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  • How to know where my loss is?

    Hello,
    Need some info please. My system has been up and running since end of September of 2016, so still new at this. Haven't had a very high kw day until these last few, where my peaks have been at 7900 watts, according to my reporting graph from the solar edge website. It seems that it has hit a flat spot and will not go over 8k. My system is 30 LG 315 panels, using microinverters, and a solar edge SE7600 inverter. Math and fantasyland says I should be maxed out at 9.45 kw, but that is fantasyland. So my question... What is a fair expected loss, from what I have experienced today and yesterday at peak times looks like a 15% loss. The temps are in the low 40's and sky is crystal clear. Where is my limiting factor? Inverter shows 8.4kw max on the screen, so that shouldn't keep it below 8k. I do realize that it isn't summer yet and the panels are not directly near peak. Still made 54kw today and same as yesterday..But surprising, is that the flat top of my power curve, with nothing over 8k. If this is what it is, I 'm content, just curious what to expect this summer. Located in South Carolina.. Thanks in advance.

  • #2
    What is your array orientation and tilt? The inverter is limiting output, which is normal, and often a good design choice to optimize cost effectiveness. This time of year through May is when clipping normally occurs, peak power will drop in the heat of the summer.
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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    • #3
      You have a Solar Edge system, do you have any shading? What is your tilt and azimuth. Looks South Carolina is Between 32 and 35 degrees. Best all around tilt would be in that range. Lower will give higher summer production, higher tilt, higher winter production. Grid tie systems favor long summer day's production. Off Grid you are concerned with producing enough power in the short days of winter. If you have local conditions with morning fog, marine layer a more westerly azimuth would benefit. Afternoon shading would likely favor a more easterly exposure.
      2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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      • #4
        Thanks for the replies. My tilt is 28 degrees and azimuth is 100 degrees. I figured it was clipping because of the temps, and also figured this was the max due to the cool weather we are now experiencing. My system does not have batteries yet, and may do this in the future. So this is a typical function of the inverter to limit my output to under 8kw, and I should not expect higher output? Then, the only other thing to get more power is the fact that days are longer in summer, and that means more time producing energy...

        BTW.. no shading after 8:30am. My 7kw and higher is output is between 9:30 and 1:30 and 7.9kw from 10:15-12:45

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        • #5
          The STC, (standard test conditions) are a level playing field that all panels are rated by. They are flash tested with a 1000 watt per square meter light and at 25 degrees Celsius. Real world conditions rarely equal these conditions, consequently, solar panels rarely put out their rated output. Your tilt angle is less than optimum for the suns angle at this time of the year. Your peak output should increase as the sun continues to ride higher in the sky as we get closer to summer. Your azimuth is considerably easterly oriented, which is what it is. A true solar south orientation will give the highest output. You will be missing out on a considerable portion of the mid afternoon potential.

          Your inverter is rated based on it's AC output power, not DC solar input. You should see in your inverter's documents the max. recommended DC input limit. It will always be higher than it's rated output based on real world output of your array and your inverter's conversion efficiencies. Any excess input will be clipped but you will be able to run closer to peak output for a higher part of the day. You will notice your peak input numbers will not be for a very long portion of the day.
          2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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          • #6
            Originally posted by SteveH View Post
            Hello,
            Need some info please. My system has been up and running since end of September of 2016, so still new at this. Haven't had a very high kw day until these last few, where my peaks have been at 7900 watts, according to my reporting graph from the solar edge website. It seems that it has hit a flat spot and will not go over 8k. My system is 30 LG 315 panels, using microinverters, and a solar edge SE7600 inverter. Math and fantasyland says I should be maxed out at 9.45 kw, but that is fantasyland. So my question... What is a fair expected loss, from what I have experienced today and yesterday at peak times looks like a 15% loss. The temps are in the low 40's and sky is crystal clear. Where is my limiting factor? Inverter shows 8.4kw max on the screen, so that shouldn't keep it below 8k. I do realize that it isn't summer yet and the panels are not directly near peak. Still made 54kw today and same as yesterday..But surprising, is that the flat top of my power curve, with nothing over 8k. If this is what it is, I 'm content, just curious what to expect this summer. Located in South Carolina.. Thanks in advance.
            Your limiting factor is your array's orientation. Your max. output is less than you thought it would be because of the orientation of the array. An azimuth of 100 deg. will have more output before solar noon and, given the same approx. tilt, the max. output of a way off south array such as you have will always be less than the max. output of a south facing array.

            Do this:
            Run PVWatts for your actual orientation. Use 10 % system losses
            Choose the hourly output option.
            Look for a mostly clear day near the dates for which you have your measured output. Note the pattern of hourly output and max. value of hourly output.

            Repeat the above for the same input except change the array azimuth to south facing (180 degree).

            Compare outputs for the same day's clear output.

            Q.E.D.

