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01/14/2007: "sun angle/overhang design"

Alack, alas, and argh! Not only has the mighty Google search failed me, but so has my next-favourite,! How have they failed me, you ask? It's not necessarily that they have failed to find me an answer to my question, but they have fully failed in finding the answer with the correct level of information that I need. In one case, there's far too much. In most of the others, little or none. What to do now??

The question, in case you're wondering (and I know you are) is, "What are the winter and summer sun angles for my location?"

Your question is likely, "Why do you need that information?" The simple answer is, I want those angles so I can properly apply passive solar design to the cohousing development I'm spearheading. That might be enough of an answer, but I'm going to explain a bit further to illuminate why I need a certain amount of information. (Pun not really intended, but I'll take credit where I can.)

In passive solar design, you use window overhangs to prevent winter shading of your windows, and ensure summer shading of same. That way in the winter, the sunlight comes in and warms your home up, but in the summer it doesn't. To be able to do this properly, I need the angle of the sun at its lowest during the winter and at its highest during the summer. Then it's a matter of simple trigonometry to figure out how big an overhang you need for a window of height A that is X far off the ground, facing south. No biggie.

Problem is, most of the sites I've found only tell you that much, and give no angle whatsoever. Some give angles, but they're generally for locations that are nowhere near me, and thus the angles are useless. I did find one site that will give me exactly what I need, but only if I can properly supply my longitude, lattitude, elevation, time (solar or clock?), date, year, timezone... way too much information. I THINK the lowest the sun gets would correspond to the winter solistice, December 21 or 22, and the highest the summer solstice of June 21 or 22, but I'm not sure. Plus, my elevation isn't a fact I know off the top of my head, (let alone how much it alters the angle).

What I'm really looking for is simply a table: major cities in Canada and their winter and summer sun angles. That's all I need. And that is what I can't find. Being past the point of Google exhaustion, I found out my elevation (pretty low after such a failed search - ha, ha), and played around with dates until I trial-and-errored a winter sun angle (70 degrees) and a summer sun angle (23 degrees) into existence. (I played with the dates until the azimuth came closest to the maximum of +/- 23.45 degrees.) Gad, how wearying. All that work just to find a maximum and a minimum.

Hmm... and now that I actually put that down on paper graphically, I wonder if it's correct. That's a heck of a difference. Does it make sense? Well, if the sun azimuth goes between +23.45 and -23.45, that's 47 degrees of travel... 47+23=70. Hmm. I guess it pans out... yeah, that's probably right. Just seems like a pretty drastic difference. Hrmph.

If anyone out there knows of a source for the information which I seek, PLEASE let me know. I will promptly archive it into such that others can find it and be spared the trials I've been subject to. For now, I have my winter and summer angles,and will be content for the moment. And now that I've mastered that particular calculator, I can provide the same information to you for your location, should you so desire it. Now on to my trigonometry!

Replies: 5 Comments

on Sunday, January 14th, Boose said

I don't know if it helps any further, but Waterloo is at 45/20N by 72/31W, at an elevation of 329m (1,079ft). Plugging those figures into your sun-time website and assuming a clock-time of noon, I got pretty much the same sun-angle figures that you did. It only took me about ten minutes, but I already had your work to compare it to.

I got the altitude from Wikipedia and the lat/long from

Have fun!

on Monday, January 15th, mr.ska said

I got the elevation from the same source, and the lat/long (rounded to 43.5 and -80.5) from the university's weather station website. Yeah, it only took me a few minutes to get the figures, but I *know* I've found a source of winter and summer sun angles for Canada before. That's what is really sticking in my craw. (And hence my use of so I never have to lose a bookmark again.)

on Monday, January 15th, roberthahn said

I haven't bothered to look, but have you tried Environment Canada at all?

on Tuesday, January 16th, mr.ska said

Just did, no luck.

on Thursday, January 18th, mr.ska said

Apparently Sketchup has a built-in sun and will project shadows, but assumes a latitude of 40 degrees. At least, the free one does... does that mean there's a professional one available for a cost? Hmm.

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