The spheric trigonometric formulas don't account for refraction, which might give a few Watts more of power using the solar panels. At high latitude >55 deg the sun is already down below the horizon in summer time (talking about the northern hemisphere) and still visible to the eye and of course to the panel.
Formulas to determine the relative position is not the most difficult part to control the tracker. The tracker itself must either travel at synchronous speed with the appearant sun movement or be triggerd every once in a while.
It takes a lot of mechanical work and parts to achieve the desired function.
It's more or less like a hunter calculating the ballistic curve of a bullet.
Hans