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Do I Need a Solar Charge Controller?

Posted on January 26, 2022January 26, 2022

If you have a battery bank for your solar panel system, a charge controller is essential to keep your deep cycle batteries properly charged and safe over the long term.

Essentially, a charge controller is a voltage or current regulator that keeps the electric cells in your solar system’s batteries from overcharging. Most batteries require 12-14 volts to be fully charged and exceeding this voltage can damage the batteries.

Not sure if you need a solar charge controller? Our pros at Solar Bear Orlando discuss when one is needed!

What is a Solar Charge Controller?

A solar charge controller is a key component to solar systems that have a battery bank, such as off-grid or backup power systems. The main job of a solar charge controller is to regulate the amount of voltage going into the battery bank for your solar array.

The charge controller ensures that the batteries are not overcharged during the day when solar output is high and that they don’t send stored power back to solar panels at night.

If you have a storage battery installed into your grid-tied home system, you will not need a charge controller. Generally, your solar inverter will maintain your battery health.

Charge controllers are best used with off-grid systems such as for an off-grid cabin, or an RV.

How do Solar Charge Controllers Work?

Electricity flows from high voltage to low voltage and solar panels produce most of their energy during the middle of the day which means that their voltage is high while the battery bank’s voltage is low. In this case, excess electricity is sent to be stored in the battery.

At night, the battery has a higher voltage than your solar array, because they are all charged up from the day. To keep this high voltage from flowing into the solar panels, the solar charge controller works to keep the electricity in place in the battery.

When the battery charger is empty, the charge controller sends power to the battery for a quick charge. Once the battery is close to being full or is in use, the solar charge controller will send a trickle charge to keep the battery charged and ready to supply power when needed.

Further, charge controllers can automatically disconnect non-critical loads from the battery bak if the voltage falls below a certain threshold. This is called “Low Voltage Disconnect” (LVD) and effectively prevents batteries from overcharging.

PWM and MPPT Charge Controllers

There are two types of charge controllers, an MPPT (maximum power point tracking) and a PWM (pulse width modulation) charge controller. There are key differences between the two, which we will discuss below.

PWM Solar Charge Controllers

A PWM charge controller is connected to a solar array with a battery bank. While the battery charges, the voltage of the battery increases, leading to increased voltage in the solar panel that is charging the battery.

With a PWM charge controller, a 12-volt solar panel is needed to charge a 12-volt battery, and so on. If you use a PWM charge controller with 48V solar panels and a 12V battery the controller will not harvest the extra energy produced, it will only harvest up to 12V.

PWM charge controllers are less efficient than an MPPT but could be a great choice depending on your specific needs.

MPPT Charge Controllers

MPPT charge controllers are more sophisticated than PWM charge controllers, and work by measuring the Voltage at Maximum Power or VMP input of the solar panel, and then down-converts the PV voltages to match the battery voltages.

Essentially, MPPT controllers take the high voltage from the solar panels and reduce it so that it matches the battery’s voltage.

When using an MPPT solar charge controller, you can use a solar array with a higher voltage than your battery system because the charge controller will reduce the voltage to not overwhelm your battery.

If you want a more efficient way to control voltage and don’t want to worry about the voltage differences between your solar array and your batteries, it is wise to invest in an MPPT charge controller.