MPPT charge controller

adeel
adeel Registered Users Posts: 5 ✭✭
Hello
i am doing one experiment and i have to record the voltage and current of the PV panel. PV panel is of 50 Watt capacity. Voc is 18V.
PV panel is connected with a MPPT, battery and current sensor and in the end with data logger. i recorded the data after every thirty seconds. i got fluctuation in the voltage and current even the weather was very clear and no shading effect. Can please somebody explain me this behaviour? Data is right or some equipment is not working rightly.
I will be obliged. Thanks in advance for the help. was there

Comments

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    It would appear the voltage is too low, promoting the controller to hunt for the maximum power point, assuming of course this is a 12V nominal system, if the voltage were 36 Voc, or 2 panels in series, my bet would be that a more stable voltage/current profile would be the result. Generally you want to be double the nominal voltage in terms of array voltage to obtain the benifits of MPPT.
    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.
  • adeel
    adeel Registered Users Posts: 5 ✭✭
    Thank you very much for your reply and time. Actually i cannot connect two panels as i have to check only one Panel and then compare it with other one of same capacity. we have done alteration in the other panel to keep it cool.
    you think these results are not correct or what can i interpret from the graph. thanks again
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    It looks fairly normal to me.  The mppt controller "sweeps" regularly in an attempt to find the most effective current/voltage combination for the light conditions prevailing at the time of the sweep.  The algorithms used to do this vary a bit between controllers (some also have the option to alter the algorithms), but that's the basic idea.  The voltage spike & current drops look like sweeps to me.

    Depending on tilt etc., ~2a average current from a 50w panel isn't terrible.  As Mcgivor noted, the mppt controller would normally used on higher voltage pv, so you may have trouble charging a cold battery with hot panels, and/or doing an equalization.
    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
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    In order to do a comparison between panels of 12V  nominal, I would suggest using  a PWM controller as the MPPT would be looking for a higher voltage, which isn't available, so it resets and tries again. PWM is beautiful in its  simplicity, it holds the voltage just above the battery voltage, supplying current as needed. Using an MPPT controller outside of its comfort zone will give eronious results, which are demonstrated by the recorded graphs, MPPT needs a higher voltage, if 18V is the VOC, this is too low for MPPT, what is the VMP?  Remember the battery needs at least 14.4V minimum just to  receive a charge, having such a low headroom Will confuse an MPPT controller, the rationale behind using PWM for the experiment.  
    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.
  • adeel
    adeel Registered Users Posts: 5 ✭✭
    Dear "mcgivor" and "Estragon" thank you very much for your time and your suggestions.
    Vmp is 18V, Imp is 2.78A, Voc is 21.6V, Isc is 3.06 A. it is attached with the single battery of 12V.
    I have checked the PWM controllers it is not as expensive as MPPT so i think i will buy it.

    i need one suggestion from you about the specification of the PWM controller. the available in the market have the following specifications
    Rated voltage 12V/24V adaptive. Rated current 10 A. will it be fine for my system?

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    That would be fine with what you have, always remember to connect the battery first so the voltage auto select, locks to the correct voltage, PWM controllers are generally much cheaper. 
    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.
  • adeel
    adeel Registered Users Posts: 5 ✭✭
    Can i dare to ask one more question?
    Will it be fine to connect two PV panels  of same capacity (Vmp 18V, Imp is 2.78A, Voc is 21.6V, Isc is 3.06 A) connected with two PWM controllers of same capacity and all these connected to a single battery of 12 V rating with capacity of 65 AH.
    With this configuration will i  be able to compare the performance of these two PV panels?
    sorry for any inconvenience and Thanks a lot for the suggestion/s
  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    This is pretty low power for a typical MPPT controller system.  About 30 watts maybe ? Hard for me to tell voltages too closely but low PV voltage looks to be around 16.x volts and high current maybe 2 amps or so ?

    What is the current scale reading ? If it's the battery current, then it kinda looks like the maximum power point PV voltage is more like 16 or 16.5 volts, which is corresponding to maximum power into the battery. (If showing Batt current)  That should be OK for a low battery.

    MPPT controllers will normally have some amount of voltage drop between battery voltage and PV voltage at however close to 100% duty cycle it can obtain.  A higher input voltage will help that issue.

    Also, if it's battery voltage being shown, if it is measuring the MPP voltage accurately, looks like the MPP V happens when the controller first drops the PV input voltage down low and would be wasting energy the rest of the time since it is off the max power point. That would
    always be the case too it is always changing.  Again, it's hard to read max power point at low powers, but it would not change in a sawtooth pattern like this.
    Even it it's measuring PV current, they will both be pretty close at this small-ish voltage difference.

    Just 2 cents for today.
    boB







  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited October 2017 #10
    Yes it is possible to parallel the outputs of 2 controllers to a single battery, but remember as the voltage increases close to 14.4V the current will drop off, so maximum performance will not be seen. Adding a load around 6A when fully charged, will prompt the panels to provide power to the load.
    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.
  • nickdearing88
    nickdearing88 Registered Users Posts: 100 ✭✭✭
    I'm curious, what brand and model MPPT controller are you testing with? It would be interesting to see how various sweep methods compare in efficiency. Morningstar touts to having the most efficient (and quick) sweep, but an independent comparison would be great.
    Current system: 8-100w Renogy panels mono/poly, 2 strings of 4 panels in series - 24v 100Ah AGM Battleborn LiFePO4 batteries - Morningstar MPPT40 CC - 1500W Samlex PSW inverter
  • adeel
    adeel Registered Users Posts: 5 ✭✭
    dear nickdearing88 i am using the chinese version of the MPPT and it model number is  SSCM-1224-5A  
  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,040 ✭✭✭✭✭

    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.