Renewable energy industries have ample reason for optimism in 2019: The year is expected to be one of steady growth as renewable power prices continue to decline and solar developers take advantage of investment tax credits poised to ratchet down during the next several years.

The industry is keeping an eye on whether wind and solar power will surpass 10 percent of total U.S. electricity generation, up from about 8 percent in 2017, John Rogers, a senior energy analyst for the Union of Concerned Scientists, told Bloomberg Environment.

“I think it’s sort of helping people move past the...