[need help] pv output

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corazon
corazon Registered Users Posts: 2 ✭
in Solar Beginners Corner #1
halo, i'm new on this technology, i want to ask is it possible to find the output of pv module if its not connected to load?
according to Pmax=Vm.Im or Pmax=Voc.Isc.FF
from multimeter i can get the value of Voc and Isc but i'm stuck how to find the value of Vm and Im
please help me, thanks before :D
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  • Shawn-H
    Shawn-H Solar Expert Posts: 107 ✭✭
    #2
    I need to know more about the components and what you have charge controllers load diversion devices things like that
    100% Off-grid in the White Mountains of Arizona. 36 Kyocera 265w mounted on four DPW 9 module pole top mounts, midnite solar combiners, breakers, & lightning arresters, 1 midnight solar classic 150, & 3 classic 150 lights, 3 x 1574 AH GB Industries forklift batteries total of 4722 AH @24v. Feeding a Outback power systems FW500 with 2 x VFX 3624, with the x240. 2 Honda EU3000is gensets with the 240 combiner and control box running LP, and 1 Honda EU2000is Gas. 
    System #2 is a off grid water system @ 1590w (6 Kyocera 265's) on a 6 module DPW top of pole mount. Feeding a Granfas deep well pump and pump controller at 580 feet. 2 x 2800 gallon above ground poly storage tanks, and 1 x 1200 gallon underground  cistern and a Granfas 24v booster pump feeding a 90 gallon carbon fiber pressure tank.
    Vag woodstove for heat.
    Follow our journey at
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    edited November 2015 #3
    corazon said:
    halo, i'm new on this technology, i want to ask is it possible to find the output of pv module if its not connected to load?
    according to Pmax=Vm.Im or Pmax=Voc.Isc.FF
    from multimeter i can get the value of Voc and Isc but i'm stuck how to find the value of Vm and Im
    please help me, thanks before :D
    You cannot reliably tell the output of a PV module (cell or panel?) without a variable load. The only things you can measure are Voc and Isc. It is true that IF you know the fudge factor (FF?) for a particular cell design you can estimate the output as Voc x Isc x FF.

    As a rule of thumb for crystalline silicon cells Vmp is about 80% of Voc. The ratio between Isc and Imp will vary more widely.

    To actually measure Vmp and Imp you need to attach a variable resistance load and tune it to the Maximum Power Point before measuring. Or hook it up to an MPPT inverter or to a CC charging in Bulk mode into a depleted battery bank. And the whole time you need to use a calibrated reference light source or have the panels facing directly toward the noon sun on a clear day. Even in the latter case the panel temperature will be an uncontrolled variable.

    SMA SB 3000, old BP panels.
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  • corazon
    corazon Registered Users Posts: 2 ✭
    #4
    thanks a lot @inetdog , i nearly understand,  so if  my panel not conected to any load (inverter, solar charge controller or variable resistance load), and i only measurimg the Voc and Isc with multimeter, i cant calculate Pout of my pv module (panel) right?
    btw what is the difference between Pmp and Pout? 


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  • oil pan 4
    oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    #5
    If you are only working with Voc times Isc you will get an unrealistic amount of wattage.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 7,013 ✭✭✭✭✭✭
    #6
    You should get a pretty close reading of power out with Isc.  Close enough for government work...
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • corazon
    corazon Registered Users Posts: 2 ✭
    #7
     

    from equation 5.12, i need value of Imp and Vmp to get the FF (fill factor) value.
    if i cant measure the Vmp or Imp since my PV panel not connected to any load, can i use eq 5.13 to get the FF? 

    thanks before
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