new solar pump

scoot scoot
scoot scoot Registered Users Posts: 3
in Solar Water Pumping #1
I am wanting to use a solar pump that requires 72-144 volts and 800-1500 watts. I am wanting to use Canadian Solar CSI CS6P-235PX 235W Solar Panel. My problem is i don't know how many panels and what configuration I need to meet the middle of the road requirements of this pump. Any help is appreciated
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,716 admin
    #2
    Re: new solar pump

    What brand and model of pump? Need to know more about its input power requirements. Solar panels are not very "accurate" or "stable" in their voltage/current output. Their voltage changes with temperature and loads.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • scoot scoot
    scoot scoot Registered Users Posts: 3
    #3
    Re: new solar pump

    Ok Lets try again if a pump calls for 72 volts and 1300 watts, how would you configure solar panels with Imp of 7.66 and Voc of 30 volts? If you hooked parallel 6 panels at 230 watts you would have 1380 watts but only 30 volts. If you hooked 3 panels in series you would have 90 volts but only 230 watts. How would you match both requirements of the pump?
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #4
    Re: new solar pump

    again, what model/make of pump so one can look up the power ( Amps and Volts) needed by the pump and to compare to the various configurations of the panels.

    HTH
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
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    West Chilcotin, BC, Canada
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,716 admin
    #5
    Re: new solar pump
    solar pump that requires 72-144 volts and 800-1500 watts. I am wanting to use Canadian Solar CSI CS6P-235PX 235W Solar Panel

    Panel spec. appears to be:
    Pmax=235W
    Vmp=29.8V
    Imp=7.90A
    Voc=36.9V
    Isc=8.46A

    So, say the pump will accept a Vmp range of 72-144 volts:
    • 72 volts pump min / 29.8 volts Vmp-stc = 2.4 panels in series
    • 3 panels (whole number) * 29.8 Vmp = 89.4 volts Vmp-stc
    The amount of power in such a string:
    • 89.4 volts Vmp * 7.90 Amps Imp = 706.3 watts per string
    As a real rough approximation, assume panels + wiring will run at 80% of rated output (dirt on panels, age, voltage drop):
    • 706.3 watts * 0.80 derating = 565 watts "nominal" output power on typical warmish day
    So, you would need around 2 to 3 parallel strings of panels to operate the pump.... ASSUMING that the Vmp/Imp requirements are met, and the Voc-cold does not exceed the pump's maximum input voltage.

    You could do the same thing with 4 panels in series:
    • 4 panels (whole number) * 29.8 Vmp = 119.2 volts Vmp-stc
    • 119.2 volts Vmp * 7.90 amps Imp * 0.80 derating = 753 watts nominal per string.
    The reason we are asking about the pump itself is many pumps have electronic switching power supplies the input to better match the IV curve of the solar panels to the IV load curve of the pump motor.

    A 4 string panel can easily exceed 144 volts on a cold day with no load (say water tank is full), and could damage your pump controller/electronics.

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