A tit-for-tat imposition of trade tariffs has pitted China against the U.S. and Europe and could slow the growth of photovoltaic installations worldwide, according to a report in The Washington Post.

China was setting tariffs as high as 57% on U.S.-produced polysilicon, a key ingredient used in the manufacture of PV panels. The U.S. and the European have imposed tariffs of their own on Chinese-made panels, and the combination will not only hurt U.S. polysilicon manufacturers but boost prices worldwide, The Post said.

REC Silicon has a manufacturing plant in Moses Lake, Washington, that employs more than 500 workers. The plant exports 80% of the polysilicon it produces to China, but some customers there are already canceling orders.

In 2012, the U.S. produced 24% of the global supply of polysilicon.

Prices have been falling for more than a decade

The trade dispute may eventually mean higher prices, but the long-term trend has been in the other direction.

NPD Solarbuzz, a solar market research company, reports solar module prices have dropped steadily over the past decade in both the U.S. and Europe.

By March of this year, Solarbuzz reported prices for 329 modules had fallen below $2 per watt. The lowest price for a multi-crystalline module was $1.06 per watt (the module cost is about 35% to 40% of the total installed cost of a PV system).