Talk:Solar azimuth angle
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I added another formula for the azimuth that is popular, and cited by Seinfeld and Pandis in Atmospheric Chemistry and Physics. I also clarified the conventions for azimuth, although I had some difficulty with the wording, so if anyone wants to take a stab at clarifying that please go ahead. I addressed the serious shortcomings of using inverse sine to find the azimuth angle since it is has many solutions, and most calculators and spreadsheets will only return solutions between -90 and 90 degrees. Finally I added a link to the NREL sun position calculator which I think is an excellent standard. --Mikofski 19:45, 22 August 2007 (UTC)
Measured from north or south?
The first paragraph says,
- It is most often defined as the angle from due north in a clockwise direction.
The paragraph before the last two formulas says,
- the azimuth angle ... should be interpreted as the angle east of south
Is the latter saying "measured from north to a direction east of south?" If so, the description seems awkward.
If all angles are clockwise from north, why not say "between 0° and 180°" instead of "east of south" which may be read as "measured east from due south?"
Some do measure azimuth from south:
- the solar azimuth angle is measured from south to the horizontal projection of the sun’s rays on a horizontal plane, and it is negative in the east of south and positive in the west of south (Duffie and Beckman, 2006).
There are two main conventions
This causes a lot of confusion, because not only does it affect the numerical value assigned to the solar azimuth, but also the formulas used to calculate that value. The conventions are predominant in specific fields.
This is the traditional convention, that states that the solar azimuth is measured counter-clockwise from south. EG: if you are looking north, then your view has an azimuth of 180° or -180°. If you are looking east, your view's azimuth is 90°, and a westward view would be -90°. Yes, this convention defines the range from -180° to 180°. This is the convention used by Seinfeld and Pandis in Atmospheric Chemistry and Physics, from Air Pollution to Climate Change, which is listed as a reference. I assume it is also the convention in Sukhatme's Solar Energy: Principles of Thermal Collection and Storage.
Solar Energy Convention
Solar energy and photovoltaic professionals will adhere to the due north clockwise convention, which is unfortunately left-handed and northern hemisphere centric. This is the convention used by NREL (aka SERI) in their 2 solar position calculators, SPA and SOLPOS, which are both linked to from this wiki post. In this convention, east is still 90° and west is still 270°, but south is now 180°, and north is zero. This is the method I am most familiar with.
Because 2 conventions aren't enough, Duffie has his own, he says that an angle east of south should be negative. This is the only place I've seen this proposed, and it just adds confusion, because this text is so widely used by students. Too bad. --Mikofski (talk) 21:06, 7 May 2013 (UTC)