What is the optimal tilt angle of a fixed solar panel to maximize yearly incident solar radiation?

What is the optimal tilt angle of a fixed solar panel to maximize yearly incident solar radiation?
What the essay looks like : http://mrbertman.com/IA/solarPanel.pdf (see this link for what I mean by limits in integration for calculation of total yearly sunlight incident on solar panel)

Calculation of Position of Sun in Sky (very useful) – https://www.academia.edu/26323374/The_Sun_s_position_in_the_sky

Copy of My Maths EE Draft – https://docs.google.com/document/d/105yLB1P4reIyoaNXZnq31BDFdV-VL5m-RbjSjnkym-A/edit

Concepts :

LABORATORY 1: EARTH-SUN RELATIONSHIPS AND INSOLATION RECEIPT


https://www.sku.ac.ir/Datafiles/BookLibrary/45/John%20A.%20Duffie,%20William%20A.%20Beckman(auth.)-Solar%20Engineering%20of%20Thermal%20Processes,%20Fourth%20Edition%20(2013).pdf (has many definitions)
https://www.itacanet.org/the-sun-as-a-source-of-energy/part-3-calculating-solar-angles/ (more complex)

Please ask me to clarify anything