Sunlight incidence angle varies throughout the year due to the rotation of the earth around its own axis and its elliptical orbit. While sunlight falls to the earth with steep angle in summer in the Northern Hemisphere, it falls with shallow angle in winter. Sunlight should fall with steep angle to extract maximum power from PV panels. Therefore optimum fixed tilt angles of PV panels should be changed monthly and seasonally. In the mathematical analysis of the study, the monthly, seasonal and the annual optimum fixed tilt angles of PV panels depending on solar angles are calculated for Bilecik city. In the experimental study, optimum fixed tilt angles for May, June, July and August are determined by PV panels placed at 10°, 20°, 30°, 40°, 50° and 60° tilt angles. The mathematical analysis results are compared with the experimental results.