can get quotes.

    Does such a service exist or are we reliant on installers to provide their advice which will of course favour their solution over other providers?


  • Registered Users Posts: 10,926 ✭✭✭✭ Calahonda52


    unkel wrote: »
    South and west is fine, even on different buildings. I'd generally recommend to go big, it doesn't cost an awful lot more to have a 6kW system compared to say a 3kW system. For prices of systems, have a look in the quotes thread. It's quite likely we will get a feed in tariff (where you get paid if you produce more electricity than you consume) and if we do a big system will pay for itself very quickly

    FIT will not the financial saviour, maybe 2.5 to 3 cents kWh for domestic PV


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 58,868 CMod ✭✭✭✭ unkel


    FIT will not the financial saviour, maybe 2.5 to 3 cents kWh for domestic PV

    I've never seen figures that low mentioned before. What do you base that on?

    It's all guessing of course but a lot of people have mentioned 5-6c, which I too feel is a reasonable FIT, as it is roughly the average wholesale price of electricity

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



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  • Registered Users Posts: 76 ✭✭ Energy1


    Would it not be better to store or use it anyways and get more valve than exporting.


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 58,868 CMod ✭✭✭✭ unkel


    Exporting is best as someone else will use it. Obviously best as in best for all of us as a collective. Not for an individual who doesn't get paid for it.

    It was a big mistake to give a heavy subsidy for batteries, I have no idea what imbecile was behind that decision. A FIT is far more environmentally friendly than a subsidy and a far more effective spend of tax payers' money in terms of extra renewable electricity production per tax euro spent on it

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Registered Users Posts: 76 ✭✭ Energy1


    Well there are plenty of devices that ensure you use it and not exported back. Diverter to hot water, batteries, EV, topping up A2W. Exporting would be my last resort you need to consider electrical losses too.


  • Registered Users Posts: 1,835 ✭✭✭ garo


    Electrical transmission losses are minimal compared to the losses in storing and extracting the energy from a battery.


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 58,868 CMod ✭✭✭✭ unkel


    Energy1 wrote: »
    Well there are plenty of devices that ensure you use it and not exported back. Diverter to hot water, batteries, EV, topping up A2W.

    They are all terrible use of PV. Inefficient and with huge losses. Exporting would be much better

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



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  • Registered Users Posts: 76 ✭✭ Energy1


    unkel wrote: »
    They are all terrible use of PV. Inefficient and with huge losses. Exporting would be much better

    Where is the losses from diverting to the immersion? Exporting is pointless and not worth it. More value in using it


  • Registered Users Posts: 1,835 ✭✭✭ garo


    If you have reasonably efficient boiler heating water with a diverter will save you 5c per kWh. So once a Fit comes in that pays more, it is not worth it. If you have a heat pump, it will save even less.

    Edit: By it I mean the diverter will save even less.


  • Registered Users Posts: 1,835 ✭✭✭ garo


    unkel wrote: »
    They are all terrible use of PV. Inefficient and with huge losses. Exporting would be much better

    From a societal value perspective I agree on everything except EV and A2W. They are valid consumption. But from an individual perspective, until there is a Fit, energy1 is correct. They are all better than exporting.


  • Registered Users Posts: 76 ✭✭ Energy1


    garo wrote: »
    If you have reasonably efficient boiler heating water with a diverter will save you 5c per kWh. So once a Fit comes in that pays more, it is not worth it. If you have a heat pump, it will save even less.

    What I mean is if you have excess PV panels by not send it to the A2W, this will save the heat pump coming on which is typically .19 cents per kWh or am I missing something? A diverter doesn’t needs a minimum amount either it’s 100% divertable?


  • Registered Users Posts: 2,722 ✭✭✭ graememk


    Energy1 wrote: »
    What I mean is if you have excess PV panels by not send it to the A2W, this will save the heat pump coming on which is typically .19 cents per kWh or am I missing something? A diverter doesn’t needs a minimum amount either it’s 100% divertable?

    I don't think you can just divert that to an a2w system, the heat pump is running or not. And heat pumps are around 300-400% efficient so for your 1kwh of electricity your getting 3-4kwh of heat into your house. (& Most people run the heat pumps on the night rate with under floor heating)

    And if your paying 19c/kwh, switch! I'm paying around 15c day and 7c night.

    Don't be afraid of export, you'll end up spending more than you'd save.

    Hot water diverters do have their uses and it might not be all cost based. If your reason for getting it is anything other than "I don't want to export" it could be viable.


  • Registered Users Posts: 1,835 ✭✭✭ garo


    Yep as graememk says a heat pump cannot just be switched off every time a cloud rolls over.


  • Registered Users Posts: 76 ✭✭ Energy1


    graememk wrote: »
    I don't think you can just divert that to an a2w system, the heat pump is running or not. And heat pumps are around 300-400% efficient so for your 1kwh of electricity your getting 3-4kwh of heat into your house. (& Most people run the heat pumps on the night rate with under floor heating)

    And if your paying 19c/kwh, switch! I'm paying around 15c day and 7c night.

    Don't be afraid of export, you'll end up spending more than you'd save.

    Hot water diverters do have their uses and it might not be all cost based. If your reason for getting it is anything other than "I don't want to export" it could be viable.

    I’m not on a day night rate meter, I get electric staff discount too so I won’t be switching. That’s the standard rate.

    Does the hot water tank for A2W not keep
    Topping itself up as the hot water or heat is used? I presume to does therefore you can use excess PV power to do this work. In that sense the excess power from the PV which would not normally be used would be diverted and therefore heat the water instead if the pump. If you are paying 15 cent or 9 cent the PV excess is free therefore cheaper!!

    I have a diverter at present all excess is divertered regardless of amount and that neglects the need to use alternative energy


  • Registered Users Posts: 76 ✭✭ Energy1


    garo wrote: »
    Yep as graememk says a heat pump cannot just be switched off every time a cloud rolls over.

    My point is the excess from the PV means the pump won’t need to be on as much.


  • Registered Users Posts: 1,835 ✭✭✭ garo


    A heat pump usually runs more at night or in the winter so while solar will contribute towards its running costs, not as much as you might expect. A heat pump has a typical CoP of 3-4 so a kWh used by the HP is worth 3-4 kWh used by the diverter.


  • Registered Users Posts: 11,209 ✭✭✭✭ KCross


    Energy1 wrote: »
    Does the hot water tank for A2W not keep
    Topping itself up as the hot water or heat is used? I presume to does therefore you can use excess PV power to do this work. In that sense the excess power from the PV which would not normally be used would be diverted and therefore heat the water instead if the pump. If you are paying 15 cent or 9 cent the PV excess is free therefore cheaper!!

    I think the point you are missing is that you have to pay for the diverter. The cost of that usually doesnt cover itself and certainly wouldnt cover itself if you are heating hot water with a heat pump on night rate.

    The heat pump will give you a full tank of hot water on night rate (runs once for 20-30mins) which is at 7c/kWh and is typically 400% efficient. Therefore you need to use those figures for comparison not standard rates.

    Paying for a diverter, which only takes the excess, will never recoup its upfront costs in that scenario.


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