Power Systems & Energy Course:
Wind Generation Basics

Jason MacDowell


Atmospheric Circulation

Uneven heating of the earth
by the sun drives global
atmospheric circulation

Source: />
Earth’s rotation causes large
E-W component of wind via
Coriolis effect

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Cyclonic Flow

L

H

• Flow from high pressure system to low pressure system causes
rotation of air due to Coriolis effect
• Rotation is clockwise along isobars around high pressure system

counterclockwise around low pressure system (storm)
• Wind velocity greatest where isobars are more closely spaced
(greater pressure gradient)
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Weather Systems

At any given time, the
earth has numerous
high and low pressure
weather systems

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Local Atmospheric Circulation

Source: />
Localized atmospheric heating also drives wind

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Vertical Wind Shear
Atmospheric boundary layer is the
layer affected by surface friction
Friction with the earth’s surface
causes vertical wind shear
• Increasing velocity with height
• Change in direction

Above boundary layer, wind flow is
geostrophic, and non-turbulent
Inside boundary layer:

• General wind direction shifted more
toward pressure gradient
• Turbulent flow, “mixes” wind to the
surface

Wind velocity
and direction

Boundary level is thinner:

• Over water, and smoother ground
• At night, due to decreased convection

Wind speed at hub height (~80m) can
be far greater than at ground level

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Orographic Effects
Mountain passes funnel wind

Mountain wind shadows block wind

Ridges enhance wind velocity

Mountain waves can enhance velocity
Source: />
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Wind Resources in the US

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Wind Classification
Germanischer Lloyd, Certification Agency, and International Electrotechnical
Commission (IEC) Standards detail specific loading conditions that need to be
evaluated:

IEC Wind

Class
V Average

I

II

III

IV

S

10

8.5

7.5

6

70.0

59.5

52.5

42

Specified

by
Designer

(m/s)
V 50 yr Extreme
(m/s)

Turbulence models, deterministic gusts, sudden directional changes, ice loading,
atmospheric density, wind shear, wind upflow angle etc…

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0
_Finding

Wind

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Siting

High-Resolution Wind Maps

A


Potential
Development Sites

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Measuring the wind
Met Mast

ENRON WIND - Met Mast Configuration
50m mast system
0.5 m

ENRON WND - Met Mast Details
Mast & Boom Orientation

0.5 m
1.5 m
2.0m (1.5m)

N

2.0m (1.5m)

0.5 m

120°


0.5 m

150°

°
90

2.0m (1.5m)

2.0m (1.5m)

[Values in brackets = minimum]

°
90

0.5 m

0.5 m
2.0m (1.5m)

2.0m (1.5m)
h5
h4

[Values in brackets = minimum]

Requirement for booms > 1.5m
0.5 m


…

0.5 m
1.5 m
2.0m (1.5m)

2.0m (1.5m)

2.0m (1.5m)

2.0m (1.5m)

0.5 m

h3

2/3

1/3

0.5 m

30°
h2

[Values in brackets = minimum]

h1


Heights of sensors
h 1 = Wind vanes @ 23,5m
h 2 = Anemometers @ 25m
h 3 = anemometers @ 37.5m
h 4 = wind vanes / temperature probe @ 48,5m
h 5 = anemometers @ 50m

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Instrumentation

Wind Vane

Temperature
Probe

Anemometer

Barometric
Probe

Data Logger: 1 Hz sample rate
10 minute averaging interval
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Analyzing the wind
Statistical methods

a

 h2 
v 2 = v1  
 h1 

( 1 2)
a = ln v v

ln(h1 h2 )

Further formulas for calculation of wind
characteristics:
(Empiric formulas according IEC standards)

(1)

(2)

Vref = 5 x Vm

(3)

Ve1 = 0.75 x Ve50

(4)


Ve50 = 1.4 x Vref

(5)

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Site Suitability
Rule of Thumb Measures

Assess slopes – greater than 20% within 100m - ????
Wake losses for individual WTG higher than 8% - ????
Overall average wake loss higher than 5% - ????
Separation distances less than 2.5 rotor diameters - ?????

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Wind Turbines

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Wind Turbines as a Power Source
Power Sources

Overhead Transmission

Distribution Substation
Distribution Lines

Commercial
Load
Industrial
Load
Residential
Load
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Wind Turbine Components

GE 1.5 MW
1200-1700 Households

Rotor

35 metric tons
77 meters diameter

Nacelle


52 metric tons

Tower

120+ metric tons
60 to 100 meters
Image source:
hokiesports.com

Automobile
(for scale)

Image source:
GE Energy
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Wind Turbine Components
Generator

Gear Box
Blades
Nacelle
Rotor
Hub
Main
Shaft


Tower

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Modern Wind Turbines

Electrical Pitch
Drives

GE 1.6 xle
• 1.6 MW
• 82.5 M Rotor Diameter
• 100 M Tower

Doubly-Fed
Generator

• 98% Availability
• Speed 10-20 RPM

Main Shaft &
Bearing

• Variable Pitch

Gearbox


Epoxy-Glass
Composite Blades

GE 1.5 Series WTG
52 metric ton nacelle
35 metric ton rotor

Transformer &
Electrical

Power Electronic
Converter

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Fundamentals of Wind Turbines

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Wind Turbine Basics
Converting one form of energy to another

Kinetic
Energy

Mechanical
Energy
Rotor
45 - 52%

Gearbox
95 – 97%

Electrical
Energy
Generator +
Power Converter
90 – 95%

42 – 50% Efficient Today… Theoretical Maximum is 59% (no losses)

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Aerodynamic Lift – Bernoulli Effect
Bernoulli’s principle:

Increased speed of fluid
flow results in a decrease
of pressure
Fast air

movement

Slow air movement

Resulting
air power
Incoming
air

Vacuum

Angle of incidence
Positive
pressure

Horizontal

The air moves faster above the rotor blade than under it. This creates lift.
All modern WTGSs are lift machines
© 2016 General Electric International, Inc. All rights reserved. Not for distribution without permission.
“WindInternational,
Energy Handbook”,
et.al.;
ISBN: 0471489972;
edition (November

15, 2001)
© 2016 General Electric
Inc.Tony
AllBurton
rights
reserved.
Not for 1st
distribution
without
permission.

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Aerodynamic Forces on Wind Turbine Blade
Wind

Rotational Speed

Equation for Lift (L)

r = air density
v =airspeed
A = airfoil area
CL = coefficient of lift

Angle of Attack

Axial Thrust


Circumferential
Component
Parasitic Drag

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