tutorial on wind power

8/22/2019 Tutorial on Wind Power

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Introduction to

DESIGN OF WIND POWER GENERATING STATIONS

presented to

ME 195-3 Senior Design Projects Class

Department of Mechanical and Aerospace Engineering

San Jose State University

byTai-Ran Hsu, Professor

on

October 28, 2009


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Overview of Wind Power Station


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121.2 GW = 1.5%worldwide electricity

Total solar PV power

generation = 6 GW

in 2008

A Promising Fast Growing Clean Power Source

Source: Wikipedia 2009


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The Top Ten Wind Power Producing Countries

in the World 2008

05000

1000015000200002500030000

USA

Germ

any

Spain

China

India Ita

ly

Fran

ce UK

Denm

ark

Portu

gal

Countries

Powe

rGeneration

(MW)

Source: Wikipedia 2009


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0.15 MW

10 m,

26 ft

Altamont

Region

Wind Industry Growth Trends Larger multi-MW turbines

Demand for new innovative technologies Led by Europeans

Offshore & low wind regime focus in U.S.


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Large Wind Turbines

450 base to blade

Each blade 112

Span greater than 747

163+ tons total

Foundation 20+ feetdeep

Rated at 1.5 5megawatt

Supply at least 350homes


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Wind 2030

A goal set by

US Department of Energy in July 2008:

20% of US electricity generation by wind energy

by Year 2030

Total US electricity generation in 2005 was 4017 GW


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Wind

Turbine Gear BoxElectric

Generator

Power

Electronics

Power

Storage

Horizontal axis wind turbine

Vertical axis wind turbine Batteries

Capacitor banks

Grid power system

Pumped water

Flywheel

Thermal

Superconducting magnetic

WIND

Major Components in Wind Power Plants

Wind Turbogenerator


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Design of Wind Power Station


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Major Tasks in Design and Construction ofWind Power Generating Stations

A. Site selection

B. Local wind resource survey

C. Selection of wind turbogenerators or wind farm

with multiple wind turbines

D. Power transmission and storage

G. Construction of power generating stations

E. Public safety and liability

F. Environmental impacts wildlife protections


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A. Site Selection

Flat Plain Hill tops

Offshore

In North

Sea

Rooftops of (high rise)

buildings and structures

Possible sites:


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The purpose of site visits is to look for the following facts:

Available open space for wind power generating station

Consistently bent trees and vegetation as a sure sign of strong winds.

Accessibility for construction, monitoring and maintenances, and power transmission

Check for potential site constraints:

Competing land uses

Permission for the wind plant or its transmission lines,

Probable local land owners resistance to selling the necessary land and easements.

Availability of possible location for a wind monitoring station.

Site Visits:


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B. Wind Resource Survey- A major task in wind power generating station design

Wind resource is expressed in terms of the wind power density and

wind speed in the locality

Wind Power Densityis a useful way to evaluate the wind resource available at a

potential site.

Viable wind speed for power generation:

Minimum threshold speed: 4 m/s

Viable speed: 11 m/s

The wind power density, measured in watts per square meter, indicates

how much energy is available at the site for conversion by a wind turbine

Wind contains energy that can be converted to electricity using wind turbines

The amount of electricity that wind turbines produce depends upon the amount

of energy in the wind passing through the area swept by the wind turbine blades

in a unit of time.


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Average World Wind Energy Resources

(wind velocity at m/s)


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5.0 -5.5

5.5 -6.0

6.0 -6.5

6.5 -7.0

Wind speed in

SF Bay Area (m/s):

Wind resource in

various parts ofUSA is

available from US

Geological survey


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0

500

1000

1500

2000

2500

0 5 10 15 20

Wind Speed (m/s)

Powe

r/Area(W/m^2)

Wind Power vs. Wind Speed:

High power output is possible with:

High tower for higher wind speed

Long blades for large swept area

Wind power generation: 3VAW

Wind velocity Why it is important?


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(a) Vertical extrapolation of wind speed based on the 1/7 power law

(b) Mean wind speed is based on the Rayleigh speed distribution of equivalent wind power density. Wind speed is

for standard sea-level conditions. To maintain the same power density, speed increases 3%/1000 m (5%/5000 ft)of elevation.

