alt Hacker NewsThis isn't true at all unless you narrowly dwfine "the entire system".
Each feeder can be aluminum if you put special goop on any copper connections. Breakers accept it just fine, etc.
You should avoid it for smaller wiring, though. There's special 8000 series aluminum if you're trying to be serious with Al feeders
The goop is generally considered to be unnecessary. What you need is a termination that is rated for aluminum wire, and these are very, very common as long as the wire in question is fairly large (8AWG or so and larger).