Additional Panel

kampf2000
kampf2000 Registered Users Posts: 4 ✭
in General Solar Power Topics #1
I want to add a fourth panel to a 3 panel set of 17.5 volt 100 watt panels.  I can't find a compatible 17.5v panel.  Best I can find is a 18v +/-.3v 100 watt panel.  Is this close enough to add to the set?
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    The voltage is close enough, just make sure the controller can accept the total VOC of 4 in series.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
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  • kampf2000
    kampf2000 Registered Users Posts: 4 ✭
    #3
    Sets are wired in series.  I plan to add 1 of the new panels to each set of three for 2 sets of 80v +/- each.

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  • Estragon
    Estragon Registered Users Posts: 4,503 ✭✭✭✭✭
    #4
    Most controllers should be ok with that voltage, but it would be a good idea to check the manual for maximum string voltage into the controller to be certain.  If it's close (~100v or less) and your climate can get cold, adjust the string voltage (Voc, not Vmp) up to adjust for record low temp in your location.
    Off-grid.  
    Main 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
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  • DenverB
    DenverB Registered Users, Users Awaiting Email Confirmation Posts: 1 ✭
    #5
    Is there any way of testing for maximum string voltage if you don't have the manual?
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,172 ✭✭✭✭✭
    #6
    Look it up online.  Testing? Not unless you don't mind smoking the controller when you find/excede that maximum voltage.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #7
    DenverB said:
    Is there any way of testing for maximum string voltage if you don't have the manual?
    Depending on the manufacturer, some offer string calculators which are helpful in determining the maximum voltage, short of that, a voltage measurement with a digital voltmeter in the coolest temperatures under full sun is about the closest one could get. There is a certain amount of of headroom with some quality controllers, but a generic controller, who knows. Generally it's best not to push the limitations, just to be on the safe side of things. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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