panel wiring

wwctv3wwctv3 Registered Users Posts: 2
edited December 2018 in Solar Beginners Corner #1
need instructions 
diagram / sketch 
how to wire 8 panels 
side by side ( not ) end to end
24 vdc system 
—————————————
need 75.2 vdc 
in put at the charge controller 
—————————————
Panel electrical data:
240w ea.
voc - 37.6 
Isc - 8.22

please reply

Comments

  • EstragonEstragon Registered Users Posts: 3,614 ✭✭✭✭✭
    You would wire as 4 strings of 2 panels each.  Each string of 2 would be wired by connecting the +ve wire of one panel to the - ve of the other, leaving 1 +ve and 1 -ve per pair.  The +ve from each pair would go to a breaker or fuse in a combiner box, then to a common +ive bussbar.  The -ve from each pair goes straight to a -ve buss.

    A single +/- pair goes from the combiner to the controller via a breaker sized for the larger wire.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • wwctv3wwctv3 Registered Users Posts: 2
    Someone said to put all in series and parallel at the combiner.
    i dont see how that can work ---  8  panels x  37.6 VDC  will make 300 VDC

    i need 75.2 input at the Chg,
    Controller it will have to be series parallel.

    i guess it dont make a d-m as long as i get he results i want.

    Does anyone know of a pitcher of this on line
    8 panels wired side by side so that --- 75.2 volts are input to the
    chg, controller.

    Thansk



  • BB.BB. Super Moderators, Administrators Posts: 29,043 admin
    One of the more confusing issues with solar is matching your panels into a "useful" solar array for your charge controller.

    PWM (Pulse Width Modulated) controllers (less expensive type) need around Vmp-array~18 volts for a 12 volt battery bank, Vmp-array~36 volts for a 24 volt battery bank, and Vmp-array~72 volts for a 48 volt battery bank.

    Too low of Vmp-array, and your battery bank won't charge. Too high of Vmp-array, your wasting a lot of energy from the array (Vmp-array~36 volts into 12 volt battery bank, about 1/2 of the array Wattage is wasted).

    For smaller systems, PWM with smaller panels can be a good fit (less than ~400 Watt array).

    For larger system, MPPT controller (Maximum power point tracking--More expensive, tend to be more fancy) use a switching power supply to efficiently "down convert" from Varray higher voltage/lower current down to Vbatt lower voltage/higher current (upwards of 95% efficient).

    MPPT generally is more cost effective and better to design with for larger systems (typically 800 Watt or larger array). For "typical" (not cheap) MPPT type charge controller, A Vmp-array voltage of ~24 volts to 100 volts Vmp-array works just fine for charging a 12 volt battery bank...

    So, if you need 75.2 volts for the Vpanel input for your charge controller (guessing Vmp-array ~ 75.2 volts), typically that would be 2x Vmp 37.6 volt panels in series, and then make 4x series strings, and connect those in parallel for a 2s x 4p array.

    For safety, you should put a ~15-20 amp fuse/breaker (see panel specifications for series protection/fuse) in the positive lead for each array... The output of the "Combiner" circuit goes to a single positive bus bar (and all the negative are connected to their negative bus bar). And run that pair of heavy cables back to the charge controller/battery shed.

    Vmp-array of ~75.2 volts sounds like a PWM controller charging a 48 VDC battery bank. Should work OK, but there are more design issues that need to be decided (how far is the wire run from Solar Array to charge controller--Long wire runs means thicker copper cable$).

    This webpage does a good job of showing how all that Series/Parallel solar array connections are made:

    https://pveducation.com/solar-concepts/series-and-parallel-wiring/
    https://higher-octave.com/wire-solar-panels-parallel-series/  (more details on combiner box)

    The first solar power system you will make--There are lots of issue that need to be addressed. And you will be doing a lot of learning.

    If you are familiar with AC wiring in your home or even DC wiring in a boat/car--All good experience. If you are not familiar with electricity and the math+physical construction--Be very careful. Electrical not done correctly, can be a costly or even dangerous mistake.

    I suggest that we start with Paper Design(s) and then, start looking for equipment that will support those designs (costs, availability, what meets your price/performance needs).

    To get an idea of what a smaller do it yourself solar power system entails... 2ManyToyz has a lot of photos and comments. Go about 1/2 way down his page:

    http://2manytoyz.com/

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