Definition of Hydropower

Hydropower or 'water power' can be defined as the potential energy contained in water at a height. Water constantly moves through a vast global cycle, evaporating from lakes and oceans, forming clouds, precipitating as rain or snow, then falling back to the ocean. The energy of this cycle can be tapped to produce electricity or for mechanical tasks like grinding grain. One third of the solar radiation reaching the Earth is responsible for running of the hydrologic cycle. Therefore, the energy of water never fails to be replenished. Because the hydrologic cycle is a never ending system, hydropower is considered a renewable energy. Indeed, it is the largest renewable resource used for electricity generation.


Water may be utilized for power generation if it possesses enough potential energy. As water flows from highlands to lower elevations, its potential energy is reduced by evaporation, drop in elevation, friction, and turbulence. The remaining part can be converted into mechanical energy by turbines and generators convert this mechanical energy into electrical energy.

The amount of water power developed from any stream, river or lake is a function of mainly:

1. The flow rate of water
2. The head that is available 

Hydroelectric power and energy that can be generated in a hydropower plant is determined from:

P = yQHn
E = yQHnt

where P is the power in kW, y is the specific weight of water in kN/m3, Q is the discharge in m3/s, n H is the net head (gross head minus hydraulic losses) inmeters, n is the overall efficiency (%), E is the hydroelectric energy in kWh and t is the time interval for power generation in hours.