The most efficient tilt for photovoltaic panels in Riverside, California at a latitude of 33.94°:
Your photovoltaic panels need to be angled facing south.
If you're mounting the photovoltaic panels at a stationary angle, such as on your roof, the most efficient angle is 28.9°.
If you're planning to change the angle of your photovoltaic panels twice per year, the most efficient angle is 10.6° in summer months and 48.9° in winter months.
If you're planning to change the angle of your photovoltaic panels each season, the most efficient angle is 6.9° in summer months and 54.2° in winter months, and 31° in autumn and spring months.