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

    Is that 1% limitation on max. instantaneous output or 1% limitation on annual total output, or something else ?

    I'd agree that if an inverter will clip to the point that it reduces the nominally expected annual output by, say, 1%, that may be a worthy figure provided that the cost of the lost production represents a significant proportion (say 10% or so ??) of the incremental cost of upsizing an inverter. A 1% annual clipping for me might amount to, say, 90-100 kWh/yr. At ~ $0.26/kWh = $26/yr. it may be worth it to upsize the inverter - but a bit off topic - provided I'm not an excess generator.

    If I am an excess generator, downsizing an array by removing panels (at the design stage), and (possibly) keeping the same inverter becomes a more cost effective solution than increasing inverter size. Other things such as future expected needs may well dictate the need for initial excess generation however.

    The usual goal is the lowest long term cost of providing electricity through a combination of a properly sized and designed PV system and POCO supplied electricity. I'd suggest that some clipping may be in line with system design and cost goals.
    Up to 1% does equal some clipping
    we use solaredge by default so there is little need for clipping like with string inverters where it would be more common to have some clipping to keep the strings in optimal operating range year round. We also do some micro installs on request and there again clipping can not easily be avoided.
    we buy a lot of solaredge inverters and get good pricing with the difference between any model and the next up is pretty small. We do not charge customers more for this they pay by the watt with basic adders for things like MSP upgrades etc.
    we do other things that most installers don't as well like use the built in revenue grade meters reducing install cost and simplifying monitoring.
    OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

    Comment


    • Originally posted by aleenoor View Post

      Hi Sensij,
      I am not aware of SAM but in PV watts, even choosing a weather station 5 miles apart result in big variance. Also, I realize this will not be a consistent occurrence hence accounting for about 75 days..
      What sort of variance are you seeing? Weather truly is variable, and if you read more about how TMY files are created, it might explain some of the difference. If you let us know what weather stations you are using, I could walk through it and let you know how I would do it, especially with Magius's data over a few weeks to act as a reference.
      CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

      Comment


      • Originally posted by ButchDeal View Post


        we do other things that most installers don't as well like use the built in revenue grade meters reducing install cost and simplifying monitoring.
        How does opting for Rev Grade meter reduce install cost simplify monitoring ?

        Thanks
        12.1 kW Canadian Solar 295W ;SMA SB-6.0-1SP-US-40

        Comment


        • Originally posted by sensij View Post

          What sort of variance are you seeing? Weather truly is variable, and if you read more about how TMY files are created, it might explain some of the difference. If you let us know what weather stations you are using, I could walk through it and let you know how I would do it, especially with Magius's data over a few weeks to act as a reference.
          Sensij, I am in zip code 32835 and used Orlando International Airport weather data, Alternate was Tampa Airport which for some weird reason comes up as default and shows closer to my house. My DC size is 11.8KW 180 degree (S) and 26.6 tilt. AC size is 2x5KW inverters.
          12.1 kW Canadian Solar 295W ;SMA SB-6.0-1SP-US-40

          Comment


          • Originally posted by aleenoor View Post

            How does opting for Rev Grade meter reduce install cost simplify monitoring ?

            Thanks
            When a revenue grade meter is required for incentives then one needs to be provided. The internal one uses the same monitoring portal as the solaredge inverter. An external one tprequires more components and electrician time to install as well as a monitoring connection usually cell .
            OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

            Comment


            • Originally posted by ButchDeal View Post

              Up to 1% does equal some clipping
              we use solaredge by default so there is little need for clipping like with string inverters where it would be more common to have some clipping to keep the strings in optimal operating range year round. We also do some micro installs on request and there again clipping can not easily be avoided.
              we buy a lot of solaredge inverters and get good pricing with the difference between any model and the next up is pretty small. We do not charge customers more for this they pay by the watt with basic adders for things like MSP upgrades etc.
              we do other things that most installers don't as well like use the built in revenue grade meters reducing install cost and simplifying monitoring.
              I appreciate your design mandates, and I don't doubt your veracity, and I'm aware that 1% does equal some clipping. However, my question stemmed from my confusion about what "1% clipping" means in your context. Is that a limitation of clipping of no more than 1% of instantaneous output of the solar panels for any input situation, probably under high irradiance conditions, or is it a limitation such that no more of 1% of the annual total input to the inverter will be lost due to clipping ? Not arguing. Just wondering.

              Comment


              • As Aurora is calculatin it is 1% of annual. The team shoots for zero clipping with solaredge but is allowed to do up to 1% without approval. We sometimes have some when there is limited feeding usually due to MSP limits.
                OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

                Comment


                • Originally posted by ButchDeal View Post
                  As Aurora is calculatin it is 1% of annual. The team shoots for zero clipping with solaredge but is allowed to do up to 1% without approval. We sometimes have some when there is limited feeding usually due to MSP limits.
                  Understood. Thank you.

