Joe, sure - it's technically a "power purchase agreement" (Apple will be getting some power in return) - but payment appears to be in exchange for whatever their "130MW" corner of the park is good for.
You say "we do not know all the terms of the PPA", followed by "there is no doubt that payment is dependent upon output". Since you don't know, your certainty on the matter is perplexing. Apple is cash-rich to the tune of $160 billion, so as Keith points out this drop-in-the-bucket appears to be worth far more in greenwashing and tax credits than energy to the company, or reduced emissions to California.
First Solar is quite a bit less certain than you are. An excerpt from the CYA/disclaimer which accompanies your press release:
These forward-looking statements are often characterized by the use of words such as "estimate," "expect," "anticipate," "project," "plan," "intend," "believe," "forecast," "foresee," "likely," "may," "should," "goal," "target," "might," "will," "could," "predict," "continue" and the negative or plural of these words and other comparable terminology. Forward-looking statements are only predictions based on our current expectations and our projections about future events. You should not place undue reliance on these forward-looking statements. We undertake no obligation to update any of these forward-looking statements for any reason. These forward-looking statements involve known and unknown risks, uncertainties, and other factors that may cause our actual results, levels of activity, performance, or achievements to differ materially from those expressed or implied by these statements.
As a significant shareholder in Apple, I hope this PR investment permits them to continue to make great computers and cellphones, if not reduce their carbon output.