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8lightminutesaway's avatar

Shadow length question?

Asked by 8lightminutesaway (1408points) May 22nd, 2008

I’m designing a solar array for a strangely designed house. I need to find out how to calculate the furthest south a shadow will travel in a given day. There will be panels lined up behind one another and i want to make sure no shadows from one line of panels hit the ones behind them, but I also want to use as much roof area as possible. Initially I was under the impression that the shadow would travel the furthest southwards at noon but recently discovered this to not be true. How do I find this out?

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3 Answers

XCNuse's avatar

I’d say the easiest (no math involved really), common sense way that I’d do it is make a fixture as high as your panels will be at the highest point, put it on say a driveway, and take some chalk or make a mark and watch for the furthest point it gets.

Remember though this will fail in the sense of changing seasons, as the season changes so does the position of the sun relative to the opposite season.

otherwise I know the extremely complicated geometry method but.. that involves stuff I still really don’t understand (i hate the unit circle) and all calculus involved with sine cosine and tangent.

I mean unless you find something on google about the whole seasons way, how soon do you plan on putting it up? Can you watch the shadows for both seasons, or is it more immediate?

8lightminutesaway's avatar

I have to finish designing this within the next couple days. I thought it wouldn’t be too bad until i discovered the longest reach south is not at noon, its a different times throughout the year.

bpeoples's avatar

Use sketchup!

Model the house (roughly) in Google Sketchup, and then “place the model” (rotationally and lat/long) and then turn on shadows.

You can then track through the year exactly where the shadows will go. I’ve done this to do sun studies for several shade structures, works great!

You’re also talking about how far “south” the shadows will go? Does that mean you’re in the southern hemisphere, or at least in the tropics? If you’re north of the Tropic of Cancer or south of the Tropic of Capricorn (above about 24-degrees latitude) the sun will never go past directly above you.

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