jpmihalk is right, and right on : )
Solar is simple a direct charging to your House batteries, when no other power source is available. Now, it doesn't mean that solar power is not 'allowed' during those times, since it IS hooked up directly to the batteries, but it just means that it's power is not 'used' since other 'stronger' power is available, such as shore, generator, or even the engine alternator while you are driving.
Solar is what's used when you are parked, and the engine turned off, with no shore power or generator running. It simple takes the sun's power, converts it to 12v, and sends it down to your batteries, thru a Controller that monitors it and makes sure that it doesn't 'overcharge' your batteries. Simple.
Solar's advantage to RVrs is simple to limit the amount of time you use your generator to charge your batteries when you are not on shore power. Will you need your generator anyway? Yes. Air Conditioners, electric water heating, etc., will need your generator to operate, but Solar can fill in the gaps and give you more time 'off grid' without running it as much.
If your coach has an AGS(AutomaticGeneratorStarter), then you have a 'complete' system to provide automatic cranking of your generator, when needed, and automatic solar power in between!
two Campers, two Electric cars