Say I have a 12 volt battery bank and my turbine is producing 20 volts. What prevents damage to my batteries from the excess voltage?
Excessive voltage will not damage the battery and eight volts is really nothing to worry about. When you're charging a battery, the voltage should be higher. If you put a meter on a 12 volt trickle charger most run at 14 to 18 volts. The battery will draw what it needs to charge and the remaining voltage will be lost.