since 2008 in the U.S. energy.gov website more than 60% Energy.gov 1.8 million Department of Energy estimated more Office of Energy and Renewable Energy more than 60% United States Energy Department 1.8 million U.S. Department of Energy Solar Energy in the United States energy.gov Solar Energy in the United States Solar Energy in the United States dropped by 60% says dropped nearly 60 percent Office of Energy and Renewable Energy 1.8 million