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  • SolarEdge HD Wave clipping

    Hi all.

    I am looking at:

    Qty 18 LG 330N1C-A5 (330W) solar panels with SolarEdge P400 Optimizers
    SolarEdge HD Wave SE5000H-US Inverter with 25 year warranty
    SolarEdge ModBus (consumption) meter
    Solar Edge WiFi Kit
    Main Electrical Panel Upgrade
    Unirac Solar Mount Racking

    10 of the panels will be on a south-facing roof with a 23 degree tilt
    8 of the panels will be on a east-facing roof with a 23 degree tilt

    I realize that the SolarEdge SE5000H-US can handle the theoretical max of 330 x 18 = 5940W on its inputs, but anything above 5040 watts (21A x 240v) will be lost, right?

    Using pvwatts, I generated the hourly data for the two strings and then processed the numbers. Using the STC rating of 330W with an 8% system loss, I could theoretically see 189 hours with over 5040 watts of production the first year. Using LG rated degradation of 0.55%, that drops to 135 hours the second year, 117 hours the third year, etc,:

    year 1: 189 hours, 38.333 kWh lost
    year 2: 135 hours, 21.603 kWh lost
    year 3: 117 hours, 17.967 kWh lost
    year 4: 99 hours, 14.895 kWh lost
    year 5: 93 hours, 12.121 kWh lost
    year 6: 76 hours, 9.752 kWh lost
    year 7: 65 hours, 7.768 kWh lost
    year 8: 55 hours, 6.040 kWh lost
    year 9: 44 hours, 4.609 kWh lost
    year 10: 33 hours, 3.520 kWh lost


    The maximum output is happening on March 27 during the noon hour, where the first year I could see 5815 watts produced.

    I am trying to decide if I should tell the installer that I want to wait for the SolarEdge SE6000H-US to avoid this clipping. The SE6000H-US is not that much more than the SE5000H-US, but I might have to wait an extra month to get it.

    Am I am understanding the situation correctly? Or is the hourly data from pvwats too granular to use for this kind of calculation?

    Anyone have any thoughts or advise?

    Thanks,

    John

  • #2
    The way you are doing it makes sense. Just make sure you have the DC to AC ratio in the advanced settings set low enough that the model isn't already clipping. What is the sum of the kWh clipped over 10 years? Looks like a bit over 100 kWh.. at .20/ kWh, that would be $20. You think saving that little bit extra would be worth waiting for?
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

    Comment


    • #3
      Those 2 array directions will never add up to anything near 5940 W; with system loss of 5% they would need to exceed
      5300W DC before any clipping would occur. My guess is never; I don't think PVwatts can solve this problem.
      Bruce Roe

      Comment


      • #4
        FWIW, sounds like your logic makes sense - to me anyway. The PVWatts hourly data is probably fit for the purpose your using it for.

        As a real wild SWAG, I might guess the annual deterioration might be a bit less than that 0.55 %/yr. , but I've absolutely no reasoning behind it other than mfgs. sometimes tend to be a bit conservative in things like that.

        Next number crunch is to figure the net present value (NPV) of each of those yearly kWh losses. Then, add the NPV's and compare it to the cost to step up in inverter size. If the current cost to increase the size is greater than the NPV of the lost production, the, in theory, it ain't worth it on consideration of long term costs.

        As practical considerations, my guess is the added cost of the clipping losses won't amount to much $$. What do you pay for 39 kWh of electricity ? Also, those clipping losses could disappear if your assumptions and everything else that PVWatts estimates are slightly too conservative. Also, and perhaps a greater financial impact than that might be a month's loss of current production caused by waiting for a newer piece of equipment as well as the possible problems of production sometimes associated with a newer model.

        On the other side of the ledger, the LG panels may well exceed their rated performance by a couple or several % for some time. If that's the case ( and hat seems not uncommon), the clipping would gobble up some of the added production made possible by the panels exceeding their nameplate rating.

        Bottom line if it was me: Even if the cost wasn't too great to increase the size, but I'd need to wait a month or more, I'd look at the cost of losing a whole month's production or however long the wait might be (you SURE it's only a month ??). That's probably a lot more than the NPV of any future savings by cutting future clipping losses plus any equipment price increase.

