The investigations were sparked by a complaint at the end of last year by the U.S. unit of German solar manufacturer SolarWorld. The company at the time said it was seeking to close a loophole in a prior trade case that enabled Chinese solar panel producers to evade duties by using cells manufactured in other countries, mainly Taiwan.
(Read more: Winevs. Solar Panels: China Hits Back at EU)
The Commerce Department investigation and a parallel inquiry by the U.S. International Trade Commission (ITC) could open the door to expanding duties on some imported solar panels.
In October 2012, the U.S. set steep duties on billions of dollars of solar products from China, but turned down pleas to expand the scope of its order to include Chinese panels made with non-Chinese solar cells. In response, many Chinese module producers simply began sourcing cells from Taiwan.
The ITC is to make a preliminary ruling on whether there is a reasonable indication that imports from China or Taiwan materially injure, or threaten to injure, the local industry by February 14. A negative finding would stop the investigations.
If the ITC determines that the imports could be hurting the domestic industry, the Commerce department is to make preliminary determinations about subsidies in March and dumping in June.