Like the article says, the $578M is just the prepayment. The total amount may be much greater. The facility itself was acquired from First Solar, who sold it at a loss, and it seems like Apple will be fronting the capital for the factory's construction. The deal also requires a minimum amount of capacity for Apple and also exclusivity for some unknown amount of time (perhaps the same 5 years), so it's unlikely that they'll be supplying anyone besides Apple. And this is just for one component, Apple likely makes these deals with all their suppliers.