(from the Battelle Wind Energy Resource Atlas)

>8.8 (19.7)>800>7.0 (15.7)>4007

8.0 (17.9)/8.8(19.7)

600 - 8006.4 (14.3)/7.0(15.7)

300 - 4006

7.5 (16.8)/8.0(17.9)

500 - 6006.0 (13.4)/6.4(14.3)

250 - 3005

7.0 (15.7)/7.5

(16.8)400 - 500

5.6 (12.5)/6.0(13.4)

200 - 2504

6.4 (14.3)/7.0(15.7)

300 - 4005.1 (11.5)/5.6(12.5)

150 - 2003

5.6 (12.5)/6.4(14.3)

200 - 3004.4 (9.8)/5.1(11.5)

100 - 1502


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0

500

1000

1500

2000

2500

0 5 10 15 20

Wind Speed (m/s)

Power/Area(W/m^2)

Distribution ofwind speed (red)

and energy (blue) for all of 2002

at the Lee Ranch facility in Colorado

(Ref: Wikipedia 2009)

Available Wind Energy Density and Wind Speed


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Wind speed increases with the height (altitude) Reason for high tower for wind turbine

( ) ( )n

o

oz

zzvzv

=

o

o

z

zn

v

vn

n

l

l

=where

v(z) = Extrapolated wind velocity at elevation zv(zo) = measured wind velocity at elevation zo

n = wind shear factor

Extrapolated wind velocity measured at IBM-ARC site

By SJSU student team in 2009

Formula for extrapolation:

ground cover n

smooth surface ocean, sand 0.1

low grass or fallow ground 0.16

high grass or low row crops 0.18

tall row crops or low woods 0.2

high woods with many trees suburbs, small

towns 0.3


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Conduct wind resource survey on specific site using tower with anemometersfor measuring wind speed:

Wind speed measurements:

:

Wind vane Cup anemometers

Data logger

Thermal sensor

Data logger by solar power

Wind profile measured by Sodar transmitters using Doppler effects associate

with the shift of the frequencies of the acoustical waves of the transmitted and

received at various altitude in the atmosphere.

Sodar units manufactured by Atmospheric Systems

Corporation (ASC) can detect wind profile from 15

to 250m in elevation using acoustic waves at

4-6 kHz frequencies.


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January 6, 2005 California Wind Generation

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300

350

400

0:00:00

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2:00:00

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MW

20000

22000

24000

26000

28000

30000

32000

34000

TOTAL Load, MW

Intermittent Nature of Wind Power

Hours in the Day

Watts

Wind power varies randomly in:(a) time of the days, (b) months of the year, (c) by the years


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HoursoftheDay

Wind speed, m/s

Month of the YearAverageWin

dSpeed,m/s

Required wind energy resource data for wind power generating station design:

Wind Energy on a Selected Site


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C. General Design Parameters for Wind Power Generating Station Design

Power electronics efficiency

Generator efficiency

Maximum total annual energy productionGear box efficiency

Power produced at each wind speedBlade coefficients of lift and drag at each

wind speed

Torque on gear box at each wind speedFixed or variable speed wind turbine

Optimal blade angle at each wind speedSuitable wind turbine types

Optimal RPM of rotorCapital investment

Optimal generator capacityTotal available wind energy on the site

Optimal rotor diameterAverage annual wind speed

Output-sideInput Variables

(Ref: Wind Turbine Design Optimization, Michael Schmidt, Strategic Energy Institute, Georgia Institute of Technology,

www.energy.gatech.edu)

Principal selection criteria of wind turbogenerators: The available wind energy on the site

Site visit findings

Other considerations:


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Available Wind power on the Site:

Annual Wind Energy on a Selected Site

( )bcVAP3

2

1=

Wind power by the turbine:

kW

where = mass density, kg/m3

A = rotor swept area, m2

V = wind speed, m/s

Cb = Betz limit < 0.59

( )( )2

112

rrb

VVc

+= with Vr= Vout/Vin

Variable speed rotor

Fixed speed rotor

Wind speed

% of Available wind

energy captured 100%

9 10 m/s

Rotor selection:


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Selection of Wind Turbogenerator

Horizontal Axis Wind Turbine

Vertical Axis

Wind Turbine


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1) Variable blade pitch, which gives the turbine blades the optimum angle of attack.

Allowing the angle of attack to be remotely adjusted gives greater control,

so the turbine collects the maximum amount of wind energy for the time of day and season.

2) The tall tower base allows access to stronger wind in sites with wind shear.

In some wind shear sites, every ten meters up, the wind speed can increase by 20%

and the power output by 34%.

Horizontal Wind Turbines

Advantages:

Disadvantages:

1) HAWTs have difficulty operating in near ground because of turbulent winds.

