Unbalanced series strings?

I have some design questions for anyone who might have the patience for a PV novice.

On my roof, I have room for twenty-seven 210 W modules, to be mounted in three rows of nine. If I were to wire these into two series strings, one string of 14 modules (Voc=465V, Isc=8.6A), and one string of 13 modules (Voc=432V, Isc=8.6A), what would be the consequences of combining these two strings in parallel in a rooftop combiner box and sending two wires to the inverter? Or, if I wanted to send four wires to the inverter, what are the consequences of sending two unbalanced series strings directly to the two different inputs on the inverter?

If I were to wire three series strings of nine modules in parallel, the resulting 299 V input would be near the minimum input for the inverter I want to use, and is not recommended by the manufacurer. Is there any way to make this 27 module array work, or do I need to simply stick with either 26 or 28 modules and keep the series inputs equal?

Finally, if uneven strings are an issue, what happens when shading might reduce the output of one series string below that of the other string?

Thanks, and pardon my ignorance!



  • BB.
    BB. Super Moderators, Administrators Posts: 33,442 admin
    Re: Unbalanced series strings?

    Here is a good thread on the subject:

    Two Strings in Parallel with Unequal String Voltages

    You can carry on the discussion there or here (especially if your questions apply to your specific application).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cfcf463
    cfcf463 Registered Users Posts: 5
    Re: Unbalanced series strings?

    Thanks Bill, for pointing me toward the other thread. It is helping me to understand my problem. I moved my further questions there.