U.S. solar stocks jumped Friday, after President Donald Trump opened a new front in his trade war with China, imposing fresh tariffs on imported products made from a key material used to manufacture solar panels. The president on Thursday slapped a 15% duty on products made from polysilicon, and also introduced minimum prices for some related imports, in a move aimed at protecting the U.S.' domestic solar supply chains from Chinese competition. Trump imposed the tariffs under Section 232 of the U.S. Trade Expansion Act of 1962. "For decades, America has allowed foreign countries to weaken United States producers in the polysilicon sector, eroding our economic and national security. Today, I am taking action to put a stop to these practices and revitalize the United States polysilicon sector," Trump said in the executive order.