What A Solar Charge Controller Does (Explained)

The solar charge controller is a crucial element in your PV system as it prevents the risk of overcharging your batteries. The solar panels connect to the solar charge controller, and the charge controller distributes that current to batteries and connected load devices.

Solar charge controllers regulate the voltage and current flowing from the solar panels to the batteries to ensure proper charging and prevent battery damage through overcharging. It also monitors the battery voltage to slow the current flow as the battery approaches full charge.

Some of the key points we will cover regarding solar charge controllers and how they work are:

  • How solar charge controllers regulate current and voltage in your PV System
  • The different types of solar charge controllers
  • Do you need a solar charge controller

Getting the right solar charge controller can extend the life of your batteries and keep your PV system performing at maximum so let’s explore these essential components in a bit more detail.

Charge Controller Mounted On The Wall
Charge Controller Mounted On The Wall

What Role Do Solar Charge Controllers Play?

Solar charge controllers balance the current received from the solar panels and ensure that the batteries receive the correct level of current to prevent overcharging.

Solar panels don’t produce the same current as this depends on the atmospheric conditions. They can produce variable levels of voltage and current that flow to the batteries.

Without regulation, your batteries would receive an overload of electricity. While they could absorb and charge up initially, there would be no way to stop the flow from the solar panels short of disconnecting them as they approached full charge.

Battery Protection

As more current flows into charged batteries, the internal battery plates and electrolytes would eventually fail as the incoming current has nowhere to go. This excess could cause irreversible battery damage and risk rupture or explosion.

The solar charge controller steps in and controls the flow of current to the batteries and will slow it down and gradually stop the current as the batteries reach full charge. Then, as the batteries are used, the solar charge controller will allow the necessary current to start the charging process again.

The Relationship Between The Solar Panel And The Battery

One of the most important dynamics in the PV system is the relationship between solar panels and batteries. The solar panels create the electric current in the photovoltaic cells and then distribute that current either directly to a device or storage for later use.

In smaller systems where the panel voltage does not exceed 140W, you could connect your solar panels directly to your batteries for charging. Still, you would need to monitor the progression of the battery charging carefully.

Because there is nothing between the battery and the panel, the panel will continue to send current to the battery even if it’s fully charged. This will lead to overcharging and damage to the battery’s internal structure, which is usually not fixable.

Even a small 10W panel emitting 0.7A of current can overcharge a battery if not attended to, and while lead-acid batteries are cheap, replacing them due to overcharging can become expensive, and this is why you should have a solar charge controller.

What Types Of Solar Charge Controllers Do You Get?

The two main types of solar charge controllers are MPPT (Maximum Power Point) and PWM (Pulse Width Modulation).

The MPPT Charge Controller

The MPPT controllers are far more efficient than PWM controllers as these work by comparing the solar panel’s voltage against the battery’s voltage.

MPPT controllers optimize the voltage between the battery and the panel and effectively extract maximum voltage, especially during adverse weather conditions.

While MPPT controllers are 20%-30% more efficient than PWM controllers, they are more expensive and are best suited to high voltage PV systems such as home and business-based platforms.

The PWM Charge Controller

The Pulse Width Modulation solar charge controller operates differently from the MMPT controller. It determines how much voltage the battery needs from the panels. Through a series of pulses, it controls the level of current flowing to the battery.

When the battery is in a low charge state, the pulses are longer with greater voltage and current, and once the battery requires less voltage as it reaches full charge, the pulses become shorter with less current and voltage.

The solar panel often delivers more voltage than a battery, so a lithium-ion battery can deliver around 12V- 14.4V, while the panel could be providing 16V -20V depending on its size.

The PWM controller matches the currents between the two and ensures that the battery does not overcharge or receive too much current, resulting in damage.

Does Your PV System Require A Solar Charge Controller?

Smaller PV systems like those used outdoors for charging or running small devices may not need a charge controller, but it would be better to have one to optimize both charging and performance.

Many people may not want to spend the extra money on a solar charge controller, but in reality, any PV system should have a solar charge controller.

Because PV systems are an investment, and even though you may not be spending thousands of dollars on a small portable one, you would still be investing a few hundred dollars.

Regardless of what size system you are buying, chatting with the technician regarding including a solar charge controller will form part of the system design. It will be included in larger PV arrays as you could not run a high-voltage system without one.

Remember that you want your PV system to perform at optimum when you need it and have your batteries last as long as possible, so incorporating a solar charge controller is certainly going to go a long way to achieving that.

How Charge Controllers Are Rated

Depending on your PV system’s configuration and size, there are different sizes of solar charge controllers available. Most controllers are rated for 12V or 24V, and some may be rated at 72V to accommodate larger voltages.

Charge controllers also have amperage ratings, so if you have a 200W solar panel that generates between 10A and 12A during peak generation times, your solar charge controller should be rated at 15A.

It is always better to install a solar charge controller that can accommodate a little more than the maximum voltage and amperage the system can generate.


Sol Voltaics is an affiliate and an Amazon Associate, we earn from qualifying purchases - at no extra cost to you.


Sol Voltaics Logo Icon green white