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why orientation of solar panels matters?

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  • why orientation of solar panels matters?

    Had solar panels set up on my roof and they face towards the east (ENE, in the Southern Hemisphere). I know nothing about solar panels and little about physics, but I did a little experiment that has me worried. Before midday (10 to 11 am) I am getting around 1050K from the panels. After midday I get (1 to 2pm) around 800K and both with clear sky. This indicates to me that the orientation of my solar panels is poor. Can anyone please explain the science as to why orientation of solar panels matters?

  • #2
    The output of panels will be the greatest when the sun is directly perpendicular to the panel. Even if they faced due north in your case there would be lower power produced in the morning and afternoon and higher mid day. If it is possible, face your array due north. this will give you the most production. However if the roof is not too steep < 25 degrees the difference in production will only be about 10-15% if the tilt is not optimum for your location. A steeper roof will reduce procuction further as the sun will be at a greater angle from perpendicular earlier.
    NABCEP certified Technical Sales Professional

    [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

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    • #3
      An easy to see the difference in output for different orientations and inclinations is the Sharp energy calculator.

      http://sharpusa.cleanpowerestimator.com/sharpusa.htm

      Just plug in your zip code and an annual bill amount then play with it.
      [SIGPIC][/SIGPIC]

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      • #4
        Originally posted by dope View Post
        Can anyone please explain the science as to why orientation of solar panels matters?
        Probably the biggest reason is that light travels through twice as much glass at a 45 degree angle than at 90 degreese.

        I have a small scale system that powers my yard lights and the panels are ground based, not on a roof which allows me to realign them at the start of each month.

        I know your panels are on the roof, but I can tell you that proper alignment is critical, at least on my smaller system.

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        • #5
          Originally posted by Steve View Post
          Probably the biggest reason is that light travels through twice as much glass at a 45 degree angle than at 90 degreese.

          I have a small scale system that powers my yard lights and the panels are ground based, not on a roof which allows me to realign them at the start of each month.

          I know your panels are on the roof, but I can tell you that proper alignment is critical, at least on my smaller system.
          More to do with angle of incidence. The further away from perpendicular the smaller the useable surface is. To demonstrate take a book piece of paper etc and hold it perpendicular to your eyes. Note how big the outline is. now start turning it away at an angle. note how the outline seems to get smaller. When turned away from your eyes the area that the sun hits is smaller as the sun is still at the same relative position as your eyes. Since Energy is transmitted and measured in Watts per square meter if you are getting 100 watts from a panel that is one square meter and turn it 45 degrees away from the sun the effective surface is Area divided by 1.41 Reflective losses from the glass are not counted in this but will increase also.
          NABCEP certified Technical Sales Professional

          [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

          [URL]http://www.calculator.net/voltage-drop-calculator.html[/URL] (Voltage drop Calculator among others)

          [URL="http://www.gaisma.com"]www.gaisma.com[/URL]

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          • #6
            = Before midday (10 to 11 am) I am getting around 1050K from the panels. After midday I get (1 to 2pm) around 800K and both with clear sky. This indicates to me that the orientation of my solar panels is poor. Can anyone please explain the science as to why orientation of solar panels matters?
            If orientation of panels doesnt matter, you could install them upside down. More sun, more power you get. If you have 1 square meter of panel, you need to point it exactly perpendicular to the suns direction to have a 1 square meter of sun beam. Any deviation in angle will reduce the area of sunbeam caught.Check your trigonometry and the sines and cosines will tell you how much you will loose per degree difference. You might try tracking , but might notice reduction in harvest at noon. Well the panels loose their efficiency after they heat up due to the intense sun. Again for sun's intensity, the farther you are away from the sun, the less intense the sun rays and less power. If you are on the equator or near it, 9am sun would not produce same as 12noon sun intensity, even if you are on perfect tracking.You are simply farther away from the sun at 9am than at 12 noon. The distance actually is negligible. What causes the noticable power difference is the atmospheric resistance. Ex. you have 50k feet of mixture of atmospheric gases(oxygen nitrogen, water vapor etc) at 12 noon. it will be around 75k feet of gases when you are at 30 degrees from the horizontal assuming all other conditions are equal. Have you ever wondered why it feels hotter at noon than the early or late hours of the day even when theres no cloud and you could see the sun beaming at you at both times? try to beam your panels directly to the sun at different times of the
            day and measure the output. You could see the difference yourself or you could prove that Im wrong.
            Last edited by Mike90250; 08-25-2011, 07:31 PM.

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