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  • Variations in Production

    Hi, I have two SMA Sunnyboy 6.0 inverters in my system https://www.sunnyportal.com/Template...e-88e11fdb108e , with identical number of panels in each (each has 18 Panasonic VBHN325SA16 panels, for a total of 11.7kw).

    Location is southern California.

    About 11:00am each morning one of the inverters starts producing less than the other. The exact difference varies, but the variance is always there on the graph. Overall, one produces several kwh/day less than the other.

    The array producing less is on a bit a bit more flat than the other array, it

  • #2
    Have you contacted the installer yet ? They ought to be the first contact you make. People here can only guess.

    Other than that, shading and different orientations for different parts of the array will have an impact on output.

    From what you include, that output looks pretty nominal to me. maybe some shading in the P.M.

    If you still have concerns, call the installer.
    Last edited by J.P.M.; 07-23-2018, 10:52 PM.

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    • #3
      Originally posted by J.P.M. View Post
      Have you contacted the installer yet ? They ought to be the first contact you make. People here can only guess.

      Other than that, shading and different orientations for different parts of the array will have an impact on output.

      From what you include, that output looks pretty nominal to me. maybe some shading in the P.M.

      If you still have concerns, call the installer.
      Thanks JPM for you reply.


      I noticed that my post got cut off. So I'm copying, below, the full text of what I meant to write. But to reply to your point: The installer is clueless.

      ---

      Hi, I have two 6.0 inverters in my system https://www.sunnyportal.com/Template...e-88e11fdb108e , with identical number of panels (each has 18 Panasonic VBHN325SA16 panels).

      About 11:00am each morning one of the inverters starts producing less than the other. The exact difference varies, but the variance is always there on the graph. Overall, one produces several kwh/day less than the other.

      The array producing less is on a bit a bit more flat than the other array, it is a bit lower, and on the West side (both are oriented to the south).

      Up until two weeks ago, 7/10, there some trees which were shading that same array beginning about 3pm. That explained some of the difference, but did not explain why the difference started at 11am when there was no noticeable shade. As of 7/10, I removed those trees, and yet, the variation is still there. Overall, my system is producing less now than it did two weeks ago. It is now consistently producing about 5kwh less than what pvwatts predicts it would on a clear day in July.

      So far I am getting about 65kwh/day or so in July, when pvwatts says I should be getting upwards of 70kwh.

      I am writing this as it is about 3:30pm here. There is no shade on the arrays. One is producing 3620 watts (consistent with pvwatts prediction), the other 2648. Checking the instantaneous values on the inverters, I noticed right now that the voltage is about 320 in [A] [B] and [C] in array / inverter 1, but in inverter two, the voltage is much lower in the [a] and [c], about 180-190. Do not know if that tells you anything.

      What should I be looking at? Dirt? heat? Faulty connections?

      [P.S. Is there a bug in this site with apostrophes? ]
      Last edited by ChabSin; 07-24-2018, 05:35 PM.

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      • #4
        Your voltage between equal strings should not vary much, even with some shade. I suggest that a panel
        or 3 are somehow damaged and in bypass mode. My experience is that this is more likely as the sun is
        more intense; the weaker panels can't keep up.

        A infrared temp gauge may lead you to the guilty party. Another way is to actually measure the voltage
        across a panel or groups of panels and find which isn't delivering. That is a little tricky since you really
        can't safely do much with the wiring under sun. My method is go out after dark and insert some MC4
        3 way taps into a string, perhaps at the 1/3 and 2/3 points. Using that and the ends at the combiner,
        check the voltage per panel is consistent. Finding a group of panels considerably low, next time move
        all the taps into that group and narrow it down. My voltmeter has long extensions with MC4s on the end,
        any tap not in use has the extra port plugged with a dummy MC4, wire port sealed.

        My voltmeter leads have the locking clips ground off to save time. Bruce Roe
        Last edited by bcroe; 07-24-2018, 08:16 PM.

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        • #5
          I'm not very familiar with sunnyboy at all, but on Screenshot_20180724-220450_SolarEdge.jpg my solaredge system I can narrow down each of the 3 inverters and look at each panel independently for any issues - is that not possible here? I found 2 panels that weren't powering on when my system was first installed, and I never would have known if it wasn't for this. They've only been running a couple months but you can easily tell which 2 weren't powering up for a couple days.

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          • #6
            Originally posted by ChabSin View Post

            Thanks JPM for you reply.


