A Solar Charge Controller or regulator can be considered the backbone of off-grid (battery based) solar electric systems. A charge controller limits the rate at which electric current is added to or drawn from deep cycle solar  batteries. It prevents overcharging and may prevent against over-voltage, which can reduce battery performance or lifespan, and may pose a safety risk. It may also prevent completely draining ("deep discharging") a battery, or perform controlled discharges, depending on the battery technology, to protect battery life.

Simple charge controllers stop charging a battery when they exceed a set high voltage level, and re-enable charging when battery voltage drops back below that level. Pulse width modulation (PWM) and maximum power point tracker (MPPT) technologies are more electronically sophisticated, adjusting charging rates depending on the battery's level, to allow charging closer to its maximum capacity. Charge controllers may also monitor battery temperature to prevent overheating. Some charge controller systems also display data, transmit data to remote displays, and data logging to track electric flow over time.

Charge controllers can be used in solar systems, wind systems or in solar/wind hybrid systems. Solar powered street lights use charge controllers that have an automatic capability to switch on/off a system in the evening/morning depending on the settings.

Learn more about charge controllers (Basics and Technologies)