Panels in Parallel with different Vmp

bdosborn
bdosborn Registered Users Posts: 11 ✭✭✭
in Advanced Solar Electric Technical Forum #1
I've read on this forum that when paralleling panels with differing Vmp that you should limit the difference to a maximum of 10%. My impression was that since both panels would run at the lower voltage of the lower Vmp panel you would be wasting capacity of the higher Vmp panel. However, is this really true if your using a PWM controller and both panels are at a 12v battery voltage anyways? I can see how this would be an issue with a MPPT controller but I don't see an issue with mixing grossly different Vmp with a PWM controller as long as you don't exceed the controller voltage rating. Thoughts?

Bruce
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Panels in Parallel with different Vmp

    It's a matter of how far off from 'ideal' Voltage the panel is forced to operate at.
    For instance with a "standard 12 Volt" panel that has a Vmp of 17.5 you would be losing some of the panel's power potential with a PWM type controller anyway, as it can't down-convert and 'extra' Voltage available from the panel and turn it into additional current. Basically the power you get is maxed at Imp * Voltage (not Vmp).
    If you use two panels with widely different Vmp's the power loss will simply be accentuated on the higher Voltage panel.
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  • bdosborn
    bdosborn Registered Users Posts: 11 ✭✭✭
    #3
    Re: Panels in Parallel with different Vmp

    Okay, that's what I was afraid of, I think I just lost an argument. :blush: Connecting different Vmp panels in parallel doesn't reduce the output of the higher Vmp panels by any more than connecting straight to a PWM controller. Now, lets say the same mismatched panels were connected to an MPPT controller, what happens to the output of the higher Vmp panel?

    Bruce
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Panels in Parallel with different Vmp

    With an MPPT controller, all bets are off. They choose their own "best current * Voltage" anyway. What you'd likely get is a panel Voltage above the low but below the high and full current from both (if you're lucky). Much of this will depend on the particular controller's programming & circuitry as wells as how much difference there is between the panels.
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  • bdosborn
    bdosborn Registered Users Posts: 11 ✭✭✭
    #5
    Re: Panels in Parallel with different Vmp

    Thanks I've got some 'splaining to do.
    Bruce
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