Solar panels typically have output voltages higher than is desirable for charging batteries, and so some form of regulation or control is required to avoid damaging a battery bank with too high a charging voltage.
Since shade can be in issue onboard, the best results are obtained by using one controller per panel.
Simple, inexpensive PWM controllers limit the voltage from panels to battery, but these types of controllers waste a great deal of the potential power of the solar panel.
Maximum Power Point Tracking (MPPT) controllers:
Using a Maximum Power Point (MPP) algorithm, the Genasun and Victron controllers find and use the best combination of voltage and current (amps) to be able to deliver the highest available power (watts) to the battery.
Using an MPPT solar controller will result in 10% to 30% more output from your solar panel than using a simple PWM voltage controller.
MPPT controllers also greatly reduce the effects of partial panel shading.
Want to know exactly what your solar panels (hydrogenerator, Windgenerator, etc) are producing? The Watt Wizard will tell you, continuously, and keep a record over time, as you specify.