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            • #7
              Thanks again for the replies. Yes, the roof is what it is, and there was not an economical way to twist the house for a better southern exposure. So in summary, I should get more power later in the year, because the sun will be more in line with my panels? As I asked in the beginning, my concern was that there was some sort of limit that kept me under 8kw, but there isn't, just the orientation of my panels. My inverter does show an 8.4 limit on the display.. I will keep checking. Hopefully be able to contribute my experiences on the forums. Thanks again, SteveH

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              • #8
                Originally posted by J.P.M. View Post

                Your limiting factor is your array's orientation. Your max. output is less than you thought it would be because of the orientation of the array. An azimuth of 100 deg. will have more output before solar noon and, given the same approx. tilt, the max. output of a way off south array such as you have will always be less than the max. output of a south facing array.

                Do this:
                Run PVWatts for your actual orientation. Use 10 % system losses
                Choose the hourly output option.
                Look for a mostly clear day near the dates for which you have your measured output. Note the pattern of hourly output and max. value of hourly output.

                Repeat the above for the same input except change the array azimuth to south facing (180 degree).

                Compare outputs for the same day's clear output.

                Q.E.D.
                Looks like I am doing better than what the PVWatts shows.. Guess I should be happy..

                Comment


                • #9
                  Originally posted by SteveH View Post

                  Looks like I am doing better than what the PVWatts shows.. Guess I should be happy..
                  It's good to keep in mind that PVWatts is no more than a model, and its estimates of long term average annual output, due to variables such as weather, and other things, are probably little better than +/-10% or so for any given year and perhaps +/- a lot more for shorter periods like a month, and useless for shorter periods.

                  So, as for doing better - wait a while, you'll do worse for some periods. Doesn't mean there's anything wrong necessarily, or that climate change is wrecking or helping your system, etc. Just that the model is good for long term average output, and expecting more or better numbers is an example of the folly of ignorance. No more.

                  In addition, PVWatts has been found by more than a few users to often be somewhat conservative in its output with respect to actual performance. That's why I suggested using a system loss parameter 10% rather than the 14 % default value, particularly for relatively new systems such as yours. Doing so will often give a better match with actual long term average annual system output.

                  Using PVWatts' single day output as a comparison to any day's actual output is actually misleading, as a read of the PVWatts help screens will explain.

                  Bottom line, my suggestion of output comparison to PVWatts estimated hourly output is, without question, technically a misuse of the model.

                  However, within the limitations of getting an estimate of "clear day" or any hour's "clear sky" output, using PVWatts hourly output option estimates as a comparison to specific measured or observed actual system clear sky output may have some use as ONE tool to gain some insight as to whether a system is performing as expected for the conditions encountered. Even with adjustments/estimates for how actual ambient conditions of wind and ambient temp. will affect output, the method is still no better than a rough estimate and only one trick/tool used in preliminary troubleshooting. Those parameters of wind and ambient temp. may be more reasons for your system's performance being higher than PVWatts estimates.

                  You will get more output from your array in summer because there will be more daylight and the integrated day long angle of incidence that the sun makes with your array will generally be less. That is, summer is better for how much sun your array will see, so that will increase production. But, in general, the temps. will be warmer and that will decrease array average efficiency. Overall, in most cases and as a general statement, summer is better than winter for PV array production.


                  ADD: I forgot to mention the daylight saving time adjustment. PVWatts times are all standard time. My apologies for the sloppy error.
                  Last edited by J.P.M.; 03-17-2017, 02:13 PM. Reason: Add daylight saving time comment.

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                  • #10
                    Originally posted by SteveH View Post

                    Looks like I am doing better than what the PVWatts shows.. Guess I should be happy..
                    Do you have a public link to your system's output? Here is a link to mine (internet connectivity problems is why no data for the last couple days). If you don't have it, try asking your installer to set it up, it should be free.

                    https://monitoringpublic.solaredge.c...?name=Tecolote Canyon#/dashboard
                    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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                    • #11
                      Originally posted by J.P.M. View Post
                      .....ADD: I forgot to mention the daylight saving time adjustment. PVWatts times are all standard time. My apologies for the sloppy error.
                      Too bad PV watts does not adjust to the longer days mandated by DST.

                      Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                      || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                      || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                      solar: http://tinyurl.com/LMR-Solar
                      gen: http://tinyurl.com/LMR-Lister

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                      • #12
                        Originally posted by Mike90250 View Post

                        Too bad PV watts does not adjust to the longer days mandated by DST.
                        Longer, really? Even without savings time, making measurements I had to use a daily chart to get my exact solar noon. Bruce Roe

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                        • #13
                          Originally posted by Mike90250 View Post

                          Too bad PV watts does not adjust to the longer days mandated by DST.
                          Maybe that could be something Dan K. could investigate and keep him occupied with something more productive than his usual output.

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                          • #14
                            Originally posted by bcroe View Post

                            Longer, really? Even without savings time, making measurements I had to use a daily chart to get my exact solar noon. Bruce Roe
                            Depending on the precision required, a pretty good, useful and easy 1st approx. method for finding solar noon is to split the difference between sunrise and sunset from local sources or Accuweather, or the Weatherunderground etc. Spreadsheets from NREL are also available for any desired accuracy provided you know lat., long. (and elevation of the location in question for sunrise/set times). I have an old Nautical Almanac used in WWII given to me by a mentor. I used it for years before the net.
                            Last edited by J.P.M.; 03-19-2017, 01:40 PM.

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