array wiring , series or series parralel

I have an 18 panel 170 watt two string array should I series parralel wire this so I will have nominal voltage and higher current levels or just series wire the whole 18 panels? I have a sunny boy 2100 grid tied string inverter. It is operating close to its maximum 600 volt threshold but the array current is low in comparrison to the voltage. Currently both arrays are in series. My voltage drop under load is around 200 volts dc and output is around 700 watts average over a time period of 10 hours. production is around 7KW hours per day.


  • BB.BB. Just some guy Posts: 23,755Super Moderators admin
    Re: array wiring , series or series parralel

    Something does not sound right... What brand/model/Vmp/Imp/Voc are your solar panels.

    They are in one string of 18 or two parallel strings of 9?

    Just taking the defaults for PVWatts, Salem OR, 3.06kW solar array, we get:
    "Station Identification"
    "Lat (deg N):", 44.92
    "Long (deg W):", 123.02
    "Elev (m): ", 61
    "PV System Specifications"
    "DC Rating:"," 3.1 kW"
    "DC to AC Derate Factor:"," 0.770"
    "AC Rating:"," 2.4 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 44.9"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 7.2 cents/kWh"

    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 1.61, 107, 7.70
    2, 2.55, 159, 11.45
    3, 4.11, 293, 21.10
    4, 4.65, 311, 22.39
    5, 5.27, 356, 25.63
    6, 5.54, 353, 25.42
    7, 6.27, 410, 29.52
    8, 6.12, 396, 28.51
    9, 5.73, 367, 26.42
    10, 3.95, 264, 19.01
    11, 2.19, 146, 10.51
    12, 1.96, 135, 9.72
    "Year", 4.17, 3296, 237.31
    For August, you should be averaging around 396 kWH per month or ~13 kWH per day (assuming facing south with ~45 degree tilt from flat, not much shading)...

    From my guess, your 2,100 watt GT inverter may be a bit on the small side... You might gather more power with a 2.4-2.8 kW or so rated inverter on clear cool days (do you hit the ~2,100 watt limit much during the day?).

    But, even with a slightly small inverter, that would now account for the lower 7kW per day output (perhaps on a "bad day" with marine layer, high overcast, etc... you will see 7kW or less).

    The fact you are seeing high and low input voltages to the inverter also has me confused... If your panels are near 600 volts sometimes, then they should easily be in the 300-400+ volt range much of normal summer day.

    If you are seeing near 200 volts in the middle of the day, then your high voltage should be no more than 300-350 volts or so...

    You need to keep the input voltage for the Sunny Boy GT inverter in the correct range... I am not sure what the specs. for a SB 2100 is (could not find it on the SMA website)--but their different models have quite different input requirements (and it also matters if this is a 208 or 240 VAC grid)... Some operate down to 175 volts and others require 250 volts minimum. Some operate at 400 or 480 volts MPPT. And have either 500 or 600 volt never exceed ratings...

    Again, this is all a guess based on what you have told us so far and reading between the lines...

    I am a little confused--Are you looking for the proper string configuration? Or have you already tried a couple different configurations?

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