Solar energy represented less than 1 percent of the domestic electricity generation mix in 2012 but has experienced dramatic growth in the interim with help from both the federal government and the private sector.

Manufacturing and solar installation jobs grew by about 20 percent between September 2012 and November 2013, totaling nearly 143,000 positions across the country, according to a report released this month by the Solar Foundation. The industry installed 2.3 gigawatts of power in 2013, Energy Secretary Ernest J. Moniz said, calling it “a banner year for solar.”

Solar is also the second-largest source of new power generation in the U.S. after natural gas, said Rhone Resch, head of the Solar Energy Industries Association.

Today, about 1,100 megawatts of solar power from five projects supported by federal loan guarantees is being delivered to the grid, according to the Energy Department, and 10 percent of current domestic capacity in the resource is financed by the program.

The Energy Department’s loan office helped support the first five utility-scale photovoltaic plants in the U.S. that are larger than 100 megawatts, a spokeswoman said. The next 10 large-scale facilities were able to secure financing solely from the private sector.

The department still has billions of dollars in loan guarantee authority that Moniz has said it plans to distribute to worthy projects across the energy sector, though those would have to qualify under a different loan program from the one added under the 2009 stimulus law, which has since expired.

Without a long-term investment tax credit extension or a change to when solar companies are considered eligible to qualify for it, Resch said utility-scale growth will drop off as residential and commercial solar systems become more popular.

“The more certainty that policymakers can provide, the more investment we will have in the solar industry, and the lower our cost will be in the long run,” he said.