I would suspect a faulty voltage regulator, (and alternator diode?).

Please check battery voltage, then start engine and check battery voltage again with engine at idle.

I think that more than 14 volts at idle indicates a problem with the regulator and I would not drive the car much for fear of damaging $$$$ electrical components. Beware overcharging as this will create more problems including ruining your battery.

Your best bet might be to have the alternator tested by a pro asap.

Acky