Alternators, the same as solar panels
don't actually output 12v, they output much more. They then require regulation to bring the voltage down to suitable charging
voltages. An unregulated alternator will destroy a battery
pretty quickly. A smart charger
will regulate the voltage to accommodate battery
types and their state of charge while your most basic regulator
will pick a charging
voltage and you get down to that. Most alternators have these basic regulators inbuilt. I don't know what kind of solar
controller you are using but as long as it brings the voltage down to somewhere under 14.4v it should be fine.
Hopefully you will get more comprehensive advice from more of an expert than me!