Changes in state and federal policies are taking some shine out of the U.S. solar industry’s growth.

GTM Research lowered its forecast for installations though 2022 by 13 percent as tax reform, President Donald Trump’s tariffs on solar panels and steel and other issues threaten to drive up costs, according to a report released March 15 in conjunction with the Solar Energy Industries Association. Other obstacles include shifts in state regulations that require utilities to buy power from solar farms....