It is the energy that is stored as dynamic energy in a gravitational field by the accumulation of large amounts of water at an altitude difference from the continuation of the flow of free water, and is rendered as kinetic by water drop. The kinetic energy can then either be used locally (eg watermills), or converted into electricity or other, which store it, so that it can eventually be transported over long distances. In the earth's water cycle, energy comes mainly from the sun that evaporates, that is, it raises (in the atmosphere) large amounts of water. The energy in this cycle is harnessed by the use of hydroelectric projects (dams, dams, closed fall ducts, hydro turbines, generators, escape channels).