CFMCFM Registered Users Posts: 1
edited December 2018 in Solar Beginners Corner #1
I have 10 260 watt panels. Can I add two more 330 watt panels without a negative effect? I have a Outback Flex 80 charge controller with a 48 volt system.


  • BB.BB. Super Moderators, Administrators Posts: 28,315 admin
    The short answer is that good quality MPPT controllers will limit their output current to rated current (80 amps) in this case... And most will reduce current output as the charge controller get hot (ambient temperatures rise, poor air circulation, etc.).

    A bit longer answer is that electronics (and much of anything in life) is negatively affected by temperature rise... If your electronics run 10C (18F) hotter because of the "extra panels", the electronics will last about 1/2 as long (for every 10C rise, 1/2 life... Conversely, ever 10C drop, 2x longer life). And thermal cycling (cold at night, hot during day) can also stress solder joints, transistor packaging, etc.).

    Because solar panels get hot (in full sun), we generally assume the panels (and charge controller losses) will be around 77% of solar panel "nameplate" Standard Test Condition rating... I.e., the maximum (cost effective) suggested size of solar array on your 80 Amp controller would be:
    • 80 amps * 59 volts charging * 0.77 panel+controller derate = 3,634 Watt array "cost effective" maximum
    • 3,634 * 1/260 Watt panels = ~14 panels C.E. maximum
    I do have a question... What is the Vmp/Imp rating of your panels... For most of the common panels, the array need closer to three panels in series with an MPPT controller on a 48 volt battery bank.

    Have your used the Outback string sizing tool?


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