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DRAFT
Having a mix of power generation approaches will usually be more dependable and less expensive than relying on only one. Solar + alternator charging is a common and effective approach but there are times when one of these (or some other source) might do the majority of heavy lifting. It depends on your particular use case.
Alternator charging is usually the biggest bang-for-buck charging offgrid. It is automatic and will charge whenever you are driving. Consider the alternator as the backbone of your charging if you drive daily or near daily.
For many people a plain combiner (relay, solenoid, VSR, isolator will be cheap and highly effective for Bulk charging.
However, some cases suggest a more expensive DC-DC charger setup:
Some solar should probably be included in every build; it is a silent, long-lived charging source that can output whatever voltage your batteries need.
Having panel permanently mounted on the vehicle can be a quality of life upgrade; it is charging anytime the sun is falling on them.
Consider mounted solar as a backbone of your charging if you spend a lot of time in open areas. Camping in non-forested areas, for example.
Portable solar can augment the mounted panel, can be placed in sun, and can usually be angled for maximal harvest.
Consider mounted solar as a backbone of your charging if you spend a lot of time in areas of shade adjacent to areas with clear sun. In a forest with canopy openings, for example.
Having access to shore power (grid power) is like winning the vandweller lottery. It is cheap and practically unlimited. As long as you can keep your demand under ~1500w you can do whatever you want.
Consider shore power charging to be the backbone of your charging system if you regularly have access to shore power. E.g. you live in a house, rent RV spots with pedestal power, “moochdock” in driveways with access to an outdoor outlet.
You can get away with a very simple, low-power, single-stage shore power charging setup,
You will need to spend money on a more powerful charger if your time is limited (only a couple hours each day). A multistage charger will be important for charging lead banks without solar.
A generator can provide steady power regardless of ambient weather or other conditions. Generators are uncommon in vandwelling scenarios because most are charging by other means.
Consider shore power charging to be the backbone of your charging system if you already own the genny and solar is not able to meet needs due to weather or other conditions. In general, generator charging is most effective in the morning. Not only does morning charging work when the sun is low, but it will boost battery voltage up to where PWM controllers can find their feet.