Mismatched modules and multiple strings

newenergy
newenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
in Advanced Solar Electric Technical Forum #1
Perhaps this is something that makes so little difference that it's not worth worrying about, but.....

Say you buy 20 modules and are going to install them in 2 strings of 10 on the same inverter. The modules are all the same model, but they vary slightly in output.

Would you get better performance by putting all of the higher output modules in one string and the lower in the other?

Or would it be better to mix them so that you tried to get strings of the same voltage?

Or do you need more detail, like maybe it's good to try to balance the voltages of the strings, but you should try to keep modules that produce similar currents on the same string?

Or whatever your thoughts are...
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    Re: Mismatched modules and multiple strings
    newenergy wrote: »
    it's good to try to balance the voltages of the strings, but you should try to keep modules that produce similar currents on the same string?

    If the modules are all in the same batch, I would not bother at all. If you measure them, they will age after a month, and you will need to re-balance them. And the next month....

    If you got some from fleabay, and some from a swap meet, and found one in the woods, then yes, you need to balance them
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: Mismatched modules and multiple strings

    Generally, put the matching current panels in one string, and match parallel strings by voltage.

    From a test report on MPPT controller's reaction to non-optimal conditions from Fronius (PDF file), they found that if you have two strings with differing Vmp voltages--the parallel strings will, for the most part, choose the lower Vmp point of the lower voltage string (essentially wasting the energy of the which would have been available in a higher voltage string if it was on its own MPPT grid tied inverter).

    The report also tests other conditions (like south and east facing strings on one inverter).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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