charge control systems

When using PV panels as part of an off-the-grid or hybrid system it is usually necessary to use an electrical devices called a charge controller.  A charge controller helps to manage the voltage of the system and to manage the charging of the batteries. If a battery is routinely allowed to overcharge its life expectancy will be greatly reduced. A modern Pulse Width Modulated (PWM) controller can turn on and off the circuit that connects to your batteries and PV units in order to keep the voltage more stable. If the charge in the battery gets too high it can cut the circuit to avoid overcharging. 

Some charge control systems are designed so that they will run the system at whatever voltage produces the most wattage. A good controller can sometimes increase the amount of usable energy you get out of your PV panels and batteries by as much as 15%.

In order to be effective a charge controller must be matched to the type of batteries you are using. For example a charge controller designed for lead-acid batteries should not be used to control NiCad batteries.  Also the charge controller must be of the right capacity to handle the maximum current produced by the PV array.

There are two types of controllers: series and shunt. Series controllers stop the flow of current by opening the circuit between the battery and the PV array. Shunt controllers divert the PV array current from the battery, sometimes to an artificial load. Both types use solid state battery voltage measurement devices and shunt controllers are 100% solid state.  Several charge controllers on the market use a 3 stage charging approach  with bulk, absorption, and float modes to ensure that voltage and current settings accurately match the batteries' actual state of charge. This reduces the time needed to bring the battery to full charge and can extend the life of the battery.