There are two different drivers that dictate the motion of the trackers: passive and active. Passive trackers depend solely on solar heat to guide and move the tracker.Active trackers use a controller that monitors the position of the sun’s movement in order to direct motors that move the trackers.
In most solar trackers, Light Dependent Resistors (LDRs) are used as sensor. Their difference in output is used to generate error signals. In these systems, for instance, when the outputs of eastern and western LDRs become equal, the east to west tracking ends. A computer or a processor calculates the sun’s position from formulae or algorithms using its time/date and geographical information to send signals to the motor orient the apparatus in such direction where illumination of sensors becomes equal and balanced.
In some high end solar trackers, a feedback system is employed wherein the output signal of various processes is sent back as the input to the system that it is controlling. Consequently, it can correct any errors and compensate for disturbances in the system.