29/08/2026
STOP USING PWM IF YOU'RE SERIOUS ABOUT SOLAR
A PWM charge controller isn't necessarily bad. It can be a perfectly good choice for a small solar system where the panel voltage is properly matched to the battery. The problem is when people connect a high-voltage solar panel to a low-voltage battery and expect a PWM controller to make full use of the panel. That's where things can go wrong, because a PWM controller doesn't convert the excess panel voltage into additional charging current.
Take a 550W solar panel rated at 55V connected to a 12V battery as an example. The panel can produce roughly 10A at 55V, since 550W ÷ 55V = 10A. With a PWM controller charging a battery at around 14.4V, the controller will pull the panel voltage down toward the battery voltage instead of converting that extra voltage into more current. In a simplified calculation, 14.4V × 10A gives only about 144W going into the battery. That's a huge difference from the panel's 550W rating.
So in this example, you're potentially leaving around 406W of the panel's available power unused. That's roughly 74% of the panel's rated power, while only about 26% is being utilized under these simplified conditions. Real-world results will vary because panel voltage and current change with sunlight, temperature and other factors, but the basic problem remains.
An MPPT controller works differently. Instead of simply pulling the panel voltage down to the battery voltage, it continuously searches for the panel's maximum power point and converts the higher PV voltage into additional charging current. A good MPPT controller can have around 95% efficiency, meaning most of the power available from the panel can be converted into useful charging power, minus the normal conversion losses.
This is one of the biggest reasons MPPT controllers are preferred for larger systems and for situations where the solar panel voltage is significantly higher than the battery voltage. You can also run panels at higher voltages, which can reduce current in the solar cables and help reduce voltage drop, particularly when the panels are installed some distance from the controller.
But this doesn't mean you should throw away every PWM controller. If you have a small system with a panel designed to work with your battery voltage, PWM can still be economical and practical. The problem isn't really PWM itself; it's using PWM where the voltage difference between the solar array and battery makes it a poor choice.
A cheap controller can sometimes become an expensive mistake when it prevents you from getting the power you paid for.
Would you use PWM or MPPT for a 550W, 55V panel charging a 12V battery?
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