Transcript Slide 1

Green Power
Generation
Lecture 3
Wind Power
1
•
•
•
•
•
•
•
•
•
Wind power is the conversion of wind energy into a
useful form of energy, such as using wind turbines to
make electricity
At the end of 2010, worldwide nameplate capacity of
wind-powered generators was 197 gigawatts (GW)
Energy production was 430 TWh, which is about 2.5%
of worldwide electricity usage and has doubled in the
past three years
Several countries have achieved relatively high levels
of wind power penetration, such as 21% of stationary
electricity production in Denmark
18% in Portugal,
16% in Spain,
14% in Ireland
and 9% in Germany in 2010
As of May 2009, 80 countries around the world are
using wind power on a commercial basis
2
•
•
•
•
•
•
Large-scale wind farms are connected to the electric power
transmission network; smaller facilities are used to provide
electricity to isolated locations
Utility companies increasingly buy back surplus electricity
produced by small domestic turbines
Wind energy, as an alternative to fossil fuels, is plentiful,
renewable, widely distributed, clean, and produces no greenhouse
gas emissions during operation
The construction of wind farms is not universally welcomed
because of their visual impact, but any effects on the environment
are generally among the least problematic of any power source
The intermittency of wind seldom creates problems when using
wind power to supply a low proportion of total demand, but as the
proportion rises, increased costs, a need to upgrade the grid, and
a lowered ability to supplant conventional production may occur
Power management techniques such as exporting and importing
power to neighboring areas or reducing demand when wind
production is low, can mitigate these problems.
3
•
•
•
•
Humans have been using wind power for at least 5,500
years to propel sailboats and sailing ships. Windmills
have been used for irrigation pumping and for milling
grain since the 7th century AD in what is now
Afghanistan, India, Iran and Pakistan
In the US, the development of the "water-pumping
windmill" was the major factor in allowing the farming
and ranching of vast areas otherwise devoid of readily
accessible water
Windpumps contributed to the expansion of rail
transport systems throughout the world, by pumping
water from water wells for the steam locomotives
The multi-bladed wind turbine atop a lattice tower
made of wood or steel was, for many years, a fixture of
the landscape throughout rural America
4
•
•
•
•
•
Small wind turbines for lighting of isolated rural
buildings were widespread in the first part of the 20th
century
Larger units intended for connection to a distribution
network were tried at several locations including
Balaklava USSR in 1931 and in a 1.25 megawatt (MW)
experimental unit in Vermont in 1941
When fitted with generators and battery banks, small
wind machines provided electricity to isolated farms
In July 1887, a Scottish academic, Professor James
Blyth, undertook wind power experiments that
culminated in a UK patent in 1891
In the US, Charles F. Brush produced electricity
using a wind powered machine, starting in the winter
of 1887-1888, which powered his home and
laboratory until about 1900
5
•
•
In the 1890s, the Danish scientist and inventor Poul
la Cour constructed wind turbines to generate
electricity, which was then used to produce
hydrogen
These were the first of what was to become the
modern form of wind turbine.
6
Design
•
•
•
•
A large wind farm may consist of several hundred
individual wind turbines, and cover an extended area
of hundreds of square miles, but the land between
the turbines may be used for agricultural or other
purposes
A wind farm may be located offshore to take
advantage of strong winds blowing over the surface
of an ocean or lake
As a general rule, economic wind generators require
windspeed of 10 mph (16 km/h) or greater
An ideal location would have a near constant flow of
non-turbulent wind throughout the year, with a
minimum likelihood of sudden powerful bursts of
wind.
7
•
Map of available wind power over the United States
8
•
•
•
•
•
An important factor of turbine siting is also access to
local demand or transmission capacity
Usually sites are screened on the basis of a wind atlas,
and validated with wind measurements
Meteorological wind data alone is usually not
sufficient for accurate siting of a large wind power
project
Collection of site specific data for wind speed and
direction is crucial to determining site potential in
order to finance the project
Local winds are often monitored for a year or more,
and detailed wind maps constructed before wind
generators are installed.
