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Expected Power generation on a clear sunny day

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  • Expected Power generation on a clear sunny day

    System efficiency can be affected by a number of things, but on a clear sunny day how many watts / power can be expected from 18 290w SW Mono on a 5.2k array and Sunny Boy 5.0 inverter? This is a newly installed system with 'Current Power' peaking at around 3200watts at 12 o'clock/mid day.

  • #2
    Originally posted by ReadyTempCircPump View Post
    System efficiency can be affected by a number of things, but on a clear sunny day how many watts / power can be expected from 18 290w SW Mono on a 5.2k array and Sunny Boy 5.0 inverter? This is a newly installed system with 'Current Power' peaking at around 3200watts at 12 o'clock/mid day.
    There are a LOT of variables. What temperature is it? Are the panels at a fixed angle, and what angle of incidence is the sun making? Are the panels clean? Are there any clouds in the sky? (in some cases clouds will INCREASE power) Snow on the ground? What altitude are you at?

    Let's take best case. On a day that is around 0C in full sun you would likely reach 20-25C in the panels. If you are at a relatively high altitude, and the sun is directly incident on the panels (usually only happens once a day) and it has rained recently (clean panels) you might get STC rated power, which for you is 5220 watts. Out of the inverter you'd see about 5000 watts.

    Hotter? Panels not at a perfect angle? Near sea level? Haze? Dust on the panels? You'll see a lower output. 3200 watts is less than I'd expect (I'd expect an average of about 4000 watts at noon) but not that out of range.

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    • #3
      Read out the peak DC voltage and current at the inverter. If voltage is low, there may be a panel running in bypass mode. If
      you have in parallel 2 series strings, check that they are delivering the same current. A clamp on DC ammeter is great for this.
      Bruce Roe

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      • #4
        Originally posted by ReadyTempCircPump View Post
        System efficiency can be affected by a number of things, but on a clear sunny day how many watts / power can be expected from 18 290w SW Mono on a 5.2k array and Sunny Boy 5.0 inverter? This is a newly installed system with 'Current Power' peaking at around 3200watts at 12 o'clock/mid day.
        My system (5.1KW nameplate) does around 4500 summer, 3500 winter. So, shooting from the hip, I'd say you will get 4100 next summer.
        Dennis
        SE5000 18 each SW185

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        • #5
          Temperature makes a big difference. My panels put out over rated output on bright but cold winter days (-10 to 20F). They don't do nearly as well on a a bright sunny hot day in the summer. Panel angle also needs to factor in. If the panels are fixed and its bright sunny day but the angle is not perpendicular to the panels you will not max out. Insolation due to the surroundings also makes a difference, with some snow on the ground, the sun reflects off the snow and puts more sunlight into the panel than STC conditions.

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          • #6
            Download PVWatts, read the help/info screens, use 10 % system loss parameter rather than the 14 % default, get the get the azimuth & tilt correct, use the hourly output option and look for a clear day's output near the current date, you'll get close. Latitude, orientation and time of year are biggest influences, with ambient and panel temp. also having a role.

            Your results will vary.

            FWIW: My zip = 92026, array size, 5.232 kW, orientation : AZ. 195 deg., tilt, 18.75 deg.. Last max. output measured 11/29/2016 = 3,791 W @ 1156 hrs. P.S.P. Ambient temp = 15.0 C, Ave. array temp., 43.4 C, Plane of array irradiance = 800 W/m^2. Daylong output = 23.47 kWh w/ ~ 5 % loss off that total due to late afternoon shading. The day was cloudless at my location.

            Semper Fi.
            Last edited by J.P.M.; 12-01-2016, 03:41 PM. Reason: corrected transposition error on inst. output to 3,791 W, and P.O.A. irrad. to 800 W/m^2. Confirming other numbers. Apologies for errors.

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            • #7
              Originally posted by dennis461 View Post

              My system (5.1KW nameplate) does around 4500 summer, 3500 winter. So, shooting from the hip, I'd say you will get 4100 next summer.
              I would be pretty unhappy seeing my string inverter system peaking at 2/3 capacity. Optimizing for winter and adding some panels
              can get it up to system capacity. Probably this less than optimum summer arrangement would hit max anyway. Bruce Roe

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              • #8
                Originally posted by bcroe View Post

                I would be pretty unhappy seeing my string inverter system peaking at 2/3 capacity. Optimizing for winter and adding some panels
                can get it up to system capacity. Probably this less than optimum summer arrangement would hit max anyway. Bruce Roe
                Seeing as how it's close to winter solstice, depending on orientation and shading, that 3,200 Watts might be about as much as can be expected this time of year.

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                • #9
                  Originally posted by bcroe View Post

                  I would be pretty unhappy seeing my string inverter system peaking at 2/3 capacity. Optimizing for winter and adding some panels
                  can get it up to system capacity. Probably this less than optimum summer arrangement would hit max anyway. Bruce Roe
                  Adding panels does not necessarily increase efficiency. It does raise max. rated capacity of input to inverter.
                  Panel ratings (by manufacturer ) are IMHO based on laboratory conditions.
                  My panels are roof mounted, so orientation and tilt accounts for most of my loss, neighbors tree two houses down, a little more.
                  The KWH I am getting is matching my calculations done prior to installation.

                  Hopefully the original poster used something like this, http://pvwatts.nrel.gov/.

                  Camden County, NJ, USA
                  18 SW285 panels
                  SE5000 inverter
                  grid tied
                  Dennis
                  SE5000 18 each SW185

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                  • #10
                    A lot will depend on your latitude, time of year, temperature ect.
                    ​Here in N. GA I have 5100 watts in SW panels and I logged 15.6 kwhs yesterday. I've see well over 22 kwhs during the summer. It would be more on some summer days but I don't sell back to the grid.

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                    • #11
                      here on long island new York, my son has 17 327 SP panels along with solaredge equipment... on the best days in mar/april which seem to produce the best days, he has topped out at a tad over 40... for contrast , so far in dec we have produced 16,17,and 16 for the 1st 3days.. not totally clear days, but mostly sunny... at the end of nov we had some clear days n it was up to 22/23...
                      Last edited by paris401; 12-09-2016, 10:37 AM.

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                      • #12
                        Back to the OP: Suggest you reread my 12/01/2016, 0827 hrs. post. I bet you're OK on performance, just that no one told you that output would seldom if ever meet STC rating, or that output is continuously variable and lower in the winter.

                        Semper Fi.

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