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  • Phasing panels in and out of strings

    Solaredge grid tie inverters use optimizers at the panel junction points. The optimizers are controlled by the inverter. My question is: Could strings have panels be added (10%) to during times when the inverter is below lets say 80% full input current. I recognize there is a load limit on each string, just wondering about getting more out of those cloudy days and low sun hours. There has to be a reason its not done. We only get about 60% full sun days and a lot of the year the sun angle has a negative effect. I'm thinking the extra panels are out of the string about every sunny day between 10 AM-2 PM depending on the input current which depends on the sun. Possibly the inverter won't work with optimizers appearing and disappearing. I can handle the sensing and switching part.

  • #2
    There is no reason to add more PV modules to a string with SolarEdge. As long as the string is above the minimum, if there is any light it will produce as much power as it can. The optimizers will get the DC voltage within operating limits for the inverter.

    You can add more PV modules to the inverter in additional strings or longer strings (as long as the strings are within operating limits) to get better production on cloudy days with the result that there will be clipping on non-cloudy days. Solar design is a balance of these situations. With SolarEdge the price difference from one inverter to the next is pretty small so there is rarely a need for clipping, you can just install the next size up inverter and eliminate the clipping.
    OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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    • #3
      Thanks Butch,
      I forgot to mention this is an existing grid tie inverter, upgrading to a larger inverter would be costly and would require another inspection, permit and approval by the utility co.. In hindsight, I would have purchased a larger inverter.Now I am adding load to my house and trying to cover it. The utility offers a best case scenario of break even on KW basis. They do not purchase excess.

      I was looking to avoid the clipping by only having the additional panels tied into the inverter when the inverter input was at 80% or below and removed at 100%. Once they drop out between 10-2 they would remain out till after 2PM. That would allow for partly cloudy days. This assumes I am at 80% during those before and after hours on sunny days. I know its a complicated outside the inverters basic operating design. Seems to me like it would have been an easy one if built into the inverter design. 10% more power 90% of the time with 10% more panels.

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      • #4
        Originally posted by bebo View Post

        I was looking to avoid the clipping by only having the additional panels tied into the inverter when the inverter input was at 80% or below and removed at 100%. Once they drop out between 10-2 they would remain out till after 2PM. That would allow for partly cloudy days. This assumes I am at 80% during those before and after hours on sunny days. I know its a complicated outside the inverters basic operating design. Seems to me like it would have been an easy one if built into the inverter design. 10% more power 90% of the time with 10% more panels.
        There is NO reason to avoid the clipping in this way. Leave them on ALL the time will produce MORE than trying to in some way disconnect them.
        IF you have different azimuths, you could avoid clipping AND extend your production but you would need to stay within the warranty limits of the inverter and strings.

        The inverter will produce at max level (clipping) and the optimizers will de-tune the PV array to keep the inverter at max power during the clipping times.

        OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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        • #5
          As ButchDeal explained, there is no need to switch out panels that might increase clipping, the inverter plant will
          do limiting to its capacity automatically. Aside from the issue of a control algorithm, switching high voltage DC
          circuits under power, with no damage, is a considerable engineering problem. Throwing a short on each
          individual panel might succeed.

          Your objective seems to increase power outside prime mid day hours, and under poor sun conditions (clouds),
          by adding panels. This experiment has been done many times, many ways. The approach is to aim some or
          all panels to favor the earlier and/or later sun, adjusting the angle and the number of panels to still achieve
          the original 100% output at solar noon. Achieving this without increasing inverters can be advantageous, if
          falling within the original inverter capabilities. Under clouds light will be dispersed, so all panels will be
          effective in increasing output. BUT available radiation might be at an 8-25% level, so even doubling the number
          of panels would only bring you up to 16-50%. My version looks like this. Bruce Roe

          NSnview.jpg

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          • #6
            Thanks guys,
            That's about what I had gathered so far. I just tried to make it more complicated than necessary. Actually have 4 panels being delivered tomorrow. That puts me just above rated inverter input during the high radiation hours i get. Also just below my optimizers maximum (2) string wattage.

            Thanks again

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            • #7
              The older Solaredge inverters can have modules connected up to 135% of the inverter's rating. For example an SE3000A can have up to 4,050 watts of panels connected. The new HD-Wave inverters can go to 155%.

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              • #8
                Originally posted by reader2580 View Post
                The older Solaredge inverters can have modules connected up to 135% of the inverter's rating. For example an SE3000A can have up to 4,050 watts of panels connected. The new HD-Wave inverters can go to 155%.
                Does the inverter actually convert that extra energy? My understanding is that it is locked at the inverter rater rating. So adding panels beyond 3000 Watt to an SE3000A would be throwing away the excess power generated. I would hope that I am wrong, but all indications I have seen are that the excess power is not converted.

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                • #9
                  Originally posted by Yoshsmenge View Post
                  Does the inverter actually convert that extra energy? My understanding is that it is locked at the inverter rater rating. So adding panels beyond 3000 Watt to an SE3000A would be throwing away the excess power generated. I would hope that I am wrong, but all indications I have seen are that the excess power is not converted.
                  Correct, the inverter is still limited to the name plate rating no matter how many panels are added. Most of the time panels are not producing at 100% so that is why extra panels can be added to an inverter.

                  The OP wants to be able to turn on additional strings when inverter output is 80% or less. Adding extra panels beyond the rating of the inverter would do basically the same thing. The inverter might clip at times, but it would keep the output near 100% more often with extra panels.

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                  • #10
                    You are correct, once you hit the inverter limit any extra power over the rating is not generated

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