First Solar shares spiked on the news and closed the day about 5 percent higher, while Apple ended about 2 percent higher. Apple's value rose to $710.70 billion as it became the first U.S. company to close with a market cap above $700 billion. The tech giant had touched the $700 billion level before but never managed to settle there.
Cook touched on the solar project and a wide range of company developments—including Apple Pay, the Apple Watch and the company's partnership with IBM—at the Goldman Sachs Technology and Internet Conference.
The solar farm in Monterey County would provide enough energy to power nearly 60,000 homes, Cook said. The California farm would become Apple's fourth, as the company already has two in North Carolina and one in Nevada.
He noted that all of Apple's data centers are run on renewable energy. For instance, the company pledged to run a new $2 billion Arizona data center, announced last week, on solar power.
Adoption of secure payment service Apple Pay has gone "much faster" than Cook had thought, he said. He noted that about 2,000 banks and credit unions now offer the service, which launched in October.
Addressing the wearable Apple Watch, which has drawn considerable skepticism, Cook said that "everyone will be surprised about the breadth of what it will do." He compared it to the iPod's influence on the music industry.
Cook announced late last month that the watch would ship in April.
Touching on the enterprise computing partnership announced with IBM last year, Cook said the companies' offerings complement one another. He added that Apple wanted to "change the way people work."
—CNBC's Karma Allen contributed to this report.