The most efficient tilt for photovoltaic panels in Philadelphia, Pennsylvania at a latitude of 40.01°:
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 33.5°.
If you're planning to change the angle of your photovoltaic panels twice per year, the most efficient angle is 16.2° in summer months and 54.2° in winter months.
If you're planning to change the angle of your photovoltaic panels each season, the most efficient angle is 12.5° in summer months and 59.6° in winter months, and 36.9° in autumn and spring months.