The Difference Between MPPT and PWM Solar Charge Controllers

Solar charge controllers are an important component of any solar power system that utilizes battery storage. The controllers help to regulate the flow of power from the solar panels to the batteries. If batteries are overcharged, their life is usually reduced significantly. In some instances, it could cause damage to the batteries, rendering them unusable.

Modern solar controllers also help to prevent the reverse flow of current. At night, when solar panels are not producing electricity, batteries can lose power as it flows back towards the solar panels. The controllers detect when solar panels are not producing power and they disconnect the batteries from the solar panels.

If you are planning to purchase a solar system, you will have two options when picking a solar controller. These are the Pulse Width Modulation (PWM) and the Maximum Power Point Tracking (MPPT).

The Pulse Width Modulation (PWM) Controllers

PWM solar controllers are the standard type of charge controller offered to solar system shoppers. These controllers work by slowly cutting back the amount of power being sent to the batteries as they reach full charge. When the battery bank reaches full capacity, the PWM controllers maintain a trickle of power. The result is that a small amount of power continually keeps the battery bank full.

PWM controllers work when the solar array and the battery bank need to have matching voltages. In large systems for powering the entire home, the battery and panel voltage are not usually the same. As a result, PWM controllers are most appropriate for small DIY systems.

For instance, a 12V panel will charge a 12V battery. If you have a 24V battery bank, you will need a 24V solar array. If you attempt to charge a 12V battery with a 24V solar array, over half of the power from the solar panels will go to waste. On the other hand, you charge a 24V battery bank with a 12V panel, all of the panel’s potential will be wasted as the voltage of the panel must be higher than the voltage of the battery bank.

The Maximum Power Point Tracking (MPPT) Solar Charge Controllers

MPPT controllers have a DC to DC converter inside. This enables them to take one voltage on the input and use that for charging a battery of, typically, varying voltage. For example most MPPT charge controllers require the voltage of the solar array be more than that of the battery bank, this allows for the single circuitry type that will drop voltage into what is needed. Designing it this way allows for one to string solar panels in series preventing as many wires running to the array. Typically MPPT controllers are more than 95% efficient.

Inside an MPPT charge controller is a small computer designed to apply load to the solar panel in a way that optimizes the amount of power pushed to the battery bank.

A major advantage of MPPT controllers is your flexibility in components on each side. When using PWM controllers, the solar array voltage has to be matched to the battery bank voltage which means purchasing a certain voltage of panel and typically running them all in parallel which could include many more wires. When you can choose a higher voltage panel, use smaller wires, and select a higher voltage battery bank, your system can become much more future proof from the beginning. The high-voltage systems produce less current, which means smaller conductors can be used. Also keep in mind that many solar components are sized based on current/amps, so as you increase voltage you increase capacity for the same amount of current.

Beene Brothers strives to keep this in stock for $100 as a convenience. If we don’t have it available, Amazon and Aliexpress should be able to set up you with a unit.

To Sum It Up

If you are planning to purchase a solar system, a solar charge controller is just as important as an inverter or solar panels. Thankfully there are options such as the one listed in the sidebar here which support a range of input and battery voltages. One way to cut costs is to utilize low-cost, high-voltage systems coupled with an MPPT controller.