PWM vs. MPPT Solar Charge Controllers

If you’ve been looking for a solar charge controller you’re probably wanting to accomplish a couple of things:

• Improve your solar performance by intelligently collecting the energy from solar panels and storing it in your battery. 
• Extend the life of your battery with protection from overcharging or undercharging.

If you are searching for a solar charge controller, you've also come across "PWMs." What are the differences between a PWM and an MPPT?

PWMs Can Do the Job

A PWM Controller, "Pulse Width Modulator," essentially acts as the switch between your solar array and your battery. When the voltage provided by the solar array falls outside the ideal conditions for charging your battery, the PWM will shut off that flow to protect your battery. It also protects against overcharging, which would be damaging to your battery.

The benefits of a PWM are typically lower cost, fewer electronics, and smaller physical size. There are some downsides to a PWM, however, the main issue being efficiency. The PWM will function to charge and protect your battery backup, but only within a limited range of ideal conditions.

While a well-balanced solar + battery system will run optimally through a PWM, it can become mismatched at high/low temperatures, during partial shading or cloudy days, or during lower light conditions in the morning and evening. In short, under many real-life conditions when it’s hot, cloudy, or shady, that’s when PWMs start to disappoint.

MPPTs Do the Job Better

An MPPT solar charge controller functions by changing its input voltage to get the maximum power from your solar array and then providing an ideal DC output to your battery system. The MPPT, "Maximum Power Point Tracking" controller does not depend on the input from your solar system to match the conditions your battery needs to charge; it matches those two systems. This advanced functionality allows your solar + battery system to work together for maximum efficiency in a wide variety of temperature and lighting conditions, creating optimal charging for your battery backup. This increase in efficiency can be as much as a 30-40% gain.

Practically speaking, this means you could get 30-40% more performance out of the same solar array just by switching out the solar charge controller from a PWM to an MPPT. Put another way, this also means that you could have a smaller array and get the same performance.

A significant benefit of a Victron MPPT controller is that we can bring in higher voltage from the solar array. Why is that? Firstly, we have fewer parallel connections on the roof outside, which is the main connection issue in many solar arrays. Secondly, the difference between the solar and battery voltage is greater, so there is now a higher percentage of time when we can charge. Even when conditions are not ideal (cloudy, hot, shady), we can keep charging. Of course, charging a little is better than not charging at all which is what you will get with a PWM. Finally, we have less line loss in our cables, and we can have smaller cables. When MPPTs first came onto the market 20 years ago, the most significant selling point was that the wire cost savings were more than the cost of the charge controller. Increasing the voltage allows us to move more power with smaller wires and less loss. Its a win-win anyway you look at it. 

 

Victron makes two models of MPPT solar charge controllers, the Blue Solar MPPT and Smart Solar MPPT. Reid this article to learn about the differences and use cases for both.