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  • #16
    Snifferpro,
    Here's a quick graphic with a high-low daily temperature overlay provided by my POCO. This is a 12-month graph of my system in Phoenix with a simple string inverter, 26 panels facing south on a tile roof with no shading. Plenty of clear skies all year and heat of course. My best production is March, April and part of May when we have cool nights, good breezes and temps stay reasonable. By mid-May, output is falling when night time temps remain high and sunshine cooks the panels all day. Fall is not quite as good as spring but it does recover some from the summer output drop.




    Usage SRP Power - Google Chrome 8122020 73710 AM.jpg
    Dave W. Gilbert AZ
    6.63kW grid-tie owner

    Comment


    • #17
      1) If STC means standard test conditions, this is what's on the data sheet for my Sunpower X22-360 panels :

      1000 W/m² irradiance, AM 1.5, 25°C). NREL calibration standard: SOMS current, LACCS FF and voltage. All DC voltage is fully contained within the module.

      2) The panel configuration is:
      10 Panels, 115 Azimuth, 18 Degree Pitch
      9 Panels, 295 Azimuth, 15 Degree Pitch
      4 Panels, 205 Azimuth, 37 Degree Pitch

      3) I will start using PVWatts and collect data.

      4) My 10% estimate was simple temperature difference calculation. Sounds like I got lucky. But I plan to track the output into the fall when things cool off. October will be the first month I can do a YTD comparison . (October 2019 was when I went online) Of course I'll have to account to any extreme temperature differences between 2019 and 2020.

      I wish I could wash the panels, but most are too high up. If I ever get per panel output data I could compare the 2 lowest panels, washing one and leaving the other unwashed.

      5) We are 20 miles NW of Boston, zip 01742 .

      Thanks for the guidance.

      Comment


      • #18
        Originally posted by jmand73 View Post
        1) If STC means standard test conditions, this is what's on the data sheet for my Sunpower X22-360 panels :

        1000 W/m² irradiance, AM 1.5, 25°C). NREL calibration standard: SOMS current, LACCS FF and voltage. All DC voltage is fully contained within the module.

        2) The panel configuration is:
        10 Panels, 115 Azimuth, 18 Degree Pitch
        9 Panels, 295 Azimuth, 15 Degree Pitch
        4 Panels, 205 Azimuth, 37 Degree Pitch

        3) I will start using PVWatts and collect data.

        4) My 10% estimate was simple temperature difference calculation. Sounds like I got lucky. But I plan to track the output into the fall when things cool off. October will be the first month I can do a YTD comparison . (October 2019 was when I went online) Of course I'll have to account to any extreme temperature differences between 2019 and 2020.

        I wish I could wash the panels, but most are too high up. If I ever get per panel output data I could compare the 2 lowest panels, washing one and leaving the other unwashed.

        5) We are 20 miles NW of Boston, zip 01742 .

        Thanks for the guidance.
        Rather than us continuing to hijack Snifferpro's thread, I'd respectfully request one of the mods to transfer this post to its own new thread and we continue the conversation there.

        Mods?

        Comment


        • #19
          jmand73, if you'd like to continue this in another thread, go ahead and create one and see if you can copy and paste your relevant posts to it. The forum sometimes has trouble with copy/paste, so if you can't do that, I or one of the other mods can move the message(s) for you.

          Comment


          • #20
            Originally posted by jmand73 View Post
            I tried the 'sunpower...partner.aspx#' site, but could not get past the adobe flash player required message. I did install the latest flash, but it did not help.

            Heres where I'm at... We have ten panels on the ridge line of a gambrell that face 110 degrees, and ten on the other side that face 290 degrees, and 4 that face 200 degrees. Our peak production is between 11 and 2, as all panels are in sunlight, and there are no trees or other obstructions. I downloaded peak power data at 5 minute intervals for dates in April, May, June July and August on days when there were minimal clouds. (I can tell by looking for minimal change in power output between adjacent 5 minute intervals. ) What I see is that the peak power is in APril and May. It starts to drop a bit in June, and more so in July and August. I need to spend some more time analyzing the data.

