Sudden drop in pv-in current

bmdkks
bmdkks Registered Users Posts: 2 ✭
in General Solar Power Topics #1
Hi

First my system:
Off-grid
3x300watt panels
2.4kW/3kVA 24V inverter
4x100Ah 12V deep cycle lead acid cells (connected 2-series and 2 parallel which makes, in effect, 2x100Ah 24V cells)
pv-surge protector and battery isolator switch.

My inverter can receive max pv-input of 600watt, but can connect up to 1500watt of panels.

My system has been working fantastic since I got it in April.

Since about a week ago, I have experienced incredibly low current produced from my panels. Full sun, which should produce the maxed out 600watt, now only makes 150-250watt. I checked the wiring, no problems anywhere. When I tested the current, it produced 120watt. I disconnected one panel, which the inverter showed 80watts. So I concluded all three panels are producing current, nl.40watt each test. So dead panel cancelled out. I cleaned the panels, checked wires, which was installed by professionals, and saw no problems. I get a strong 36-40v, but low current. I checked the panels for cracks and damage and could see none. I switched the batteries off with the battery isolator and the pv-current dropped a tiny amount.

What could be the problem?
I have a good basic understanding of small systems like this one as well as how currents work and would prefer not to have to pay for a technician if I don't have to. 

Any ideas what to check next? 
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Comments

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    What is the battery voltage, if close to fully charged the current will be reduced, try introducing a load like a toaster for example , if the current increases to where expected all is fine, a basic starting point.
    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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  • bmdkks
    bmdkks Registered Users Posts: 2 ✭
    edited October 2018 #3
    Battery is 25V, so it should charge at the max current. So it's far from fully charged. Fully charged or not, there is no change in pv current if I put on my fridge or use a blender.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    Use your volt meter to check the voltages at the battery bus and at the output of the charge controller (you want the voltage drop to be around 0.1 to 0.2 volts maximum between controller and battery bank).

    Check the voltage on the solar panel input to the charge controller. If PWM, the solar panel input voltage will be just a little bit higher than the battery bank voltage.... If an MPPT type charge controller, the array input voltage should be ~80% of STC of the array minimum (if 2x 30 Volt Vmp panels in series than 60v*0.8=~48 volts at Vpanel input).

    If you do not have one, get a DC current clamp DMM (digital multimeter). If you have parallel solar array panel strings (2x panels in series, and 3x parallel strings), You can check the current for each string. They should be very close together.

    https://www.amazon.com/gp/product/B07546L9RT (low cost/good enough for us DC current clamp DMM)
    https://www.amazon.com/gp/product/B019CY4FB4 (medium priced DC current clamp DMM)

    If you have parallel strings of panels and a DC combiner box with breakers... You can turn off each breaker and see how much the current drops--All should drop the same amount (24 amps in for example, 3 strings, then ~8 amps per string).

    My guess is that you have some electrical connection issues with the solar array. Turn off/disconnect the solar charger from the array, then take apart your connections and see if the crimps are OK, no corrosion, no browning from heat.

    Depending on the solar panel--Some inexpensive panels have been known to fail pretty quickly in full sun... And even some name brand ones have failed too (in 5+ years). For panel failures, measure the full current in full sun (you can short circuit the panel and use your DC clamp meter or a 10 Amp full scale DMM) to measure the Isc (short circuit current). Generally, over 50% in noon time sun is probably OK. Less than 50% Isc in full noon time sun (panel pointed at sun, no clouds, haze, or smog). and you may have one or more bad panels.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    I should add--Get the battery bank to full charge (>90% state of charge) and don't let it sit around less than 75% state of charge (no cycling)... Or you will lose the battery bank due to sulfation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #6
    Some charge controllers can get into odd states if getting pv voltage but no battery voltage. You generally want to connect batteries first with solar input off, and turn solar on only after the controller has fully booted up on battery.
    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
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