PV racks fall into two main categories: fixed (nontracking) and tracking. Without any moving parts to fail, a fixed rack is steadfastly reliable, but lacks the capability to keep the modules perpendicular to the sun throughout the day. Trackers follow the sun’s position from horizon to horizon. However, the tracker’s moving parts require maintenance, and add parts to the system that can fail, decreasing reliability.
A single-axis tracker follows the sun from east to west, but does not automatically follow the sun’s elevation, though the mounts can be adjusted seasonally. Dual-axis tracking keeps the array pointed right at the sun throughout the day, without human intervention. Dual-axis tracking can increase array output as much as 40% compared to a fixed array (see “Array Tracking & Energy Production,” below).
Tracked systems can significantly increase energy production if the site has no shading. Trackers can really pay off when the east and west horizons have minimal blocking (from trees, buildings, or mountains) or if midday weather is often cloudy. They work great for array-direct pumping where water is needed all day. But with the considerations of added cost and a minor decrease in reliability, many system owners choose a fixed rack. If, for the same output, the cost of adding more PV modules is less than or equal to the added cost of a tracker, then it is almost always better to go with a fixed array.