Technical assistance-low solar output

I have 2 Shell Solar SM110-12P modules in parallel for a total of 220watts,which are hooked up to 5x105amp.hr[GPL-31T] Lifeline AGMs through a Sunsaver MPPT controller[SS-MPPT-15L] on my boat-mounted flat.
Specs are:-
[Standard] [Typical 45deg C]


P[max] 110w [80w]
V[at Pmax]17.5v [16v]
I [at Pmax] 6.3a
warranted min Pmax 104.5w
Isc 6.9a [5.6a]
Voc 21.7v [20.0v]

In mid-summer in Greece[lat.39 deg.N] at 1200/1300 hrs with clear blue skies[although suns rays not perpendicular],I get Voc 20.6v and Isc 11.4a,for the two panels which seems excellent.
However when I hook up the controller and the batteries are at 90% full[shore power charges at 19 amps at 14.4v],even though the voltage at the controller input shows 17v,there is only a max of about 6.0 amps at both the input and output from the controller.I would expect to see 10,11 or 12 amps.
Why is this so low?It prevents me from getting my amp.hrs back into the batteries.
Is it possible that although the pv panels give good oc and sc readings, as soon as a load is applied, they exhibit a fault?
How does one test them properly?

Comments

  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    Re: Technical assistance-low solar output

    When that happens, what is the voltage of the batteries? Sounds like your batteries are absorbing which is normal.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Technical assistance-low solar output

    A couple of possibilities...

    Yes, it is possible for a panel to read Voc and Isc just fine, and yet not work properly. There are probably bypass diodes in the array and that allows Isc to read properly when shorted. And for a high resistance path (failing electrical connection) to only pass a little current (enough for a voltmeter to read Voc), but now enough to make Imp.

    To properly test the panel, place one panel (careful to watch the positive and negative connections--reverse them and it will kill your panel immediately) directly to the battery without a charge controller--and measure Imp.

    In your case, at least one of the panels is OK--And the Voc/Isc test will probably find 90%+ of the good panels.

    Next, if you can, connect only one panel at a time and see if they each work OK. It sounds like it is possible only one panel is working.

    If the battery is 90% full, then I would expect the charge controller to start reducing current to the charging battery. Below 80% State of Charge, I would expect 100% charge rate (MPPT mode). What is the battery bank voltage when charging (and what is the MPPT set point voltages).

    And, do you have the optional Remote Battery Temperature Sensor for your MS MPPT controller... For whatever reason, that controller really needs the RBTS. The controller typically reads too high of temperature with the internal temperature sensor and picks a lower charging voltage for the battery bank (which reduces charging current early).

    Are the two solar panels 100% clear of any shading (lines, masts, etc.) Any shading will dramatically reduce the output voltage from the panels.

    Have you looked at wiring the two solar panels in series? That would reduce the voltage drop in the cables from the array to the battery charger.

    Measure the voltage at the battery bank and right at the charge controllers +/- battery connections when charging. You should see, at most, a 0.05 to 0.10 voltage drop. If you see more, either you have a bad connection, or too small of diameter copper wire (for the length) from the charge controller to the battery bank (the charge controller needs to accurately measure the battery bank voltage for proper charging).

    For a typical sunny warm day, array pointing within 10 degrees perpendicular to the sun, I would expect around a maximum of 0.71 to 0.77 of solar panel rating to be max power into your battery bank if the battery is over 80% discharged and the everything else is OK (panels pointing at sun, no shade, etc.). Or a minimum of:
    • 0.71 * 220 watts * 1/14.4 batt charging volts = 10.8 amps
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Technical assistance-low solar output

    Most MPPT controllers abandon MPPT and many abandon switching power conversion when absorb or float voltages are reached. They go into slow PWM, straight pass through mode, just like a non-MPPT controller.
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: Technical assistance-low solar output
    RCinFLA wrote: »
    Most MPPT controllers abandon MPPT and many abandon switching power conversion when absorb or float voltages are reached. They go into slow PWM, straight pass through mode, just like a non-MPPT controller.

    This isn't true on Xantrex, Outback or MorningStar Mppt controllers ... what brands have you found that do this?
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,728 ✭✭✭✭✭✭
    Re: Technical assistance-low solar output

    Yea, what brands RC? Even the old mx-60 would mppt a load in absorption or float if it ever stopped sweeping... It is the main reason to do this is it not? Maybe we are having a brain fade?
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Technical assistance-low solar output

    Perhaps this is my fault... I try to describe that a MPPT controller will "behave" like a PWM controller once the Absorb/Float voltages are obtained. In other words, a MPPT controller is not maximizing power from the solar array and produces the same power output as a PWM controller.

    And I confused everyone.:blush:

    -Bill "oops" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Technical assistance-low solar output
    This isn't true on Xantrex, Outback or MorningStar Mppt controllers ... what brands have you found that do this?

    How can you determine maximum power point if you are not allowed to consume maximum power?

    I agree on the total abandonment of high freq switching, perhaps a better description is pulsing mode bursting of switching.

    To Hannies, you can not expect maximum current output if the batteries are charged to float or absorb levels where controller cuts back.

    When you say 90% charged and 14.4vdc the controller is likely already backing off.

    Simple test would be to load the batteries with loaded inverter and see if the solar amperage goes up.
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: Technical assistance-low solar output
    RCinFLA wrote: »
    I agree on the total abandonment of high freq switching, perhaps a better description is pulsing mode bursting of switching.
    .

    Buck mode charge controllers operate identically whether its in bulk/absorb or float. The only change is the duty-cycle changes to change the input to output voltage ratio.

    As for operating at the VMP, yes, you have to have a load to consume the energy, Only bulk mode will be in true Mppt, regardless if OB has some magic name for their float state
  • phred01
    phred01 Solar Expert Posts: 35
    Re: Technical assistance-low solar output
    Hannies wrote: »
    In mid-summer in Greece[lat.39 deg.N] at 1200/1300 hrs with clear blue skies[although suns rays not perpendicular],I get Voc 20.6v and Isc 11.4a,for the two panels which seems excellent.
    However when I hook up the controller and the batteries are at 90% full[shore power charges at 19 amps at 14.4v],even though the voltage at the controller input shows 17v,there is only a max of about 6.0 amps at both the input and output from the controller.I would expect to see 10,11 or 12 amps.
    Why is this so low?
    How does one test them properly?

    The problem is the interpretation of the data sheet specs. U cannot rely on Voc & Isc figures to work out what u should get. The major factor that reduces power output is the cell operating temperature. The parameters that u should look @ are Vmpp & Impp. Now the specs state with an ambient temp of 20 DegC an air flow of 1m/s the cell temp is 45 DegC so the power u will expect to get is 80w out of a 110w panel. If u look at the temperature curves a cell temp 45 DegC gives u a max of 3-4 A @17v. When u made the measurements on that day what was the ambient temperature the speed if the air flowing behind the panel. Probably with no wind and with ambient of 30 DegC + the panel cell temperature could be more than 55 DegC. My system looses 400w form a 1 KW system on a day that's 38 DegC