Hydropower has always been the largest renewable energy in terms of overall percentage of installed capacity but by 2018, it may no longer hold that title.
In 2015 about 153 MW of hydropower capacity was installed in the United States according to the Office of Energy Projects Energy Infrastructure Update released by the Federal Energy Regulatory Commission (FERC). During the same timeframe there were 7,977 MW of wind capacity added to the U.S. grid. Of all the energy sources, wind installed the most MW of capacity in 2015, beating the 5,942 MW of gas and the 2,157 MW of solar that came online last year according to FERC data.