In solar radiation geometry, the angle made in a horizontal plane between the horizontal line due south and the projection of the normal to the surface (tilted plane), is called:
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Think of "Azimuth" as the Compass Direction. If you are rotating your solar panel left or right (East or West) relative to South, you are changing its Surface Azimuth Angle.
1. Defining the Surface Azimuth Angle ($\gamma$): The
Surface azimuth angle is the angle made in a horizontal plane between the south-pointing line (the standard reference in the northern hemisphere) and the horizontal projection of the normal to the collector surface.
• If the collector faces due south, the surface azimuth angle is
$0^\circ$.
• Angles are usually measured positive toward the west and negative toward the east.
2. Contrasting with Other Angles:
• Zenith Angle ($\theta_z$): The angle between the sun's rays and the vertical (normal to the horizontal plane).
• Declination ($\delta$): The angular position of the sun at solar noon relative to the plane of the equator.
• Solar Attitude (Altitude) Angle ($\alpha$): The vertical angle between the sun's rays and the horizontal plane.
[Image showing solar geometry angles including Surface Azimuth and Zenith]
Therefore, the specific angle describing the orientation of a tilted plane relative to the south in a horizontal plane is the surface azimuth angle.