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Head And Flow For Hydro Calculator

Work out head and flow for hydro instantly with clear inputs, formula shown and shareable results.

About Head And Flow For Hydro Calculator

Rearranging the hydro power equation gives the flow needed for a target output: Q = P / (9.81 x net head x efficiency). Net head is gross head less penstock friction, which typically consumes 5-10%. Head and flow together determine the turbine type through specific speed.

Formulas

Required flow

Q (m3/s) = P (kW) / (9.81 x net head x overall efficiency)

Net head

Net head = gross head x (1 - penstock loss %)

Worked example

With the default values below, Head And Flow For Hydro Calculator returns Flow Required of 2.1726. Change any input above and every figure here is recalculated in your browser.

Inputs used

Target Power Outputminimum 0 kW
500 kW
Available Gross Headminimum 0.01 m
30 m
Penstock Head Lossaccepts 0–50 %
8 %
Overall Efficiencyaccepts 1–100 %
85 %

Results

Flow Required
2.1726
Net Head
27.600
Head Lost In Penstock
2.400
Indicative Turbine Type
Francis

Step by step

  1. 1Values used
  2. 2Required flow
  3. 3Net head
  4. 4Flow Required= 2.1726
  5. 5Net Head= 27.600
  6. 6Head Lost In Penstock= 2.400
  7. 7Indicative Turbine Type= Francis

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Abstraction volumes, environmental flows and licence conditions govern what may actually be diverted. Confirm with the water authority before design.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Abstraction volumes, environmental flows and licence conditions govern what may actually be diverted. Confirm with the water authority before design.

Frequently Asked Questions

Can the required flow always be abstracted?

No. An environmental or compensation flow must be left in the river, and abstraction is usually licensed with a hands-off flow below which no water may be taken. Design around the flow duration curve, not the peak.

How is penstock loss reduced?

Larger diameter pipe, smoother lining and fewer bends. Doubling the diameter cuts friction loss by a factor of about 32, which usually justifies the extra pipe cost on long penstocks.

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