But purchasing renewable energy also drives down its price, by allowing the industry to develop economies of scale and streamline its operations. This strategy is essentially the way most technology innovations work, by first selling to early adopters who are willing to pay a premium and then pushing prices down to mass-market acceptance.

Considering that the market for fossil fuel energy is so much larger than that for renewable energy, I'm going to say that Apple's choice will have a bigger positive effect on the renewable sector than on prices for non-renewable energy.