Download - Lecture 8- Hydroelectric Energy
Part I
Asst/Prof Qin Xiaosheng School of Civil & Environmental Engineering
Tel : 67905288 Email : [email protected]
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