Hydro-electric power is electricity produced by the flow of fresh water from lakes, rivers, and streams. As water flows downwards thanks to gravity the kinetic energy it carries increases. This kinetic energy can be converted into mechanical energy – e.g. by turning a turbine – and from there into electrical energy. In the right location hydro-electric generation is far more cost effective than PV solar cells or wind turbines in terms of Watts generated per £ spent. Some say its you get as much as 10 x as much energy for your money using hydro compared to pv.
Hydro electric was produces 6% of the worlds electricity but this is going up more and more as more self built and community oriented small hydro electric initiatives are happening.