PWM throws away a third of your panels

A charge controller sits between your panels and your battery. There are two kinds, and picking wrong wastes a large slice of the array you paid for.

PWM essentially connects the panel to the battery and chops the connection to regulate. Simple and cheap — but it drags panel voltage down to battery voltage, and the extra voltage your panel was producing is simply lost.

MPPT is a smart DC-DC converter. It runs the panel at its optimal voltage, then converts the excess voltage into extra current for the battery. Nothing gets thrown away.

The gap widens in cold weather — panel voltage rises when cold, so PWM wastes even more — and with higher-voltage panels.

The math that decides it: if MPPT costs $80 more and recovers 25% of a 400W array, that's like getting 100W of free panel. Panels cost more than $80 per 100W.

Sizing it: array watts ÷ system voltage, plus about 25% headroom for cold-weather voltage spikes and edge-of-cloud effects.