Modern Wind
Energy and its Origins
U.S. Use of
Renewable
Energy
Source: Annual Energy Review 1999, U.S. Energy Information Administration.
What Makes Wind
Global Wind Patterns
Wind Energy History
•
•
•
•
•
•
•
•
1 A.D. (Anno Domini, or “The Year of Our Lord”)
– Hero of Alexandria (a Greek mathematician) uses a wind machine to
power an organ
~ 400 A.D.
– Wind driven Buddhist prayer wheels
1200 to 1850
– Golden era of windmills in western Europe – 50,000
– 9,000 in Holland; 10,000 in England; 18,000 in Germany
1850’s
– Multiblade turbines for water pumping made and marketed in U.S.
1882
– Thomas Edison commissions first commercial electric generating
stations in NYC and London
1900
– Competition from alternative energy sources reduces windmill
population to fewer than 10,000
1850 – 1930
– Heyday of the small multiblade turbines in the US midwast
• As many as 6,000,000 units installed
1936+
– US Rural Electrification Administration extends the grid to most
formerly isolated rural sites
5
• Grid electricity rapidly displaces multiblade turbine uses
6
Manufacturing Market Share
Source: American Wind Energy Association
7
WindEnergy
Energy Capacity
US U.S.
Wind
Capacity
10000
8000
6000
MW
4000
2000
0
2000
2001
2002
2003
2004
2005
8
Orientation
Turbines can be categorized into two overarching
classes based on the orientation of the rotor
Vertical Axis
Horizontal Axis
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www.kidwind.org
Vertical-Axis Turbines
Advantages
Disadvantages
o Omni-directional
- accepts wind from any
direction
o Components can be
mounted at ground level
- ease of service
- lighter weight towers
o Can theoretically use
less materials to capture
the same amount of
wind
o Rotors generally near ground
where wind is poorer
o Centrifugal force stresses
blades
o Poor self-starting capabilities
o Requires support at top of
turbine rotor
o Requires entire rotor to be
removed to replace bearings
o Overall poor performance and
reliability
Horizontal-Axis Wind Turbines
Small (<10 kW)
Intermediate(10-250 kW)
oVillage Power
oHomes
oHybrid Systems
oFarms
oDistributed Power
oRemote
Applications
(e.g., water
pumping,
Telecom sites, ice
making)
Large (250 kW-2+ MW)
oCentral Station Wind Farms
oDistributed Power
oSchools
Recent Capacity
Enhancements
2000
850 kW
265’
2006
5 MW
600’
2003
1.8 MW
350’
13
Large Wind Turbines
 Common Utility-Scale
Turbines
328’ base to blade
Each blade is 112’
200 tons total
Foundation 20’ deep
Rated at 1.5-2
megawatts
o Supply about 500
homes
o
o
o
o
o
Wind Turbine Components
Horizontal Axis
Wind Turbines
• Rotors are
usually Up-wind
of tower
• Some machines
have down-wind
rotors, but only
commercially
available ones
are small
turbines
How a Wind Turbine Operates
The NEED Project 2014
Airfoil Nomenclature
wind turbines use the same aerodynamic principals as aircraft
KidWind Project |
www.kidwind.org
Lift & Drag Forces
• The Lift Force is
perpendicular to the
direction of motion. We
want to make this force
BIG.
• The Drag Force is
parallel to the direction
of motion. We want to
make this force small.
α = low
α = medium
<10 degrees
α = High
Stall!!
Apparent Wind &
Angle of Attack
ΩR
Ωr
α
V
V
VR = Relative Wind
α = angle of attack = angle between the chord line and the direction of the
relative wind, VR .
VR = wind speed seen by the airfoil – vector sum of V (free stream wind) and
ΩR (tip speed).
Tip-Speed Ratio
Tip-speed ratio is the ratio of the
speed of the rotating blade tip to
the speed of the free stream wind.
There is an optimum angle of attack
which creates the highest lift to
drag ratio.
Because angle of attack is
dependant on wind speed, there
is an optimum tip-speed ratio
ΩR
TSR =
V
Where,
Ω = rotational speed in radians /sec
R = Rotor Radius
V = Wind “Free Stream” Velocity
ΩR
ΩR
RR
Performance Over Range of Tip
Speed Ratios
• Power Coefficient Varies with Tip Speed Ratio
• Characterized by Cp vs Tip Speed Ratio Curve
0.4
Cp
0.3
0.2
0.1
0.0
0
2
4
6
8
Tip Speed Ratio
10
12
Twist & Taper
• Speed through the air of a
point on the blade
changes with distance
from hub
• Therefore, tip speed ratio
varies as well
• To optimize angle of
attack all along blade, it
must twist from root to tip
Pitch Control vs. Stall Control
• Pitch Control
– Blades rotate out of the
wind when wind speed
becomes too great
• Stall Control
– Blades are at a fixed
pitch that starts to stall
when wind speed is too
great
– Pitch can be adjusted for
particular location’s wind
regime
• Active Stall Control
– Many larger turbines
today have active pitch
control that turns the
blades towards stall
when wind speeds are
too great
Airfoil in stall
• Stall arises due to separation of flow from airfoil
• Stall results in decreasing lift coefficient with
increasing angle of attack
• Stall behavior complicated due to blade rotation
Rotor Solidity
Solidity is the ratio of total rotor
planform area to total swept area
R
Low solidity (0.10) = high speed, low torque
a
A
High solidity (>0.80) = low speed, high torque
Solidity = 3a/A
Number of Blades – One
• Rotor must move more
rapidly to capture same
amount of wind
– Gearbox ratio reduced
– Added weight of
counterbalance negates
some benefits of lighter
design
– Higher speed means more
noise, visual, and wildlife
impacts
• Blades easier to install
because entire rotor can be
assembled on ground
• Captures 10% less energy
than two blade design
• Ultimately provide no cost
savings
Number of Blades - Two
• Advantages &
disadvantages similar to
one blade
• Need teetering hub and
or shock absorbers
because of gyroscopic
imbalances
• Capture 5% less energy
than three blade
designs
Number of Blades - Three
• Balance of
gyroscopic forces
• Slower rotation
– increases gearbox
& transmission
costs
– More aesthetic,
less noise, fewer
bird strikes
Wind Turbine Perspective
Workers
Blade
112’ long
Nacelle
56 tons
Tower
3 sections
The NEED Project 2014
Wind Farms
Potential Impacts and Issues





Property Values
Noise
Visual Impact
Land Use
Wildlife Impact
Properly siting a wind turbine can mitigate many of these issues.
Impacts of Wind Power: Noise
The NEED Project
• Environmental benefits
• No emissions
• No fuel needed
• Distributed power
• Remote locations
Limitations of Wind Power
 Power density is very low.
 Needs a very large number of wind mills to
produce modest amounts of power.
 Cost.
 Environmental costs.
 material and maintenance costs.
 Noise, birds and appearance.
 Cannot meet large scale and transportation
energy needs.
Wind Turbine
Noise Levels
The Future of Wind Energy
 Future of wind energy can be bright if
government policies subsidize and
encourage its use.
 Technology improvements unlikely to
have a major impact.
 Can become cost competitive for
electricity generation if fossil energy
costs skyrocket.