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Solar PV batteries

  • 27-01-2020 12:15pm
    #1
    Registered Users Posts: 11,830 ✭✭✭✭ Gael23


    Are these batteries worth the investment? Hard to justify if they only provide enough energy to heat water


Comments

  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 58,874 CMod ✭✭✭✭ unkel


    Batteries connected to a solar PV system are not used to heat water.

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



  • Registered Users Posts: 11,830 ✭✭✭✭ Gael23


    unkel wrote: »
    Batteries connected to a solar PV system are not used to heat water.

    So they just feed your regular power supply?


  • Registered Users Posts: 438 ✭✭ mike_2009


    Primarily the battery would charge during the day, feed your house overnight and any excess PV can go to your hot water IF you have a diverter installed. You could turn on your immersion during a sunny day without a battery or diverter if you prefer.
    They don't make financial sense and the SEAI are cutting back the grant.
    I went for one and love it - at the moment I'm pairing my battery with nightsaver electricity so I pay less during the day until the PV generation picks up later in the spring. Best of both worlds in my opinion but I wouldn't have gone there without a grant.


  • Registered Users Posts: 11,830 ✭✭✭✭ Gael23


    The house was built after 2011 so it looks like I can’t get any grant


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 58,874 CMod ✭✭✭✭ unkel


    A few solar PV panels installed, DIY, will take care of your base house consumption. If you buy well, then even without subsidies, you could look at a payback time of around 10-12 years, which is not bad at all.

    And of course everyone really should make a contribution to fighting climate change if and when they can...

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



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  • Registered Users Posts: 11,830 ✭✭✭✭ Gael23


    unkel wrote: »
    A few solar PV panels installed, DIY, will take care of your base house consumption. If you buy well, then even without subsidies, you could look at a payback time of around 10-12 years, which is not bad at all.

    And of course everyone really should make a contribution to fighting climate change if and when they can...
    So you can generate enough electricity to power your home with the 5kw battery?


  • Registered Users Posts: 51 ✭✭ old_house


    Gael23 wrote: »
    So you can generate enough electricity to power your home with the 5kw battery?
    No, the battery is really only meant to soak up energy that would otherwise be fed back into the grid for free. You would basically charge the battery with excess electricity that is generated by the solar panels but cannot be consumed at the time. When the sun goes down and you come home and switch on the tv you can use this energy to power you trough (part of) the evening, depending on your consumption. You do not need a battery at all, you can just use the electricity from your panels whenever it's there and buy the rest from your electricity supplier. At some point in the near future you will be able to sell electricity back to the grid instead of storing it in a battery.
    BTW, the unit for the storage capacity would be kwh as in kilowatthours. If you have a 5kwh battery you can (theoretically) store enough energy to power a 1000w-device for 5 hours or an 2000w device for 2.5 hours and so on. Practically you don't want to fully discharge the battery, so the real capacity would be less.


  • Registered Users Posts: 11,830 ✭✭✭✭ Gael23


    Is there any wiring needed to switch between the battery and mains power supply?


  • Registered Users Posts: 64 ✭✭ Zardaz


    Gael23 wrote: »
    Is there any wiring needed to switch between the battery and mains power supply?

    No, the battery and Solar Hybrid Inverter are permanently wired together by the installer (though there is an isolation switch between them for safety).

    The Inverter will automatically charge the battery with any excess solar power (if any), and will automatically discharge the battery to run your stuff as required.

    No user intervention required, (though you can configure things like charge/discharge rates and times and thresholds if you want to, and know what your are doing)

    Note that the battery system will be limited as regards total capacity (usually 2-8 KWh), and power (a few KW). In other words, it can only store enough power for a fraction of a day, and can only supply a fraction of the peak load of a house.
    (This keeps costs down, and reduces stress on the battery, so it doesn't wear out too soon.)

    For example, if you run an electric shower (say 8KW) , then it will only supply ~1/4 of the needed power from the battery, and the other 3/4 will come from the grid.

    But, if the battery is charged up during the day, then it can keep the "base load" of your house (fridge, lights, gas boiler etc) running during any cloudy periods during the day, and for several hours in the evening/overnight without using the grid.


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