Maximum power point tracking –MPPT or sometimes just power point tracking–PPT
An 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 or utility grid. To put it simply, they convert a higher voltage DC output from solar panels (and a few wind generators) down to the lower voltage needed to charge batteries.
PV solar systems have varying relationships to inverter systems, external grids, battery banks, and other electrical loads. The central problem addressed by MPPT is that the efficiency of power transfer from the solar cell depends on the amount of available sunlight, solar panel temperature and the load‘s electrical characteristics. As these conditions vary, the load characteristic that gives the highest power transfer changes. The system is optimized when the load characteristic changes to keep power transfer at highest efficiency. This optimal load characteristic is called the MAXIMUM POWER POINT (MPP). MPPT is the process of adjusting the load characteristic as the conditions change. Circuits can be designed to present optimal loads to the photovoltaic cells and then convert the voltage, current, or frequency to suit other devices or systems.
The main difference between PWM and MPPT charge control devices is that the MPPT devices are more efficient. MPPT charge control devices have 30 % more efficient in charge efficiency according to PWM type. Panel voltage and battery voltage should be matched in PWM systems.
In conclusion, to get most out of the solar energy, using today technologies you should use MPPT as first choice.