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PV Watt potential (as a percentage) vs. the suns angle from solar noon

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  • PV Watt potential (as a percentage) vs. the suns angle from solar noon

    For fixed panels facing due south, this simple cosine function based PDF will tell you the maximum PV Watts possible (as a percentage) vs. the suns angle of deviation from due south (solar noon).


    Sun_Angle_vs_Watts.pdf
    Last edited by Silver_Is_Money; 05-22-2016, 06:51 PM.

  • #2
    Than you. But the link is not working for me (Firefox browser.)
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      It does not work for me either. I am also using Firefox web browser.

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      • #4
        Sun's maximum
        angle potential
        from PV Watts
        Solar noon Utilization
        Sunrise 90 0%
        80 17%
        70 34%
        60 50%
        50 64%
        40 77%
        30 87%
        20 94%
        10 98%
        Solar Noon 0 100%
        10 98%
        20 94%
        30 87%
        40 77%
        50 64%
        60 50%
        70 34%
        80 17%
        Sunset 90 0%

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        • #5
          ??? What is this ?

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          • #6
            Originally posted by J.P.M. View Post
            ??? What is this ?
            Maybe its an estimate of the output of a panel in outer space. It certainly doesn't describe my panels. All mine put out more than zero
            anytime its not pretty dark. With a couple panels back to back, the one facing AWAY from the sun does 5 to 10% of the other.

            Bruce Roe

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            • #7
              Originally posted by J.P.M. View Post
              ??? What is this ?
              What I mean is, what is this describing ? I'm all for information, but this needs some definition before going further, and I'd guess a lot of work after that to be useful.

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              • #8
                Originally posted by J.P.M. View Post

                What I mean is, what is this describing ? I'm all for information, but this needs some definition before going further, and I'd guess a lot of work after that to be useful.
                After reading it appears he is saying the angle of the sun striking a solar panel is a function of Cosine Law which is just plain false. If that were true a 2-axis tracker would produce 100% power from dawn to dusk every day of the year.

                Cosine of 90 degrees = 0 or 0% power.
                Cosine of 0 degrees = 1 or 100% power.

                Sorry Silver but that is Junk Science.
                Last edited by Sunking; 07-11-2016, 09:27 PM.
                MSEE, PE

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                • #9
                  Originally posted by Sunking View Post
                  After reading it appears he is saying the angle of the sun striking a solar panel is a function of Cosine Law which is just plain false. If that were true a 2-axis tracker would produce 100% power from dawn to dusk every day of the year.

                  Cosine of 90 degrees = 0 or 0% power.
                  Cosine of 0 degrees = 1 or 100% power.

                  Sorry Silver but that is Junk Science.
                  Here we go.

                  If anyone cares, and perhaps to clear things up some some:

                  1.) The Cosine of the angle of beam radiation striking a flat surface ~ = (Cos(Zenith angle)*Cos(surface tilt angle)) + (Sin(Zenith angle)* Sin(surface tilt angle)*Cos(solar azimuth angle - surface azimuth angle)) (see Duffie & Beckman/others for how the angles are defined). The angle of incidence can be described in terms of several angles and trigonometric functions of those angles.

                  If what the OP wrote is meant to represent some f("cosine law"), whatever that means, it is probably correct to say that what the OP wrote is incorrect.

                  However, the solar position relative to a surface of arbitrary orientation on the earth is a function of several trigonometric relationships, three of which are cosine functions.

                  If the surface in question is stationary, the received solar radiation over the course of a day will be a function of many things, one of which is the Cos of the angle of incidence of beam radiation. Diffuse insolation is a loose f(incidence angle). Other influencing variables are cloud cover, atmospheric quality and others. Seasonal variations in solar position are accounted for in the zenith angle and the azimuth angle which are f(declination angle and hour angle functions). Also see NREL or a nautical almanac for more info.

                  2.) As for a dual axis (or gimbaled) tracking system, a dual axis tracker can be made to track the sun with a fairly low day long incidence angle and will thus intercept pretty close to 100% of the incident beam insolation, and pretty close to 100 % of the diffuse insolation. However, since the intensity of both of those varies, the solar device's output will vary.

                  3.) It looks to me anyway, that indeed, at least without more information, Silver is Money's post qualifies as junk science, if for no other reasons than poor definition and lack of detail.
                  Last edited by J.P.M.; 07-12-2016, 11:54 AM.

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                  • Apollo59
                    Apollo59 commented
                    Editing a comment
                    It's been a while since my trigonometry years, I have to say I did get a bit sleepy I enjoy your and Sunking and others posts, this is a great site, (my 1st day here), and I have lots of interest, can't wait till you flash out my junk configuration on my question guys! Thanks!
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