The charge controller in a PV system is a voltage regulation device which protects the battery bank. If the module were allowed to constantly charge battery bank, then in times of low load, the modules would be capable of supplying more energy to the batteries than the batteries could hold. Simply, more electrical energy would be going into the battery bank than would be drawn out. A lead acid battery which is normally used, would reach a state of over charge. The batteries would boil off too much water, requiring extra maintenance. The batteries would be damaged. If the load were to constantly discharge of battery, the load would completely discharge the battery. Simply, more electrical energy would be drawn out of the battery than would be going in. This will reduce the battery life. Controllers job is to sense the level of charge of the battery by measuring its voltage and to disconnect the module or the load.
