It's not protecting U.S. panel manufacturers, it's protecting coal and gas.

If anything, the American government should welcome cheap solar panels. The industry has created thousands of jobs across the country. And who was complaining in the first place about Chinese competition -- bankrupt Suniva, majority owned by the Chinese, and bankrupt SolarWorld, owned by the Germans. This horse had left the barn.

Nonetheless, the USA has imposed a 30 percent surcharge on imported Chinese solar panels. The damage to the industry could be extreme:

This decision will cause roughly 23,000 American jobs to be lost this year, including many in manufacturing, and will cancel of billions of dollars in investments in the U.S. economy. #SaveSolarJobs

— Solar Industry (@SEIA) January 22, 2018

Solar panels are only a portion of the cost of a solar installation; about 2/3 of the price is in "soft costs" -- commissions, installation, wiring, labor. So the 30 percent tariff translates to a 10 percent increase overall, which as one expert notes,

3. A 10% cost increase puts the total cost of utility-scale silicon solar in the US... back to where it was in late 2015 or early 2016.

At current pace of cost reduction, in another 1.5 years, costs will be back down to where they were last month.

— Ramez Naam (@ramez) January 23, 2018

But it is still going to damage the industry; as Ramez Naam concludes:

6. None of this is to voice even the tiniest bit of support for Trump's move on tariffs. It's stupid, job destroying, bad for the planet, etc.. We need to be moving faster, not slower. It will cause real damage to the solar industry for a couple years.

But it won't stop solar.

— Ramez Naam (@ramez) January 23, 2018

So why is this happening? Ostensibly, to protect domestic panel suppliers, but the ones that brought the challenge in the first place are already gone. But as Vaclav Smil noted in Energy and Civilization: A History, energy is money.

...every economic activity is fundamentally nothing but a conversion of one kind of energy to another, and monies are just a convenient (and often rather unrepresentative) proxy for valuing the energy flows.

American gas and coal can be converted into real American dollars on a continuing basis, at great profit to friends of the current government while driving the current economic boom. Whereas solar power is a one-shot purchase and install, and after that, the source of power is free. It is hard to monetise a sunbeam.

This might have something to do with it. SoE hugging a Bob Murray, coal company exec. pic.twitter.com/3BGkCDfPQO

— This is not a drill (@jswainhart) January 23, 2018

It is just part of the ongoing campaign to kill solar and promote fossil fuels; they are just getting started.