Voltage Readings (2 Panels in parallel)

Jakachira
Jakachira Solar Expert Posts: 47 ✭✭
in Solar Beginners Corner #1
I did a quick test between my two different panels

150Watts (19.8Vmp, 25.4Voc) A
100Watts (17.0Vmp, 22,3Voc) B

I connected these two panels in parallel and the results are as follows

18.4Vmp and current added up to 11.7amps (Imp) all shown on my controller. The open-circuit voltage was 25.4, the same as the A's voltage (shouldn't it be 22.3V ie B's voltage)

Now, what is really happening here? My understanding is the Vmp should be pulled down to B's voltage 17.0V.

Looks like panels with different voltages in parallel results in an average voltage of all panels concened.What am I missing here?
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #2
    Re: Voltage Readings (2 Panels in parallel)

    What brand/model of charge controller (MPPT or PWM)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Jakachira
    Jakachira Solar Expert Posts: 47 ✭✭
    #3
    Re: Voltage Readings (2 Panels in parallel)

    i'm using Steca PR3030 with LCD currently.. it was just a test, i am replacing that controller with a MPPT one later this year either Morningstar MPPT 45A or Rogue MPPT (if Marc releases a version with highier input voltage as he told me)
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: Voltage Readings (2 Panels in parallel)

    under load it averaged, but without a load there's nothing to pull down the highest voltage so you will see the highest voltage available.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Voltage Readings (2 Panels in parallel)

    Panels are a current source; they try for their Imp output and will let Voltage go where it may. The Voc readings are irrelevant, and you should expect to see the high Voc with the two panels together.

    Back to current.
    150 Watts @ 19.8 Vmp is roughly 7.5 Imp
    100 Watts @ 17.0 Vmp is roughly 5.8 Imp
    Together that would be 13.3 Amps for the two, if insolation and other conditions were right. You got 11.7 Amps, a difference of 1.6 from "ideal". With the lower Wattage panel's Voltage "pulled up" by the higher Wattage panel its current contribution goes down, just as if it were connected to less than "ideal" resistance (i.e. closer to current at Voc than current at Imp or below).
    To get an accurate picture of what is going on you need to check the current from each panel, rather than the Voltage. You will probably see something like 7.5 Amps from the larger panel and 4.2 from the smaller one (but not exactly).

    On the whole, 11.7 Amps @ 18.4 Volts is pretty good: 215 Watts from 250 Watts of panel. 86% efficiency? I wouldn't complain about it.
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