9
•
•
•
•
The wind blows faster at higher altitudes because of
the reduced influence of drag
The increase in velocity with altitude is most dramatic
near the surface and is affected by topography,
surface roughness, and upwind obstacles such as
trees or buildings
Typically, the increase of wind speeds with increasing
height follows a wind profile power law, which predicts
that wind speed rises proportionally to the seventh
root of altitude
Doubling the altitude of a turbine, then, increases the
expected wind speeds by 10% and the expected power
by 34%.
10
•
•
•
The modern wind power industry began in 1979 with
the serial production of wind turbines by Danish
manufacturers Kuriant, Vestas, Nordtank, and Bonus
These early turbines were small by today's
standards, with capacities of 20–30 kW each
Since then, they have increased greatly in size, with
the Enercon E-126 capable of delivering up to 7 MW,
while wind turbine production has expanded to many
countries.
11
•
•
•
•
Wind is a form of solar energy
Winds are caused by the uneven heating of the
atmosphere by the sun, the irregularities of the
earth's surface, and rotation of the earth
Wind flow patterns are modified by the earth's
terrain, bodies of water, and vegetative cover
This wind flow, or motion energy, when "harvested"
by modern wind turbines, can be used to generate
electricity
12
Wind Energy
•
•
•
•
•
The terms "wind energy" or "wind power" describe
the process by which the wind is used to generate
mechanical power or electricity
Wind turbines convert the kinetic energy in the wind
into mechanical power
This mechanical power can be used for specific
tasks (such as grinding grain or pumping water) or a
generator can convert this mechanical power into
electricity to power homes, businesses, schools,
and the like
Wind turbines, like aircraft propeller blades, turn in
the moving air and power an electric generator that
supplies an electric current
Simply stated, a wind turbine is the opposite of a
fan. Instead of using electricity to make wind, like a
13
fan, wind turbines use wind to make electricity
•
•
•
•
•
•
•
The wind turns the blades, which spin a shaft, which
connects to a generator and makes electricity
Modern wind turbines fall into two basic groups
• The horizontal-axis variety, like the traditional
farm windmills used for pumping water
• The vertical-axis design, like the eggbeater-style
Darrieus model, named after its French inventor
• Most large modern wind turbines are horizontalaxis turbines.
Horizontal turbine components include:
Blade or rotor, which converts the energy in the wind
to rotational shaft energy;
A drive train, usually including a gearbox and a
generator;
A tower that supports the rotor and drive train;
Other equipment, including controls, electrical
cables, ground support equipment, and
14
interconnection equipment.
•
•
•
•
•
•
Wind turbines are often grouped together into a single wind
power plant, also known as a wind farm, and generate bulk
electrical power
Electricity from these turbines is fed into a utility grid and
distributed to customers, just as with conventional power plants
Wind turbines are available in a variety of sizes, and therefore
power ratings
The largest machine has blades that span more than the length of
a football field, stands 20 building stories high, and produces
enough electricity to power 1,400 homes
A small home-sized wind machine has rotors between 8 and 25
feet in diameter and stands upwards of 30 feet and can supply the
power needs of an all-electric home or small business
Utility-scale turbines range in size from 50 to 750 kilowatts. Single
small turbines, below 50 kilowatts, are used for homes,
telecommunications dishes, or water pumping.
