MPPT vs PWM solar charge controllers

A solar controller regulates panel output to properly charge a battery. Two technologies. (1) PWM (Pulse Width Modulation): cheap, simple, wastes any panel voltage above battery voltage. A 30V panel feeding a 12V battery loses ~40 percent of available energy. Only use PWM when panel voltage closely matches battery voltage (e.g. a nominal 12V panel on a 12V bank). (2) MPPT (Maximum Power Point Tracking): DC-DC converter finds the optimal voltage/current point on the panel's IV curve and converts it to battery voltage. Recovers most of that lost energy. Cost 3-5x PWM but pays back within a season if you have real solar (>200W). Sizing: MPPT amp rating should match battery, not panel, a 30A MPPT can handle up to 30A INTO the battery regardless of panel wattage. For a 12V system: 30A MPPT = up to 400W of panel; 50A MPPT = up to 700W. Multiple panels: series wiring INCREASES voltage (best for long cable runs and MPPT harvesting), parallel wiring INCREASES current (best when shading is a concern because one shaded panel doesn't kill the string). Never mix panels of different wattage in series, string current drops to the weakest panel. Common failure: reverse-polarity destroys the controller instantly, no fuse will save it. Wire correctly the first time.