PWM and MPPT Charge Controllers: differences and best use cases in Southern Africa

Solar charge controllers are designed to transfer the power from solar panels to a battery and a load. Two solar charge controllers technologies are available in South Africa: PWM and MPPT. Below are the criteria to consider when selecting the best charge controller for your needs.

PWM solar charge controllers

Pulse Width Modulation controllers (PWM) charge the battery with short current pulses at the same charge voltage as the solar panel output voltage, without limiting their current output. They are affordable and ideal for small, rugged solar systems, often found in small amperage (10A to 60A).

PWM solar controllers offer an efficiency of 80 to 85%, whereas MPPT ones reach up to 97%. This makes a noticeable difference if the electric load of your system is constant and high. If your system is powering a gate motor, LED security light or remote camera, an inexpensive PWM 10A or 30A solar charge controller is sufficient. In other words, PWM controllers work best in small PV systems where efficiency is not critical. They are particularly well suited to Southern African conditions, with warm and sunny weather.

Always connect a PWM controller in the exact order: battery first, then load, then solar panel. Disconnect the system in the exact reverse order: solar panel, load, then battery.

MPPT solar charge controllers

Maximum Power Point Tracking controllers (MPPT) convert the maximum power voltage from the array of PV panels to the voltage required to optimally charge the battery bank. The voltage of the solar array does not have to match the battery's voltage.

MPPT controllers are designed for large solar arrays in domestic and commercial applications where energy efficiency is critical. These controllers ere very efficient and maximise the power extracted from your solar panels in most conditions. They are well suited for cold climates and to manage the input voltage from a large array of PV panels. In cloudy weather, the MPPT will decrease the charge current while maintaining the optimal charge voltage to the battery bank. As the clouds disappear, the MPPT will increase the charge current, while keeping the charge voltage at its optimum point.

Sizing a solar charge controller

Charge controllers are rated by amperage and voltage.

Use a safety factor of 25% when calculating the amperage of your solar charge controller: a 120W solar panel charging a 12V battery bank associated with a 12V DC load will require a charge controller rated for at least (1.25x120W)/12V = 12.5A.

PWM controllers necessitate that the PV voltage matches the battery and load voltage. MPPT controllers typically work with a wide PV voltage range.

View all Solar Charge Controllers available for sale in South Africa.