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Solar PV output with Rapid Shut down system

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  • Solar PV output with Rapid Shut down system

    Hi Recently about two weeks ago we had our Solar PV system operational. Here are the specs
    13.65 Kwp system (42 Hanwha Duo-G5 325 Watt Panels)
    2 SMA US-40 6.0 Inverters
    midnite Rapid Shut down system
    2 Arrays of 21 Panels
    Each Array with two strings in 12/9 configuration.

    The problem I see is that even with a capacity of 13.65 Kwp, I have never seen the PV output to go over 6500 watts at any given time (On a bright sunny day @about 68-70 degree F).

    No Shading, my roof is Flat with an Azimuth of 203.

    I was expecting that I at least get 10K-12K output, but max I see is 6.5K. Spoke to the installer, he is also baffled. He is saying perhaps the Rapid Shut down system might be causing a problem.

    When monitoring the DC side instantaneous values, I do see as soon as String A crosses 2500 Watts, String B starts to degrade rapidly and combined the total Wattage never crosses 3200 - 3300 watts. For example Yesterday @ ~ 3:30 PM, String A showed 2485 Watts ( 2485/12 = 207 watts/panel), but String B dropped down to 714 Watts (714/9 = 79 watts/panel).

    Next, I Plan to run the system for a day or two without the Rapid Shut down system for a couple of days and see if that makes a difference.

    Anybody else experience something similar, Any insight will be greatly appreciated.

    Thanks again.

    Roger
    Attached Files

  • #2
    Kind of hard to diagnose/troubleshoot without being on site. Also not a good sign when the guy who installed the system and is on site is baffled.

    For starters, what's your latitude and what are the array angle(s ?) with respect to the horizontal ? Since you mentioned a roof azimuth, and azimuth won't matter if arrays or panels are horizontal, I assume the arrays are at some angle to the horizontal with array centerlines parallel to major roof centerlines so as to produce an array azimuth of 203 deg. Unless you're at a very high latitude and the arrays are horizontal, I doubt orientation is part of the problem as regards to low output.

    The different output/panel you write of usually indicates different string orientations if everything else is nominal. So, are all string orientations (however many strings there are) the same ?

    Have you had a cloudless & sunny day or two and observed the same outputs as mentioned at such times and times of day ?

    I'm confused about how many strings you have. Two strings on each inverter and two inverters = 4 strings, right ? You mention String A and string B. If 4 strings, what are strings C and D doing ? Or, are there two string A and 2 string B ?

    All the wiring and string configurations check out per the drawings/schematics ? The schematics are correct ?

    Loose/broken connections ?

    The inverters are operating nominally and per spec ?

    String voltages are within expected ranges ?

    Do you have graphical output for each inverter that you can post ?
    Last edited by J.P.M.; 04-20-2019, 10:35 AM.

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    • #3
      I do own an SMA system with one inverter, but do not own two SMA inverters so take this with a grain of salt.

      That screen shot of power vs time looks like it came from Sunny Portal. Did your installer link both inverters to Sunny Portal? Go to Sunny Portal, click on inverters in the left menu bar. There should be two inverters listed. If not, your installer did not link both inverters to Sunny Portal.

      Since you were able to look at power values by string, I assume you logged into the SMA inverter directly by typing in the IP address 192.168.x.y. If you are wondering what IP address your SMA inverter pulled from your router, go to each inverter and knock on the knock screen. Keep knocking until you see the IP address. I assume your installer set up your user password during install.

      Log into each inverter directly by typing in the IP address.

      I am also curious about how each string is wired and the model of rapid shutdown you used. On (bad) FEATURE of the SMA rapidshutdown box is that it parallels my two of my three strings together then splits them back out at the inverter. My three input MPPT inverter is essentially reduced to a two input MPPT inverter.

      Comment


      • #4
        2 Arrays of 21 panels each, Each array has two strings (12 Panels and 9 Panels), so a total of 4 strings (2 strings per inverter). Yes both the inverters are logged on the sunnyportal.

        The SMA tech was on the line and also could not figure out, it definitely looks like some setting in the inverter that is limiting the total output. He took a bunch of screenshots and will get back to me after consulting a senior tech at SMA.

        I checked the Voltage and Current of each string using a multimeter when the full sun was out and they were correct (~430V and 7.9 amps for stringA with 12 panels, and ~325V and 7.9 amps for stringB with 9 panels), but when you see the instantaneous values of DC side at the inverter, String B (with 9 panels) is clipped down to .7 amps ( this behaviour was seen on both the inverters), limiting the total output to 3250 W per inverter.

        so we will wait and see.

        If anybody had a similar experience and how they fixed it, will like to hear it or have any ideas.

        thanks.

        Comment


        • #5
          Do you have installer login rights to each inverter? If yes, you can go to Device Parameters, Device, Inverter to view maximum power settings. You can't view the "Currently set active Limit" or Currently set apparent power limit" of the inverter when logging in as User. In User login, the you can only see the Maximum Active Power, but not the Currently set active limits.

          I have to assume that the installer and SMA technical support checked these items, but you can't be too sure.

          Also, have you checked your events log for any weird events? Just curious. That's how I found out that my SMA 7.7 was doing something strange.

          Comment


          • #6
            Originally posted by oregon_phil View Post
            Do you have installer login rights to each inverter? If yes, you can go to Device Parameters, Device, Inverter to view maximum power settings. You can't view the "Currently set active Limit" or Currently set apparent power limit" of the inverter when logging in as User. In User login, the you can only see the Maximum Active Power, but not the Currently set active limits.

            I have to assume that the installer and SMA technical support checked these items, but you can't be too sure.

            Also, have you checked your events log for any weird events? Just curious. That's how I found out that my SMA 7.7 was doing something strange.
            Yes, I have the installer login rights. attached is the device/inverter settings. this is for 1 inverter (sunnyboy 6.0), I have two of these.

            Capture.JPGCapture.JPG

            Comment


            • #7
              These are my System and Device Control settings for my SMA 7.7. There is a setting for active power limitation %.

              My Firmware version: 2.4.81.R

              Attached Files

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