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  • Inverter sizing question

    I thought running an inverter at its max capacity was worse then running it at a lesser load and it would run cooler.

    i just read this and is this correct, that running an inverter at its peak is more efficient ?
    and if the inverter is larger than the array output that it would produce less electricity than the smaller inverter running at peak ?
    Thanks.

    From the website
    "On the other hand, you don't want to install a solar inverter that's too big (i.e. has a lower array-to-inverter ratio) because your inverter is going to be most efficient if it's running close to its overall capacity. If the inverter is too large compared to the array, it will not produce the desired amount of electricity."

  • #2
    I think a lot depends on the inverter. The Solaredge HD Wave inverters are supposedly 99% efficient and can run at a DC to AC ratio of 1.5 to 1.
    I don't know what website you are quoting from?

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    • #3
      Thanks, yes this would be a SolarEdge HD 6k verses the 7.6k if that helps any.

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      • #4
        Originally posted by Jasper7821 View Post
        I thought running an inverter at its max capacity was worse then running it at a lesser load and it would run cooler.

        i just read this and is this correct, that running an inverter at its peak is more efficient ?
        and if the inverter is larger than the array output that it would produce less electricity than the smaller inverter running at peak ?
        Thanks.

        From the website
        "On the other hand, you don't want to install a solar inverter that's too big (i.e. has a lower array-to-inverter ratio) because your inverter is going to be most efficient if it's running close to its overall capacity. If the inverter is too large compared to the array, it will not produce the desired amount of electricity."
        Some inverters are more efficient at their peak. SolarEdge has a very flat curve and is nearly as efficient at half capacity as full. Most are most efficient slightly below peak though.

        There is confusion as some inverter manufacturers in the past. Particularly enphase which makes micro inverters and in the past was incapable (or unwilling) of producing large enough micro inverters to NOT clip with larger PV modules. The produced a lot of documents and training that were very miss leading claiming that the system was more efficient when designed to clip. This was an inverter centric view of things twisted to consider only an inverter with limited capacity. In this limited case the INVERTER (but not the array) would produce more power.
        If you consider the array though, with options of using ANY inverter (not just enphases limited models at the time) then the array is producing less than it could be producing with the clipping.

        Some installers have this model so engrained that they apply this to all things, mistakenly still to this day.
        OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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        • #5
          I have a similar question as I have noticed in my new 14 kW install that the inverter is peaking and it seems like if I had a second inverter, I could produce more? In this case I have a SE11400 and as you can see it is peaking at just about 11.397 kW. Does it make sense to add an SE3000 to obtain the extra electricity being produced by the panels?

          Capture.PNG

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          • #6
            I talked to tech support at SolarEdge (very nice and informative) and they said with the 6.7kw system I'm getting it's fine to use the SE6000H-US but with my situation I'd be better off with the SE7600H-US. They said I'm in the prime location for solar. Sunny Arizona and I have a flat roof and zero shade so the panels can be set to the optimal position without any shade.
            They said during peak times, I'd probably produce close to the rated system.
            Plus, I have a plug-in hybrid and the 7.6 has an available car charger. BUT if I did that, then I have to pay the $500 to install it in the garage. The garage is on the opposite side of the electrical panel so I don't know why they want $500 to install in the garage instead of outside.
            I already have a 240v level 2charger, but I'm always trying to see what my car draws and trying not to run anything else for a few hours while my car goes from empty to full and reading the meter outside. I I had the 7.6 inverter I could tell when exactly the car plus inefficiency is drawing.

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            • #7
              Originally posted by Jasper7821 View Post
              I talked to tech support at SolarEdge (very nice and informative) and they said with the 6.7kw system I'm getting it's fine to use the SE6000H-US but with my situation I'd be better off with the SE7600H-US. They said I'm in the prime location for solar. Sunny Arizona and I have a flat roof and zero shade so the panels can be set to the optimal position without any shade.
              They said during peak times, I'd probably produce close to the rated system.
              Plus, I have a plug-in hybrid and the 7.6 has an available car charger. BUT if I did that, then I have to pay the $500 to install it in the garage. The garage is on the opposite side of the electrical panel so I don't know why they want $500 to install in the garage instead of outside.
              I already have a 240v level 2charger, but I'm always trying to see what my car draws and trying not to run anything else for a few hours while my car goes from empty to full and reading the meter outside. I I had the 7.6 inverter I could tell when exactly the car plus inefficiency is drawing.
              A comment/question or two:

              You have a flat roof, but is it horizontal ? Most roof sections are flat. Some are horizontal, others are not.

              I'd be careful about the interpretation of "close to rated output". First off, rated output of the inverter, or rated output of the array ? Your very nice and informative person at SolarEdge is probably talking the STC rated output of the array, but that's unclear as you've written it.

              If it is STC output that's being referenced, unless the array is tilted at some angle to the horizontal, the best output of the array is probably not going to be 6.7kW, and even if it is, you'll most likely only see that for short periods of a few minutes or so a few times/yr.

              A slightly separate but shading related issue, in a prior post, you mentioned changing tilt from 15 to 20 degrees. What is the planned array orientation, tilt and azimuth at this time ? If it's a tilted array on a horizontal roof, know that you will need some separation between rows of panels to avoid shading of some panels by the panels closer to the equator.

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              • #8
                Originally posted by liquix View Post
                I have a similar question as I have noticed in my new 14 kW install that the inverter is peaking and it seems like if I had a second inverter, I could produce more? In this case I have a SE11400 and as you can see it is peaking at just about 11.397 kW. Does it make sense to add an SE3000 to obtain the extra electricity being produced by the panels?

                Capture.PNG
                Your graph does not show any clipping and shows a nice neat parabola as it should.
                OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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                • #9
                  Thank you!

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                  • #10
                    Thanks, yes it was the array the tech was talking about that should produce close to rated due to my conditions. The roof part that the solar would go onto is tilted a few degrees to the west for rain runoff.
                    and the company I am buying the solar from that I calculated and it came out better at 20 degrees rather than the 15 degrees they have the install for. They said exactly what you're saying and at 20 degrees tilt they're may be a bit of shading and at 15 degrees there was not. And it was 182 degrees they were installing the two rows at.
                    Last edited by Jasper7821; 04-16-2019, 08:09 AM.

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