Controllers, or charge regulators, prevent excessive overcharge of the batteries  within a remote power system. Two different methods of charge control are generally used, series and shunt type, though both typically use battery voltage (set point) to determine when charging should be reduced or stopped completely.

In a series-type controller the current flowing into a battery will occasionally be broken by opening the circuit between the array and the battery. Unlike other types of generators, solar modules can be short circuited or open circuited without causing damage to them. Simple controllers contain a relay that opens the charging circuit, terminating the charge at a pre-set high voltage and, once a pre-set low voltage is reached, closes the circuit, allowing charging to continue. In a shunt-type controller, this same array current is directed to a resistor of some type effectively short circuiting the solar modules. More sophisticated controllers known as “pulse width modulation” or “narrow width” controllers have several stages and charging sequences to assure the battery is being fully charged.

Charge controllers are rated and sized to the systems they protect by the short circuit array current and voltage. Most common are 12, 24 and 48 volts controllers with current ratings running from 1 amp to over 100 amps. Because of light reflection from snow, cold temperatures and the “edge of cloud effect”, sporadically increased current levels are not uncommon. For this and safety reasons, the size of a controller’s amperage must be increased by a minimum of

twenty five percent. On small systems where a 10 watt or smaller module charges 100 amp hour battery or larger, no regulator is required if the number of daylight hours exceeds that of the nighttimes’ summer use only. However, the use of an inline blocking diode is required to prevent the solar module from draining the battery at night.