One of three panels failing?

garynappi Registered Users Posts: 120 ✭✭
edited December 2020 in General Solar Power Topics #1
Today because I've had charging issues I ran a spot check of my 12 volt system (exterior lighting and water features only) and found the following individual currents and voltages in mid day (optimum tilt aspect, not winter) :

Note all three were tested alone, and NOT in parallel.

200w NewPowa 5.4 amps and 16.5 Vdc
150w NewPowa 1.4 amps and 13.0 Vdc
125w BP solar (~10 years old) 6.2A and 14 Vdc.

The Newpowa 150 was bought in May and the seller wrote me suggesting that my connection method was at fault? Is she off base? or is it prohibited (I never read this) to connect panels from different makers and wattages.

"May I know if you are paralleling these panels with different wattage? If so, it is not recommended.
Because the low wattage panel will pull down the output of the high wattage panel."

Any help would be appreciated.


  • MichaelK
    MichaelK Registered Users Posts: 235 ✭✭✭
    She is absolutely correct.  Voltages don't need to match exactly, but they should be within 5% of each other.  A 16.5V panel and 13.0V panel are far more than 5% different.  If those two panels were wired in series, you'd get ~29.5V at ~1.4amps.  The extra amps from the NewPowa would be totally wasted.
    System 1) 15 Renogy 300w + 4 250W Astronergy panels,  Midnight 200 CC, 8 Trojan L16 bat., Schneider XW6848 NA inverter, AC-Delco 6000w gen.
    System 2) 8 YingLi 250W panels, Midnight 200CC, three 8V Rolls batteries, Schneider Conext 4024 inverter (workshop)
  • garynappi
    garynappi Registered Users Posts: 120 ✭✭
    Hi Michael, and thanks, but maybe I did not explain my situation.

    The reason I tested was not HOW I tested. I understand the electrical issue when all three are in the circuit, and that's the REASON I tested.

    The WAY I tested I found that when only the one panel was connected (150w NewPowa 1.4 amps and 13.0 Vdc)

    The one panel tested LOW, without ANY other panel connected. So I'm saying the one panel (150w NewPowa) is malfunctioning and she has continued to suggest that if the panel is bad, "I" caused it.

    The specs on the 150 panel are...
    Vmp 17.0
    Imp 8.2A
    Isc  9.36a

    I changed the 15A breaker, and tested it (the NewPowa 150) in full sun and got 7.5A with the DMM as the only load. However with the CC connected I get 1.4 to 1.6A out of the NewPowa.

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited December 2020 #4
    You need to check the open circuit voltage, Voc, and short circuit current, Isc both in full sun, if you have not done so. This will reveal if the panels output is within spec, the Isc value may be slightly below listed,  but should be relatively close.
    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.
  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,076 ✭✭✭✭✭
    Isc will vary considerably depending on the angle of the panel to the sun. Take a loose panel and test it while aiming it toward and away from the sun. 

    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.