Apple Inc (AAPL.O) will buy about $850 million of power from a new California solar farm to cut its energy bill, the iPhone maker said on Tuesday as its stock market value closed above $700 billion for the first time. The First Solar Inc (FSLR.O) plant, with the capacity to power the equivalent of 60,000 homes, will be used to supply electricity for Apple’s new campus in Silicon Valley, and its other offices and 52 stores in the state, Chief Executive Tim Cook said at a Goldman Sachs technology conference in San Francisco.