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  • Enphase microinverter efficiency

    Hi. When looking at the enphase iq6+ specs, I note that the inverter is designed to support panels up to 400W (I am thinking about using 360W panels). However, when I look at the spec sheet, the maximum output listed is 280VA, which is their 1.17A * 240VAC. If the panel is putting out 360 Watts at peak, why would the inverter not be able to support 360 watts of production? This is less than the 97% efficiency listed in the spec.

    thx
    mike

  • #2
    Originally posted by fresnoboy View Post
    Hi. When looking at the enphase iq6+ specs, I note that the inverter is designed to support panels up to 400W (I am thinking about using 360W panels). However, when I look at the spec sheet, the maximum output listed is 280VA, which is their 1.17A * 240VAC. If the panel is putting out 360 Watts at peak, why would the inverter not be able to support 360 watts of production? This is less than the 97% efficiency listed in the spec.

    thx
    mike
    good question I guess it depends how you define 'efficiency'. Apparently Enphase defines it as ratio between output power it produces and input power it utilizes: the fact you panel is capable of 360W doesn't matter as it is only capable of utilizing 280/0.97 = 288W of solar energy, the rest of it won't be converted. Basically if your panel is capable of producing 10A @ 36V only 8A will be used.

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    • #3
      The Inverter does not know and does not care that your Solar Panel can potentially generate more than 280 Watts.
      The Enphase Inverter will consume whatever Watts it needs to produce 280 Watts Output or run at the MPPT, whichever is LESS.
      But with a 400 Watt Panel connected, vs a 360 Watt Panel, you will get more Watts Output in the morning and evening = more Total Watt-Hours per day.
      The 400 Watt Panel will ...
      a) Ramp the Enphase up to max 280 Watts output faster in the morning
      b) Hold the Enphase at max 280 Watts output during the afternoon ( cloudy )
      c) Keep the Enphase at max 280 Watts output longer in the evening
      d) On hot days, keep the Enphase at max 280 Watt output longer

      So, a 400 Watt PV Panel is an advantage over a 360 Watt Panel.
      Last edited by NEOH; 09-15-2017, 12:23 PM.

      Comment


      • #4
        Originally posted by NEOH View Post
        The Inverter does not know and does not care that your Solar Panel can potentially generate more than 360 Watts.
        The Enphase Inverter will consume whatever Watts it needs to produce 360 Watts Output or run at the MPPT, whichever is LESS.
        But with a 400 Watt Panel connected, vs a 360 Watt Panel, you will get more Watts Output in the morning and evening = more Total Watt-Hours per day.
        The 400 Watt Panel will ...
        a) Ramp the Enphase up to max 360 Watts output faster in the morning
        b) Hold the Enphase at max 360 Watts output during the afternoon
        c) Keep the Enphase at max 360 Watts output longer in the evening
        d) On hot days, keep the Enphase maxed at 360 Watt output longer

        So, a 400 Watt PV Panel is an advantage over a 360 Watt Panel.
        Yea, so get the 400 Watt panel and have a system with built in clipping. For the example given, probably not a problem, but needs a bit eval. to est. what the clipped output may be worth.
        Last edited by J.P.M.; 09-15-2017, 12:11 PM.

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        • #5
          Originally posted by NEOH View Post
          The Inverter does not know and does not care that your Solar Panel can potentially generate more than 360 Watts.
          The Enphase Inverter will consume whatever Watts it needs to produce 360 Watts Output or run at the MPPT, whichever is LESS.
          But with a 400 Watt Panel connected, vs a 360 Watt Panel, you will get more Watts Output in the morning and evening = more Total Watt-Hours per day.
          The 400 Watt Panel will ...
          a) Ramp the Enphase up to max 280 Watts output faster in the morning
          b) Hold the Enphase at max 280 Watts output during the afternoon
          c) Keep the Enphase at max 280 Watts output longer in the evening
          d) On hot days, keep the Enphase maxed at 280 Watt output longer

          So, a 400 Watt PV Panel is an advantage over a 360 Watt Panel.
          Sorry, I don't understand. You are saying it's only going to produce 280 watts out no matter what, even if the panel can produce more power than that? This seems like a broken definition of efficiency as well.

          I am still confused as to why they say to use the iq6+ if I had a panel that went up to 400W. Why don't they make an inverter that doesn't clip?

          So if I really wanted the maximum harvest of energy if I was using 360W panels (because I had limited roof area), it sounds like I shouldn't go with an Enphase product, or am I missing something?

