The solar azimuth angle is the angular distance between due South and the projection of the line of sight to the sun on the ground. A positive solar azimuth angle indicates a position East of South, and a negative azimuth angle indicates West of South.
Note that in this calculation, Southern Hemisphere observers will compute azimuth angles around +/- 180 degrees near noon. Comments would be appreciated concerning whether or not this should be modified such that solar noon is associated with an azimuth value of 0.
The azimuth angle is calculated as follows:
cos (Az) = (sin (Al) * sin (L) - sin (D)) / (cos (Al) * cos (L))
where:
L = Latitude (negative for Southern Hemisphere)
Az = Solar azimuth angle
D = Declination (negative for Southern Hemisphere)
Al = Solar altitude angle
The sign of the azimuth angle also needs to be made equal to the sign of the hour angle when using the above equation.