200 amp main breaker panel with a 30 amp 2 pole installed for solar, my understanding of 705.12(2) will require 250 al for a residential application is this correct? NEC 2011
Assuming ordinary conditions of use. Do a search on "conditions of use" if you are unsure.
Your 30A breaker, which is probably for a 5kW solar inverter, will require #10 Cu wire. Place this at the opposite end of the busbar from the 200A main, to comply with 705.12(D).
Your main breaker will require that which is ordinarily required for this building loads panel, whether or not the solar is present. Since the 205A of ampacity in 250 kcmil AL meets or exceeds the main breaker, the 250 kcmil AL wire is acceptable and conservative, as long as you do not need to upsize to curtail voltage drop.
There are other reasons why you would be able to use a smaller main wire:
1. If this is a service instead of a feeder
2. If you can take advantage of the "next size up rule", 240.4(B)