15
Wind Energy Resources in the United States
•
•
•
•
•
Wind energy is very abundant in many parts of the
United States
Wind resources are characterized by wind-power
density classes, ranging from class 1 (the lowest) to
class 7 (the highest)
Good wind resources (e.g., class 3 and above, which
have an average annual wind speed of at least 13
miles per hour) are found in many locations
Wind speed is a critical feature of wind resources,
because the energy in wind is proportional to the cube
of the wind speed
In other words, a stronger wind means a lot more
power
16
Cost Issues
•
•
•
Even though the cost of wind power has decreased
dramatically in the past 10 years, the technology
requires a higher initial investment than fossil-fueled
generators
Roughly 80% of the cost is the machinery, with the
balance being site preparation and installation
If wind generating systems are compared with fossilfueled systems on a "life-cycle" cost basis (counting
fuel and operating expenses for the life of the
generator), however, wind costs are much more
competitive with other generating technologies
because there is no fuel to purchase and minimal
operating expenses.
17
Environmental Concerns
•
•
Although wind power plants have relatively little impact
on the environment compared to fossil fuel power
plants, there is some concern over the noise produced
by the rotor blades, aesthetic (visual) impacts, and birds
and bats having been killed (avian/bat mortality) by
flying into the rotors
Most of these problems have been resolved or greatly
reduced through technological development or by
properly siting wind plants
18
Supply and Transport Issues
• The major challenge to using wind as a source of
power is that it is intermittent and does not always
blow when electricity is needed
• Wind cannot be stored (although wind-generated
electricity can be stored, if batteries are used), and not
all winds can be harnessed to meet the timing of
electricity demands
• Further, good wind sites are often located in remote
locations far from areas of electric power demand
(such as cities)
• Finally, wind resource development may compete with
other uses for the land, and those alternative uses
may be more highly valued than electricity generation
• However, wind turbines can be located on land that is
also used for grazing or even farming
19
•
Wind Turbines
•
•
•
•
•
A wind turbine is a device that converts kinetic
energy from the wind into mechanical energy
If the mechanical energy is used to produce
electricity, the device may be called a wind
generator or wind charger
If the mechanical energy is used to drive machinery,
such as for grinding grain or pumping water, the
device is called a windmill or wind pump
Developed for over a millennium, today's wind
turbines are manufactured in a range of vertical and
horizontal axis types
The smallest turbines are used for applications
such as battery charging or auxiliary power on
sailing boats; while large grid-connected arrays of
turbines are becoming an increasingly large source
20
of commercial electric power.
•
•
•
•
The first electricity generating wind turbine, was a
battery charging machine installed in July 1887 by
Scottish academic James Blyth to light his holiday
home in Marykirk, Scotland
Some months later American inventor Charles F Brush
built the first automatically operated wind turbine for
electricity production in Cleveland, Ohio
Although Blyth's turbine was considered
uneconomical in the United Kingdom electricity
generation by wind turbines was more cost effective in
countries with widely scattered populations
In Denmark by 1900, there were about 2500 windmills
for mechanical loads such as pumps and mills,
producing an estimated combined peak power of
about 30 MW
21
•
•
•
•
The largest machines were on 24-metre (79 ft) towers
with four-bladed 23-metre (75 ft) diameter rotors
By 1908 there were 72 wind-driven electric generators
operating in the US from 5 kW to 25 kW
Around the time of World War I, American windmill
makers were producing 100,000 farm windmills each
year, mostly for water-pumping
By the 1930s, windmills for electricity were common
on farms, mostly in the United States where
distribution systems had not yet been installed. In
this period, high-tensile steel was cheap, and
windmills were placed atop prefabricated open steel
lattice towers
22
•
•
•
•
•
•
•
A forerunner of modern horizontal-axis wind
generators was in service at Yalta, USSR in 1931
This was a 100 kW generator on a 30-metre (98 ft)
tower, connected to the local 6.3 kV distribution
system
It was reported to have an annual capacity factor of
32 per cent, not much different from current wind
machines
In the fall of 1941, the first megawatt-class wind
turbine was synchronized to a utility grid in Vermont
The Smith-Putnam wind turbine only ran for 1,100
hours before suffering a critical failure
The unit was not repaired because of shortage of
materials during the war
The first utility grid-connected wind turbine to
operate in the U.K. was built by John Brown &
Company in 1951 in the Orkney Islands
23
•
•
•
•
•
•
•
A quantitative measure of the wind energy available at any
location is called the Wind Power Density (WPD)
It is a calculation of the mean annual power available per square
meter of swept area of a turbine, and is tabulated for different
heights above ground
Calculation of wind power density includes the effect of wind
velocity and air density
Color-coded maps are prepared for a particular area described,
for example, as "Mean Annual Power Density at 50 Meters."
