The tilt angle is the angle from horizontal of the photovoltaic modules in the array. For a fixed array, the tilt angle is the angle from horizontal of the array where 0° = horizontal, and 90° = vertical. For arrays with one-axis tracking, the tilt angle is the angle from horizontal of the tracking axis. The tilt angle does not apply to arrays with two-axis tracking.
The PVWatts® default value for the tilt angle depends on the array type: For a fixed array, the default value is 20 degrees, and for one-axis tracking the default value is zero. A common rule of thumb for fixed arrays is to set the tilt angle to the latitude of the system's location to maximize the system's total electrical output over the year. Use a lower tilt angle favor peak production in the summer months when the sun is high in the sky, or a higher tilt angle to increase output during winter months. Higher tilt angles tend to cost more for racking and mounting hardware, and may increase the risk of wind damage to the array.
For an array installed on a building's roof, you may want to choose a tilt angle equal to the roof pitch. Use the table below to convert roof pitch in ratio of rise (vertical) over run (horizontal) to tilt angle.
| Roof Pitch (rise/run) | Tilt Angle (deg) |
|---|---|
| 4/12 | 18.4 |
| 5/12 | 22.6 |
| 6/12 | 26.6 |
| 7/12 | 30.3 |
| 8/12 | 33.7 |
| 9/12 | 36.9 |
| 10/12 | 39.8 |
| 11/12 | 42.5 |
| 12/12 | 45.0 |