The fixed setup angles of photovoltaic (PV) panels are typically optimized properly in order to maximize the electrical energy harvest. In the present work, the sunlight availability or sky coverage conditions of sufficiently small time intervals for everyday around the year are counted in the modeling for computation of solar energy on the PV panel in order to optimize the panel tilt angles. Maximal energy harvest in a year is the objective of choosing the optimal tilt angles. The analysis calculates vectors of instantaneous sunray and solar panel normal direction to consider the ‘cosine’ effect. The energy harvested in every 6 min by a PV panel of per square meter is summated for day-long period from sunrise to sunset when the sun elevation angle is above 5 deg. The general model is applied to the authors’ local city, Tucson, Arizona, USA. The results show that the annual solar energy received by a solar panel tilted with a fixed angle of equal to the local latitude could reach to 2297 kWh/m2 with the 10-year averaged sky coverage conditions of every 6 min considered. However, if a PV panel is inclined using the discovered optimal angles with two times, four-seasonal, and monthly adjustments, the gain in the yearly solar energy harvest can be 7.59%, 7.60%, and 9.19%, respectively, greater than that with the fixed angle equal to local latitude.