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Solar PV & New Build

  • 02-05-2019 11:37am
    #1
    stiofan85
    Registered Users Posts: 505 ✭✭✭


    Hi folks,

    We're moving into a new build (A3, no solar but a heat pump) and we would like to add Solar PV after we move in, purely for environmental reasons - we would really like to be as close to neutral on our electricity usage as possible.

    We're also hoping to buy an EV or plug-in Hybrid next year. Most driving is local, creche-run etc. and 10km jaunt in and out of Dublin from the Suburbs at the weekend.

    A couple of questions:

    1 - Does Solar PV & a new build (A3) make any sense?
    2 - I'm hoping that by leaving an EV at home charging during the day that my fuel costs would essentially be zero from the Solar. Is this a reasonable expectation?

    Even though we're not financially motivated, I want to run the numbers first to make sure I can afford it.

    Thanks


Comments

  • #2
    stiofan85
    Registered Users Posts: 505 ✭✭✭stiofan85


    Oh and just to add, I'm planning to go Solar PV + battery, but only if it makes sense. Thanks


  • #3
    KCross
    Registered Users Posts: 12,070 ✭✭✭✭KCross


    Get an energy monitor and see what your usage is like over a prolonged period. Then you will be able to answer it for yourself.

    Being A rated I'd say your energy usage is going to be quite low and your hot water costs will also be quite low via the heat pump. So, dont pay for any hot water diverters. You'll never get your money back on those when you have a HP for heating your hot water.

    You need to see if you can utilise the energy during the day... an EV is a good option for that particularly if you have a car at home for many hours of the day.
    You would do something like this....
    - Plug the car in at night and charge to say, 80%
    - Do your school run, shops etc
    - Plug the car in and have any excess energy go to the car via the likes of a Zappi charge point.
    - While the car isnt plugged in let the excess go to the grid for free... it will be cheaper than paying for a hot water diverter.

    I dont think you will be able to get 100% free driving as that would require your car to be connected all day.... the car has to be usable so you need a base amount of charge in the car when you wake up so that will have to be done via night rate electricity.... you'll just have to tweak that based on your usual driving pattern.

    I'm against the battery side of things.... it doesnt add up financially even more so in an A rated house with a HP.

    Some energy monitor data needs to be your first step here so you can run numbers that are applicable to you as everyone will have their own figures that are only applicable to them.


  • #4
    stiofan85
    Registered Users Posts: 505 ✭✭✭stiofan85


    KCross wrote: »
    Get an energy monitor and see what your usage is like over a prolonged period. Then you will be able to answer it for yourself.

    Being A rated I'd say your energy usage is going to be quite low and your hot water costs will also be quite low via the heat pump. So, dont pay for any hot water diverters. You'll never get your money back on those when you have a HP for heating your hot water.

    You need to see if you can utilise the energy during the day... an EV is a good option for that particularly if you have a car at home for many hours of the day.
    You would do something like this....
    - Plug the car in at night and charge to say, 80%
    - Do your school run, shops etc
    - Plug the car in and have any excess energy go to the car via the likes of a Zappi charge point.
    - While the car isnt plugged in let the excess go to the grid for free... it will be cheaper than paying for a hot water diverter.

    I dont think you will be able to get 100% free driving as that would require your car to be connected all day.... the car has to be usable so you need a base amount of charge in the car when you wake up so that will have to be done via night rate electricity.... you'll just have to tweak that based on your usual driving pattern.

    I'm against the battery side of things.... it doesnt add up financially even more so in an A rated house with a HP.

    Some energy monitor data needs to be your first step here so you can run numbers that are applicable to you as everyone will have their own figures that are only applicable to them.

    Good advice, particularly around the logistics of the school run.

    On the battery side of things, I had this suspicion. I think we use somewhere in the order of 10kwH per day at the moment in a house half the size, but with gas for heating. I suspect we'll use a similar amount if not more in the new house with hot water being powered from the heat pump.

    At that rate, I figured the battery would make sense?


  • #5
    KCross
    Registered Users Posts: 12,070 ✭✭✭✭KCross


    stiofan85 wrote: »
    On the battery side of things, I had this suspicion. I think we use somewhere in the order of 10kwH per day at the moment in a house half the size, but with gas for heating. I suspect we'll use a similar amount if not more in the new house with hot water being powered from the heat pump.

    At that rate, I figured the battery would make sense?

    You might use the same amount of electricity but the key thing to understand with HP's is that they dont work like traditional gas/oil central heating.

    It runs 24/7 but will do alot of its work at night. Night rate electricity is half the price of day rate electricity so when you calculate your savings you need to base it off the price of the electricity you are displacing not the price of daytime electricity.... that increases your payback period significantly.

    e.g. The HP will heat the water at night at 8c/kWh. You cant then heat the water using excess Solar energy and say its saving you 16c/kWh (i.e. the day rate)!

    In addition the heat pump will be 200-400% efficient whereas excess energy from the Solar heating water via a heating element is <100% efficient.... i.e. 1kWh in gives 1kWh worth of heat to the water.... with the HP 1kWh of electricity will give 2-4kWh of heat to the water (its called Coefficent of Performance... COP)... making sense?

    So, if you heat 1kWh's worth of hot water it will cost ~3c via the HP. How much hot water you use then needs to be determined but at 3c it takes a LONG time to get payback for a hot water diverter when you have a HP.

