It was a year ago this week that Apple Chief Executive Officer Tim Cook responded to a climate-change heckler at the company’s annual shareholder meeting with an impassioned rebuttal in which he famously told investors who care only about profits to “get out of the stock.”

Now Cook is putting his prodigious sums of money where his mouth is, proclaiming the “biggest, boldest and most ambitious project ever,” an $850 million agreement to buy solar power from First Solar, the biggest U.S. developer of solar farms. The deal will supply enough electricity to power all of Apple’s California stores, offices, headquarters and a data center, Cook said Tuesday at the Goldman Sachs technology conference in San Francisco.

It’s the biggest-ever solar procurement deal for a company that isn’t a utility, and it nearly triples Apple’s stake in solar, according to an analysis by Bloomberg New Energy Finance (BNEF). “The investment amount is enormous,” said Michel Di Capua, head of North American research at BNEF. “This is a really big deal.”