Hydropower Engineering

How hydropower works, the power equation, heads and efficiencies, classification of hydro plants (run-of-river, storage, pumped storage; low, medium, high head), components (intake, penstock, surge tank, powerhouse, tailrace), turbine selection by specific speed, load and capacity factors, and small hydro.

Hydropower Engineering

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📑 Contents (6 sections)

Last reviewed 4 Nov 2026 · 3 min read

1. The power equation

Water falling through a head $H$ turns potential energy into shaft power.

FormulaHydropower output

P = η ρ g Q H

$P$ — power (W); $ρ$ = 1000 kg/m³; $g$ = 9.81 m/s²
$Q$ — discharge (m³/s); $H$ — net head (m)
$η$ — overall efficiency (turbine × generator), typically 0.8–0.9

In kilowatts: $P \approx 9.81 η Q H$ kW.

Worked ExamplePower of a small plant

$Q = 20$ m³/s, net head $H = 50$ m, $η = 0.85$ . $P = 9.81 \times 0.85 \times 20 \times 50 = 8, 338.5$ kW $\approx 8.3$ MW.

Heads

Term	Meaning
Gross head	Difference between headwater (reservoir) level and tailwater level
Net (effective) head	Gross head minus losses in the intake, penstock and fittings
Design head	The head at which the turbine runs at best efficiency

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