What is a hydroelectric power plant?
A hydroelectric power plant is a power station that converts the energy of falling or flowing water into electricity using a turbine and a generator. Water flows from a higher to a lower level, drives the turbine on the way, and the generator on the same shaft produces electricity. Hydropower is a renewable energy source with no combustion.
How much power does it produce?
Output depends on two things: how much water flows through (the flow rate) and how large the height difference is (the head).
P = ρ × g × Q × H × η
- ρ = density of water (about 1,000 kg/m³)
- g = gravitational acceleration (9.81 m/s²)
- Q = flow rate in m³/s
- H = head in metres
- η = combined efficiency of turbine and generator
Worked example: with 1 m³/s, a 5 metre head and an efficiency of 0.85, output is 1,000 × 9.81 × 1 × 5 × 0.85 ≈ 42 kW. This shows why mountainous regions with high heads can harness far more hydropower than flat land.
Types
- Storage (high-head) plant: a reservoir behind a dam provides a large head.
- Run-of-river (low-head) plant: built at a weir on a river, with little head but a large flow.
- Pumped storage plant: pumps water uphill when there is surplus electricity and releases it when demand rises; mainly a form of energy storage.
- Tidal and hydrokinetic plants: use tidal range or current without a conventional weir.
Ecology
A key design issue is fish passage. Modern schemes use fish-friendly turbines, fish passes and screens.
Small-scale hydro
A private water wheel or micro-turbine in a stream sounds attractive, but with a low head the output is small, as the example shows. Work in or near a watercourse also usually needs consent from the relevant water authority.
Related terms
- Hydrokinetic power plant
- Pumped storage plant
- Tidal power plant
- Weir
- Lock
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