A MPPT, or maximum power point tracker is an electronic DC to DC converter that optimizes the match between the solar array (PV panels), and the battery bank, utility power, DC motor, or DC pump.

MPPT is electronic tracking, and has nothing to do with moving the panels. Instead, the controller looks at the output of the panels, and compares it to the battery voltage. It then figures out what is the best power that the panel can put out to charge the battery. It takes this and converts it to best voltage to get maximum AMPS into the battery. (Remember, it is Amps into the battery that counts). Most modern MPPT's are around 92-97% efficient in the conversion. You typically get a 20 to 30% power gain. Actual gain can vary widely depending weather, temperature, battery state of charge, and other factors.