In the United States, the results of the above calculation are
included in an index developed by the US National Renewable
Energy Lab and referred to as "NREL CLASS."
The larger the WPD calculation, the higher it is rated by class.
Classes range from Class 1 (200 watts/square meter or less at 50
meters altitude) to Class 7 (800 to 2000 watts/square meter)
Commercial wind farms generally are sited in Class 3 or higher
areas, although isolated points in an otherwise Class 1 area may
be practical to exploit
24
Types
•
Wind turbines can rotate about either a horizontal or a
vertical axis, the former being both older and more
common
The three primary types:VAWT Savonius, HAWT
towered; VAWT Darrieus as they appear in operation
25
Horizontal axis
•
•
•
•
Components of a horizontal axis wind turbine
(gearbox, rotor shaft and brake assembly) being
lifted into position
Horizontal-axis wind turbines (HAWT) have the main
rotor shaft and electrical generator at the top of a
tower, and must be pointed into the wind
Small turbines are pointed by a simple wind vane,
while large turbines generally use a wind sensor
coupled with a servo motor
Most have a gearbox, which turns the slow rotation
of the blades into a quicker rotation that is more
suitable to drive an electrical generator
26
•
•
•
•
•
Since a tower produces turbulence behind it, the
turbine is usually positioned upwind of its supporting
tower
Turbine blades are made stiff to prevent the blades
from being pushed into the tower by high winds
Additionally, the blades are placed a considerable
distance in front of the tower and are sometimes
tilted forward into the wind a small amount
Downwind machines have been built, despite the
problem of turbulence (mast wake), because they
don't need an additional mechanism for keeping them
in line with the wind, and because in high winds the
blades can be allowed to bend which reduces their
swept area and thus their wind resistance
Since cyclical (that is repetitive) turbulence may lead
to fatigue failures, most HAWTs are of upwind design
27
•
•
•
•
•
•
Turbines used in wind farms for commercial
production of electric power are usually three-bladed
and pointed into the wind by computer-controlled
motors
These have high tip speeds of over 320 kilometers per
hour (200 mph), high efficiency, and low torque ripple,
which contribute to good reliability
The blades are usually colored light gray to blend in
with the clouds and range in length from 20 to 40
meters (66 to 130 ft) or more
The tubular steel towers range from 60 to 90 meters
(200 to 300 ft) tall
The blades rotate at 10-22 revolutions per minute
At 22 rotations per minute the tip speed exceeds
300 feet per second (91 m/s)
28
•
•
•
A gear box is commonly used for stepping up the
speed of the generator, although designs may also
use direct drive of an annular generator
Some models operate at constant speed, but more
energy can be collected by variable-speed turbines
which use a solid-state power converter to interface to
the transmission system
All turbines are equipped with protective features to
avoid damage at high wind speeds, by feathering the
blades into the wind which ceases their rotation,
supplemented by brakes
29
Vertical axis design
•
•
•
•
Vertical-axis wind turbines (or VAWTs) have the main
rotor shaft arranged vertically
Key advantages of this arrangement are that the
turbine does not need to be pointed into the wind to be
effective
This is an advantage on sites where the wind direction
is highly variable, for example when integrated into
buildings
the rotor prior to fabricating a prototype.
