Transverse Incidence Angle

The profile plane is a vertical plane passing through a horizontal line perpendicular to a given azimuth (in horizontal-axis tracking systems, this is the axis) and containing the sun.

The transverse incidence angle is the angle between the normal to a tilted plane of the given azimuth and the corresponding profile plane.

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