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  • 12 solar panels wiring

    Dear guys,

    I have 12 solar panels. Each panel Basic specs as below:-

    Nominal output (Pmpp) 250

    Voltage at Pmax (Vmpp) 30.5

    Current at Pmax (Impp) 8.2

    Open circuit voltage (Voc) 37.5

    Short circuit current (Isc) 8.7


    I am willing to buy an inverter with built in MPPT charge controller. Specs of the inverter as below:-

    PV INPUT (DC)
    Nominal DC Voltage / Maximum DC Voltage 360 VDC / 500 VDC
    Start-up Voltage / Initial Feeding Voltage 116 VDC / 150 VDC
    MPP Voltage Range 250 VDC ~ 450 VDC
    Maximum Input Current 1 / 1 x 13 A

    GRID OUTPUT (AC)
    Nominal Output Voltage 208/220/230/240 VAC
    Output Voltage Range 184 - 264.5 VAC
    Nominal Output Current 13.1 A*

    BATTERY & CHARGER
    Nominal DC Voltage 48 VDC
    Maximum Charging Current 25A


    So here comes the question:-

    I need to know how to wire the panels in series or parallel configuration or series/parallel combination so as to remain in the specifications of the inverter?

    Please note I will have four batteries installed of 200AH each connected in series.

    Any help would be highly appreciated

  • #2
    I am going to let you answer your own question. First piece of information you need is the panel Voc. Take the panel Voc and multiply by 1.25 and you should get 47 volts. Note maximum Voc input of the inverter is 500 Voc. So how many panels could you possible put in series without exceeding the Voc input? Answer is max panels = 10

    Now figure the minimum amount of panels you can use in series. You use the Panel Vmp voltage of 30.5 volts, and the minimum voltage for the inverter is 250 volts. So you need a minimum of 250 volts / 30.5 volts = 8.2 panels which means a minimum of 9 panels in series.

    So by now you have figured you are somewhat screwed with 12 panels. It takes a minimum of 9 panels in series and no more than 10 in series. So either loose 2 panels, or buy 6 to 8 more panels. Your choice.
    MSEE, PE

    Comment


    • #3
      Originally posted by Sunking View Post
      I am going to let you answer your own question. First piece of information you need is the panel Voc. Take the panel Voc and multiply by 1.25 and you should get 47 volts. Note maximum Voc input of the inverter is 500 Voc. So how many panels could you possible put in series without exceeding the Voc input? Answer is max panels = 10

      Now figure the minimum amount of panels you can use in series. You use the Panel Vmp voltage of 30.5 volts, and the minimum voltage for the inverter is 250 volts. So you need a minimum of 250 volts / 30.5 volts = 8.2 panels which means a minimum of 9 panels in series.

      So by now you have figured you are somewhat screwed with 12 panels. It takes a minimum of 9 panels in series and no more than 10 in series. So either loose 2 panels, or buy 6 to 8 more panels. Your choice.
      Thanks for the detailed response.

      Regarding the panels wiring, can we do a combination of series/parallel to use the 12 panels because the inverters supports 3250 watt of DC input.

      Also you have not guided me regarding the amperes requirement to make to sure the panels don't input more amperes than the specs of inverter.

      Comment


      • #4
        Originally posted by inelastic View Post
        Thanks for the detailed response.

        Regarding the panels wiring, can we do a combination of series/parallel to use the 12 panels because the inverters supports 3250 watt of DC input.

        Also you have not guided me regarding the amperes requirement to make to sure the panels don't input more amperes than the specs of inverter.
        There is no option to run a combination of series/parallel system with only 12 panels. You need a minimum of 9 and a maximum of 10 for a series circuit. If you put the first 9 in series you are left with only 3 which is too low a number for a second series circuit. Either use 10 of your 12 panels or; add 6 more to get two series strings of 9 in parallel or; 8 more to get two strings of 10 in parallel for your system.

        Since the amperage of the series circuit is equal to the amperage of one panel you are only looking at 8.7 amps which is within your inverter input spec.

        Comment


        • #5
          Originally posted by inelastic View Post
          Also you have not guided me regarding the amperes requirement to make to sure the panels don't input more amperes than the specs of inverter.
          Oops my bad, I did not look at the Inverter max current input of 13 amps.

          More bad news. You can only run one series string of 10 panels and that is it. You panel current is 8.2 amps, so you cannot add a second string.
          MSEE, PE

          Comment


          • #6
            What type inverter would give you a voltage range of 250 to 450 vdc but only 13 amps?

            Can you provide a model number for that equipment?

