The most important job of all solar charge controllers is to properly charge the batteries and to give them as long a life as possible. Choosing the most suitable charge controller is simple and only requires two steps:

       Step 1 – Voltage selection
Select a charge controller that is compatiblewith the system voltage. The standard configurations are 12, 24, and 48 volts.If you are wiring your batteries for 24 volts you need a charge controller thatis rated at 24 volts.
Some controllers are voltage specific, meaningthat the voltage cannot be changed or substituted. Other more sophisticatedcontrollers include a voltage auto-detect feature, which allows it to be usedwith different voltage settings.

       Step 2– Current capacity
Select a charge controller that can handle themaximum output current of the solar panel (or solar array). The maximumpossible current that a PV panel can generate is the “short circuit current,”indicated as Isc in the panel’s label or specs sheet.
There are two types of charge controllers:
Pulse width modulation (PWM)
Maximum power point tracking (MPPT)

       The difference between these two types ofcontrollers is that the PWM is not as efficient the MPPT. The MPPT is the mostcommon these days and can gain you up to 30% more power than the PWMcontrollers. The MPPT charge controllers also allow the strings of panels to beconnected in series for higher voltages, keeping the amperage lower and thewire size smaller, especially for long-wire runs to the PV array.    
When picking a charge controller, there area few steps that you must follow to make sure that you get the right controllerfor the job. The best thing that you can do is to use the manufacturer’s sizingtools that are offered on their web sites. The other option is to give themanufacturer a call —their salespeople will usually be happy to help you topick the best controller.