Confused by lack of Output

Climber53Climber53 Registered Users, Users Awaiting Email Confirmation Posts: 1
I have 8 100 Watt 12 Volt panels at 5.3 Amps in series parralel going to a 4 slot (4 red 4 black) combiner box..  I have created a spread sheet for all of the infor and trying to compute my Wattage and Amperage out put. Since I am in Series its 24 Volt out put but I thought I would have 800 Watts of Output and If i am using OHMS law correct im only getting 580 watts,  What am I doing wrong.  I can email a  copy of spreadsheet if needed.


  • BB.BB. Super Moderators, Administrators Posts: 32,921 admin
    Welcome to the forum Climber53,

    You can upload or simply paste your spread sheet here (I think that works).

    I don't know where you are located... But about the best you would expect to see from a solar array is around 75 to 77% of the rated output on a cool clear day near solar noon.

    800 Watts * 75% or panel+controller derating = 600 Watts @ operating temperature near solar noon (even then, maybe only a few times a year)

    The marketing numbers are based on a 75F degree room under a "flash tester" (simulated sun for a few seconds).

    When solar panels heat up, the Vmp tends to fall by almost 80% (very hot day, no wind).

    Any dust in the air, not near solar noon, panels not pointing at sun, dust on panels, and depending on your batteries (near full or less than 80% State of Charge), etc... You will not get "full rated power" from solar panels...

    If you are in subzero (F) weather, yes, you can get more voltage and with an MPPT type solar charge controller, you can get near 100% of rated power.

    Is this a 12 volt battery bank with an MPPT (maximum power point tracking) solar charge controller?

    It sounds like your system is working fine... Depending on charge controller type (MPPT or PWM--Pulse Width Modulated), voltage of the battery bank, the Vmp rating of panels, the Vpanel-max input voltage for a solar charge controller, etc... The "optimum" vs non-optimum operating point(s) depend on your answers.

    If you are within 10% of "expected" power ratings--You are probably fine. If you have an MPPT charge controller--The "optimum" Vmp-array is around 2x battery charging voltage)... If you go with a higher voltage array (makes sense if you have a long cable run from array to "battery shed"--But you might otherwise lose a couple percent of harvest (extra wire loss, MPPT not operating at ~2x Vbatt-charging, etc).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,974 ✭✭✭✭✭
    Here are some examples of info panels that include NOCT wattage (Normal Operating Cell Temperature)

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former, 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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