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What is the minimum head and flow I need?

Firstly you always want as much head as possible, and more is always better. Assuming you’ve maximised the head you then need enough flow to make it economically viable, then more is always better due to the economies of scale from building larger systems. It is the combination of minimum head and flow that determine the power output.

The following table gives indicative minimums – but remember more is always better. The table shows the minimum annual mean (i.e. average) flow rate required for a given head to generate a maximum power output of 25 kW, which as discussed here is considered the smallest economically viable hydropower system. Any more flow for the same head will generate more power, and there is no upper limit.

Low-head Hydropower Sites High-head Hydropower Sites
Max. Power Output GrossHead
2 m
5 m
10 m
25 m
50 m
100 m
25 kW 1.9 m3/s 0.75 m3/s 0.38 m3/s 0.15 m3/s 75 litres/s 38 litres/s

See here for more information on how to calculate the power output from the head and flow available at your site.


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