First, let's go over what solar regulators actually are. With solar power generators it's always a stand-alone device, whose main function is to manage the charging process of the battery: keep it from overcharging and not to let it be used when empty. This device is pretty much obligatory for a solar panel system. The only exception when a solar system with batteries can function safely without a charge controller is when battery capacity greatly surpasses the wattage of panels, like in solar vehicles, and there is basically no risk of overcharging it.
There are two main types of solar controllers:
PWM-controller (pulse width modulation) and
MPPT-controllers (maximum power point tracking). The first is much cheaper but should only be used when the voltage of panels is equal or slightly higher than the voltage of batteries. MPPT regulators, on the other hand, are more expensive, more efficient and sometimes have more features. Now let's look at their functions more closely.