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why is the angle of rays of sunlight so important in determining the amount of energy collected by the earth?

what i am trying to say is, why is the angle of rays of the sun so important to the energy collected by earth/

4 COMMENTS

  1. I would guess that rays of sunlight that pass through more air before reaching the surface of the earth (small angles) lose more energy than those that don’t (e.g., where the angle is 90 degrees).

  2. Its a matter of geometry. The Earth is a sphere and on the equator the sun light comes in at 90 degrees through the atmosphere. If you setup on the pole the sun comes in at 15 or 20 degrees so more atmosphere is encountered. But, if you mount thr solar panel at the best angle for where you are it isn’t too much different (other than timing of course) where ever you are.

  3. let’s look at a 12×12 square.
    hold it perpendicular to the sun, so, for the purposes of this discussion, you have 144 units of energy spread over 144 units of area.
    next, consider a 3-4-5 triangle.
    put the “5” side down, and let’s calculate the energy distribution if the sun’s rays are perpendicular to the “4” side. it’s still 12 wide, but the part on the ground is now 15 units, so you have 144 units of solar energy spread out over 12*15 or 180 square units of ground. alternatively stated, a 144 square within this area gets 144/180 or 80% of what it would have gotten if the sun were 90 degrees overhead.
    even worse, head farther north, so the sun shines through a 12×12 grid, but it’s on the “3” side of the 3-4-5 triangle. the ground area is still 12 wide, but it’s 5/3 longer or 20. so the ground area is 12×20, or 240 square units. and, if you calculate a 12×12 area within the ground footprint, you only get 144/240 or 60% of the energy within the same original 12×12 grid.
    alternatively, if you look at the energy of the sun, when it’s only 10% up in the sky, you could cut out a 10×10 hole in a piece of cardboard. if you hold that cardboard perpendicular to the sun’s rays, it would cast a shadow (ie a patch of light) that would be 10 wide, but 100 or so long. the energy passing through hole is spread way out.
    if you were to use the same cardboard, with the sun directly overhead, the resulting sun spot would only be 10×10. same amount of energy, in a much smaller area. that means it’s hotter.
    but it’s even worse. when the sun is low in the sky, the energy has to pass through more atmosphere, which sops up some of the energy. so, even if you measure a 10×10 grid, perpendicular to the sun, it will be quite a bit cooler (less energy) when the sun is at a low angle, than when it is directly overhead.
    the reason it passes through more atmosphere is that, for example, there is 50 miles of atmosphere. so when the sun is over head, the light passes through 50 miles of atmosphere. however, when the sun is low in the sky, the light travels at an angle, and must pass through much more atmosphere.
    and, to be honest, i’m not really sure which effect, more atmosphere, or wider distribution of energy, has the greater effect, but i’d guess the angle (wider distribution) is more important.

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