The basic formula for sizing a solar panel charge controller is to take the short circuit current (Isc) of the array, and multiply it by 1.56. (What is short circuit current? Glossary of Alternative Energy Terms & Why 1.56? See Sizing PWM Solar Charge Controllers and Sizing MPPT Charge Controllers). Be sure that the solar controller you select can handle at least that many amps.

Please protect this important part of your system with appropriate overcurrent protection before and after the solar controller (see Enclosures, Electrical & Safety for options).

Solar Charge Controller Types

Now that you know what size solar controller to look for, identify which type of solar charge controller is right for your application: MPPT, PWM, and PWM shunt controllers. 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 controllers are used less often and mostly in applications where electrical interference is an issue. 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.