Are You do research and wanted to go with a 24v solar pv setup on the roof (520 watts total), but still have a 12v battery bank?. So You'll need an MPPT controller for this, and the Tracer by SainSonic 30amp controller works great. MPPT circuit solar controllers are considerably more elaborate than PWM. The voltage of the solar panel changes with time of day and temperature. The optimum voltage for battery charging changes as the state of charge...