The term solar tracker refers to a device that moves solar panels throughout the day, so solar panels are ideally within a few degrees of the sun. Depending on the type of tracker used, solar tracking can increase a panel’s solar harvest anywhere from 15 to 50 percent.
The two main types of solar trackers are single axis and dual axis. Single axis trackers rotate panels around a single axis that is oriented along the cardinal North-South or East-West direction. The axis of rotation is usually tilted to accommodate the angle of the seasonal sun at your particular latitude. The single axis tracker is relatively inexpensive and can increase panel harvest by as much as 15%. But they operate best at or near the equator.
Dual axis trackers conventionally rotate around one vertical axis and tilt on a second, orthogonal axis to accommodate latitude and seasonal changes. This tilting motion is the main advantage that dual axis trackers offer. They can more precisely follow the sun through the seasons. Conventional dual axis trackers operate best at middle latitudes (about 30° north or south of the equator).
Most dual axis trackers work on a simple principle: If a tracker can spin on a vertical axis and tilt on an orthogonal axis, then a large enough portion of the sky will be trackable to harvest both morning and evening sunlight. However, putting this simple principle into practice has resulted in somewhat complex mechanical challenges.
The first complication is how to create a durable machine that can rotate about a vertical axis. The traditional solution to this challenge is to use a slewing drive. These drives include a motor and screw assembly, and a large ring of hardened ball bearing to support the load of the entire array. They can usually rotate 240 out of 360 degrees around the vertical axis, but this limited range of motion is where we find a second deficiency in conventional dual axis tracker designs.
Not only are slewing drives expensive and prone to failure, but due to their limited range of motion, most dual axis trackers must be oriented toward the equator, just like a single axis tracker. While this limitation might seem benign, two consequences quickly emerge. One: these tracker do not operate well at extreme latitudes (they get lost when the sun moves beyond their range). And two: They must be fixed in one place (ground mounted). They can’t be portable.