          Thx
          mike


          Comment


          • #6
            Originally posted by NEOH View Post
            The Inverter does not know and does not care that your Solar Panel can potentially generate more than 360 Watts.
            The Enphase Inverter will consume whatever Watts it needs to produce 360 Watts Output or run at the MPPT, whichever is LESS.
            But with a 400 Watt Panel connected, vs a 360 Watt Panel, you will get more Watts Output in the morning and evening = more Total Watt-Hours per day.
            The 400 Watt Panel will ...
            a) Ramp the Enphase up to max 360 Watts output faster in the morning
            b) Hold the Enphase at max 360 Watts output during the afternoon
            c) Keep the Enphase at max 360 Watts output longer in the evening
            d) On hot days, keep the Enphase maxed at 360 Watt output longer

            So, a 400 Watt PV Panel is an advantage over a 360 Watt Panel.
            the max output for the inverter is 280W, not 360W. Clipping 360W panel at 288W would look like this: Production_3.png



            it wil loose 'chunk' of energy on top of the curve compare to unclipping inverters but it would 'gain' chunk on the sides compare to the smaller matching panels. I guess the clipping variant is more desirable since panels are relatively cheap and the system would age better. If the goal is to harvest all energy panels can possibly produce then unclipping solution is the correct one. If the clipping one produces enough energy and extra cost for the panels is acceptable it could be preferable as it would produce more consistent output through the lifetime of the system.
            Last edited by max2k; 09-15-2017, 12:36 PM.

            Comment


            • #7
              Originally posted by max2k View Post

              the max output for the inverter is 280W, not 360W. Clipping 360W panel at 288W would look like this: Production_3.png



              it wil loose 'chunk' of energy on top of the curve compare to unclipping inverters but it would 'gain' chunk on the sides compare to the smaller matching panels. I guess the clipping variant is more desirable since panels are relatively cheap and the system would age better. If the goal is to harvest all energy panels can possibly produce then unclipping solution is the correct one. If the clipping one produces enough energy and extra cost for the panels is acceptable it could be preferable as it would produce more consistent output through the lifetime of the system.
              I'd suggest a design goal of meeting the required/defined duty in the safest, most practical and cost effective way possible. That usually means compromises along the way in most areas except safety. Life cycle values of costs for all scenarios need to be balanced against NPV's of production under the same scenarios to maximize estimates of ROI.

              Comment


              • #8
                Originally posted by max2k View Post

                good question I guess it depends how you define 'efficiency'. Apparently Enphase defines it as ratio between output power it produces and input power it utilizes: the fact you panel is capable of 360W doesn't matter as it is only capable of utilizing 280/0.97 = 288W of solar energy, the rest of it won't be converted. Basically if your panel is capable of producing 10A @ 36V only 8A will be used.
                This is not exactly how Enphase defines it. They are reporting the "CEC Weighted Efficiency". More about how that is determined can be found here. Some relevant text from that link:

                Inverter efficiency is the ratio of the usable AC output power to the sum of the DC input power and any AC input power. Typical grid-tied inverter efficiencies exceed 95% under most operating conditions. Efficiency changes as a function of AC output power, DC voltage, and sometimes inverter temperature. Sandia National Laboratories and BEW have worked together to develop a test protocol to measure inverter efficiency as a function of AC output power and DC voltage. This protocol has been adopted by the California Energy Commission (CEC) and any inverter used in a CEC approved PV system must be tested by an independent lab to this protocol.
                "Capacity Factor" is the figure of merit that more directly communicates the expected output of the system relative to its nameplate rating, but it is generally evaluated on a system level, not by component.
                Last edited by sensij; 09-15-2017, 12:58 PM.
                CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                Comment


                • #9
                  Originally posted by J.P.M. View Post

                  I'd suggest a design goal of meeting the required/defined duty in the safest, most practical and cost effective way possible. That usually means compromises along the way in most areas except safety. Life cycle values of costs for all scenarios need to be balanced against NPV's of production under the same scenarios to maximize estimates of ROI.
                  I am not arguing against that - it's just we are building a larger home, and while it's efficient, it will use a fair amount of energy (I have a rack of computer servers to power 24x7), and out here in PG&E land, where higher use bands are north of 36 cents/kwh, squeezing out more energy from a limited roof surface can really pay off.

                  As I related in another thread, I am also a ham radio operator, so am sensitive to RF interference. The Solaredge equipment, which would normally be the goto solution for my situation (according to my installer) is not viable, as they seem to be the absolute worst in terms of RF interference generation, and routinely cause harmful interference from their optimizers despite Part 15 limitations.

                  Hence my look at microinverters and the efficiency question. I don't have that much usable roof area in the proper orientation, so am trying to push total power generation as high as I can within reason, as the numbers indicate it would pay off.

                  thx
                  mike



                  Comment


                  • #10
                    Originally posted by max2k View Post

                    the max output for the inverter is 280W, not 360W. Clipping 360W panel at 288W would look like this: Production_3.png










                    it wil loose 'chunk' of energy on top of the curve compare to unclipping inverters but it would 'gain' chunk on the sides compare to the smaller matching panels. I guess the clipping variant is more desirable since panels are relatively cheap and the system would age better. If the goal is to harvest all energy panels can possibly produce then unclipping solution is the correct one. If the clipping one produces enough energy and extra cost for the panels is acceptable it could be preferable as it would produce more consistent output through the lifetime of the system.
                    Yes, I did edit my post to 280 Watts, but you had already "quoted".
                    It is fixed now.

