PWM charge controllers are cheap and simple. They work by connecting the panel directly to the battery, with a switch to modulate current. MPPT controllers, by contrast, run a DC-DC conversion that lets the panel operate at its actual maximum power point regardless of battery voltage.
On paper, MPPT is 20 to 30 percent more efficient. In a temperate climate, that gap is closer to 15 percent. In a hot African climate, it stretches toward 30 percent, because panels lose voltage faster than current when they heat up, and MPPT can recover that voltage in a way PWM cannot.
What that means in practice: a 100 W panel in Lagos in March will deliver maybe 75 W through a PWM controller and 88 to 92 W through a good MPPT. Multiply by 12 panels and you are looking at a real difference in daily yield, especially in shoulder seasons.
The partial shade case is even more dramatic. If a tree shadows one cell out of 36, a PWM controller can lose 30 to 40 percent of the panel's output. An MPPT controller with a proper bypass diode design recovers most of it.
So when does PWM still make sense? Cost-sensitive tiny systems, basic solar home kits, and any setup under about 10 A of charge current. We still ship PWM-DX series controllers for kiosks and rural lighting projects where every dollar counts and loads are predictable. But anything residential or commercial should be MPPT. The price gap is small now, and the yield gap is not.