Should you use a tracking array?
Tracking arrays follow the sun across the sky to increase the amount of sunshine on the PV array. There are several different types- Passive vs. Active, Single-axis vs. Dual-Axes, and variations in the axis geometry (axis tilt and array tilt). The most popular tracker is the passive single-axis type with rotation around the inclined north-south PV array axis. A useful option is to specify winter and summer tilt angles (10° and 60° suggested for Arizona) for seasonal adjustment (its generally easy to do) to enhance system performance.
Tracking vs. tilt is not an easy decision. The choice depends on seasonal load needs (energy required, gallons of water pumped, etc.). The chart below compares passive single inclined axis trackers with fixed tilt array mounts. Both are seasonally adjusted to 10° tilt in the summer and 60° tilt in the winter.
Total Daily Irradiation (Kw-hr/mē) in example illustrated above
June 10° Fixed Tilt South facing 7.96
June 10° Tilted axis, single-axis tracking 11.10
December 60° Fixed Tilt South facing 5.11
December 60° Tilted axis, single-axis tracking 5.80
Note that while the tracker greatly enhances the sunshine on the array in the summer, the enhancement is lower in the winter. On very overcast days the performance will be about the same.
Decision criteria:
1. Use a fixed tilt array when the energy requirement is constant year round or peaks in the winter (such as all night lighting). For this situation the higher costs of a tracker are not justified by the minimal additional output in the winter and extra output in the summer represents no extra value.
2. Use a tracker when summer loads (or water required) are the main concern in sizing the system. Most water pumps will benefit even more than the relative higher output in the morning and afternoon indicates as the efficiency of the pump also increases at higher power levels.