Series-parallel panel wiring

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JYanke
JYanke Registered Users Posts: 39 ✭✭
in Off Grid Solar & Battery Systems #1
Hello everyone,

Is there an advantage/disadvantage one way or the other for series-parallel wiring of a PV array based on the two diagrams below? The panel specs are as follows:

(1) 80watt panel
Voc: 20.23
isc: 4.68

MPPT charge controller specs
max pv wattage: 700 watts
max pv voc: 100v
max pv isc: 60a

15A double pole breaker on + and - between array and CC

MC4 4mm^2 wire from array to CC

diagram1

Total array- (6) panels
voc: 60.69 v
isc: 9.36 a



Diagram2

Total array- (6) panels
voc: 40.46 v
isc: 14.04 a


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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,046 ✭✭✭✭✭
    edited January 2023 #2
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    You haven't mentioned system voltage but diagram would work great for both 12 volt and 24 volts. Also with only two strings you don't need to fuse the panels prior to entering the charge controller.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • JYanke
    JYanke Registered Users Posts: 39 ✭✭
    #3
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    Thanks for the info. 

    System voltage is a 12v battery bank. Im using the breaker between the panels and CC as a means of disconnect purpose more than anything. 

    I guess Im looking more at the advantage/disadvantage of having a higher voltage with less amperage as shown in diagram1

    versus the slightly lower voltage and higher amperage as shown in diagram2.

    Does it really matter either way with having a MPPt controller?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #4
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    More or less... A good starting point is for 2x the battery bank charging voltage (i.e., 15.0 volts charging => 30 Volt Vmp array)...

    Going with a lower voltage array, the MPPT becomes less efficient. And with a, for example, 18 volt Vmp-array and 15.0 volt charging battery bank, on warm/hot days, MPPT adds "nothing" energy wise (just behaves like an expensive PWM type charge controller).

    MPPT controllers only operate in "MPPT Mode" when the Vmp-array voltage is (roughly) at least 1.3x battery charging voltage (remember, as solar panels heat up, Vmp-array falls).

    One huge advantage with MPPT controllers is that you can run the solar array at much higher Vmp-array working voltages. This reduces the array current, fewer parallel strings and fewer series protection fuses/breakers/combiner box circuits), and alltrows you to use much smaller AWG cables and send power for 100's of feet relatively cheaply (again smaller AWG cables).

    The disadvantage is that MPPT controllers are slightly less efficient at higher Vmp-array voltages (something like 1% or 2% less efficient)... Not enough to worry about, but you still need to ensure good cooling/ventilation for the MPPT controllers, especially with higher array voltages.

    An example from Outback:
    https://www.solar-electric.com/lib/wind-sun/Flexmax-manual.pdf

    Note that other vendors may derate output current at higher Vmp-array voltages. And always design so that Voc-array-cold does not exceed Vpanel-max input voltage for the charge controller.

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