        I have no advice other than the above, FWIW, and to collect all opinions, remember that none of us is as smart as all of us, and then take your best shot. Even what looks like a poor decision in retrospect is not that end of the world. Sounds like you could be out a few bucks either way depending on how well your assumptions about future outcomes and conditions match the actual situation. Given the $$ amounts we're probably talking here, chances are you won't wind up in the poorhouse either way or most anything in between.

        Comment


        • #5
          Originally posted by sensij View Post
          The way you are doing it makes sense. Just make sure you have the DC to AC ratio in the advanced settings set low enough that the model isn't already clipping.
          I had not noticed the DC to AC ratio setting. Changing it from the default of 1.1 to 1.0 did not make a noticeable difference.
          For "reality", I am not sure what to set it for, since I will have a single inverter with two separate strings with different orientations. Would I just use 18 x 330 = 5940 divided by 5040 for each array?

          Originally posted by sensij View Post
          What is the sum of the kWh clipped over 10 years? Looks like a bit over 100 kWh.. at .20/ kWh, that would be $20. You think saving that little bit extra would be worth waiting for?
          Wow! Talk about over thinking something. Thanks, Sensij, for reminding me what matters. ~136kWh would cost me around $13 at current PNM rates. Definitely not worth waiting.

          Comment


          • #6
            Originally posted by J.P.M. View Post
            Bottom line if it was me: Even if the cost wasn't too great to increase the size, but I'd need to wait a month or more, I'd look at the cost of losing a whole month's production or however long the wait might be (you SURE it's only a month ??). That's probably a lot more than the NPV of any future savings by cutting future clipping losses plus any equipment price increase.
            Another excellent point, that i had not considered. By the time my system is up and running (with the SE5000H-US), I will be about to hit my most expensive month of the year. Last year, August cost me $141. I work from home, and running the evaporative cooler all day long chews up some watts. We have been running low to mid nineties for the last few days and August will be at least that bad every day of the month.

            Comment


            • #7
              Originally posted by bcroe View Post
              Those 2 array directions will never add up to anything near 5940 W; with system loss of 5% they would need to exceed
              5300W DC before any clipping would occur. My guess is never; I don't think PVwatts can solve this problem.
              Bruce Roe
              Albuquerque is one of the sweet spots that is close to ideal for solar efficiency. We are almost as high as Denver, and get full sun well over 300 days each year. It is also very dry here. All in all, we get a lot more of the sun's energy than most places in the country.

              That all being said, you are probably correct. PVwatts claims that I will hit a peak of 5815W for the noon hour on March 27, but what does that mean? Is that averaged over the hour? They don't list it as Wh, just W. So, is that the peak during that hour?

              Comment


              • #8
                Originally posted by jpoet View Post

                Albuquerque is one of the sweet spots that is close to ideal for solar efficiency. We are almost as high as Denver, and get full sun well over 300 days each year. It is also very dry here. All in all, we get a lot more of the sun's energy than most places in the country.

                That all being said, you are probably correct. PVwatts claims that I will hit a peak of 5815W for the noon hour on March 27, but what does that mean? Is that averaged over the hour? They don't list it as Wh, just W. So, is that the peak during that hour?
                The 2 arrays peak at different times. Perhaps if you are cloud free you could use PVwatts. Plot the actual hourly DC power of each
                array, then plot the hourly total, compare to 5300W. Something like I did with 1 and 3 here. Bruce Roe

                PVm16Jn16.jpg

                Comment


                • #9
                  Originally posted by jpoet View Post

                  Albuquerque is one of the sweet spots that is close to ideal for solar efficiency. We are almost as high as Denver, and get full sun well over 300 days each year. It is also very dry here. All in all, we get a lot more of the sun's energy than most places in the country.

                  That all being said, you are probably correct. PVwatts claims that I will hit a peak of 5815W for the noon hour on March 27, but what does that mean? Is that averaged over the hour? They don't list it as Wh, just W. So, is that the peak during that hour?
                  I lived in Albuquerque (NW, off Coors on the mesa) for several years. Strongly agree on that area being about as close to the best solar weather on the planet. Air's also about as dry as a popcorn fart.

