U.S. Dept. of  Energy, Sept. 2016.
http://energy.gov/sites/prod/files/2016/09/f33/Revolutiona%CC%82%E2%82%ACNow%202016%20Report_2.pdf

"Decades of investments by the federal government and industry in five key clean energy technologies are making an impact today. The cost of land-based wind power, utility and distributed photovoltaic (PV) solar power, light emitting diodes (LEDs), and electric vehicles (EVs) has fallen by 41% to as high as 94% since 2008. These cost reductions have enabled widespread adoption of these technologies with deployment increasing across the board."