            Comment


            • #7
              Originally posted by SunEagle View Post
              What type inverter would give you a voltage range of 250 to 450 vdc but only 13 amps?
              An unit between 3000 and 5000 Kva. His real problem is a mismatch between panels and inverter. Another example of not knowing what you are doing. You see it many times each day here. Someone goes out and buys stuff and then tries to find an application. Sound familiar?
              MSEE, PE

              Comment


              • #8
                Originally posted by Sunking View Post
                An unit between 3000 and 5000 Kva. His real problem is a mismatch between panels and inverter. Another example of not knowing what you are doing. You see it many times each day here. Someone goes out and buys stuff and then tries to find an application. Sound familiar?
                LOL. Been there and done that too. Although I am a fast learner.

                Comment


                • #9
                  guys why are you multiplying the panel's voc with 1.25?

                  Becuz I am living in an environment where there is not much cold in winters. Avg remains 18 Celsius in winters while summers average 35 Celsius.

                  Comment


                  • #10
                    Originally posted by inelastic View Post
                    guys why are you multiplying the panel's voc with 1.25?.
                    Because you did not specify any climate and I used the max. You do not use the average low temp, you use the coldest record day. Nor did you specify the panel Temperature Coefficient. Most likely the correction factor will be between 1.1 and 1.25.

                    At 1.1 the Voc = 39.27 so 550 Vdc / 39.27 Vdc-panel = 14 panels
                    At 1.25 the Voc = 44.63 so 550 Vdc / 44.63 Vdc-panel = 12 panels

                    The exact answer really comes from your weather data of coldest temps and the panels Temp Coefficient. All we can do here without exact numbers is assume lowest temp and apply NEC correction factor.
                    MSEE, PE

                    Comment


                    • #11
                      And here goes the specs for the solar panels i bought.

                      Nominal output (Pmpp) W 250
                      Voltage at Pmax (Vmpp) V 30.5
                      Current at Pmax (Impp) A 8.2
                      Open circuit voltage (Voc) V 37.5
                      Short circuit current (Isc) A 8.7
                      Output tolerance % +3/-0
                      No. of cells & connections pcs 60 in series
                      Cell type - 6" Mono-crystalline silicon
                      Module efficiency % 15.5
                      Temperature coefficient of Pmpp %/K -0.44
                      Temperature coefficient of Voc %/K -0.34
                      Temperature coefficient of Isc %/K 0.052


                      The lowest temperature we faced was 1 Celsius and that too in night time. Normally in winters it is around 18 Celsius.

                      The highest temperature 48 Celsius. Normally it is 35 Celsius.

                      Now you have complete information to guide me. Thanks for the help

                      Comment


                      • #12
                        OK based on 10 degree C to be safe your Voc = 40 volts. You can take it from there.
                        MSEE, PE

                        Comment


                        • #13
                          Guys thanks for all the information.

                          The inverter specs show this
                          MPP Voltage Range 250 VDC ~ 450 VDC
                          Number of MPP Trackers / Maximum Input Current 1 / 1 x 13 A

                          Is not this too less a charge controller to handle solar panels DC input of 3000 watts. I mean would this result in wastage's of electricity produced by panels?

                          Comment


                          • #14
                            Originally posted by inelastic View Post
                            Guys thanks for all the information.

                            The inverter specs show this
                            MPP Voltage Range 250 VDC ~ 450 VDC
                            Number of MPP Trackers / Maximum Input Current 1 / 1 x 13 A

                            Is not this too less a charge controller to handle solar panels DC input of 3000 watts. I mean would this result in wastage's of electricity produced by panels?
                            No as it gives you 1 amp of headroom. 3000 watt input @ 250 volts = 12 amps.

                            3000 watts @ 450 volts = 6.7 amps.
                            MSEE, PE

                            Comment


                            • #15
                              Guys thank you for your effort to share information/knowledge.

                              I have got the setup installed since 2 weeks, and its been working perfectly
                              I have installed 12 panels in total.

                              Normal temperature during the day time nowadays is 30^C in which the voltage shown on the multimeter/inverter-lcd is 330-350V.
                              Now i am a bit concerned/worried about the coming of month of dec/jan/feb, in which day time temperatures reach till 2^C. Our lowest record temperature -1^C at night time.

                              Now considering this temperature range, is it safe to use the 12 panels considering the specs of the inverter/controller as the inverter has built-in mppt charge controller.

                              PV INPUT (DC)
                              Nominal DC Voltage / Maximum DC Voltage 360 VDC / 500 VDC
                              Start-up Voltage / Initial Feeding Voltage 116 VDC / 150 VDC
                              MPP Voltage Range 250 VDC ~ 450 VDC
                              Maximum Input Current 1 / 1 x 13 A

                              Comment

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