Batteries are often the bottle neck of off grid solar PV systems.

Overcharging and deep discharge are the main causes of their premature failure. A charge controller is used to maintain the proper charging.

As we know, the brighter the sun, the higher the voltage; basic old charge controllers just short or disconnect the solar panels when a certain voltage is reached. Nowadays, controllers match better batteries behavior and offer a 3 stage charging cycle: bulk charging followed by absorption and float.

2 types of controllers are in use. MPPT and PWM. MPPT are more performant, providing 10 to 30% more power to the battery. Both controllers type; PWM or MPPT offers battery low voltage protection: a disconnect turning off whatever is connected to the load terminal until the battery reaches a usable voltage.

A single LED indicator, a series of LED or a digital meter for the more sophisticated allows to monitor the controller.