            I noticed that my post got cut off. So I'm copying, below, the full text of what I meant to write. But to reply to your point: The installer is clueless.

            ---

            Hi, I have two 6.0 inverters in my system https://www.sunnyportal.com/Template...e-88e11fdb108e , with identical number of panels (each has 18 Panasonic VBHN325SA16 panels).

            About 11:00am each morning one of the inverters starts producing less than the other. The exact difference varies, but the variance is always there on the graph. Overall, one produces several kwh/day less than the other.

            The array producing less is on a bit a bit more flat than the other array, it is a bit lower, and on the West side (both are oriented to the south).

            Up until two weeks ago, 7/10, there some trees which were shading that same array beginning about 3pm. That explained some of the difference, but did not explain why the difference started at 11am when there was no noticeable shade. As of 7/10, I removed those trees, and yet, the variation is still there. Overall, my system is producing less now than it did two weeks ago. It is now consistently producing about 5kwh less than what pvwatts predicts it would on a clear day in July.

            So far I am getting about 65kwh/day or so in July, when pvwatts says I should be getting upwards of 70kwh.

            I am writing this as it is about 3:30pm here. There is no shade on the arrays. One is producing 3620 watts (consistent with pvwatts prediction), the other 2648. Checking the instantaneous values on the inverters, I noticed right now that the voltage is about 320 in [A] [B] and [C] in array / inverter 1, but in inverter two, the voltage is much lower in the [a] and [c], about 180-190. Do not know if that tells you anything.

            What should I be looking at? Dirt? heat? Faulty connections?

            [P.S. Is there a bug in this site with apostrophes? ]
            What is the azimuth and tilt of each array ? Know that if they are not the same, the output will be different.
            Also, and as you report, the array with the lower tilt will not produce as much power, although if both arrays are facing pretty much south, and at the same azimuth, each array's output ought to be mostly symmetric around solar noon which happens ~ 1300 hrs. P.D.T this time of year depending on your longitude, with a bit less afternoon output due to increased temps.

            As for shading, the graphs you included for 07/22, 07/23 and 07/24 look very close to one another in shape, at least to my eyeball, and as far as choppy afternoon output is concerned, and the rest of the graphs don't look that unusual for "mostly" sunny days. However, the similarities for those three days looks to me like almost a smoking gun for shading. To that end, small amounts of shade when arrays use string inverters will extract a bigger penalty on output than most folks realize. A stink vent or partial shade on 1 -2 panels from a chimney or dormer, or even a satellite dish or a flag, etc. can can have a big effect on output of an entire string. Anything different in shade possibilities going on for the period 07/22- 07/24 ? A flag ? outdoor drying clothes?

            As for the other possible causes you mention, anything is possible but,
            - It's likely that the arrays are about equally fouled. As an aside, hose the array off ~ 1X/month with hose water - nothing fancy. Just be sure to do it in the early A.M. before the sun gets a chance to heat up the glazing.
            - Heat usually does not produce as sharp of a variation in output as f(time) as your graphs seem to show. Power drops from increased temps. are more gradual than what the those graphs show.
            - Wiring ? Always a possibility, but why only in the afternoon ?
            - Low(er) voltage ? probably shading, but again voltage changes tend to be more gradual. Current changes as f(irradiance) will be faster.
            - Are you sure the arrays are both facing south ?

            All that aside, the output on the 19th, from the smoothness of the graph, seems to be for a cloudless sky. If shading did not decrease output on the 19th as appears it did not decrease output, then what caused the similar shapes of the graphs on the 22d - 24th ? Less sun ? In about the same fashion with respect to time and intensity ? I'd kind of doubt that. Believe it or not, it's entirely possible that the skies you think are cloudless are not completely clear. Although I'm at a loss to explain the similarities in the graphs for the 07/22 - 07/24 period, the graph for the 19th, by virtue of its smoothness, would lead me to believe shading is not a problem. The similarities in the graphs of 07/22 - 07/24 would lead me to think shading is the culprit. Might be other causes but whoever diagnoses the problem will, in all likelihood, need to be on site.

            So, what should you be looking at ? Right now, if I were you, I'd be looking at your ass kicking foot and figuring out how to get it in the installer's butt. The installer is the best place to get an answer and part of what you paid for. If you accept poor customer service, especially for a recently installed array, no one can remedy that but you, or the BBB or the court system - probably small claims court.

            Good luck.

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