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Small Off Grid PV systems

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  • Small Off Grid PV systems

    Hey folks, I have set up a couple of very small off grid PV systems, but am still a total novice.

    I'm trying to calculate the efficiency of a pre-existing system so I can improve upon it. I know people consider this a backwards route,but I'm working with the materials at hand.

    There is one 240 watt panel connected to a solar charger controller and a 1000 watt inverter. There are (4) 6 volt 220 Ah deep cycle batteries connected in series parallel creating a 12 volt 440 Ah battery bank.

    These are my calculations to figure out whether this is an efficient configuration or not. Please feel free to correct them if they are incorrect!

    Reccomended charging current is 5 to 13%.

    440Ah x.05=22amps maximum
    440Ah x .13=57.2 amps maximum

    So my maximum amperage range for my battery bank is 22 to 57.2

    For my panel ( this is a formula I found on a forum)
    240 watts x .77 panel charge controller derating x 1/29 volts charging= 6.37 amps
    so it would seem my battery bank has a muvh higher amperage capacity then what my panel has. How should I revise this system for better efficiency? I know undercharged batteries can create sulfation which has not happened yet, but I'm concerned it will.

    Let me know your thoughts! Also I'm on a budget so trying to add, replace or subtract parts in an economical way!
    Thank you.

  • #2
    Welcome to the forum, Your first post, I see. Maybe the mods can split this off into it's own thread.
    You need an MPPT controller to step down the higher voltage of a 240 watt panel, (guessing somewhere around the high 29's to low 30's). You have the potential to get just short of 20 amps out of that panel when stepped down to 12 volts.
    2.2kw Suntech mono, Classic 200, NEW Trace SW4024


    • #3
      I created a new thread with the OP's post to alleviate any issues with the other thread.

      To answer the OP. I would say you need between 37 and 55 charging amps for that 440Ah battery system. (Which is calculated using a C/12 to C/8 charge rate.)

      That would require about a 60amp quality MPPT CC and about 600watts of panels.

      The existing system's battery is too big for only 240watts of panels.