30
•
•
•
•
•
•
The key disadvantages include
The low rotational speed with the consequential
higher torque and hence higher cost of the drive train,
The inherently lower power coefficient
The 360 degree rotation of the aerofoil within the wind
flow during each cycle and hence the highly dynamic
loading on the blade
The pulsating torque generated by some rotor
designs on the drive train
The difficulty of modeling the wind flow accurately
and hence the challenges of analyzing and designing
31
•
•
•
•
•
•
•
With a vertical axis, the generator and gearbox can be placed
near the ground, hence avoiding the need of a tower and
improving accessibility for maintenance.
Drawbacks of this configuration include
(i) wind speeds are lower close to the ground, so less wind
energy is available for a given size turbine
(ii) wind shear is more severe close to the ground, so the rotor
experiences higher loads
Air flow near the ground and other objects can create turbulent
flow, which can introduce problems associated with vibration,
such as noise and bearing wear which may increase the
maintenance or shorten the service life
However, when a turbine is mounted on a rooftop, the building
generally redirects wind over the roof and this can double the
wind speed at the turbine
If the height of the rooftop mounted turbine tower is
approximately 50% of the building height, this is near the
optimum for maximum wind energy and minimum wind
turbulence. It should be borne in mind that wind speeds within
the built environment are generally much lower than at exposed
rural sites
32
Darrieus wind turbine
•
•
•
•
•
•
"Eggbeater" turbines, or Darrieus turbines, were
named after the French inventor, Georges Darrieus
They have good efficiency, but produce large torque
ripple and cyclical stress on the tower, which
contributes to poor reliability
They also generally require some external power
source, or an additional Savonius rotor to start turning,
because the starting torque is very low
The torque ripple is reduced by using three or more
blades which results in greater solidity of the rotor
Solidity is measured by blade area divided by the rotor
area
Newer Darrieus type turbines are not held up by guywires but have an external superstructure connected to
the top bearing
33
Giromill
•
•
•
•
A subtype of Darrieus turbine with straight, as
opposed to curved, blades
The cycloturbine variety has variable pitch to reduce
the torque pulsation and is self-starting
The advantages of variable pitch are:
• High starting torque
• A wide, relatively flat torque curve; a lower blade
speed ratio
• A higher coefficient of performance
• more efficient operation in turbulent winds
• A lower blade speed ratio which lowers blade
bending stresses
Straight, V, or curved blades may be used.
34
Savonius wind turbine
•
•
•
These are drag-type devices with two (or more)
scoops that are used in anemometers, Flettner vents
(commonly seen on bus and van roofs), and in some
high-reliability low-efficiency power turbines
They are always self-starting if there are at least three
scoops
They sometimes have long helical scoops to give a
smooth torque
35
36
•
•
•
•
Wind turbines are designed to exploit the wind
energy that exists at a location
Aerodynamic modeling is used to determine the
optimum tower height, control systems, number of
blades and blade shape
Wind turbines convert wind energy to electricity for
distribution
Conventional horizontal axis turbines can be divided
into three components
• The rotor component, which is approximately 20%
of the wind turbine cost, includes the blades for
converting wind energy to low speed rotational
energy
• The generator component, which is approximately
34% of the wind turbine cost, includes the
electrical generator, the control electronics, and
hub) weighs 48,000 pounds (22,000 kg).
37
•
•
•
•
Most likely a gearbox (e.g. planetary gearbox,
adjustable-speed drive or continuously variable
transmission) component for converting the low
speed incoming rotation to high speed rotation
suitable for generating electricity
The structural support component, which is
approximately 15% of the wind turbine cost,
includes the tower and rotor yaw mechanism
A 1.5 MW wind turbine of a type frequently seen in
the United States has a tower 80 meters high. The
rotor assembly (blades and hub) weighs
48,000 pounds (22,000 kg)
The nacelle, which contains the generator
component, weighs 115,000 pounds (52,000 kg)
38
•
•
The concrete base for the tower is constructed
using 58,000 pounds (26,000 kg) of reinforcing
steel and contains 250 cubic yards (190 cubic
meters) of concrete.
The base is 50 feet (15 m) in diameter and 8 feet
(2.4 m) thick near the center
39
40