Charging vehicles from on-site generation is straightforward when the vehicle is present while generation is happening, and impossible when it is not. Almost every practical difficulty follows from that.
The systems that work are the ones designed around when vehicles are actually parked, rather than around how much is generated.
The dwell overlap is the constraint
Generation peaks in the middle of the day. Residential vehicles are usually elsewhere then. Workplace vehicles are present, which is why workplace charging pairs with generation far better than home charging does.
Establish the overlap between generation hours and vehicle presence before designing anything. Where there is little overlap, the honest answer is that charging will draw from the grid regardless of what is generated.
Surplus following
The useful mode is charging with what would otherwise be exported: measure generation and site consumption, and allocate the difference to charging. As a cloud passes, the charging rate reduces rather than the site importing.
This requires measurement at the right point, a control loop that responds within a sensible interval, and chargers that can vary their output smoothly rather than switching on and off.
Minimum current is a real limit
AC charging cannot be reduced below a minimum current and continue. Below that the session must stop, and restarting has its own delay and its own effect on the vehicle.
That means a system following a fluctuating surplus can oscillate: stopping when a cloud passes, restarting after, repeatedly. Hysteresis and a minimum dwell at each state are what prevent that, and they cost some of the theoretical benefit.
Export tariff decides whether it is worth it
The saving from self-consumption is the difference between the import price and whatever you would have received for exporting. Where export is well compensated, the benefit is modest. Where it is poorly compensated or unavailable, self-consumption is worth considerably more.
This single number determines whether solar-aware charging is a meaningful commercial measure or a marketing feature, and it varies by market and connection.
Blended modes are usually the practical answer
Pure surplus following can leave a vehicle undercharged on a dull day. Most drivers want a guaranteed minimum charge with surplus used opportunistically above it.
That means a target state of charge by a departure time, met from the grid if necessary, with generation preferred whenever available. It is less elegant and it is what people actually want.
Where storage changes the picture
A battery decouples generation from vehicle presence, which is the fundamental constraint. Generation charges the battery during the day, the battery charges vehicles in the evening.
That works and it adds capital, conversion losses and a second system to maintain. Whether it pays depends on the same export tariff arithmetic, applied twice.