If designed correctly, then 100% effective.. solar is designed to meet a goal, that is, a specific known power consumption over a 24 hour period with battery capacity to allow for 5 days autonomy.
so that's the ideal, in practice, DIY RV installs rarely meet this goal.
generator size only needs to meet peak demand unless you have a system that acts as a UPS system.
One of the limiting aspects of an RV is roof real estate, it is often not possible to install sufficient PV to satisfy demand, hence many diy installs give solar a bad 'wrap' mainly due to poor design and over expectations.
having said that, there are ways to increase apparent PV area with stacking and sliding systems such as pictured here. This is a set on my daughters RV, there is a total of 1400 Watts on a 22ft roof. we could have maxed it out at 2400 Watts, but there was no need as this suits their requirements.
the system is designed to power the A/C overnight and has a battery capacity of 16,800 W/hrs
the system is all Victron and is designed as a UPS with generator backup.
the main inverter/ats/charger is a Victron multiplus 2 unit @3000VA