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  • Solar output

    Hi everyone
    I just got my system up and running.
    2 fronius 7.6 inverters on three phase delta 240. Have 50 355w panels 25 to each inverter.
    13 on mppt1 and 12 on mppt2 each inverter.
    My question is that with full sun I will not max out till early afternoon. However if I have clouds I will peak as soon as the clouds have move over even in the late mornings. Is this normal?

  • #2
    Originally posted by wardneal View Post
    with full sun I will not max out till early afternoon. However if I have clouds I will peak as soon as the clouds have move over even in the late mornings. Is this normal?
    should be a short peak. It is could edge effect, it is a combination of lensing and the array getting cool while the cloud was shading it, then dumping full power on the the cool array.
    It is normal.
    OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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    • #3
      Here's an example of a cloudy day followed by a full sun day for me. You can see that I'm peaking out at almost 7KW on the overcast day and only 6.7KW on the Sunny day. I actually produced 0.85kWh more on the cloudy day and the peak was about 45min earlier than typical. As Butch mentioned, this is because the panels cool down a good bit when clouds pass over and lensing, and then produce better for a short while after the sun comes back out since they're at a lower temperature and the atmospheric lens effect.
      Attached Files

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      • #4
        Thanks for the information. I just got both MPPT1 and MPPT2 turned on and got the fronius string power management turned on, Going to see if it is any better than just having it the way that it was set up with just the MPPT1 on and no power management.

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        • #5
          Hey all. Just joined this forum. I have a 12.1KW system on my home. It will be one year in operation next month. Over this time period the highest output I've seen is 11KW/H. And that was a perfect cool sunny day. Most days I'll get 9-10KW/H with a total output of 60KW. I understand that the system itself uses power and loses power thru the lines. Does this seem normal to ya'll? BTW, I'm a newbie to solar. Thanks.

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          • #6
            Originally posted by BertHamm View Post
            Hey all. Just joined this forum. I have a 12.1KW system on my home. It will be one year in operation next month. Over this time period the highest output I've seen is 11KW/H. And that was a perfect cool sunny day. Most days I'll get 9-10KW/H with a total output of 60KW. I understand that the system itself uses power and loses power thru the lines. Does this seem normal to ya'll? BTW, I'm a newbie to solar. Thanks.
            what is KW/H ?

            I think you are looking at instant output of 11kW and 9-10kW

            over time it produces kWh but not kW/h (you get kWh by multiplying time and kW not by dividing).

            Your total output would be 60kWh (not KW).

            Yes it is normal
            your system is 12.1kW at STC - Standard Test Conditions.

            Your roof is NOT STC. The hotter the modules get (and they get hot from exposure to the sun) the lower their efficiency. That is why you are seeing your best production on a cool sunny day. You may get up higher on a cold windy day (wind helps cool the PV modules), but your generally going to see less than STC. How much less depends on conditions and the PV modules.
            OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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            • #7
              Originally posted by BertHamm View Post
              Hey all. Just joined this forum. I have a 12.1KW system on my home. It will be one year in operation next month. Over this time period the highest output I've seen is 11KW/H. And that was a perfect cool sunny day. Most days I'll get 9-10KW/H with a total output of 60KW. I understand that the system itself uses power and loses power thru the lines. Does this seem normal to ya'll? BTW, I'm a newbie to solar. Thanks.
              It is unlikely you will get 12.1 kW instantaneous output or perhaps slightly more from a 12.1 kW system except occasionally and then only for brief amounts of time such as a minute or two maximum.

              Reasons:

              1.)The actual instantaneous input to your system will rarely be as much as with the 1kW/m^2 input that's used to test/rate panels for their STC rating. Sometimes, reflections from 1 or several clouds on a partly cloudy day will momentarily enhance the actual input to an array, but that will be temporary. Hard to say with much precision, but bright sun plane of array irradiance on a panel might be variously something like ~ 800 - 1,000 W/m^2, or almost always less than the STC irradiance. That lower input will decrease system output somewhat proportionally.

              2.) Panel output is measured and panels are rated when the panel temp. is held at 25 deg. C. But, during actual operation and under bright sun (but usually not as bright as STC irradiance of 1 kW/m^2), a panel, being a dark object sitting in the sun will be ~ 25 C - 30 C or so above the ambient air temp., as conditions might and will vary with wind and irradiance as Butch notes.

              So, for example, if the ambient temp. is 10 C, a panel's temp. might be 35 C to 40 C or so. Now, as a panel's temp. increases, it's efficiency and thus it's output drops something like ~ 0.5% or a bit less per degree C of temp. increase.

              There are other things in play, but those are two of the big ones. FWIW, your array sounds like it's operating normally.
              Last edited by J.P.M.; 07-02-2018, 12:04 PM. Reason: Spelling.

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              • #8
                Yeah it seems mostly normal to me. On a 105F vs 90F day (15F delta or 8.33C delta) I get about 2.5% lower output (comparing multiple days of each within a week or two of each other) that's just under 0.3% drop per deg C, which is what my panels are rated at.

                As for what your daily output (which would be time of year dependent) should be. If that 60kWh was summer time, that would seem a bit small to me for a 12kW system, but that's going to be dependent upon where you're at, what azimuth, pitch, any shading, ... it may be just what's expected. Have you checked PVWatts to get what you should expect (if you do you probably want to cut the loss factor down to at least 10% from the default 14%.) Do they seem to line up with what your annual production is? Month productions?

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