Can I mount and extra string of panels facing a different direction?

Kgelles
Kgelles Solar Expert Posts: 25 ✭
in Off Grid Solar & Battery Systems #1
I have six identical panels. Four are already mounted facing south (two strings consisting of two panels in each string.)
The panels are 224 watt Sharp grid-tie panels but I am using them for my off-grid setup by utilizing a Tristar MPPT CC.

Question: Can I add one more string of two panels facing west and wire these in parallel with the other panels? I am trying to get a little more power from the afternoon sun so I can use the extra power to run a window ac unit as the afternoon warms up.

So, in short I would end up with three strings consisting of two panels each. I would then join the strings in the combiner box (each with a separate fuse of course).

Thanks,
Karl
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Can I mount and extra string of panels facing a different direction?

    Will not hurt anything... But you will, most likely, have less than optimum harvest (MPPT may be confused a bit).

    If you have the hardware, go ahead and install and see what happens. You should collect more energy with the 2 extra panel in any case--And if you see issues, you still have the option of installing a second MPPT controller when funds/needs permit.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Kgelles
    Kgelles Solar Expert Posts: 25 ✭
    #3
    Re: Can I mount and extra string of panels facing a different direction?

    OK. I'll give it a try. Thanks for the help.
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  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    #4
    Re: Can I mount and extra string of panels facing a different direction?

    This is how my panels are, haven't had any problems at all. My first string faced south, but that's about all the south-facing roof I have. The second set faces west, and I recently (after a couple years) added two more strings facing west. All four strings are paralleled and run to the same charge controller.

    I get all the production I expect at midday, and sometimes in summer I wish I had ALL strings facing west as I can easily tell the point when the south-facing set stop producing in the afternoon. I have a fairly rapid drop of 1/4 of the total, and the west panels continue to produce for several hours more. (Of course by then the bank is charged, so the only time I see the drop is when I have a high-power load - like A/C - running.)
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  • CATraveler
    CATraveler Solar Expert Posts: 98 ✭✭✭✭
    #5
    Re: Can I mount and extra string of panels facing a different direction?

    Bill, Why would a MPPT get confused? Is this different than 6 panels facing south and a cloud covers 2 panels then 4? Or do MPPT controller get confused with shading?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Re: Can I mount and extra string of panels facing a different direction?

    The MPPT controller is trying to maximize the equation Pmp=Vmp*Imp and when you have an array with non-identical panels in parallel, there can be several Pmp operating points where Pmp peaks... One for the 2 strings in hot sun (lower Vmp), and another for the cooler string not directly facing the sun.

    So, the MPPT controller has several "local peaks" for Pmp to pick maximum power--But there is (from what I understand) no guarantee it will pick the first peak vs the real maximum peak that may be a few volts away.

    It is not a huge issue--but it is not "optimum" (and in fact, there is no "one real optimum" operating point because each array has a different Vmp because of the different panel temperatures). That is why one of the posters here that used to design and test MPPT controllers always recommends using a separate MPPT controller for arrays that are facing different directions.

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