PWM stands for Pulse-Width Modulation. This comes into play when the batter bank is full. As it is charging, the solar charge controller lets in as much current as the PV panel can generate in order to achieve the target voltage for the charge stage of the controller. As the battery reaches its target voltage, the controller will then switch between the battery banks to the panel array. The battery bank will then be disconnected, which regulates the battery voltage and makes it constant. This quick switch method is called PWM, and what this does is it makes sure that your battery bank is charged while preventing the process of overcharging.
The PWM controller will usually operate slightly above the maximum power point. Figure shows the operating range for PWM controllers.
