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  • Watt Hour / Output

    Recently added solar. The system was described to me as a 14.88 KW PV system. The system is composed of 48 Silfab SLA310M and 48 Enphase Energy micro inverters (model number iQ6)
    At peak production during the day, the system seems to clamp/max out at generating 11600 watts/hour. Maybe I do not understand something here, as I was thinking i should be betting close to 14800 watts per hour at peak.

    310w per panel x 48 = 14880

    Any insights would be great.
    Thanks

  • #2
    Originally posted by fatcat View Post
    Recently added solar. The system was described to me as a 14.88 KW PV system. The system is composed of 48 Silfab SLA310M and 48 Enphase Energy micro inverters (model number iQ6)
    At peak production during the day, the system seems to clamp/max out at generating 11600 watts/hour. Maybe I do not understand something here, as I was thinking i should be betting close to 14800 watts per hour at peak.

    310w per panel x 48 = 14880

    Any insights would be great.
    Thanks
    Well you are rarely going to hit 14.88kW production as that is STC (Standard Test Condition) but you system is using iQ6 enphase micros which are 230w each or 11kW total production.
    This is called clipping. This is a bit more than I would design an array for. I would have use the iQ6+ which is 280w each or 13.44kw total. (well I personally would have done this with SolarEdge and less clipping that way).

    But you might have other reasons that they did this like shadows or azimuth of the array etc.

    https://enphase.com/sites/default/fi...s_DS_EN-US.pdf
    OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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    • #3
      Maybe somebody used the NOCT rating to size the micros. Not endorsing micro use, but for what seems to be a small price increase, the IQ6+ might well have been a better choice.

      Perhaps another example of consumer not being as informed as possible.

      Comment


      • #4
        Additional info:
        side of houseAzimuth: 6
        Attached Files

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        • #5
          Attached on the thead is the enphase customer facing web reporting tool . At max production, it looks to be generating 2888 what hours every 15 minutes. Definitely seems to be under performing.

          Comment


          • #6
            Might help if you understand the difference between Watts and Watt Hours.

            Watts: is heat power being generated at any give moment.

            Watt Hours = Watts x Hours: Energy used or generated over a period of times. Example a 100 watt light bulb consumes 1000 watt hours in 10 hours. 100 watts x 10 hours = 1000 watt hours.

            As Butch said your system is rated rated 14.88 KW but you will never see that amount of power ever. All it means is if you have a 3 Sun Hour Day your system will generate roughly 14.88 Kw x 3 Hours = 44.6 Kwh. However with Clipping, you will not even see that.
            MSEE, PE

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            • #7
              I'm an residential enduser so I was a bit naive here. Thank you for your explanations.

              To summarize my situation:
              The 14.88 KW system is being clipped by the iQ6 micro inverters. While the panels can produce a theoretical 310w, the system can only process/induct 230w per panel.
              At peak, system produces 2888 watts per 15 minute interval ( 11.5 KW for that hour). That means that i'm running at about 77% of what the theoretical STC output would be. Ugh.

              Comment


              • #8
                Maybe somebody used the NOCT rating to size the micros. Not endorsing micro use, but for what seems to be a small price increase, the IQ6+ might well have been a better choice.

                Perhaps another example of consumer not being as informed as possible.

                Comment


                • #9
                  Originally posted by Sunking View Post
                  Might help if you understand the difference between Watts and Watt Hours.

                  Watts: is heat power being generated at any give moment.

                  Watt Hours = Watts x Hours: Energy used or generated over a period of times. Example a 100 watt light bulb consumes 1000 watt hours in 10 hours. 100 watts x 10 hours = 1000 watt hours.

                  As Butch said your system is rated rated 14.88 KW but you will never see that amount of power ever. All it means is if you have a 3 Sun Hour Day your system will generate roughly 14.88 Kw x 3 Hours = 44.6 Kwh. However with Clipping, you will not even see that.
                  As it turns out, if there are 3 kWh/m^2 per day insolation at a location as it is usually defined, or what anachronistically and confusingly is called 3 sun-hours per day, depending on things like array orientation, time of year, panel temps. and probably some other things, the array output for such a day may be more or less than the 44.6 kWh.

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                  • #10
                    Originally posted by J.P.M. View Post

                    As it turns out, if there are 3 kWh/m^2 per day insolation at a location as it is usually defined, or what anachronistically and confusingly is called 3 sun-hours per day, depending on things like array orientation, time of year, panel temps. and probably some other things, the array output for such a day may be more or less than the 44.6 kWh.
                    I did say roughly right?
                    MSEE, PE

                    Comment


                    • #11
                      Originally posted by fatcat View Post
                      At peak, system produces 2888 watts per 15 minute interval ( 11.5 KW for that hour). That means that i'm running at about 77% of what the theoretical STC output would be. Ugh.
                      No Sir it generated 2888 watts hours (2.888 Kwh) in 15 minutes (.25 hours). To do that the panels had to generate 11.55 Kw on average for 15 minutes.

                      11.552 Kw x .25 hours = 2.888 Kwh.

                      Output power from the panels is Dynamic meaning the power varies from 1 second to the next. As a general analyses in the morning when when the sun hits the panels, the power will be very low say 5% of rated power. As the sun gets higher in the sky as solar noon approaches the power will climb. For a few brief minutes around Solar Noon, power will peak. Peak will never be the rated power, more like 80 to 85% or rated power. Even less with clipping. Then after Solar Noon power decreases with the sitting sun.

                      The specs are for design purposes to achieve a average year round generations. Example if your goal is to generate 10 Kwh of usable energy per day. The designer will look at solar tables to determine your daily average Sun Hours to determine Panel Wattage. He sees your yearly day average is 4 Sun Hours. That tells him he needs 2500 watt system. 10 Kwh / 4 h = 2500 watts. Do not confuse Sun Hours with the hours of daylight. You will never see a 2500 watt system generate 2500 watts. In summer months you will see daily generation in excess of 10 Kwh and less in winter months.
                      Last edited by Sunking; 05-14-2018, 03:29 PM.
                      MSEE, PE

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                      • #12
                        Thank you for the clarification.. incidentally, 11552/48 is approx 240w, which i believe is the max output of the iQ6

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                        • #13
                          Originally posted by fatcat View Post
                          Thank you for the clarification.. incidentally, 11552/48 is approx 240w, which i believe is the max output of the iQ6
                          OK make sense to you now?

                          MSEE, PE

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                          • #14
                            Yes, i believe so. Thank you

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                            • #15
                              Attached today's output for reference. (There's little or no shade on my roof.)
                              Attached Files

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