            I suppose the difference is possibly attributed to temperature. July and August have been very hot, and formula I found says multiply the temperature coeffiecent , .29%/Degree F, by the difference between 68 and ambient temperature, and add 30 for the roof. So if its 98, the panel output is derated by about 10%. Also, in June the panels were covered with yellow pollen, but that is since gone, and the panels seem clean. I can't really wash them as JPM suggested, but given that the pollen did not decrease the output too much, I don't think the flim on them is a big problem.

            Bottom line is if I factor in the first year burn in reduction, the system may be operating within spec. But not having someone watching the output for trouble is disconcerting. Is this standard practice in the industry?
            I live in the San Diego Area (Southern California). My highest daily production on my less than one year old 4.8 KW system (12 panels) was 33.1 Kwh on April 15, 2020. My highest in May was 31.9 on May 4, 2020. And then one of my MI failed in June and SunPower was able to fix it remotely, but since then, my daily maximum has barely exceeded 28 Kwh in June, July and August. As for September 2020, my highest daily production was 27.17 kwh on September 6, 2020. I am wondering why my system can barely produce over 28 kwh and yet it was able to produce over 33 kwh in April. I have called SunPower tech support and I was told that my system was working fine and that as long as my system is producing over 24 kwh a day, then it has met its estimated production capacity. I have removed a palm tree that was blocking about 3 panels in the morning and even washed all the panels, but my production has not improved at all.

            Comment


            • #21
              Originally posted by ziddo1982 View Post

              I live in the San Diego Area (Southern California). My highest daily production on my less than one year old 4.8 KW system (12 panels) was 33.1 Kwh on April 15, 2020. My highest in May was 31.9 on May 4, 2020. And then one of my MI failed in June and SunPower was able to fix it remotely, but since then, my daily maximum has barely exceeded 28 Kwh in June, July and August. As for September 2020, my highest daily production was 27.17 kwh on September 6, 2020. I am wondering why my system can barely produce over 28 kwh and yet it was able to produce over 33 kwh in April. I have called SunPower tech support and I was told that my system was working fine and that as long as my system is producing over 24 kwh a day, then it has met its estimated production capacity. I have removed a palm tree that was blocking about 3 panels in the morning and even washed all the panels, but my production has not improved at all.
              It only takes a slight bit of smoke or cloud to have a big impact on sun intensity, and
              panel output. Are your skies really clear? I would check if all the unshaded panels
              are delivering near the same peak power, if yes it is working. Bruce Roe

              Comment


              • #22
                Originally posted by ziddo1982 View Post

                I live in the San Diego Area (Southern California). My highest daily production on my less than one year old 4.8 KW system (12 panels) was 33.1 Kwh on April 15, 2020. My highest in May was 31.9 on May 4, 2020. And then one of my MI failed in June and SunPower was able to fix it remotely, but since then, my daily maximum has barely exceeded 28 Kwh in June, July and August. As for September 2020, my highest daily production was 27.17 kwh on September 6, 2020. I am wondering why my system can barely produce over 28 kwh and yet it was able to produce over 33 kwh in April. I have called SunPower tech support and I was told that my system was working fine and that as long as my system is producing over 24 kwh a day, then it has met its estimated production capacity. I have removed a palm tree that was blocking about 3 panels in the morning and even washed all the panels, but my production has not improved at all.
                Keep in mind that array output varies with the sun's daily position change, ave. temps., wind regimes and the cloudiness (or lack of clouds) a location has.
                Still. something seems amiss compared to other systems in the area.

                Without knowing anything about your array's orientation and shading, it's no more than a dart throw as to what your output might be, or what, if anything is amiss.

                Check out something called PVOutput.org. You'll find a lot of info on arrays around the world, including the San Diego area, maybe one in your neighborhood. Find one with an orientation similar to yours and compare output per installed STC kW.

                Also check out something called PVWatts. It's a modeling algorithm from NREL for homeowners and it may help provide some insights. Read all the help screens a couple of times before you start. get the inputs as close to correct as possible and use a 10 % system loss parameter. Just remember that the model is not a predictor of performance. It's best use for you at this time is to get a feel for possible output on clear days.