                  However, having lived there makes me want to reinforce the idea that waiting for an updated inverter or believing what a vendor estimates for delivery may cost more than a month's production. Reason I feel that way: One of the reasons I left Albuquerque, in spite of the climate and that area being about the most gorgeous place I've ever seen much less lived in, was because I learned that vendors there are just about completely and universally unreliable for most anything and that starts with there ability (or lack of it ) to deliver on contracts, starting with schedule commitments and/or even showing up. If they're telling you a month, I'd start there and begin making daily phone calls - not that such calls will actually do much good beyond making you fee like your staying on top of them - but I'd sure not believe much of what they promised until it was done, inspected and run.

                  Just sayin'.

                  As long as you've treated both arrays as separate for purposes of PVWatts, That is, you've run PVWatts independently for each array and summed the results, those results will probably be representative of what the total system will produce over an entire TMY (Typical Meteorological Year).

                  As for what PVWatts may give for output for any particular hour, read the PVWatts help/info screens, and then read the parts of the TMY manual that explain how the data that PVWatts uses is derived, the logic behind it, and why its output is not suitable for short term estimates of output.

                  As for what's listed as Watts: If 1 Watt of power is produced (or used/consumed) continuously for 1 hour, one Watt-hour is produced (or used).

                  As for time increments: For PV sizing/preliminary design purposes, there is not much need to get information in time increments smaller than one hour. If PVWatts suggests (note: does not predict or promise) that over an hour, a system might produce power at an average rate of 5,815 Watts, that system will produce 5,815 Watt-hours of energy over that hour, or 5.815 kWh.

                  Power is expressed in Watts (W) which is the time rate of doing work. Energy is expressed as (power in Watts) X (time in hours).

                  One Watt is work done at the rate of 1 Joule (J) per second. 1 Joule = 1 Newton (N)-meter. So, 1 Watt = 1(N-m)/sec.

                  See Google for details.
                  Last edited by J.P.M.; 06-10-2017, 10:30 AM.

                  Comment


                  • #10
                    Originally posted by bcroe View Post

                    The 2 arrays peak at different times. Perhaps if you are cloud free you could use PVwatts. Plot the actual hourly DC power of each
                    array, then plot the hourly total, compare to 5300W. Something like I did with 1 and 3 here. Bruce Roe
                    PVm16Jn16.jpg
                    Bruce: For PVWatts output, if each array orientation is treated separately and the results are added, sum will likely be what the total system will put out over the course of a year +/- the usual tolerances and caveats. The hourly totals may be treated in the same fashion with the same limitations that go with any modeling scheme.

                    If the PVWatts hourly output option is used, and those results are summed, the max. summed (two orientation's total output) may/might be close to, or at least somewhat representative of, what might be expected on a clear day with favorable temp. and wind vector conditions.

                    I believe I understand what your writing. With respect, I'm not sure you understand how PVWatts can, with a bit of imagination, do about the same as your saying, but on a modeling basis, that is, not based on actual data. And also can, with a bit of spreadsheet knowledge, produce graphical images similar to those you produce and show.

                    Respectfully,
                    Last edited by J.P.M.; 06-10-2017, 10:45 AM.

                    Comment


                    • #11
                      I just ran your system with 2 PVWatts runs treating each array as a separate system and summing the hourly results.

                      Turns out, doing it that way, the max. hourly system output that the model spits out, using your inputs and TMY3 Kirkland data is ~ 5,329 Watt-hours.

                      I was under the (probably) incorrect assumption you were doing the input as I described and as I have now done. In that case, Bruce was probably closer to the mark than I was, at least in the common sense dept. by writing that a max. output of anything close to 5,940 W is very unlikely.

                      Your max. hourly output will probably not be near that 5815 W as you write.

