• PWM: A PWM (Pulse Width Modulated) solar charge controller is the traditional style. They are robust, inexpensive and widely used in solar panel applications.
• PWM-Shunt: PWM shunt controllers are used less often and mostly in applications where electrical interference is an issue.
• MPPT: The MPPT (Maximum Power Point Tracking) solar controller is the shining star of today's solar systems. These controllers actually detect the optimum operating voltage and amperage of the solar panel array and match that with the battery bank. The result is additional 15-30% more power out of your solar array versus a PWM solar controller. Although the MPPT solar charge controller is more expensive than its PWM counterpart, it is generally worth the investment for any solar electric system over 200 watts.
Since renewable energy power systems almost always gather power and store it in batteries, almost every system requires a charge controller. A solar charge controller will protect your batteries from being overcharged by your solar panels and it will block any reverse current (from the batteries) as well. Solar charge controllers will actually protect every aspect of your solar power system from your batteries to your solar panels. Temperature sensors are an inexpensive addition that help the charge controller more accurately regulate the charge of the battery bank.