Hydro Power Calculator
These calculations are intended to help in the surveying or assessment of a site to generate
The two vital factors to consider are the flow and the head of the stream or river.
The flow is the volume of water which can be captured and re-directed to turn the
turbine generator, and the head is the distance the water will fall on its way to the
generator. The larger the flow - i.e. the more water there is, and the higher the head
- i.e. the higher the distance the water falls - the more energy is available for conversion
to electricity. Double the flow and double the power, double the head and double the power
A low head site has a head of below 30 feet. In this case you need to have a large volume
of water flow if you are to generate much electricity. A high head site has a head of above
60 feet. In this case you can get away with not having a large flow of water, because
gravity will give what you have an energy boost.
The key equation to remember is the following:
Power = Head x Flow x Gravity - System Effiency
where power is measured in Watts, head in meters or feet, flow in liters per second or
gallons per minute, and acceleration due to gravity. Effiency depends on the many factors.
typical values are between 50% and 75%.
When evaluating a site it may be difficult to measure the head. If possible you could use
water hose. Run the hose between the water source and the turbine location. Make sure the
water is not flowing or static, and there are is not any air in the line. You can then measure
the pressure and convert that to the head, using the calculator above.