MPPT vs PWM
Before solar panels became interesting for people that are on the grid, there were only 36-cell ones for charging 12 Volt batteries (and if you had a 24V battery you’d need two panels in series, to make 72 cells). With 36 cells the panel runs at about 18 Volt, and when it gets warm in summer, the Voltage will drop but still be enough to charge a 12 Volt battery (which really takes about 15 Volt).
A solar charge controller is needed in virtually all solar power systems that utilize batteries. The job of the solar charge controller is to regulate the power going from the solar panels to the batteries. Overcharging batteries will at the least significantly reduce battery life and at worst damage the batteries to the point that they are unusable.
Below is a video explaining the main difference between MPPT vs PWM charge controllers.