This really isn't a problem, except for the alarm with is alerting you to a situation that isn't a really a problem.
An engine's alternator warning light and alarm are set up to go off whenever the alternator stops
charging. This is measured by comparing the voltage at the outlet of the alternator to the battery. If the battery voltage is higher than the alternator, the alarm goes off because in an alternator only charging system this means the alternator has failed. An internally regulated alternator is never going to run the voltage up as high as a solar system during bulk charging, hence your annoying, and meaningless, alarms.
What you have is not a problem, except for the
noise. My alternator system only has a warning light, which comes on all the time on sunny days when the solar system brings the voltage up. It's not a problem, it's not even really a "conflict" everything is working as it should... except for your damn buzzer.
You have a couple ways to deal with this.
Disconnect the buzzer, but if this is the same buzzer as your
oil pressure you might want to try something else.
Disconnect the entire alternator alarm circuit. On a
boat, you'll have other ways of seeing if the alternator has failed, and other charging systems, so this isn't such a bad idea.
You can set the alternator to run a few tenths of a volt above the solar system. This has the unfortunate effect of overcharging by the alternator, or undercharging with the solar system, but can
work if you are aware of the issue and can manage it.