The American decision was made by civil servants in a quasi-judicial process that is heavily insulated by law from political interference and does not represent a deliberate attempt by the Obama administration to confront China on trade policy. But that distinction has been largely lost in China, where the solar panel issue has been one of many causes embraced online by the country’s vociferous ultranationalists, who put heavy pressure on Chinese officials to respond forcefully to perceived snubs to China.

Further complicating matters is a similar case against China and Vietnam over the manufacture of steel towers for wind turbines, charging that steep government subsidies were giving foreign companies an unfair advantage over American manufacturers. A preliminary ruling is due on May 30 in that case.

The solar tariffs, which are retroactive to 90 days before the decision is officially published in the next several days, are in addition to antisubsidy tariffs of 2.9 to 4.73 percent that the department imposed in March.

SolarWorld Industries America, which led the coalition of manufacturers that filed the solar dumping case, welcomed the department’s ruling. The decision “is a very positive step in the process. It’s also in line with what we expected,” said Ben Santarris, a company spokesman. “We consider this a bellwether case. It underscores the importance of manufacturing to the U.S. economy.”

Alan Price, a partner who heads the international trade practice at Wiley Rein, the law firm representing the United States companies in both the solar and wind cases, said that China posed a particular threat to America’s developing green energy sector.

“China’s method is straightforward: it sets forth industry-specific Five-Year Plans and then uses all forms of national and local subsidies and other governmental support to quickly transfer jobs, supply chains, intellectual property and wealth, to the permanent detriment of U.S. and global manufacturers,” he said. “China’s ability to ramp up and overwhelm an industry is unique and particularly devastating with new and emerging technologies, where global competitors may be less established and can be knocked out more easily and quickly.”

Several large Chinese manufacturers expressed disappointment with the decision and said they would try to convince the Commerce Department that it was unjustified.