Transverse Incidence Angle

Let us call Profile Plane the plane passing through a horizontal line perpendicular to a given azimuth (in tracking systems with horizontal axis, this is the axis), and the sun.

We call Transversal incidence angle the angle between the normal to a tilted plane of this given azimuth, and the corresponding profile plane.

In horizontal axis tracking systems, this corresponds to 90° - Phi-angle of the tracker.