"It's allowing us to bring solar to more people," he said.
The expansion will increase the Petaluma operations staff from 28 now to almost 50 by mid-2014, Cox said.
The company, which was launched seven years ago, is headquartered in San Mateo and has 14 operations centers today, three in Northern California. It is in 14 states.
The California expansion, announced this week, will almost double the company's presence in the state.
Earlier this year, the company opened two of its largest operations centers, in Riverside and Stockton. In August, it inaugurated a San Fernando Valley regional operations center in Chatsworth.
With 24 locations, SolarCity will have a location within 30 miles of more than 90 percent of the state's population, said spokeswoman Molly Canales.
The expansion will add at least 260 new jobs to the approximately 2,100 it employs already in California. Nationally, the company employs about 4,000 workers.
Cox said the company tries to hire local talent and uses local trades workers when it needs assistance on a job, for roofing or tile help, for example.
"There's a ripple effect," he said. "We often set up accounts with local mom-and-pop electrical suppliers. There's one across the street from where we are in Petaluma now."
The local expansion will allow the company to better accommodate solar installations in Napa and Sonoma counties, which had been served by the Berkeley office, and to begin reaching farther north.
"We're trying to reduce drive times between our office-warehouse and the homes we're traveling to," Cox said. "We're reducing our ecological footprint and improving the quality of life for our employees.
"It allows us to get into new areas where we should be but maybe haven't traditionally traveled to."
The company has more than 37,000 residential customers in California, Canales said, and about 900 commercial customers.
The company offers solar power, energy efficiency and electric vehicle services. Its staff handles the design, permitting, monitoring and maintenance of their products.
It, along with other green energy sources, is competing for residential power customers, who in Sonoma County will soon have a choice among PG&E, Sonoma County's startup public power agency and a number of solar contractors.