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  • Mix and Match panels

    Hello,

    I have 14 Jinko panels of 310W and 7 REC panels of 365W.

    What is the best way to connect those panel to Growatt SPF 3000 inverter?
    How many string of panel can I connect: parallel / Serrie?

    Regards,.
    Key

  • #2
    I looked up Growatt SPF 3000 and found that they have two different models, one for 24V and one for 48V.

    Both are single-string inverters, so you will have to series/parallel panels. For both, the MPPT input voltage is 30VDC to 115VDC and maximum is 145VDC. You want as high as possible, but you also want to be sure that you never exceed 145VDC.

    I assume that your Jinko and REC panels are 60-cell panels, with an output voltage roughly 37V at optimum, 46V maximum.

    If you put four panels in series, the nominal output voltage will be too high and the peak would go far above the maximum for the inverter (46*4=184V>145V), so that would be too dangerous. You'll have to limit yourself to series connections of 3 panels.

    The logical choice is to wire strings of two Jinkos and one REC in series, and put all 7 strings in parallel. That works out cleanly with 14 Jinkos and 7 RECs. On a bright, sunny day at noon, this can generate more power than the inverter needs, but that won't do any damage. The inverter will just limit output safely. Extra power capacity is not a problem.

    All of the above is from someone who has never used a Growatt inverter. If you want a more authorititive answer, contact your Growatt dealer or contact Growatt directly: service@ginverter.com
    Last edited by bob-n; 10-26-2020, 09:49 PM.
    7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

    Comment


    • #3
      Hi Bob-n,

      Thank you for your response. The Growatt that I had is 48V version.

      Both of the Jinko and REC panels are 72 cells with the following specs:

      Jinko 365W: (7 pcs) 365Wp
      39.7V
      9.2A
      48.2V
      9.57A
      REC 310W: (14 pcs) 310Wp
      36.7V
      8.53A
      45.3V
      9.02A

      1- Can I connect 2 Jinko and 1 REC in series (39.7 *2 + 36.7 = 116V) then parallel it to become one string?
      2- Can I connect 2 REC and 1 Jinko in series (36.7 *2 + 39.7 = 113V) then parallel it to become one string?

      a- Will 3V different between 2 brand cause any issue?
      b- Any power loss for the above string connection?

      3- How many string can I connect to the inverter?
      4- Which string is better?



      Comment


      • #4
        Please recheck your counts. Your first message says 14 Jinko and the second message says 14 REC.

        (1 & 2) Yes, you can connect different brands in series like that. If those are the only panels you have and you want to use them all, that's the best approach. As long as the open circuit output of the three panels (48.2+48.2+45.3=141.7V) sums to less than the abs max of the inverter (145V).

        (a) The voltage difference is not a concern when wired in series. However, it won't be as good to have a 2J1R string in parallel with a 1J2R string. If you have lots of Jinkos, stick with all 2J1R strings. If you have lots of RECs, use all 2R1J strings.

        (b) I don't know of any reason for power loss in this configuration.

        (3) I don't think that the inverter cares if you connect 100 strings to it. It will only put out a limited amount of power, no matter how much power the strings can generate, but it will be happy as long as you don't exceed three panels in series.

        For safety, you need one circuit breaker per string when you have lots of strings in parallel. That's a separate discussion.
        7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

        Comment


        • #5
          Panels in series, need to match Imp (+-10%)
          Panels in parallel, need to match Vmp (+-10%) ( of the sum of the panel string )

          How this works:
          panels in Parallel, will be limited to the lowest voltage panel
          panels in Series, the string is limited to the lowest amp panel
          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

          solar: http://tinyurl.com/LMR-Solar
          gen: http://tinyurl.com/LMR-Lister

          Comment


          • #6
            Mike,

            I agree with you almost completely. But I'm not sure why you say that "Panels in series, need to match Imp (+-10%)".

            If they don't put out the same current,as you say, the string will be limited by the lowest current panel, and less productive than it would be had they matched. But that's still a productive string. Given the stack of panels that monogram has and his/her desire for the best way to use them all, putting dissimilar panels in series seems like a good plan.

            We've talked here at length about the merits of people planning before buying, and the more they know, the smarter their decisions. Monogram is coming at this already having a stack of panels and an inverter. I'm guessing he/she either bought them on a whim at what seemed like a wicked good price or was given them. We're advising him/her with those assumptions.

            Am I missing something?
            7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

            Comment


            • #7
              If it was my panels then I would wire 2 of the 310 watt along with 1 of the 365 watt panels wired in series and then go with multiple strings in parallel that does not exceed the Growatt max input wattage for the battery voltage of 48V. Based on the specs I saw that comes to 4500 watts max or about 4 strings of 985watts each.

              What you have to also look at is the total Voc voltage for those 3 panels in series. That comes to 45.3v + 45.3v + 48.2v = 138.8V which is below the inverter max input rating of 145V.

              You will also require some type of combination box with over current protection for each string of panels.

              I just saw another spec for a Growatt 3000 that only has a max of 1800 watts input. So please make sure you look at the specifications for your inverter and follow those rules
              Last edited by SunEagle; 10-29-2020, 10:31 PM.

              Comment


              • #8
                If you put a 4A panel in string of 6 amp panels, you limit the string to just 4A. Won't damage anything much, but you could loosing more power than if you just left the 4A panel out completely. So the matching 10% is a guide.
                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

                solar: http://tinyurl.com/LMR-Solar
                gen: http://tinyurl.com/LMR-Lister

                Comment


                • #9
                  "...go with multiple strings in parallel that does not exceed the Growatt max input wattage..."

