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Ratio between the Nominal AC power of the PV inverter and the battery inverter

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  • Ratio between the Nominal AC power of the PV inverter and the battery inverter

    Hello ,

    i just found this amazing forum and this already helped alot with my project .

    i am planning an off grid PV system for a small colthing factory and until now i calculated the nombres of panels needed 208 ,375 Wp so the total is 78 KWp ,
    i am trying now to find the right Inverters so i used the "SMA sunny design web" and saw that one of the parameters used in the portal to check the system compatibility is the ratio between the Nominal AC power of the PV inverter (Sunny Tripower) and the battery inverter (Sunny Island), which should be lower than 2. What is the reasoning behind of this?
    my many questions are and i am sorry for that :

    is the sunny Island a charge controller?
    how to calculate the sizing of sunny island ?
    and how to determine the voltage of the batteries ? because i have a big system like what i have ,i think with 48 V batteries i am gonna need a **** ton of batteries and wiring which is bad,and i could not find a batteries with bigger voltage ..

  • #2
    Instead of looking for batteries with a higher voltage than 48V, plan on taking many lower voltage batteries in series to get the inverter input voltage you need.
    For example, if you have an inverter that accepts 48V you can make this up from a series string of four 12V batteries, a series string of six 8V batteries, eight 6V batteries, or even 24 2V batteries. The advantage to using lower voltage batteries is that you can get much higher Amp-Hour ratings in a single case at the lower voltages (the size and weight of a battery are roughly proportional to its Watt-hour rating independent of voltage.
    You get a much more reliable and easy to maintain system be using a single series string of high AH, low voltage batteries than you get by combing lower AH higher voltage batteries in a way which requires you to put batteries or strings in parallel. Parallel configurations make it much harder to balance the charging and discharging cycles equally over all batteries for best life.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.


    • #3
      thank you for the answer .
      i am using 4x STP 20000 ,so each inverter has 20 Kwp , i was wondering what is input A and input B ,does that mean that each input has a 10 Kwp capacity? (two independent MPP trackers.?)
      Last edited by Photonoob; 03-08-2019, 09:58 AM.


      • #4
        > each input has a 10 Kwp capacity

        Whats a Kwp ?
        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A



        • #5
          Originally posted by Mike90250 View Post
          > each input has a 10 Kwp capacity

          Whats a Kwp ?
          i already figured out :

          i calculated the power from the PV modules which is 78 Kwp and 208 Modules , than i choosed 4xSTP 20000 .
          i wanted to know the configuration of the Modules ,how many in series and how many in parallel for each inverter , my calculation is that : 18 Modules in series and 3 in parallel .
          since i have 208 Modules ,it means 52 Modules for each inverter ,the input A and input B are the 2 MPPT tracker for each inverter and for more efficiency i have to use them both so Input A : has 17 Modules in series x2 and input B has 18x1 =52 Modules x4= 208 Modules .

          so i hope i am right ,i still don"t know how to choose the sunny Island and the number of batteries