Finding watts

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  • Takis
    Member
    • Oct 2019
    • 64

    #1

    Finding watts

    Hello friends

    in the summer time, i've doubled my solar panel array and now i have 1980w for my 24v system.

    At the first time of setting the system up, the watts were 1680w which was great. (Clear sky, great sun angle).

    I had the system turned off for about a month, and when i turned it back on, the max watts (also with clear sky/ perfect sun angle) were sometimes 1400 (barely 1480). I've tried to draw the maximum many days-times (different temperatures - any kind of ambient). Panels are clean, no external damages, no hot spots etc, and it's has been rained.
    I know that the maximum you can get from your system is about 80%. But that would be ~1600. Now days with cloudy weather i get 500w and today with very cloudy weather i got 200w out of 2000.

    In the attached photo i have draw my system and some weak (in my opinion) points A,B,C
    IMG_20211014_185730.jpg
  • Mike90250
    Moderator
    • May 2009
    • 16020

    #2
    With hardly any sort of cloud cover, expect 10% or less of rated output. I have 5Kw of panels and in cloudy weather, I get 300w. That's why I have 2, diesel generators for winter use,

    If your batteries are full, they will not draw power from panels in full sun.
    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister

    Comment

    • Takis
      Member
      • Oct 2019
      • 64

      #3
      Originally posted by Mike90250
      With hardly any sort of cloud cover, expect 10% or less of rated output. I have 5Kw of panels and in cloudy weather, I get 300w. That's why I have 2, diesel generators for winter use,

      If your batteries are full, they will not draw power from panels in full sun.
      But what caused to get 1600w at the first days and a month later (also summer time) it was ~200w lower ? That's the hard to find out !
      All tests had been done with full batteries and full load to the inverter 3000w

      Comment

      • J.P.M.
        Solar Fanatic
        • Aug 2013
        • 15005

        #4
        Back to basics.
        To a rough 1st approximation, the output of an array is roughly proportional to the irradiance it receives.

        You do seem to know that the output of an array or a panel varies with many inputs, but maybe you don't know that one of those variations - which is annual - is caused by the annual apparent movement of the sun to the north and back south again (or south to north in the southern hemisphere) which is due to the earth's axis being tilted relative to the plane of its orbit around the sun ?

        Without knowing any more than you've written/included so far, it reads to me like what you're seeing under clear skies is pretty normal seasonal variation due to that annual variation in solar incidence angles.

        As for output under cloudy conditions, as Mike writes, that will vary from minute to minute, but when it's cloudy, it'll be close to zero at sunrise/sunset and maybe/often between maybe 5 % to 20% of full output around midday or more, depending on atmospheric conditions.

        Comment

        • SunEagle
          Super Moderator
          • Oct 2012
          • 15153

          #5
          It is October and depending on if you live in the Northern hemisphere it is Fall and in the Southern it is Spring time. Based on what I understand most pv panels will not produce anything close to nameplate wattage during those times even at high Noon.

          Unless you have made some changes to the wiring or parts of the panels are no longer producing due to component failure or shade I would say the lower output is normal.

          Comment

          • Mike90250
            Moderator
            • May 2009
            • 16020

            #6
            Simply leaving the system turned off, would not reduce the output when powered back up. Unless there was a bad wire or connection. But testing has to be done in bright clear, haze free skys, any clouds and it's all over.
            Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
            || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
            || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

            solar: http://tinyurl.com/LMR-Solar
            gen: http://tinyurl.com/LMR-Lister

            Comment

            • bcroe
              Solar Fanatic
              • Jan 2012
              • 5208

              #7
              Originally posted by Takis

              But what caused to get 1600w at the first days and a month later (also summer time) it was ~200w lower ? That's the hard to find out !
              All tests had been done with full batteries and full load to the inverter 3000w
              That is the way of renewable energy, you take what you can get, when you can. If
              the noon sun is lower than another month, it must pass through more dust. The smoke
              from fires half a continent away has had a severe effect here.

              With the panel cost now a small part of the total, I have compensated by more than
              doubling the number of panels. The equipment has something to do under clouds,
              and I have arranged panels (facing E and W) to maintain about the same peak as before,
              but over a longer day. good luck, Bruce Roe

              Comment

              • Takis
                Member
                • Oct 2019
                • 64

                #8
                Today, finally since July, I have got 1550w with partial clouds. That's almost 80%.
                ​​​
                i live in North hemisphere and now it's autumn.

                ​​​​​​ Thank you all for your answers.

                Comment

                • Ampster
                  Solar Fanatic
                  • Jun 2017
                  • 3658

                  #9
                  Good to hear that the Watts found you.
                  9 kW solar, 42kWh LFP storage. EV owner since 2012

                  Comment

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