The most efficient tilt for photovoltaic panels in Denver, Colorado at a latitude of 39.76°:
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 33.3°.
If you're planning to change the angle of your photovoltaic panels twice per year, the most efficient angle is 16° in summer months and 54° in winter months.
If you're planning to change the angle of your photovoltaic panels each season, the most efficient angle is 12.3° in summer months and 59.4° in winter months, and 36.7° in autumn and spring months.