Independent power producers have been delivering reliable power worldwide for well over 100 years. The first Hydropower plant in the US went online in 1882, and Hydro in 2014 accounted for 6% of all electricity generated in the US: about 48% of all US renewable energy generation (1). But hydro is important world-wide. The capacity of Three Gorges dam in China is 18,000 MW, more than half of all the capacity in the state of Georgia.
Energy is produced when moving water, in a large river or waterfall, is piped into a turbine where blades, turned by the moving water, spin a generator. Since this source of clean, reliable energy has been in service for so long, it is considered to be a fully mature technology.
While initial investment in hydro is normally greater than for many other renewable technologies, operational issues are minimized due to a relatively simple technology and a long history of operational costs with infrequent downtime from equipment failure and retooling requirements. Hydro power operating costs are low at around $0.006 per kwh.
(1) Source: U.S. Energy Information Administration (May 2015).