2) The tall towers and blades up to 90 meters long are difficult to transport.

Transportation can now cost 20% of equipment costs.

3) Tall HAWTs are difficult to install, needing very tall and expensive cranes and skilled operators.

4) Massive tower construction is required to support the heavy blades, gearbox, and generator.

5) Tall HAWTs may affect airport radar.6) Their height makes them obtrusively visible across large areas, disrupting the appearance

of the landscape and sometimes creating local opposition.

7) Downwind variants suffer from fatigue and structural failure caused by turbulence.

8) HAWTs require an additional yaw control mechanism to turn the blades toward the wind.


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Vertical Axis Wind Turbines

Advantages:

1) Does not need to be pointed into the wind to be effective

2) The generator and gear box can be placed near ground

no need to be supported by a tower, and for easy maintenance

3) Does not need a yaw mechanism to turn the rotor against the wind

Disadvantages:

1) Difficult to be mounted on a tower. So it is almost all installed on the ground

- low wind speed in low attitude with low efficiency

2) Air flow near ground level with high turbulence

- cause excessive vibration, noise and bearing wear a serious maintenance problem

3) May need guy wires to hold the turbine vertical guy wires are not practical solutions

4) Major load on thrust bearings need frequent replacement not an easy job

Unique advantages:

1) More suited for roof-top installation

2) Optimum height of turbine 50% of building height


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Design of Horizontal Axis Wind Turbines

Basic Structure:

HubNacelle

Tower

Rotor

& Blades

Controls, Transformer andPower Electronics

The rotor typically has

three blades.

Blade diameter can be as large

as 40 m

The nacelle yaws or rotates to keep

the turbine faced into the wind

The nacelle also houses the gear

box and generator


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Interior of a Nacelle


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Design of Horizontal Axis Wind Turbines

Odd number of rotor blades

(= 3, the optimum number from aerodynamics principle)

A large rotor captures more energy but cost more

Blades have slight twist optimized to capture the max.

amount of wind power

The power captured by a horizontal axis wind turbine is:

pcVAW3

2

1 =

where = mass density of air

A = rotor swept area

V = wind velocity

cp = coefficient relating to efficiencyThe coefficient cp is:

592.027

16

2

11

2

==

+

=in

out

in

out

p

V

V

V

V

c = Betz limit

meaning the efficiency of HAWTcannot exceed 59%


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Other design considerations:

1) Synchronous or asynchronous electric generator

2) Fixed speed or variable speed

3) A large rotor-to-generator ratio captures more energy at low wind speeds

4) A small rotor-to-generator ratio captures more energy at high wind speed

5) So, this ratio must be optimized for site specific wind speed distribution

6) The variable speed captures more energy at almost all wind speeds.- cost more in hardware and power electronics control system


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Mechanical Engineering Design ofWind Power Generating Station

Performance Design

Structural Design


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Performance Design

Design Objectives:

Design for maximum LIFT and minimum drag for the airfoil

cross-section of the turbine blades using aerodynamicsprinciple

Design the yaw mechanism that provides fast response to

change of wind direction using mecahtronics principle


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Lift & Drag Forces The Lift Force is

perpendicular to thedirection of motion. Wewant to make this force

BIG.

The Drag Force isparallel to the directionof motion. We want tomake this force small.

= low

= medium


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Airfoil ShapeJust like the wings of an airplane,

wind turbine blades use the airfoil

shape to create lift and maximizeefficiency.


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Tip-Speed Ratio

Tip-speed ratio is the ratio of thespeed of the rotating blade tipto the speed of the free streamwind.

There is an optimum angle ofattack which creates thehighest lift to drag ratio.

Because angle of attack isdependant on wind speed,

there is an optimum tip-speedratio

R

VTSR =

Where,

= rotational speed in radians /sec

R = Rotor Radius

V = Wind Free Stream Velocity

R

R

P f O R f Ti


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PerformanceOverRangeofTipSpeedRatios

PowerCoefficientVarieswithTipSpeedRatio CharacterizedbyCpvs TipSpeedRatioCurve

0.4

0.3

0.2

0.1

0.0

Cp

121086420

Tip Speed Ratio


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Wind Turbine Structural Design

Loading

STATIC LOADING Constant in time, e.g. weight

CYCLIC LOADING Structural vibration induced

STOAHASTIC LOADING Load varying with time

e.g. aerodynamic induced loading with varying wind velocity

DYNAMIC LOADING Inertia forces induced by

varying rotor speed, and Coriolis forces.

