05-08-2011, 10:30 AM
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Hydroelectric power
Introduction
Flowing water contains energy
Energy can be captured and turned into electricity
Hydroelectric
Wave
Tidal
Hydroelectric power currently the largest source of renewable electricity
History
First use of water power 250 BC
First electricity generation with water in 1882
using a waterwheel
Niagara Falls 1893
One of the first hydroelectric power plants (2,2 MW)
20th century
Fossil fuel more efficient larger hydro dams environmental problems
World total energy consumption
World hydroelectricity consumption
Fossil fuel reserves
Hydrologic cycle
Hydroelectric power generation
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 water flow and fall height (head)
Power (kW) = 5.9 x flow x head
Hydroelectric power plants
High construction costs
Long life time
up to 100 years
Sizes of plants
Large plants
More than 30 Megawatts (MW)
Fall height (head) can be over 1000 m
Small plants
1-30 MW
Micro plants
Up to 100 kilowatts (kW)
Hydroelectric plant types
Up to 95% of the hydro energy can be used
Restricted typically to 60% due to large construction costs
Availability of water a necessity
Types of facilities
Impoundment
Diversion
Pumped storage
Impoundment
Uses a dam to store river water in a reservoir
Reservoir functions as energy storage
Electricity generation control by water flow
Reservoir covers a vast area of land
Suitable for large power plants
Diversion
A diversion facility channels part of a river through a canal
The canal leads the water to the turbine
Reduces energy losses occurring in natural water streams
Suitable for smaller hydroelectric plants
Does not require a dam Lower environmental impact
Pumped storage
Water reservoirs (impoundments) for storing energy
Low electricity demand
Water is pumped from a lower to a higher reservoir
Requires electricity
High electricity demand
Water is released back to the lower reservoir
Generates electricity
Turbine technologies
Larger turbines have higher efficiencies but cost more
One to several turbines in a plant
Main types are
Pelton turbine
Francis turbine
Propeller turbine
Pelton turbine
Resembles a waterwheel
One or more jets of water spins the wheel
Used for high-head sites (> 100 m)
Unit size up to 200 MW
Axial turbine
Francis turbine
Most common water turbine
Radial turbine
Operational range
Up to 400 m head
Up to 800 MW unit size
Propeller turbine
Same structure as a boat propeller
Operational range
Up to 50 m head
Up to 100 MW unit size
Kaplan turbine
Propeller turbine with adjustable blade pitch
Up to 400 MW unit size
Planning and construction issues
Power generation capacity
Location
Distance to electricity grid, power plants, habitats, etc.
Topographical and geological issues
Existing water facilities
Can be partly integrated with the power plant
Environmental impact
Legal and institutional issues
Environmental impact
Advantages
Emission free, cheap, renewable energy source
Disadvantages
Dam covers a vast area under water
requires local people to move
Silt layer build-up in dam
Disrupts the normal flow of the river
Lowers oxygen level in water
Turbine causes fish injury and death
Mitigation techniques
Fish passages
Aided movement of fish
Management of water quality and flow
Various aeration techniques
Maintaining minimum flow of water downstreams
Environmental friendly turbines
Maintain oxygen concentration in water
Less harmful to fish
Future of hydroelectric power
Only one fourth of the worldwide theoretical potential exploited
North-America and Europe already exploited most of theirs
Most of the remaining potential in Africa and Asia
Environmental, social and economic constraints for further expansion
Future developments
New small scale plants with low head
Improvements and refurbishments of old and abandoned power plants
