Having a mix of power generation approaches will usually be more dependable and less expensive than relying on only one. For example, it is expensive (and maybe impossible) get Big Current with solar alone and difficult (or even impossible) to complete charging on alternator alone. But small amounts of both combine to make a workable and inexpensive charging system.
For this reason the solar + alternator combination is the most common and effective charging approach for vehicle dwellers. But there are times when one of these (or some other source) might do the majority of heavy lifting, or other forms of charging might be best suited to your particular use case.
Note: charging concurrently from multiple sources is normal and generally beneficial.
Alternator charging is usually the biggest bang-for-buck charging offgrid.1) It is automatic2) 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. Direct charging like this will often be most efficient in early morning when bank voltage is the lowest.
However, some cases suggest a more expensive DC-DC charger setup:
DC-DC charging tends to have the same current output all through Bulk stage, no matter what the bank voltage is.
Alternator-only charging can work with lithium banks but for technical reasons solar or shore-power charging is usually required with lead batteries.
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 emplaced in open areas with good insolation. Camping in non-forested areas, for example.
Consider mounted solar as a backbone of your charging if you spend a lot of time emplaced 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 practically whatever you want. Run a space heater? Microwave? Induction cooktop? Charge your batteries? Sure (just not all at the same time).
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, can use power at school/work, “moochdock” in driveways with access to an outdoor outlet. Even if you have to pay for the use of the power it will still be cheaper than off-grid approaches.
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.
More information in this article.
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. But when they are present they are, effectively, a form of portable shore power.
Consider generator 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.