A Charge Controller is used to regulate the output of your Solar Modules. They are also used to regulate the output of wind generators and hydroelectric generators. Essentially a charge controller is there to prevent the overcharging of your battery or battery bank. When your battery or battery bank is completely charged, your charge controller will reduce or stop the solar charge so as not to damage the battery.
It’s important to select a charge controller that will be able to handle more than the amperes of your solar modules. What this means is that while most solar panels will not produce more than their rated amperes it is possible for them to do so for small amount of time under ideal conditions. On a bring cold day its not unheard of for a solar module to momentarily produce 15% more than tis rated amperes. It is recommended to leave a 25% margin on the controller you choose. For example, a 47 amp solar array would should use a 60 amp charge controller rather than a 50 amp charge controller to account for the possible spike.