PV System Estimation Calculator

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Badar
Badar Solar Expert Posts: 38 ✭
in General Solar Power Topics #1
I found an excel file which calculates PV size, Battery bank, Inverter size, Charge Controller.

Check it. I am confused on two points.
1: Where it asks "Nominal Voltage of Module"
2: Where it tells about modules in series and modules in parallel.

Give it a try.



Regards,

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  • SolInvictus
    SolInvictus Solar Expert Posts: 138 ✭
    #2
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    Re: PV System Estimation Calculator

    From the spreadsheet:
    DC Voltage System ÷ Nominal Module Voltage = Modules in Series × Modules in Parallel = Total Modules
    48.00 ÷ 49 = 0.98 × 5 = 4.90

    "DC Voltage System" refers to the nominal voltage of the battery array, usually 12 V, 24 V or 48 V.

    "Nominal Module Voltage" refers to the nominal voltage of a single PV panel, either 12 V or 24 V. PV panels containing 36 PV cells in series are sized for 12 V battery arrays, and PV panels containing 72 cells in series are sized for 24 V battery arrays. This equation assumes the PV panels are for off-grid applications and are not sized for grid-tied applications which are the least expensive ones. It assumes you will use a PWM (Pulse Width Modulated) charge controller, not a MPPT charger controller.

    For example, if the battery array has a nominal voltage of 48 V and the PV panels are 12 V nominal (Voc = ~22 V, Vmp = ~18 V), then you enter:

    DC Voltage System = 48
    Nominal Module Voltage = 12
    Modules in parallel = 5

    The spreadsheet computes:

    Modules in series = 4
    Total modules = 20

    The displayed equation is confusing and not mathematically correct because ("DC Voltage System" x "Nominal Module Voltage") does not equal ("Modules in Series" x "Modules in parallel").
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  • SolInvictus
    SolInvictus Solar Expert Posts: 138 ✭
    #3
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    Re: PV System Estimation Calculator

    The spreadsheet does not have an entry for the efficiency of the wiring nor charge controller.

    Assuming 90% efficiency for the inverter is too optimistic because it is near the peak efficiency of a sine wave inverter. You should assume the inverter will be operated at power levels that have a lower efficiency than at its peak. You could include the efficiencies of the charge controller, wiring, temperature derating of the PV panels and aging here. 75% would be an appropriate value.

    Lead-acid batteries are not 80% efficient when they get old. 75% is a better assumption.

    The method of sizing the inverter is incorrect ("Estimated Surge Watts (In Rush =Min of 3-6 times Total Connected Watts)") because it is unlikely that all of the loads will be turned on simultaneously. The continuous rating of the inverter should be at least 1225.4 W because all of the loads could be running simultaneously. The surge rating should be at least (748 W (pump) + 158.4 W (fans)) * 5 = 4,532 W. An inverter with a continuous rating of 2,000 W to 3,000 W should be adequate provided you get a decent one. A cheap Chinese inverter would probably require a higher continuous rating than 3,000 W.
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