The Commerce Department said Chinese companies were "dumping" solar cells and panels in the United States at prices 18.32 percent to 249.96 percent below fair value, although some individual companies received lower anti-dumping duty rates than in a preliminary decision earlier this year.

The department also set additional countervailing duties ranging from 14.78 to 15.97 percent to combat Chinese government subsidies, significantly higher than preliminary levels.

In a decision that disappointed U.S. producers and cheered U.S. companies that install solar panels, the department turned down pleas to expand the scope of its order to include Chinese panels made with non-Chinese solar cells.

SolarWorld Americas, the driving force behind the U.S. case, fears that will encourage Chinese producers to simply move cell production to nearby countries to avoid U.S. duties.

The United States imported about $3.1 billion worth of solar cells and panels from China in 2011, although that figure contains some product not covered by the investigation.

The duty decision was expected to further strain trade U.S.-China relations, following a congressional panel report on Monday urging American companies not to do business with two Chinese telecommunications companies because of security concerns.

The United States also has slapped preliminary duties on wind turbine towers from China and is expected to launch a new probe next week into charges that imports of Chinese hardwood plywood are unfairly priced and subsidized.

"We have the most squabbles with our biggest trading partners," said Scott Miller, a trade policy specialist with the Center for Strategic and International Studies, explaining the steady stream of U.S.-China trade spats.

Total U.S.-China trade surpassed $500 billion last year, with U.S. imports from China a record $399.4 billion and U.S. exports to China a record $104.0 billion.

In the solar sector, producers in the United States and Europe complain China's rapid expansion of solar panel manufacturing has created massive oversupply, erasing profits and sending company share prices into a tailspin.

SolarWorld's German parent has also been behind a charge in Europe for duties on Chinese solar panel imports.

China has warned the U.S. and European cases could damage trade ties and cripple development of the global solar and clean energy sector. It has already struck back by launching an investigation into imports of solar-grade polysilicon from both the United States and South Korea.

Chinese manufacturer Suntech Power Holdings on Wednesday was hit with a final anti-dumping duty of 31.73 percent and a countervailing duty of 14.78 percent. The final anti-dumping duty rate was in line with its preliminary rate, but the final countervailing duty rate was increased from 2.90 percent earlier.

Trina Solar received a final 18.32 percent anti-dumping duty and a 15.97 percent countervailing duty, compared to preliminary rates of 31 percent and 4.73 percent.

A separate U.S. government agency, the U.S. International Trade Commission, must give its approval for the duties to take force, although importers have been required to post bonds or cash deposits based on the preliminary rates.

The ITC vote is set for November.

The Obama administration has heavily backed solar and other renewable energy since taking office, pledging about $16 bln for 26 projects through its clean energy loan program.

Republican presidential challenger Mitt Romney has criticized the support, saying the federal government should not be in the business of picking winners and losers.