The Wisdom of Mahatma Gandhi:

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• The Wisdom of Mahatma Gandhi
• Earth provides enough for everyones need,
• but there is not enough for everyones greed.

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Wind Power

• Dr. Dave Irvine-Halliday

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Wind Energy

• Wind energy is also another form of solar energy
• The sun's radiation heats different parts of the
  earth at different rates (Ex. day night)
• Different surfaces (for example, water and land)
  absorb or reflect radiation heat at different
  rates
• This causes different parts of the atmosphere to
  warm differently
• As a result hot air rises, reducing atmospheric
  pressure and cooler air is drawn in to replace it
• This creates the wind flow
• Wind energy is one of the oldest types of
  renewable energy generation

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Relative Density of Solar,
Wind Hydro Energy e.g. 1kw/m2 -
10kW/m2 100kW/m2 respectively
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Wind Turbines

• Systems used to capture the wind energy
• May convert it to either electrical or mechanical
  energy( Water pumps, grinding mill)
• Energy in the wind is converted into a mechanical
  torque by the rotor blades of the wind mill
• An electrical generator is coupled to the rotor
  shaft in order to produce electrical energy

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Two Main Types of Wind Turbines
Vertical Axis
Horizontal Axis
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• Islamic
  Windmill
• The first practical windmills were the
  vertical axle windmills invented in eastern
  Persia by the Persian geographer Estakhri in the
  ninth century.12 The authenticity of an
  earlier anecdote of a windmill involving the
  second caliph Umar (634644 AD) is questioned on
  the grounds of being a 10th-century amendment.3
  Made of six to twelve sails covered in reed
  matting or cloth material, these windmills were
  used to grind corn or draw up water, and quite
  different from the European versions. A similar
  type of vertical shaft windmill with rectangle
  blades, used for irrigation, can also be found in
  13th-century China (during the Jurchen Jin
  Dynasty in the north), introduced by the travels
  of Yelü Chucai to Turkestan in 1219.4

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Everest Base Camp, 2000
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The Rotor

• The rotor blades are one of the most critical
  components of a wind turbine generator
• To get optimum performance they should be well
  engineered using principals of aerodynamics
• Common materials for blades are glass fiber or
  carbon fiber reinforced plastics, aluminum alloys
  (for small ones)

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The Generator

• In large wind turbines either an asynchronous
  (induction) or synchronous generator is used
• Wind turbines for solid state lighting should
  preferably give a DC output
• A DC generator (or motor) can be used

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Maximum Rotor EfficiencyBetz limit

• A German physicist Albert Betz showed that the
  maximum possible rotor efficiency is 59.3
• This is know as the Betz limit, Cp
• For well designed practical wind turbines
• Cp 45 - 50

Proof of Betz limit See section 6.5 of Masters
(2004) 1 or http//www.windpower.org/en/stat/bet
zpro.htm
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Wind Energy Conversion Systems

• In addition to the Betz limit there are power
  loses in the gear boxes, bearings and yawing
• Also there are power loses in the electrical
  generator
• Thus the practical power extracted from the wind
  is

?m mechanical power transmission system
efficiency(gt90 for good designs) ?e electrical
generator efficiency (gt90 for good generators)
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Estimating The Energy Output

• The available energy is given by
• E Energy density x Area of the rotor
• However the rotor does not extract the total
  energy in the wind
• Well designed rotor would have an efficiency of
• about 40
• There will be losses in the generator as well as
  in power transmission system, yawing losses and
  power conditioning losses (about 10 each)
• Therefore a more accurate estimation of the
  energy is
• E Energy density x A x 40 x 90 x 90 x 90
• E Energy density x A x 29
• Consider the seasonal variations as well

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Power in the Wind
Consider a cube of air mass (m) moving at
velocity v
v
m
Then the kinetic energy, Ek
A
v
Power through area A
- mass flow through A
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Power in the wind (ctd.)
Mass flow rate through A
? - density of air ?0 1.225 kg/m3 at 15C and
1atm. From (2) (3) the power crossing through A

Power in the wind is proportional to the cube of
the wind speed and the swept area of the rotor
blades. Air density ? varies with the
temperature and altitude (pressure).
t temperature (in C ) H altitude in meters
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Power in the Wind (ctd.)
Power in the wind per square meter of cross
section at 15C and 1atm.
Power (W/m2)
Wind speed m/s
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Power in the Wind (ctd.)Impact of the tower
height

• The wind near the surface is slowed considerably
  by the irregularities (trees, buildings etc.)
• Taller towers will get the turbine into higher
  winds

v wind speed at tower height H v0 wind speed
at tower height H0 ? - friction coefficient
depends on the terrain
Terrain characteristics Friction coefficient ?
Smooth hard ground, calm water 0.10
Tall grass on level ground 0.15
High crops, hedges and shrubs 0.20
Wooded countryside, many trees 0.25
Small town with trees and shrubs 0.30
Large city with tall buildings 0.40
Reference 1 Reference 1
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Power in the Wind (ctd.)Rotor cross sectional
area facing the wind

• For a horizontal axis turbine with a rotor
  diameter D

• For a vertical axis turbine (Darrieus rotor)

Figure source http//www.therenewableenergycentre
.co.uk/wind_power/
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Wind Turbine Power Curves

• The output of a wind turbine with the wind speed
  is given by its power curve (considering Betz
  limit and other loses)
• This can be obtained from manufacturers data
• At lower speeds the power output drops sharply
  (cube law) and therefore the turbine starts
  producing power only after a certain speed (cut
  in speed, vC)
• The rated wind speed (vR) is the speed at which
  the turbine provides its rated electrical power
  output and the conversion efficiency reaches a
  maximum
• Hence the power output is kept constant by
  adjusting the generator or mechanical system
  parameters
• Beyond a certain speed the turbine is shut down
  to avoid excessive loading and damage to the
  turbine blades and the mechanical system (cut off
  speed, vF)

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• Scottish Wind Turbine
• Delivers Its Rated Output at 100mph?

