Part I

Asst/Prof Qin Xiaosheng School of Civil & Environmental Engineering

Tel : 67905288 Email : xsqin@ntu.edu.sg

MA9001 - Introduction to Energy

5. Hydroelectric Energy

Introduction

Hydropower is extracted from the natural potential of usable water resources

Flowing water contains energy can be captured

and turned into electricity

Hydroelectric

Wave

Tidal

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chinatravelplanner.com

Hydroelectric power currently the largest and cheapest source of renewable electricity

History

First use of water power 250 BC

First electricity generation with water in 1882

using a waterwheel on Fox river in Wisconsin

Niagara Falls 1893

One of the first hydroelectric power plants (2.2 MW)

20th century

Most new hydro-electric development focus on larger hydro dams environmental problems

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(www.cairns.com.au)

(www.dailycognition.com)

Sources of Electric Power - US

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Renewable Energy Sources - US

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Wisconsin Valley Improvement Company, http://www.wvic.com/hydro-facts.htm

World hydroelectricity consumption

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Worldwide hydroelectricity installed capacity reached 816 GW in 2005 750 GW of

large plants, and 66 GW of small hydro installations

(EnergyInsight.net, 2007)

Fossil fuel reserves

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Location of the World's Main Fossil Fuel Reserves (2010 World Coal Institute)

oil & gas will last another 50-100 years

coal will last over 200 years

A shift towards renewable energy sources

So

lar e

ne

rgy

Water

vapor

Evaporation

Condensationand precipitation

Hyd

rosta

tic h

ea

d

Runoff Runoff

Hydrologic cycle

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(Wikipedia, 2010)

Hydroelectric power generator

Water falls down from a high altitude and passes through a turbine

The turbine drives a generator

The generator produces electricity

Power generation depends on fall height and flow rate

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/www.ncgreenpower.org

how hydroelectric power is created

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Kinetic

Energy

Electrical

Energy

Mechanical

Energy

Potential

Energy

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a. Dam: The structure that creates the reservoir as well as maintains the head pond at a certain level of water

b. Head water: the water upstream of the dam whereas tail water is at the downstream of dam

c. Tail water: water below a dam or waterpower development

Components of the system

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Components of the system

d. Forebay: a pool of water in front of a larger body of water e. Afterbay: the tail race of a hydroelectric power plant at

the outlet of the turbines f. Penstock: a tunnel carries the water from the forebay into

the power house

Penstocks at the Ohakuri Dam, New Zealand (Wikpedia, 2010)

(Taylor & Francis, 2007)

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Components of the system

g. Turbine: a rotary engine that extracts energy from water flow and converts it into useful work.

h. Generator: an electrical machine coupled to the turbine shaft. Rotor: an assembly of electromagnets (poles) which rotates Stator: a system of conductors (armature windings)

(Monster Guide, 2008) (Photos.com, 2010)

Types of Hydroelectric Installation

Boyle, Renewable Energy, 2nd edition, Oxford University Press, 2003

• Head

– Water must fall from a higher elevation to a lower one to release its stored energy.

– The difference between these elevations (the water levels in the forebay and the afterbay) is called head

• Dams: three categories

– high-head (250 or more m)

– medium-head (50 to 250 m)

– low-head (less than 50 m)

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Turbine technologies

Selection of turbines based on particular

application and effective head

Larger turbines have higher efficiencies but cost more

Runner turning part of the turbine

Types: Impulse turbines and Reaction turbines

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Impulse turbines

Use water jets to hit bucket on the runner

Use the velocity of the water to move the runner, converting the potential energy to high velocity kinetic energy

As water discharges under atmospheric pressure no pressure drop across turbines

Relatively low flow applications

Types: Pelton, turgo, cross-flow

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Pelton turbine

One or more jets of water spins the wheel

Resembles a waterwheel

Used for medium to high-head sites (100~1000 m), flow: 1-50 m3/s

Unit capacity: up to 200 MW

Efficiency: up to 92%

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http://re.emsd.gov.hk

http://ucmr.com

Turgo Turbine

© Copyright 2008 VARSPEED Hydro Ltd

A modification of the Pelton wheel

the runner (wheel) of a Turgo

turbine is like a Pelton wheel sliced

in half

The incoming jet of water strikes

the plane of the runner on one side

– usually at an angle of about 20°

Used for medium to medium head sites (50 - 250 m), flow: 1-10 m3/s

Efficiency: 87%-90%

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Cross-flow turbine

Water passes through a drum-type turbine transversely go

through runner twice

Used for low- to medium head condition (5-100 m), low flow condition (1- 10 m3/s)

Low price & good regulation

micro hydropower

Efficiency: 84% - 87% (flat efficiency curve)

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(Wikipedia, 2010)

Reaction turbines

The reaction turbine is turned by reactive force rather than by a direct push or impulse.

The runner is fully immersed in water and is enclosed in a pressure casing.

Power is derived from pressure drop

Higher flow rates and wider range of heads compared with impulse turbines

Types: Francis, Kaplan

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(Wikipedia, 2010)

Francis turbine

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(Wikipedia, 2010)

Most common water turbine

has a runner with fixed vanes

Combines radial and axial flow

Operational range

10-800 m head

Up to 800 MW unit size

Flow: up to 1000 m3/s

Efficiency over 90%

Kaplan turbine

A propeller-type water turbine adjustable blade

pitch

Operational range

1 to 100 m head (low to medium)

up to 1000 m3/s flow

Up to 100 MW unit size

Kaplan turbine efficiencies are typically over 90%

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(Wikipedia, 2010)

Boyle, Renewable Energy, 2nd edition, Oxford University Press, 2003

Types of Hydropower Turbines

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Turbine selection

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(Tridentes Energy, 2009)

Chart for selecting turbines of hydropower plant