Hydro System Overview

Hydropower is based on simple concepts. Moving water turns a turbine, the turbine spins a generator, and electricity is produced. Many other components may be in a system, but it all begins with the energy already within the moving water.
Water power is the combination of head and flow. Both must be present to produce electricity. Consider a typical hydro system, water is diverted from a stream into a pipeline, where it is directed downhill and through the turbine (flow). The vertical drop (head) creates pressure at the bottom end of the pipeline. The pressurized water emerging from the end of the pipe creates the force that drives the turbine. More flow or more head produces more electricity. Electrical power output will always be slightly less than water power input due to turbine and system inefficiencies. Head is water pressure, which is created by the difference in elevation between the water intake and the turbine. Head can be expressed as vertical distance (feet or meters), or as pressure, such as pounds per square inch (psi). Net head is the pressure available at the turbine when water is flowing, which will always be less than the pressure when the water is turned off (static head), due to the friction between the water and the pipe. Pipeline diameter has an effect on net head. Flow is water quantity, and is expressed as “volume per time,” such as gallons per minute (gpm), cubic feet per second (cfs), or liters per minute. Design flow is the maximum flow for which your hydro system is designed. It will likely be less than the maximum flow of your stream (especially during the rainy season), more than your minimum flow, and a compromise between potential electrical output and system cost. Head and flow are the two most important things you need to know about your site. You must have these measurements before you can seriously discuss your project, how much electricity it will generate, or the cost of components. Every aspect of a hydro system revolves around head and flow.

Useful Hydro Power Conversions

1 horsepower = 746 watts
1 kilowatt = 1.34 horsepower
1 foot of head = 0.43 pounds per square inch (psi)
1 psi = 2.31 feet of head
1 gallon per minute (gpm) = 0.0022 cubic feet per second (cfs)
1 gpm = 0.000063 cubic meters per second
1 gpm = 3.8 liters per minute
1 cfs = 449 gpm
1 cfs = 0.283 cubic meters per second
1 cfs = 1,700 liters per minute