    Similar analysis needs to be done for other devices like charging your car, delay timers for your washing machine etc..... dont make the mistake of using the full day rate price of electricity as your payback price.

    Only things that have to run by day are actually saving you 16c/kWh.... background load items like TV, internet, kettle etc.


  • #6
    stiofan85
    Registered Users Posts: 505 ✭✭✭stiofan85


    Compelling arguments, thank you for the detail.

    I think your guidance on the energy monitor is spot on - understanding usage over time will be key to understanding the real finances of the whole thing.

    Really helpful, thank you


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  • #7
    Gumbo
    Moderators, Society & Culture Moderators Posts: 38,429 Mod ✭✭✭✭Gumbo


    The Solar PV wont charge the car completely.
    To stay Planning Compliant, your looking at about 2.1kw array.
    Most chargers need 3,3kw minimum to charge the car so you will always be supplementing the grid use.

    Then, even on sunny days, with clouds, the system will peak at the full power but spike up and down.

    I have a 3kw system that peaks at about 3.4kw but it doesn't retain that for long due to clouds etc

    PV and battery to store the energy during the day that the HP doesn't use, then power the home in the evening from the battery.
    If the car gets some charge etc, that's a bonus but I wouldn't be basing my purchase on 100% free fuel for the car.


  • #8
    stiofan85
    Registered Users Posts: 505 ✭✭✭stiofan85


    kceire wrote: »
    The Solar PV wont charge the car completely.
    To stay Planning Compliant, your looking at about 2.1kw array.
    Most chargers need 3,3kw minimum to charge the car so you will always be supplementing the grid use.

    Then, even on sunny days, with clouds, the system will peak at the full power but spike up and down.

    I have a 3kw system that peaks at about 3.4kw but it doesn't retain that for long due to clouds etc

    PV and battery to store the energy during the day that the HP doesn't use, then power the home in the evening from the battery.
    If the car gets some charge etc, that's a bonus but I wouldn't be basing my purchase on 100% free fuel for the car.

    Hi KCeire,

    Applying for planning is not a problem and doesn't bother me.

    Maybe I wasn't clear in my OP - my purchase is not based on driving an EV for free, I am more hoping the cost to run would be reduced - I guess that depends on the size of the array. Even still, it wouldn't deter me. I'm just interested in the real costs vs my notional expectations from lack of experience. Motivation is primarily environmental, but I just want to check if the plan is realistic.

    Your outline is what I was thinking - charge battery/ car during day with whatever PV is available plus whatever supplement needed from grid. Use battery in evening.

    Back to the earlier point, I think I need actual usage data before I can make any real calls.


  • #9
    unkel
    Registered Users Posts: 64,745 ✭✭✭✭unkel


    Surprised nobody has mentioned yet that unfortunately you don't qualify for the Solar PV grants as your house is too new. That's a pity as there is a subsidy up to €3,800 available

    Most EVs can charge at 6A (about 1.4kW) so you need at least a 2kwp (7 panel) system for this to work. If your main motivation is for environmental reasons, I would go ahead with a simple system like this. No battery. No immersion diverter. The total cost of the hardware from the biggest supplier in Ireland is €1700 + VAT. Then you need to pay someone to install the panels (about €250) and an electrician to install the inverter and hook it up to your consumer unit (€250). Rough prices, but total should be about €2,600 all in to you

    You will save money on your electricity bill, but don't expect miracles. You will be able to charge your car when you plug it in on blue sky days. You will have made a big step for the environment :)

    When you buy an EV you will get a subsidy of €600 to install a charger. You could chose to install a more expensive smart charger that can charge your car from the sun when you are not using the electricity otherwise


  • #10
    stiofan85
    Registered Users Posts: 505 ✭✭✭stiofan85


    unkel wrote: »
    Surprised nobody has mentioned yet that unfortunately you don't qualify for the Solar PV grants as your house is too new. That's a pity as there is a subsidy up to €3,800 available

    Most EVs can charge at 6A (about 1.4kW) so you need at least a 2kwp (7 panel) system for this to work. If your main motivation is for environmental reasons, I would go ahead with a simple system like this. No battery. No immersion diverter. The total cost of the hardware from the biggest supplier in Ireland is €1700 + VAT. Then you need to pay someone to install the panels (about €250) and an electrician to install the inverter and hook it up to your consumer unit (€250). Rough prices, but total should be about €2,600 all in to you

    You will save money on your electricity bill, but don't expect miracles. You will be able to charge your car when you plug it in on blue sky days. You will have made a big step for the environment :)

    When you buy an EV you will get a subsidy of €600 to install a charger. You could chose to install a more expensive smart charger that can charge your car from the sun when you are not using the electricity otherwise

    That's a bit poxy about the grant, although it is one of the reasons I posted the thread in the first place - I was unsure about the implications for a new build.

    I like your honest assessment though, so thank you. I'm quite handy from a DIY perspective and have an Engineering background so I'd be happy out to research the equipment and potentially install some of it (save for the final connection obviously).

    TBH, after starting this thread I reflected on my motivations - it's rather simple. I use X kWh electricity per day, at ~320g CO2 per kWh. Can I get say, 50% of X from Solar PV? In my mind, that's motivation enough. The payback period etc... is secondary. So I'll do my research and make up my mind.

    Thanks!


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