What is a Solar Charge Controller?

Solar Technology FAQs
Solar Technology FAQs What is a Solar Charge Controller.

A solar charge controller, also known as a solar charge regulator, regulates solar-generated voltage and current to and from a battery and runs electrical loads.

A solar array that relies solely on batteries needs a charge regulator to ensure the battery runs safely, which prolongs battery life. Without it, the flow to and from the battery would go unregulated, causing damage to the battery and the system.

The application of a charge controller for solar is necessary for off-grid solar arrays because they rely solely on batteries to store excess solar power and hybrid systems because they use both the grid and batteries. Grid-tied homes that don’t use battery backup don’t need a charge controller because the excess electricity gets directed to the power grid with a solar inverter. However, they also won’t provide power during an outage like a hybrid or off-grid array.

What a Charge Controller Does

Charge regulators help prevent batteries from overcharging or the battery from losing power at night. Electricity naturally flows from high to low voltage. During the day, the solar panels have a higher voltage, but at night when the solar panels don’t have sunlight to convert into an electrical current, the battery has a higher voltage. The system needs a charge regulator to keep the electricity from going back to the solar panels. Without a charge controller, the voltage and current coming from the solar panels and into a solar battery or batteries would probably also provide more power than the battery could handle, creating gassing and battery damage. There are two charge controller types to consider when determining which charge controller to use for your solar array. These include PWM and MPPT, charge controllers.

PWM Charge Controller

A PWM charge controller connects the solar panels directly to the battery, which means the charge controller operates at the battery voltage. For the charge controller to work, the voltage of the solar panels needs to match the voltage rating of the battery. These regulators don’t work well with partial lighting. The need for optimal sun exposure and solar panels that match the battery voltage makes these best for small systems that don’t need to maximize the solar panel output.

MPPT Charge Controller

MPPT charge controllers operate above the battery voltage, which means the charge regulator can handle a solar array with a higher voltage than the battery. These systems are best for larger solar arrays that experience fluctuating weather conditions that make maximizing the solar output desirable. This charge controller type finds the best PowerPoint so it can optimize low light conditions. This feature makes this charge controller ideal for most situations. However, the price tag is also higher.

Charge Controllers and Electrical Loads

The main job of a charge controller is to maintain safe voltage and current flow to the solar battery and stop the battery from back-feeding to the solar panels at night or during a storm when the sun isn’t powering them. However, charge controllers also protect the battery from undercharging with battery load control. A charge regulator controls the electrical load drawing power from the battery with low voltage disconnect (LVD) switching. The LVD on a charge controller keeps the battery from over-discharging by disconnecting loads when the battery reaches a certain discharge level until the battery can recharge. The LVD in charge controllers helps prolong the battery life, especially for lead-acid batteries. Lead-acid battery plates become sulfated when left in a partially charged state for extended periods. Lithium batteries also won’t last as long if they continue at too high or low a charge for a prolonged time.

The Relationship Between Charge Controllers and Solar Batteries

Charge controllers and solar batteries have a close relationship. Batteries allow the system to operate at night and during poor weather, and the charge regulator helps the battery from over or undercharging. Both help extend the life and usability of the system. Another way to use a charge controller is inside the battery. Batteries with charge controllers make finding a compatible charge controller a non-issue.

Batteries with Charge Controllers

Some batteries, like the Goal Zero Yeti and the Tesla Powerwall, have charge controllers in them. These charge controllers are designed specifically for these batteries, making the system safer. All of Go Solar Group’s Battery Backup options have built-in charge controllers.


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