If you're using a system of gears to drive the alternator, how noisy is that going to be? Why use gears versus belt drive which seems like it would be quieter and likely have less resistance.
One challenge I visualize is the turbo location is not standard on most vehicles, so to adapt gears, brackets, bearings, etc (same would apply with belt drive) is going to be very much a custom fabrication for each installation. Would you limit the application list to a small number of vehicles at first that all share the same powertrain?
Many newer manufacturers have gone to a system of modulating when the alternator is actually charging, thereby reducing the load on the engine when extra electrical charge is not needed. How does the efficiency of your proposed system compare with the efficiency gains of the modulation approach? Can you create a business case for your design over the modulation scheme that likely is more easily retrofitted to vehicles since it would involve mostly wires and software?
-Rod