                  I don't know how you can have problems with too many panels in parallel. On a low-light day, early morning, and late evening, you'll get more power. On a bright day, the panels will put out lots of voltage, closer to open-circuit voltage, and the inverter will only pull as much power as it can (some call this clipping). In some cases, it might be a less efficient use of roof space. In other cases, it might be wasting money on panels. But monogram already has the panels and wants to use them all.

                  Given that constraint, why not? The extra panels will give more total generated energy.

                  As a side benefit, if one or more panels die, the array will still produce quite nicely.

                  It will cost more for mounting hardware. It will cost more for circuit breakers. But those should be small expenses compared to the extra energy produced morning, night, and cloudy days. Those are the calculations that I would encourage monogram to run.
                  7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

                  Comment


                  • #10
                    Originally posted by bob-n View Post
                    "...go with multiple strings in parallel that does not exceed the Growatt max input wattage..."

                    I don't know how you can have problems with too many panels in parallel. On a low-light day, early morning, and late evening, you'll get more power. On a bright day, the panels will put out lots of voltage, closer to open-circuit voltage, and the inverter will only pull as much power as it can (some call this clipping). In some cases, it might be a less efficient use of roof space. In other cases, it might be wasting money on panels. But monogram already has the panels and wants to use them all.

                    Given that constraint, why not? The extra panels will give more total generated energy.

                    As a side benefit, if one or more panels die, the array will still produce quite nicely.

                    It will cost more for mounting hardware. It will cost more for circuit breakers. But those should be small expenses compared to the extra energy produced morning, night, and cloudy days. Those are the calculations that I would encourage monogram to run.
                    For some reason most grid tie inverters will just "clip" if too much wattage is connected to it but a lot of off grid or battery chargers will not tolerate too much input wattage and may even fail.

                    Since the OP never provided a true part number for their Growatt I have no idea what you can connect to it or what may exceed its specifications.

                    Comment


                    • #11
                      SunEagle has lots of experience and I respect and appreciate that. Please disregard my comment about not worrying about too much power and follow SunEagle's advice.
                      7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

                      Comment


                      • #12
                        Thank you all for your response,

                        If I do this: 2 x 310W + 365W = 985W
                        3 x 310W = 930W
                        3 x 365 = 1095W
                        What is the best connection should I use to get the most wattage out of it when connect to the Growatt?


                        Here is the spec for my Growatt inverter:

                        2020-10-30_162241.jpg

                        Comment


                        • #13
                          Originally posted by monogram View Post
                          Thank you all for your response,

                          If I do this: 2 x 310W + 365W = 985W
                          3 x 310W = 930W
                          3 x 365 = 1095W
                          What is the best connection should I use to get the most wattage out of it when connect to the Growatt?


                          Here is the spec for my Growatt inverter:

                          2020-10-30_162241.jpg
                          Based on the number of 310w and 365w panels I feel while it is not the best solution having strings of 2 x 310w & 1 365w will allow you to use 12 panels and get up to almost 4000watts inputed to the inverter. But if you choose to use more panels you will have to make sure all are not inputting at the same time. Maybe have another set pointed in a different compass direction then you might be able to charge the batteries for longer yet never exceed that 4500w input max.

                          I am unfamiliar with the Growatt and if it can handle being over wattaged or not. So maybe starting with those 12 panels to see what it gets on the input side before you add any more wattage.

                          You also have to look at a combiner box that has an over current device (fuse or breaker) for each string of panels. If you start at 4 and decide to go with more your box will need to be able to expand.

                          Mixing panels types is not an exact science. You will have to be very observant in the beginning to make sure you do not trash your hardware.

                          Comment


                          • #14
                            If I go with 2 x 310W & 365W, will I get maximum power at 985W or just 930W (As the voltage on 365W panel has to reduce to match 310W voltage)?

                            Once the 3 panels are in series, can I connect another set like that to make one string of 3S2P?

                            Base on my inverter spec, I can only connect up to 2 strings of 3S2P, right?

                            I am in California and with my house rooftop facing south, therefore I think I might connect extra panels to 60A MakeSky Blue Charge Controller (that I have on hand), do you think if that ok for it?

                            yes, I do have combiner box with breaker on each string, main breaker and also lightning breaker.

                            Comment


                            • #15
                              It seems that you're confusing voltage, current and power.

                              Current flows in a path. When you have three panels in series, the same current flows through each panel.
                              Voltage adds along a string. When you have three panels in series, you get the sum of the voltage of each panel.

                              Here are the specs you listed:
                              Jinko 365W: (7 pcs) 365Wp
                              39.7V 9.2A at maximum power point (MPP)
                              REC 310W: (14 pcs) 310Wp
                              36.7V 8.53A at MPP

                              The Jinko will put out 9.2A at maximum. The REC will put out 8.53A at maximum. If you put them in series, you're limited by the lowest. So all three will be limited to 8.53A. The total voltage is the sum of 36.7+36.7+39.7=113.1V. If everything was ideal, that will give you a peak power of 8.53*113.1=965 watts from the three panels at high noon on a clear day. But things aren't ideal when you mix panels. You may be limited to less. Also, as the panels age, they will put out less power (roughly 1/2% per year drop).

                              Based on your inverter spec, you must limit each string to 145V, which is three panels in series.
                              Based on your inverter spec, your maximum array power is 4500 watts. That limits you to four parallel strings at 965 watts per string. If you don't get the full 965 watts per string, you might be able to take advantage of a fifth string.
                              7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

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