Resource Potential

The amount of water power available for a particular site can be determined using the following formula:

Water Power = Head x Flow x Gravity x Density


  • "Water Power" is given in watts
  • "Head" is given in metres
  • "Flow" is the volumetric rate at which water is moving through the pipe, in cubic metres per second
  • "Gravity" is the acceleration due to gravity and is approximately equal to 10 metres per second-squared
  • "Density" is the density of water and is approximately equal to 1000 kg per cubic metre

The static head (or gross head) is equal to the vertical distance in metres between the water intake of the system and the point where the water enters the generator. For reaction turbines the static head includes the vertical distance from the turbine to the bottom of the draft pipe where the water is released.

The dynamic head is equal to the static head minus the friction head losses that occur in the pipework (penstock) between the water intake point and the hydroelectric generator, and is used to determine the amount of water power available.

The amount of water power that can be harnessed and converted into electrical power also depends on the efficiency of the turbine, and the efficiency of the electric generator.

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