For a very long time, people have used the force of water flowing in rivers and streams to create mechanical energy. One of the first energy sources used to create electricity was hydropower which up until 2019, accounted for the majority of all renewable electricity produced annually in the United States. In the United States, utility-scale power generation totaled 6.3% in 2021, and utility-scale renewable electricity generation totaled 31.5%. Over time, primarily as a result of increases in energy production from other sources, hydroelectricity's proportion of total U.S. electricity generation has fallen.
Hydroelectricity depends on the water cycle. Understanding hydropower requires knowledge of the water cycle. Three phases make up the water cycle:-
Water found on the surface of waterways, lakes, and seas is heated by solar energy, which causes the evaporation of the water. Rain and snow are produced when water vapour condenses into clouds and falls as precipitation. The cycle is repeated as precipitation accumulates in streams and rivers, empties into seas and lakes and then evaporates.