                FWIW, I'm in 92026 w/a 5.232 kW Sunpower system at an orientation of 195.75 deg. az., 19.75 deg. tilt. The array has a 3.5 % annual shading penalty. It has been operating flawlessly since 10/13/2013. By my estimate and a lot of measurement, the array's performance has deteriorated about 3 % or so due to age.
                My array's highest daily April 2020 output was 33.39 kWh or 6.38 kWh/day per installed STC kW.
                My array's 05/15/2020 daily output was 33.20 kWh, or 6.35 kWh/ installed STC kW.
                For June, 2020, my average output was 29.73 kWh or 5.68 kWh/day per installed STC kW.
                For July, 2020, my average output was 32.18 kWh or 6.15 kWh/day per installed STC kW.
                For Aug., 2020 my average output was 30.29 kWh or 5.79 kWh/day per installed STC kW.

                My array's 09/06/2020 output was 26.91 kWh or 5.14 kWh/day per installed STC kW. Besides being about 2-3% fouled that day, system production was lower that day probably due to two factors: the ave. amb. air temp. on my roof between 0800 and 1700 hrs. P.D.T. was 45.5 C (113.9 F). That was the hottest aver. temp. I've recorded on my roof since the array was installed. The amb. at ground level, BTW, averaged 39 C (102.2 F), and the wind velocity was only 1.1 m/sec. (~ 2.5 M.P.H.) at the array. All that resulted in an average PV cell temp. of ~ 71 C (158 F), all of which knocked the day long system efficiency down to ~ 0.145 or so. See my comment to Bruce's observation about the dirty air situation we're experiencing just now.


                .

                Comment


                • #23
                  Originally posted by bcroe View Post

                  It only takes a slight bit of smoke or cloud to have a big impact on sun intensity, and
                  panel output. Are your skies really clear? I would check if all the unshaded panels
                  are delivering near the same peak power, if yes it is working. Bruce Roe
                  Bruce: On the possible effect of smoke/ash:

                  On 09/06/2020, the pyranometer on my roof recorded daylong Global Horizontal Insolation (GHI) of 6.536 kWh/m^2.
                  A pretty reliable model I use to estimate very clear sky Global Horizontal Irradiance and insolation calc'ed out a daylong clear sky insolation of 6.926 kWh/m^2 for 09/06/2020
                  The Extraterrestrial Horizontal insolation for 09/06/2020 at my location was 9.528 kWh/m^2.

                  The modeled insolation is supposed to be close to the max. theoretically possible daylong insolation under very clear skies. I've seen higher daylong totals a few times but not many. More common are days where the daylong values are 90 - 95 % of those max. theoretical max. values.

                  09/06/2020 was the last non smoke day around here. The smoke /haze started for my area on 09/07/2020. I've been a bit surprised at how consistent the attenuation of the GHI has been.

                  Between 09/07 and 09/14, the historical (6 prior year) average ratio of actual (pyranometer measured and recorded) terrestrial day long GHI to theoretical max. terrestrial day long GHI = 0.836.
                  For the period 09/07/2020 to 09/14/2020 only, the ratio of actual (pyranometer measured and recorded) terrestrial day long GHI to theoretical max. day long GHI = 0.694.

                  So, while the data sample is small - only 6 prior years to compare to and only 7 days of data for each year (so far), the measured and recorded day long GHI values for the Great 2020 Smokeout show that the ave. reduction in atmospheric transmission of solar energy at my location due to smoke/haze might be approximated as something like : 1-(0.694/0.836) = ~ 0.17, or 17 % or so reduction.

                  It gets complicated to estimate the reduction of array output caused by the smoke due to the air temp. and wind's effect on array/cell temps. but I'd suspect to a 1st approx. that array output would reduction would be a bit less than the insolation reduction - that is array output is down, but by something less than 17 %, mostly due to the likely slight increase in cell eff, enabled the decrease in cell temps. as a result of decreased energy input.

                  Anyway, to the extent any of the above makes any sense, all above applies to my location only, but I'd suggest it also may be applicable to Ziddo 1982 seeing as how he's in the San Diego area.

                  Rspectfully,

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