Common Structural Failure Modes

Over-stress Stress concentration near abrupt geometry

change areas

Vibration-induced fatigue failure

Failure due to resonant vibration

L di H i t l A i Wi d T bi


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Loading on Horizontal Axis Wind Turbines

A. Loading on Blades

Aerodynamic load:

Intermittent with varying magnitudes along the

blade length stochastic loads

Lift forces for bending

Drag forces for torsion

Centrifugal forces from rotation at high speed

Gravitation load in large blades

BLADES

ROTOR

B. Loading on Rotor

Weight of blades bending

Aerodynamic forces on blades bending

Coriolis force axial thrust

Centrifugal forces on blades bending Electromagnetic forces by the generator torsion vibration

Yaw forces bending

MAIN SHAFT

C. Loading on Main Shaft

Weight of blades shear

Electromagnetic force of generator torsion vibration

TOWER


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Aerodynamic forces

Uneven centrifugal forces

Rotor weights

Uneven centrifugal forces

Aerodynamic forces

Cyclic tension/compression

Intermittent bending

Intermittent shearing

D. Loading on Tower


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Loading on Vertical Axis Wind Turbines

Stochastic aerodynamic loading

cyclic bending & torsion

Weights buckling

Friction wear


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DESIGN ANALYSIS

CAD

CFD AnalysisFluid-induced forces

Aerodynamic analysisFlow patterns

Fluid-induced forces

Lift/drag coefficients

Stress Analysis

using FEM

Other Input

Loads

Componenets

Geometry

& Dimen-

sions

Phenomino-

logical Models

Material

Characteriza-

tion

Material handbook

Lab test data

(e.g., fatigue failure models)

Safe/Fail?

Fatigue

Over-stress

Resonant vibration

Solid models

F ti F il f Wi d T bi Bl d b C li St


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Fatigue Failure of Wind Turbine Blades by Cyclic Stresses:

Mean stress: 2

minmax

+=

m

Stress amplitude:2

minmax

=a Stress range: minmax =r

Fluctuating stress

Non-sinusoidal fluctuating stress

Non-fluctuating sinusoidal stress

Sinusoidal fluctuating stress

Repeated stress

Completely reversed sinusoidal stress


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Typical Fatigue (S-N) Curves for Ferrous and Non-Ferrous Metals

Note: Calculated stress can be: m, ora, orr

(Laboratory Test Data for Specific Materials)


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D. Power Transmission and Storage

January 6, 2005 California Wind Generation

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MW

20000

22000

24000

26000

28000

30000

32000

34000

TOTAL Load, MW

Two Major Cost Factors of Wind Power:

Power transmission involves hundreds miles of transmission from power generating

stations to the consumers. Transmission often require over

rugged terrains or over waters.

Power storage wind power is intermiitent in nature, There is rarely matching between

the time of power generations and that of the needs for power

Mid-day

Peak needs by business

& industry

Power storage systems are essential parts of wind power generation

Wind Power


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A Pumped-Storage Plant

Generated wind power is used to pump water to a higher elevation for energy storage

The high elevation water is released to drive hydraulic turbogenerator to generate

electricity to consumers when power is needed


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Synchronous

Inverter

CustomersDistribution

Panel

Utility

Meter

Excess energy fed to the grid for credit

Additional power requirements satisfied by the utility

IBM-ARC

Campus

A Viable Energy Storage System- Net metering with local utility power generator

Power generator

and user

To and from

utility, e.g. PG&E

Most utility generators impose limit on how much power may be swapped with

the generators a major design consideration


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E. Environmental Impact Study

Noise and vibration

Avian/Bat mortality

Avian fatality < 1 in 10,000

Visual impacts

shadow flicker

Environmental impacts by wind power generation are minor in comparison to

other means of power generations.

Major concerns are:


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Construction of Wind Power Stations

Turbine blade convoy passing

through Edenfield in the UK

Construction

sites


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Principal References

Rand, Joseph Wind Turbine Blade Design,[email protected]

Ragheb, M. Dynamics and Structural Loading in Wind Turbines

Wind turbine Design, Wikipedia,

http://en.wikipedia.org/wki/wind_turbine_design

Schmidt, Michael Wind Turbine Design Optimization,www.energy.gatech.edu

Basic Principles of Wind Resource Evaluation,

http://www.awea.org/faq/basicwr.html

Mechanical Engineering Systems Design,

Printed lecture notes by T.R. Hsu, San Jose State Unvierasity

San Jose, California, USA

tutorial on wind power

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