Choosing a Solar Charge Controller: Key Factors and Types Explained

Using photovoltaic panels to charge a battery requires a solar charge controller. This device prevents overcharging and damaging batteries.

In grid-tied systems, charge controllers are not necessary, since the inverter sends excess energy to the grid automatically. The cost of a solar charge controller can range from about $20 to $500, but keep in mind that an off-grid system has a higher total cost overall than a grid-connected system. You will be advised whether you need one by the best solar companies and everything will be set up correctly.

What Is a Solar Charge Controller?

There is no device controlling the charging process if you connect a battery directly to your solar panels. In this case, your battery will most likely be damaged by excessive voltage and current. Solar charge controllers and solar regulators serve three main purposes:

Supplying adequate voltage for the battery
Regulating the charging current (amps)
Preventing overcharge

Charge controllers are basically smart battery chargers. They are important when charging a battery using solar panels. Their voltage and current output vary depending on the amount of sunlight.

This type of charge controller has the primary function of regulating the amount of electricity in the battery, but it can also provide electrical protection by the following means:

Switching off the battery when it reaches an excessively low voltage
Preventing reverse current from the battery to the solar panels when they are not generating power
Lowering the charge voltage when the battery temperature rises

When Do I Need a Solar Charge Controller?

Normally, the use of solar charge controllers is limited to off-grid systems. Most home solar systems are connected to the grid, and therefore, the use of charge controllers is not necessary.

The charging process cannot be controlled if your solar panel system does not include batteries.

In a solar battery system, the inverter functions as a charge controller. Once the battery is fully charged, excess energy can be sent to the grid.

Based on the type of inverter, a solar power system with a battery bank can be configured differently. You can use a hybrid inverter, which connects to solar panels and batteries simultaneously, or you can have a separate solar inverter and battery inverter. The inverter has a built-in charge controller function, so a separate charger is not needed in either case.

Types of Solar Charge Controllers

There are two main types of solar charge controllers: pulse-width modulation (PWM) controllers and maximum power point tracking (MPPT) controllers.

Pulse-Width Modulation (PWM)

Solar charge controllers with PWM are simpler, more affordable, but less efficient. The controller can provide small amounts of power to keep the battery full by providing small amounts of power once the battery reaches 100% charge. Once the battery reaches 100% charge, the controller can reduce its current output gradually.
For example, if you want to charge a 12V battery with a PWM charge controller, you need photovoltaic modules rated at 12 volts.
A PWM solar charge controller typically costs $15 to $125, depending on the rated wattage and amperage. PWM controllers have a typical efficiency of less than 80%.

Pros and Cons

More affordable than MPPT charge controllers
Smaller and easier to carry around
Suitable for DIY solar energy systems
You cannot charge batteries with higher-voltage solar panels
Less efficient than MPPT charge controllers
Less efficient in cold weather

Maximum Power Point Tracking (MPPT)

An MPPT solar charge controller, also known as a smart DC-to-DC converter, can match a battery system with solar panels that are of a higher voltage.
In order to maximize the power generated by your solar panels, you need an MPPT charge controller.
At the same time, the controller keeps a suitable charging voltage for the battery system.
According to EnergySage, you can expect to pay between $28 and $324 for a MPPT solar charge controller. However, the best MPPT controllers can reach an efficiency level of over 95% depending on the model.
I will give you an example of a solar array that operates at 36 volts and 10 amps, which is equivalent to 360 watts of power. The output of this power output from a PWM charge controller cannot be used to charge a 12V battery. As a result of the MPPT charge controller, it is possible to lower the voltage to 12V while increasing the current to 40 amps, which makes it possible to charge the battery.

Pros and Cons

You can charge batteries with solar panels of higher voltage
Up to 20% more efficient than PWM charge controllers
Can handle higher wattages efficiently
MPPT technology is more expensive
Installation is more complex
Less efficient in systems smaller than 170W

Factors To Consider When Choosing a Solar Charge Controller

You need to carefully review the technical specifications of your solar charge controller before making your purchase. If there is a mismatch between your charge controller and the solar panel and battery you will not be able to operate your system, and you may even cause damage to the components.

Voltage Compatibility

The charge controller that you use should be compatible with the output voltage supplied by the solar panels and the input voltage required by the battery. These voltages are equivalent when you use a PWM controller, but the solar panel voltage can be higher when you use an MPPT controller.

Maximum Current Rating

There must also be current compatibility between components in any electrical system. If your battery system has a maximum current of 30 amps, the charge controller should not exceed that current, and your solar array should be able to handle the maximum current. You shouldn't use a 40-amp charge controller if your battery system has a maximum current of 30 amps.

Diversion Load Control

A diversion load is often used with charge controllers for renewable energy systems such as solar panels and wind turbines to dump excess energy once the batteries are fully charged.

Display and Monitoring Capabilities

If you are looking for a charge controller that can display its operating conditions, you should look for one that includes an LCD display or a Bluetooth module that allows monitoring via smartphone.

Temperature Compensation

Batteries can be damaged by high temperatures, but the best charge controllers are equipped with a temperature-compensation feature that reduces charging voltage as necessary to prevent overheating.

Efficiency

In order to determine how much solar energy gets converted into battery charge, your charge controller's efficiency is an important metric. PWM charge controllers are generally less efficient than MPPT charge controllers, but they are also less expensive. MPPT charge controllers can achieve a charging efficiency of over 95%, but they are more expensive.

Cost
A solar charge controller is one of the cheapest components of an off-grid solar system. It is not very expensive on its own. A good MPPT controller may cost just a few hundred dollars. An off-grid system, however, typically costs much more than a system connected to the grid, possibly by tens of thousands of dollars.