As a whole, the U.S. installed 2.7 gigawatts of solar in the first quarter, which is the most it has ever installed within the first three months of a year, according to the SEIA. Much of the nation’s solar growth can be credited to the solar investment tax credit, which is a 30 percent tax credit for solar systems on residential and commercial properties. This tax credit, enacted in 2006, has grown the solar industry by 10,000 percent, according to the SEIA.