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  • Originally posted by J.P.M. View Post

    Bruce:

    I forgot and I'm too lazy to root around for an answer: How many STC kW of PV do you currently have installed ?

    Thanx, J.P.M.
    I am running a 6 year old set of panels, rated 2.33 DC to AC ratio into 15KW inverter plant. It is arranged
    for the dual modes of emulating tracking under best sun, and boosting output under clouds. Bruce

    Comment


    • Originally posted by bcroe View Post

      I am running a 6 year old set of panels, rated 2.33 DC to AC ratio into 15KW inverter plant. It is arranged
      for the dual modes of emulating tracking under best sun, and boosting output under clouds. Bruce
      So that would be 2.33*15 = 34.95 STC kW of PV ?

      I'm not trying to be rude and I appreciate you don't owe me anything much less an answer, but it was supposed to be a simple question.

      Comment


      • Originally posted by J.P.M. View Post

        So that would be 2.33*15 = 34.95 STC kW of PV ?

        I'm not trying to be rude and I appreciate you don't owe me anything much less an answer, but it was supposed to be a simple question.
        That is about right, not certain some of my no name panels are fully up to their label. Bruce

        Comment


        • Originally posted by bcroe View Post

          That is about right, not certain some of my no name panels are fully up to their label. Bruce
          Understood. Thank you.

          So that would mean on what's about your best production day your array(s) are producing something like 155 kWh from 34.95 STC kW of PV ?

          If I might test your forbearance for questions a bit more: How about a SWAG for total annual output for all the installed PV you have in terms of kWh/yr. per installed STC kW ?

          Comment


          • Originally posted by J.P.M. View Post
            Understood. Thank you.

            So that would mean on what's about your best production day your array(s) are producing something like 155 kWh from 34.95 STC kW of PV ?

            If I might test your forbearance for questions a bit more: How about a SWAG for total annual output for all the installed PV you have in terms of kWh/yr. per installed STC kW ?

            You could say that, yes. The way I see it, 15KW inverters produced 155KWH mid May, because
            my limiting factor is the size of the inverter plant. All the commercial applications seen here
            recently state the inverter AC output capacity, with a DC/AC ratio, and I am following that approach.

            Not included in that statement, is the cloudy sky performance, hard to put precise numbers on. What
            I see is for clear skies, 15KW output for more than 8 hours. For rather slight clouds, output remains
            saturated much of the day. For clouds starting to eliminate hard shadow lines, output is 80%. In days
            the sun is not seen output may run 40 to 50% of capacity. In a rain storm output is usually in the range
            of 10 to 25%. Here is my daily output curve recently. Annual output depends on the weather and
            upgrades, latest is 28,500 KWH.


            PV15May19.png

            For a 15KW system installed here at Zip 61084, 42 deg lat, never ending clouds of varying weight, I claim other
            systems will not do as well as mine. My system is not optimized for the SW desert, and designs from there perform
            poorly here. Arrays I have seen:

            FIXED ARRAY.

            Less optimum annual angle
            Huge snow removal effort required more than a dozen times each winter
            Limited day hours near peak output.
            Output severely limited under less than optimum sun.


            DUAL AXIS TRACKER: Never used on sizable arrays.

            SINGLE AXIS TRACKER, E-W Scan.

            The shaft on this oft used commercial setup is parallel to the ground. At 42 deg Lat
            the incident angle drops output to about 0.7. This means the DC/AC ratio
            must be increased accordingly, this while keeping tracker complexity.
            No compensation for weaker sun at day extremes.
            Good snow rejection ONLY when used with enough ground clearance.


            FIXED ARRAY WITH MULTIPLE PANEL ORIENTATION, EASY summer/winter tilt change,
            snow gaps, and high ground clearance. Inverters will tolerate a high DC/AC ratio
            because only some of the panels are at a most favorable sun angle at any given time.

            High snow rejection, most snow would clear without manual intervention shortly.
            Careful selection of tilt will provide near level output under a day of best sun,
            partly compensating for weakness of day extremes.
            Inverters are kept at peak output most of the day under good sun.
            Under medium clouds, high DC/AC ratio produces considerably more
            than a tracker, perhaps double that of a fixed array.


            There are harder questions to ask. I have a lot more money in 6061 aluminum, SS hardware,
            concrete, wire, Rbar, and tools, than in PV panels. Adding EASY seasonal tilt change does
            increase production, at considerable cost. Combining that with easy snow control adds
            some more cost. I am glad to trade initial cost, for very little snow removal efforts.

            On the other side, DIY efforts provide huge savings. This is partly enhanced by scaled
            down DIY tools (backhoe, trencher) available when convenient, not on a preset schedule.
            Small tools help avoid erosion problems. On site materials may be repurposed for new
            construction. Arrays following my land (10% grade) are way simpler than attempting a
            perfectly level construction.

            Bruce Roe
            Last edited by bcroe; 05-18-2019, 10:40 AM.

            Comment


            • Thanks for the comprehensive answer. My take away is that your DC to AC ratio is accomplishing your goals.

              Comment


              • Originally posted by Ampster View Post
                Thanks for the comprehensive answer. My take away is that your DC to AC ratio is accomplishing your goals.
                Right, when combined with multiple panel orientations.

                Regarding DIY, I discovered long ago that most tools would pay for themselves the first
                time you used them (avoiding hired labor). Recent example, for my first PV panel
                experiment I paid $1K to have a full scale backhoe dig the 10 holes. Good work, but
                the heavy machinery so messed up my grass (on a 10% grade) that by spring there was
                a very serious erosion problem. I paid a landscaper $2.3K to get my grass restored.
                On the latest array I used my own $3.3K mini backhoe, no erosion problem, and no
                BIG DAY schedule issues. Bruce Roe

                Comment


                • Originally posted by bcroe View Post
                  .....
                  Regarding DIY, I discovered long ago that most tools would pay for themselves the first
                  time you used them (avoiding hired labor). ........
                  Yes. That is my experience. I now have a garage full of tools that I can now start giving to my son in law and my nephew who sometimes provide extra labor. Double benefit.

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