                      Doing it my way, the max. output greater than 5,040 W was ~ +289 Watts, that occurring on June 09.
                      On that date at the 10 o'clock hour, for the south and east facing arrays respectively:

                      Total POA irradiance ~ 1,149 + 1,162 = 2,311 W./m^2.
                      D.C. output ~ 3,050 + 2,618 = 5,668 W.
                      Cell temps ~ 36.3 C. and 38.1 C., south and east facing arrays respectively.
                      According to PVWatts as I've run it, long term average annual system output after clipping above 5,040 W will be something like 10,230kWh/yr. or so after annual degradation +/- some.


                      The estimated year long summation of lost production over a 5,040 Watt output amounted to a grand total of 2.335 kWh/yr.

                      Given that, or something close to it, upsizing an inverter hardly seems worth it.

                      Semi - apologies to Bruce, I should have caught what he saw right away, but my I stick by my comments about the usefulness of learning to use PVWatts and spreadsheets.

                      Comment


                      • #12
                        To come up with my numbers, I ran pvwatts twice, as summed the results:
                        1. DC System Size: 3.3kW, 180 degrees, Module Type: Premium, System Losses: 8%, Tilt: 23 degrees.
                        2. DC System Size: 2.64kW, 90 degrees, Module Type: Premium, System Losses: 8%, Tilt: 23 degrees.

                        Where did I go wrong?

                        Comment


                        • #13
                          Originally posted by jpoet View Post
                          To come up with my numbers, I ran pvwatts twice, as summed the results:
                          1. DC System Size: 3.3kW, 180 degrees, Module Type: Premium, System Losses: 8%, Tilt: 23 degrees.
                          2. DC System Size: 2.64kW, 90 degrees, Module Type: Premium, System Losses: 8%, Tilt: 23 degrees.

                          Where did I go wrong?
                          Did you sum each hour's output and combine those then look for that max. summed number, or look for the max. of each array's output without regard to when those maximums occurred and add those two numbers ?
                          Last edited by J.P.M.; 06-10-2017, 12:56 PM.

                          Comment


                          • #14
                            Originally posted by J.P.M. View Post

                            I lived in Albuquerque (NW, off Coors on the mesa) for several years. Strongly agree on that area being about as close to the best solar weather on the planet. Air's also about as dry as a popcorn fart.

                            However, having lived there makes me want to reinforce the idea that waiting for an updated inverter or believing what a vendor estimates for delivery may cost more than a month's production. Reason I feel that way: One of the reasons I left Albuquerque, in spite of the climate and that area being about the most gorgeous place I've ever seen much less lived in, was because I learned that vendors there are just about completely and universally unreliable for most anything and that starts with there ability (or lack of it ) to deliver on contracts, starting with schedule commitments and/or even showing up. If they're telling you a month, I'd start there and begin making daily phone calls - not that such calls will actually do much good beyond making you fee like your staying on top of them - but I'd sure not believe much of what they promised until it was done, inspected and run.

                            Just sayin'.
                            That is always a concern. I did go with one of the 'smaller' installers in town. They just added a second crew, so they are growing. They gave me the listed system for $3/Watt, plus another $2000 for the electrical panel upgrade and the consumption meter. The owner has been very responsive to my questions and concerns, so I think (hope) it will be okay.

                            The other bids I got were:
                            1. $4.42/Watt for SunPower
                            2. $4.23/Watt for SunPower
                            3. $4.16/Watt for QCell with Enphase

                            The QCell installer was shocked that I didn't just jump at his deal. While cheaper than the two SunPower quotes, if those were my only three choices, I would have gone with SunPower. Actually, at those prices I probably would have stuck with PNM. PNM's tiered rate structure is currently $0.09 / $0.11 / $0.15 depending on how much electricity you use. They have raised rates an average of 6%/year, for the last 10 years -- according to all of these solar installers (I have not verified the claim).

                            The LG installer was also quite willing to provide me with Hyundai panels at $3/watt, but the LG Neon2 look like much nicer option.






                            Comment


                            • #15
                              Originally posted by J.P.M. View Post

                              Did you sum each hour's output and combine those then look for that max. summed number, or look for the max. of each array's output without regard to when those maximums occurred and add those two numbers ?
                              I summed each hour between the two arrays, and then looked for any total over 5040. I wrote a python program to do it.

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