                  Comment


                  • Originally posted by aleenoor View Post

                    Sensij, I am in zip code 32835 and used Orlando International Airport weather data, Alternate was Tampa Airport which for some weird reason comes up as default and shows closer to my house. My DC size is 11.8KW 180 degree (S) and 26.6 tilt. AC size is 2x5KW inverters.
                    I can see that the TMY3 file for Orlando and the TMY2 file for Tampa have represented "typical" weather in different ways, maybe explaining some of the variance you are seeing. If I tweak the settings so that cold spring days are capable of producing at STC, the Tampa file gives ~33 kWh of clipping over the course of the year with your 2 x 5 kW inverters. Even tweaking to an essentially zero loss system capable of producing 12.2 kW of DC power with temperatures in the 50's in early March, it still shows only 48 kWh of clipping on the year.

                    Does this help?
                    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                    Comment


                    • Originally posted by sensij View Post

                      I can see that the TMY3 file for Orlando and the TMY2 file for Tampa have represented "typical" weather in different ways, maybe explaining some of the variance you are seeing. If I tweak the settings so that cold spring days are capable of producing at STC, the Tampa file gives ~33 kWh of clipping over the course of the year with your 2 x 5 kW inverters. Even tweaking to an essentially zero loss system capable of producing 12.2 kW of DC power with temperatures in the 50's in early March, it still shows only 48 kWh of clipping on the year.

                      Does this help?
                      Thanks Sensij , the numbers sound good and give me assurance that 10kW AC and 11.8kW DC is the way to go. However, can you help me understand how you did these calculations.

                      Thanks
                      12.1 kW Canadian Solar 295W ;SMA SB-6.0-1SP-US-40

                      Comment


                      • Originally posted by ButchDeal View Post

                        Well a common mistake for people more familiar with string inverters. With optimized systems you want to have some modules from each azimuth or "zone" so that it can keep for longer during the day.
                        Hi Butch,

                        I will be having two arrays; 10 panels facing south, 8 panels facing east. I assumed that each of these arrays would comprise a string into the SE5000H-US. Are you saying there would be an advantage to splitting them up into strings comprised of 5 south & 4 east panels?

                        When I signed the contract for my install, my installer mentioned that the conduit would be run through the attic for better aesthetics. When I saw the site-plan they submitted to the POCO, I noticed that it only specified one junction box from the roof. When I asked about it, they said that the east-facing array would be connected to the south-facing array via conduit over the top of the roof (across the main ridge, approx 20 feet). That conduit would be bonded to the south-facing array, then from there the conduit would go through the attic. I told them that was unacceptable. Running conduit over the top of the main ridge killed any aesthetics achieved by running the rest of the conduit through the attic. They agreed to run it all through the attic.

                        I don't really understand what is necessary for proper bonding of the two strings. Since I am making them run it all through the attic, will they now be bonded at the inverter? Is the conduit from the east-array still going to join the south-array at the point where the south-array penetrates the roof? I have not asked these questions because I figured it really didn't matter to me. If you are recommending that the strings be made up of 50% from each array, then it might matter. Splitting the arrays in half might greatly complicate their plan for running the conduit, right?

                        If each array is its own string, then the 8 east-facing panels should "light up" earlier in the morning, but then lose effectiveness earlier in the day. The 10 south-facing panels will taking a bit longer to "light-up" in the morning, but then cover more of the day. Is there a way to model splitting/joining the arrays up into different string combinations?

                        Thank you,

                        John

                        Comment


                        • Hard to see how splitting the strings up would make much difference. The strings are tied together in the inverter. The optimizer voltage is based on the number of optimizers in the string, not the direction they face. The optimizer current is based on how much the panel can produce at that voltage, and is otherwise unaffected by the rest of the circuit.

                          Butch's point might have been that you don't need two strings at all. All 18 panels could be on one string.

                          Edit: never mind that last suggestion. Max power per string for the 5000 H is 5700 W, you would be over that, so two strings required.
                          Last edited by sensij; 06-26-2017, 01:53 AM.
                          CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                          Comment


                          • Originally posted by jpoet View Post

                            Hi Butch,

                            I will be having two arrays; 10 panels facing south, 8 panels facing east. I assumed that each of these arrays would comprise a string into the SE5000H-US. Are you saying there would be an advantage to splitting them up into strings comprised of 5 south & 4 east panels?
                            No you have taken the point out of context. The original point was about an installer wanting to use two inverters to handle the multiple faces. My point was about using a single inverter being better than two smaller inverters.
                            In your case it doesn't matter, solaredge will use the light the same either way on the single inverter.
                            OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

                            Comment


                            • Originally posted by ButchDeal View Post

                              No you have taken the point out of context. The original point was about an installer wanting to use two inverters to handle the multiple faces. My point was about using a single inverter being better than two smaller inverters.
                              In your case it doesn't matter, solaredge will use the light the same either way on the single inverter.
                              Ah! Got it. Thanks, Butch,

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