Although currently only 6 percent of the electric generation mix (EIA 2016d), wind and solar are the fastest-growing generation sources due to technology improvements, federal tax credits, net metering policies, and state-level policies (e.g., renewable portfolio standards). In 2015, wind and solar accounted for 68 percent of all new electricity generating capacity additions in the United States (EIA 2016e). Technological advances and an increasingly flexible electricity grid will support a continued rapid pace of deployment for solar and wind energy, and the share for these technologies is expected to double to 12 percent by 2021 even in the absence of additional policies and before the Clean Power Plan is fully in effect. (EIA 2016a). â¢ Nuclear energy.