                    The energy above the Horizontal Line is just not available via through Enphase iq6+, ever.
                    The extra energy ( in light blue on each side ) is available by using a 360 Watt PV Panel.
                    And even more is available with a 400 Watt PV Panel.
                    And more power is available during darker clouds, fog or rainy days,too.

                    Look at the Dark Blue curve ( 280 Watt PV ) - it just touches Max Power 280 Watts at Solar Noon.
                    Look at the flat top ( 360 Watt PV ) - it holds Max Power 280 Watts for 5 full hours !
                    And a 400 Watt PV could be 6 Full hours !

                    I wish my inverter was at MAX POWER for 6 Full Hours.
                    Mine is more like the Dark Blue Curve

                    I have many more days that are either ...
                    a) too hot
                    b) too dark ( clouds )
                    c) too rainy
                    d) too snowy
                    Where my "dark blue peak" does not get anywhere near Max Power at Solar Noon
                    and I could fully use all of the energy produced by a 360 Watt or 400 Watt PV panel - ie no clipping!
                    Your graph is showing the "Best Day", not the "Worst Day".
                    Show the graph where the 400 Watt PV is only outputting 280 Watts due weather, now 100% energy is harvested ( +40% MORE KWHr ?)
                    Now the 280 Watt PV curve is in the dirt.

                    In the real world, there is a lot less clipping than you show unless you live in Arizona.
                    Last edited by NEOH; 09-15-2017, 01:22 PM.

                    Comment


                    • #11
                      Originally posted by J.P.M. View Post

                      I'd suggest a design goal of meeting the required/defined duty in the safest, most practical and cost effective way possible. That usually means compromises along the way in most areas except safety. Life cycle values of costs for all scenarios need to be balanced against NPV's of production under the same scenarios to maximize estimates of ROI.
                      I have a feeling cost efficiency/ROI would be best if it is not clipping- for grid tied system it would produce max power with given panels. Not clipping would mean no panel cost was wasted due to clipping but it would require bigger and more expensive inverters. Now if we take TOU games utilities play it might change things a bit as clipping system would produce more power in the afternoon. Would extra inverters cost and TOU rates balance out extra cost for panels may be hard to tell.

                      Comment


                      • #12
                        Originally posted by max2k View Post

                        I have a feeling cost efficiency/ROI would be best if it is not clipping- for grid tied system it would produce max power with given panels. Not clipping would mean no panel cost was wasted due to clipping but it would require bigger and more expensive inverters. Now if we take TOU games utilities play it might change things a bit as clipping system would produce more power in the afternoon. Would extra inverters cost and TOU rates balance out extra cost for panels may be hard to tell.
                        Especially when you run up against limits of what a service panel can take (100 A panel = 3800 W inverter, 200 A panel = 7600 W inverter), accepting some amount of clipping can definitely be more cost effective than pursuing upgrades to the service (or line side installation options). Historically, within the Enphase product line, we've also seen in some specific cases that going with the M250 could be less cost effective than the M215, even if the M215 introduces some clipping, although a lot of that is sensitive to the price that a given installer can get any particular model.
                        CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                        Comment


                        • #13
                          I will probably regret this but...

                          The illustration does well to show what you mean for the quicker "saturation" (for lack of the proper or better term). But, how is leaving ~3600kwh of the clipped part on the table an advantage? Why not use micro-inverters rated to the panel output?

                          I guess I missed something.

                          Comment


                          • #14
                            Does Enphase make an iq6+ micro-inverter that can output 400 Watts AC power?

                            And that lost energy only occurs on the VERY BEST ( SUNNY + COOL ) DAYS, which I have very few of.
                            All winter there would be no clipping, no lost lost energy.

                            I agree with you, if you live in Arizona. (retracted, see below)

                            EDIT:
                            Because of the "de-rating" from excessive heat, I think the PV Panels in Arizona should be "over-rated", too.
                            Last edited by NEOH; 09-15-2017, 02:13 PM.

                            Comment


                            • #15
                              Originally posted by sensij View Post

                              Especially when you run up against limits of what a service panel can take (100 A panel = 3800 W inverter, 200 A panel = 7600 W inverter), accepting some amount of clipping can definitely be more cost effective than pursuing upgrades to the service (or line side installation options). Historically, within the Enphase product line, we've also seen in some specific cases that going with the M250 could be less cost effective than the M215, even if the M215 introduces some clipping, although a lot of that is sensitive to the price that a given installer can get any particular model.
                              I get all that. This is a big house as I mentioned before. 400A service is what is being put in.

                              thx
                              mike

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