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Performance while using 1 of 3 MPPT's on an inverter

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  • Performance while using 1 of 3 MPPT's on an inverter

    Okay so this is similar to other questions asked here but not exactly the same. The situation is the same. What I want to do is start with a small array and add to it later. I am not a fan of micros so I would like to avoid them. What I want to do is buy a larger inverter than my array capacity and add to it later. I just cant seem to figure out how their efficiency is effected if I only use, say 1 (or 2) MPPT for my entire array vs splitting them up between the 3 or 4 available on the inverter. I know that for a 1 MPPT inverter I will run into a minimum voltage wall and an undersize array will likely result in very poor performance but does that also apply for an inverter with multiple MPPT's? Does each MPPT invert independently or do they all feed into 1 "inversion device" in series (or parallel)?

    Here is what I am looking at: 20x 190W (36.5V @ 5.2A), or about 3800W feeding a 7kw to 10kw Solis inverter with 3 or 4 MPPT respectively.

    Looking at the Solis inverter data sheet, it says:

    "Operating MPPT voltage range" is 100-500V
    "Full power MPPT voltage range" is about 200-500V

    So lets say I do a 2x10 array into MPPT #1. Clearly I am well within the voltage range for that one MPPT but I have nothing on MPPT 2, 3 or 4 (for the 10kw model). What happens in this case? Will the inverter work fine for that MPPT or does it depend on a sum of all 4 MPPT's to work properly? (such that you need at least 200V going through each MPPT for it to operate at its full power)

    Thanks in advance and excuse the noob
    Last edited by thejumpingsheep; 06-25-2016, 08:21 PM.

  • #2
    If you design your first string for a Vmp in the 200-500V range, you can just parallel more strings of about the same Vmp (using fuses) up to
    the capacity of the inverter. Strings with the same number of series cells are generally good. You only need a different MPPT input, for a string
    with a different Vmp. Bruce Roe

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    • #3
      In general, it is not required to use all the mppts. However, you should check the current limit for each mppt to make sure you are within its constraints.

      Running 4000 W into the inverter (regardless of how many mppts you use) won't be very efficient. You might be better off planning to buy two smaller inverters if you want to scale up over time.
      CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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