solar charging - sunlight is only available during a short window, as when camped in a forest canopy with a clear overhead view. Note that poor insolation calls for increased harvest / overpaneling, not faster charging necessarily

generator charging - for efficiency purposes the generator is shut down after Vabs is reached. Generators run most efficiently when fully loaded.

shore charging - you only have a certain amount of time on the extension cord

alternator charging - you will driving for short periods only