Installations of new solar power capacity in the U.S. slowed in the third quarter to their weakest rate since 2015, hit by the Trump administration’s tariffs on imported panels.

The cost of solar power has plunged over the past decade, making it highly competitive against fossil fuel generation in many parts of the U.S., and it also often benefits from state mandates. But the pace of development has been dependent on federal government policy, including a tax credit on investment and tariffs on imported panels, which dominate the U.S. market.

Levied from February at an initial rate of 30%, President Donald Trump’s tariffs were intended to protect U.S. panel manufacturers. But the Solar Energy Industries Association (SEIA), which represents developers and installers as well as manufacturers, said the tariffs had put a brake on investment and cost more than 20,000 jobs.

New solar generation capacity coming online in the third quarter was particularly weak, because it reflected a delay in projects being given the go-ahead late in 2017, as uncertainty over the tariffs escalated and panel prices spiked.

Large utility-scale solar projects were most affected, because their economics are more sensitive to the cost of the panels than for smaller-scale rooftop solar. Colin Smith of Wood Mackenzie, which analyzes the data for the SEIA, said that around the end of last year most of the large-scale project pipeline in the U.S. had been put on hold.

“The tariffs have had an impact,” he said. “Projects have been pushed out.”

Even though many of those delayed projects are now going ahead, solar installations are expected to be only about 2% higher this year than in 2017; a growth rate well below the pace of the industry’s expansion in the early to mid-2010s.

Justin Baca of the SEIA said, “Apart from the actual effect of the tariffs, the business uncertainty has been disruptive.”

There have been a few announcements of jobs being created or saved in U.S. solar panel manufacturing. California-based SunPower bought some of the U.S. assets of SolarWorld, a bankrupt German company that had been one of the manufacturers urging the Trump administration to restrict imports of panels. SunPower has kept about 250 people working at the former SolarWorld plant in Oregon.

The SEIA argues that those few stories of job gains have been greatly exceeded by the jobs in project development, installation and maintenance that have been lost or were never created, which it estimates at about 23,000.

Tom Werner, SunPower’s chief executive, said he expected the industry to “recalibrate”, driving costs down to offset the impact of the tariffs. “Capitalism will work,” he said. “If costs don’t come down, then some of those projects aren’t going to get built.”

There are signs that recalibration is already under way. Wood Mackenzie’s data show panel prices in the US falling steadily this year, after their jump at the end of 2017, and it has revised up slightly its forecast for installations in the next five years.

Werner said SunPower would be part of that downward trend in costs, with its new “next generation” panels that will cost 30% to 4% less than its previous generation.

Rob Kupchak, head of infrastructure and energy in the Americas for Macquarie Capital, the investment bank, said he thought the slowdown in the solar industry would prove temporary.

“We expect solar installation will only continue to ramp up,” he said.

“I think there will be a load of solar being built in this country, because it is cost competitive and relatively easier to develop than other technologies. And the cost is going to keep going down.”

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