In larger solar panel systems designed to power your whole home
PWM solar charge controllers are the standard type of charge controller available to solar buyers. They are simpler than MPPT controllers, and thus generally less expensive. PWM controllers work by slowly reducing the amount of power going into your battery as it approaches capacity. When your battery is full, PWM controllers maintain a state of “trickle”, which means they supply a tiny amount of power constantly to keep the battery topped off.
With a PWM controller, your solar panel system and your home battery need to have matching voltages. In larger solar panel systems designed to power your whole home, panel and battery voltage aren’t typically the same. As a result, PWM controllers are more suited for small DIY solar systems with a couple of low voltage panels and a small battery.
MPPT solar charge controllers are a more expensive and complex charge controller option. They provide the same switch-like protection that a PWM controller does, and will reduce the power flowing to your home battery as it nears capacity.
Unlike PWM controllers, MPPT charge controllers can pair non-matching voltages from panels and batteries. MPPT controllers adjust their input to bring in the maximum power possible from your solar array, and can also vary their output power to match the attached battery. This means that MPPT charge controllers are more efficient than PWM controllers, and more effectively utilize the full power of your solar panels to charge a home battery system.