Solar panels sit on the roof of your RV or caravan collecting energy from the sun in the solar cells and transferring that energy (through a charge/solar controller) to your battery.
 
The charge controller mounts inside the RV. Wires run from your solar panel(s) to the charge controller and from the charge controller into your battery. The purpose of the charge controller is to control the rate at which your batteries charge. The charge controller is required to prevent overcharging and in the case of an MPPT charge controller, operate the panels as efficiently as possible.
 
POA from $1299 installed