The most efficient tilt for photovoltaic panels in Reno, Nevada at a latitude of 39.55°:
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 33.2°.
If you're planning to change the angle of your photovoltaic panels twice per year, the most efficient angle is 15.8° in summer months and 53.8° in winter months.
If you're planning to change the angle of your photovoltaic panels each season, the most efficient angle is 12.1° in summer months and 59.2° in winter months, and 36.5° in autumn and spring months.