MPPT vs PWM: which solar charge controller to pick and why
The charge controller is the brain of your system. Picking wrong costs 25% of your yield forever. Technical differences and when each one makes sense.
A 100 W panel with a PWM controller charging a 12 V battery gives you ~75 W. The same panel with MPPT gives you the full 100 W. That's the deal: 25% more yield every day, forever.
What they actually do
Both push panel energy into the battery. PWM (Pulse Width Modulation) chops current to drop the panel voltage to the battery's; it wastes the rest. MPPT (Maximum Power Point Tracking) converts that extra voltage into extra current. Pricier electronics that recover what PWM throws away.
When PWM still makes sense
Small systems (<150 W) where the extra MPPT cost ($50-100) doesn't pay back. Boat battery maintainer, electric fence, small irrigation pump. Below 100 W: a $15-25 PWM is fine.
When MPPT is mandatory
Any serious system (>200 W). Especially if your panel's Vmp differs from battery voltage: modern 36-40 V panels charging a 12 V battery only work with MPPT. It also lets you wire panels in series (more voltage, less current, thinner wire).
How to size an MPPT
Three numbers: max input voltage (array Voc at -10 °C must stay below), max output current (≥ desired charge current), and battery voltage compatibility. Quick rule: MPPT amps = panel watts ÷ battery voltage × 1.25.
Brands worth considering
Victron SmartSolar (gold standard, Bluetooth app), EPEver Tracer (price/value), Renogy Rover (USA), Morningstar TriStar (industrial). Skip no-name <$35 units — they're PWM dressed as MPPT.
Stated efficiency vs measured
A good MPPT reaches 97-99% efficiency. Anonymous Chinese brands claim 99% and measure 80-85%. If you buy cheap, verify the real output current with a clamp meter to catch it.
Then pick which inverter to pair and check what wire gauge to use.
Want to know how much energy your appliances use? Calculate it here.
Open calculator