California is home to about 40 percent of the country's solar capacity and employs almost eight times more solar workers than any other state.
Massachusetts saw a larger percentage drop in employment (21 percent) but California's sheer size relative to the solar market dragged the national numbers into negative territory.
The census results did not surprise Barry Cinnamon, CEO of San Jose-based Spice Solar, which specializes in residential installations.
"I'm definitely seeing a little bit of a slowdown from the standpoint of jobs for solar in California," he said.
Why solar numbers were down
One of the biggest reasons for the decline stemmed from the fact that 2016 was a banner year for the industry. Nationally, 51,000 solar jobs were added that year and California accounted for almost half of them.
New installations in the U.S. doubled from 7.5 gigawatts in 2015 to 15 gigawatts in 2016, in many cases from customers who feared Congress would get rid of the federal government's 30 percent tax credit for solar projects.
That led to a rush to sign up for projects before the end of the year. As it turned out, Congress extended the tax credit in December 2015 but many projects were already under contract for 2016.
Specific to California, last year's extremely wet winter also led to a reduction in installations.
"That puts a big crimp in the residential market, especially," Gilliland said, "because who wants to buy solar in the rain?"