Compute Incidence Angle
This function computes the solar angle of incidence on the plane-of-array, i.e. the angle between a line perpendicular (normal) to the module surface and the beam component of the sunlight. The tilt may be constant for fixed-tilt DC Fields, or variable for tracking DC Fields.
1.) Compute the incidence angle given an array of panel tilts β and aspects γ. The angle is defined
to be zero when the light ray is normal to the surface.