Tesla Inc. plans to begin production in Buffalo by the end of this year of the solar roofing tiles that the company hopes will become a signature product for its renewable energy business.

Tesla, which acquired rooftop solar installer SolarCity in November, said Wednesday that it has started making the solar roof at its pilot production facility in Fremont, California, meeting a goal that the company set this spring.

By saying that solar roof production will shift to Buffalo by the end of December, Tesla is putting a more precise timetable on the startup of manufacturing for the solar roofing tiles in Buffalo. Tesla executives previously had said that, once pilot manufacturing began in California, they expected production to shift from Fremont to Buffalo "shortly thereafter." In the spring, Tesla executives said they expected production to begin by the end of summer.

Elon Musk, Tesla's CEO, said he expects production of the solar roof to start off slowly and then ramp up rapidly."We expect the Buffalo plant to be a powerhouse of solar panel production," he said during a conference call.

He also doesn't expect it to be easy. "This is a very challenging, technical task," Musk said.