Millions of Chinese-made solar panels were stowed in southern California warehouses between 2011 and 2013, victims of a U.S. tariff that hit just as Chinese production was ramping up.

“The story began a few years earlier, with the Chinese government’s growing panic about one of its biggest national threats: lung-clogging air pollution,” the Pacific Standard reports. “Chinese officials decided in 2010 that solar power would be the centerpiece of a five-year plan—one of Beijing’s massive centralized planning initiatives. The government worked with the China Development Bank to flood the country’s solar manufacturers with $42 billion in subsidized loans between 2010 and 2012.”

The massive industrial initiative had an effect: “As Chinese factories churned out panels, prices around the world fell. Between 2009 and 2011, the price of solar panels dropped from $2.79 to $1.59 per watt, pushing many American solar companies into bankruptcy.” With tariffs in the offing, manufacturers began shipping “boatload after boatload of panels” through the ports of Los Angeles and Long Beach.

“The Chinese are so good at manufacturing at mass quantities that they brought the price of solar panels way down to the point where no one could keep up,” Rafael Galante of L.A. Source Consulting told Yang. With tariffs around the corner, “Chinese solar panels dominated tons of warehouses in Carson,” in Los Angeles County.

But “the rise in solar panel prices after tariffs meant that companies that had stockpiled panels couldn’t always offload them. And it contributed to many of the already-purchased solar panels languishing in storage,” Yang writes.