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Wind Turbine Power Curves
Source 1
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Wind Turbine Power Curves
Ideal power curve
Practical power curves
Air-X 400W
Bergey KL1 1.2kW
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Wind Turbine Power Curves
Source Vestas
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Site Wind Power Data

• Usually given as a histogram (daily, monthly,
  yearly)
• This gives the distribution of various wind
  speeds in a given site
• May be obtained experimentally or from
  metrological data
• Usually given for 10m tower height
• The wind speed distribution are usually
  characterised using Weibull and Rayleigh
  statistics

Further reading section 6.8 of Masters (2004) 1
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Calculating Generated Energy
Generated energy can be calculated by multiplying
the site wind speed distribution by the wind
power curve of the turbine
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Calculating Generated Energy
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Size of Turbines
Vestas V80 2MW
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Wind Farms

• An array of wind turbines

Turbulence caused by the turbine affects the
output of the turbine behind it. Therefore the
turbines must be properly spaced. This affects
the land requirements of wind farms.
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Source 1
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Global Installed Wind Power Capacity
2007
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More than 50 of the installed wind power
capacity is in Europe
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In January 2008 the installed wind power capacity
in Canada was 1,856MW Currently ranks as the
worlds 11th largest nation in terms of installed
wind energy capacity.
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Wind Power Economics

• Cost (/kWh)
• Capital Cost Recovery OM / kWh
  per year
• Capital cost
• OM Cost Turbine design, operating environment
• kWh/year depends on available wind resources
• Typical capacity (utilization)factors ? 30-35
• Current prices range from 8 to 11 cents per kWh
  for large wind projects

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(Year 2003)
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Construction Cost Elements
Source American Wind Association
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Challenges

• Siting
• Avian Bats (UofC research re reasons for
  deaths)
• Noise
• Aesthetics
• Intermittent low capacity (utilization) factor
• Good wind resources are in remote locations
• Need transmission expansion
• Financing
• Operational characteristics different from
  conventional fuel sources

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Drive to Offshore

• 617MW existing, 11GW planned up to 2010
• Stronger, more uniform winds
• Construction not limited by topography
• Larger turbines feasible
• Transmission expansion needed

5MW
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Source NREL
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Intermittency

• Storage
• Pumped hydro storage
• Compressed air

Use wind power to compress air and store it
underground. The compressed air is then used to
run a gas turbine generator.
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Intermittency

• Geographic smoothing

An interconnected network of geographically
dispersed wind farms feeding a load center.
Reduced correlation of wind resources provides a
steady output.
One model proposed by DeCarolis Keith (2005)
(Ref5)
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Installing a Wind Turbine

• Minimize turbulence.
• Install the tower at least 30 feet above anything
  within 500 feet.
• Note your prevailing winds and stay upwind of any
  obstacles.
• Minimize compromises in location, voltage, and
  tower height.
• If downwind of obstacles, compensate with a
  taller tower.
• Trees grow, tower dont. So dont install near
  trees which can grow tall.
• Never attach the tower to a house if you can
  avoid it.

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Site Wind Power Data

• Wind power classes 2

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Ref.3
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Class 4
Class 3
Class 1
Class 2
Ref.2
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Installing a Wind Turbine
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Pros Cons

• In an area with good potential it is much cheaper
  than PV
• Can operate in night time too
• Good choice for winter time where daylight times
  are less

• Needs regular maintenance
• Noise
• Wind may be seasonal
• Visual impact
• Potential Hazard
• Potential Danger

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Reference

• 1 G. M. Masters, Renewable and Efficient
  Electric Power Systems Wiley-IEEE, 2004.
• 2 D. L. Elliott and M. N. Schwartz, "Wind
  energy potential in the United States," Pacific
  Northwest Laboratory PNL-SA-23109, Richland, WA,
  1993. Available at http//rredc.nrel.gov/wind/pu
  bs/atlas/chp1.html
• 3 Environment Canada, "Canadian Wind Energy
  Atlas," 2007. Available at http//www.windatlas.c
  a/en/index.php
• 4 S. Mathew, Wind Energy fundamentals,
  resource analysis and economics Springer, 2006.
• 5 J. F. DeCarolis and D. W. Keith, "The costs
  of winds variability Is there a threshold?,"
  Electricity Journal, vol. 18, pp. 69-77, 2005.

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• See a wind turbine that gets caught in extreme
  wind conditions and breaks apart
• http//www.youtube.com/watch?vc3FZtmlHwcA
• http//www.youtube.com/watch?vCqEccgR0q-ofeature
  related
• See wind and solar data for North America
• http//firstlook.3tiergroup.com/

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• Showed AERC (Jasper) LUTW Power
• Point to ENEL 619.52 during lecture
• period 15 on Wed. 29Oct2008