"We are continuing to install solar roofs at a slow pace to gather further learning from our design changes, as well as about the viability of our installation processes by implementing them in areas around the U.S. that are experiencing inclement weather," Musk wrote in Tesla's quarterly letter to shareholders.

Focus on Model 3

The fourth-quarter earnings report also indicates how far down the Buffalo solar energy business is on Tesla's list of priorities. The company is focusing intently on cutting costs and boosting production of the lower-priced Model 3 electric-powered sedan that it views as the key to consistent profitability.

Tesla devoted two paragraphs in its five-page shareholder letter to the solar energy business. And the business wasn't mentioned during an hourlong conference call with analysts.

Musk, who has said he slept on the factory floor during the Model 3 production ramp this summer, has never visited the Buffalo solar panel factory. Yet he told analysts Wednesday that he plans to make several trips to China this year to check on progress at the electric vehicle plant it is building in Shanghai.