Another reason for the turndown?
California utilities instituting what are called "Net Metering 2.0" rules that affect solar customers on the residential as well as the commercial side.
About 70 percent of the state's electricity is provided by investor-owned utilities such as San Diego Gas & Electric. Utilities are moving customers to time-of-use pricing to encourage consumers to run appliances and devices that consume a lot of energy -- such as air conditioners and washer/dryers -- when demands on the power grid are not as high.
The peak, or most expensive, rates occur in the evening.
Time-of-use rates affect solar customers because one of the primary reasons to install a solar system is to generate solar energy and sell any excess amounts back to the grid.
"If peak time shifts to the evening, that means when you're selling it in the afternoon you're not getting as good a rate," Gilliland said.
Yet another reason
The Solar Census was conducted in October and November, when the industry was very concerned about the Trump administration imposing tariffs on imports of solar modules, especially from Asia.
Two manufacturers called for the tariffs, saying the imports were unfair, but the U.S. solar industry in general was opposed to them, saying higher costs would hurt the domestic market.
President Trump had not made a ruling at the time the census was taken but 71 percent of the respondents said the pending case had already negatively impacted their businesses.