The solar charge controller is the heart of any off-grid solar system and is critical to the health of the battery. Its main function is to prevent the battery from being overcharged or undercharged. Proper charging of Valve Regulated Lead Acid (VRLA) batteries is very important to the life expectancy of the battery. If a VRLA battery is overcharged and it gasses, then the capacity is reduced; conversely, if the battery is undercharged sulfate crystals will form on the plates and reduce the capacity of the battery.


The technology and type of charge controller (refer to SunWize’s tech note on Solar Charge Controller Types for more information) is actually less important than the charge setpoints. Charge setpoints are part of the cycle strategy designed to reduce the amount of time the storage bank spends at a low state of charge. They should be set per the recommendation of the battery manufacturer.The battery has become one the most expensive components of off-grid systems. A good solar battery in a properly designed system can last 5-8 years; however, a good charge controller and proper setpoints are crucial elements in having such a long-last life expectancy.

Primary Features

Part of a good charge algorithm should be to include temperature compensation. This can be done locally with an onboard sensor if the controller is in the same environment as the batteries (i.e. same enclosure), or can be done with a remote sensor.

Battery Temperature Compensation

A good charge controller should also include indicator lights (LEDs). LEDs illustrate charging status, battery status, and/or errors.

Additional Features

Controllers can include a Low Voltage Disconnect (LVD) which disconnects the load from the battery in the event that the battery falls to a low state of charge. This feature can prevent the battery from being over-discharged, which can possibly cause permanent damage to the battery.


This is not an extensive list of attributes; solar charge controllers are coming out with new features and functions every year. The key thing to remember is you never want to lose sight of is the importance of properly charging the battery. Click Here to View Solar Charge Controllers