Renewable Energy(Wind)

8/13/2019 Renewable Energy(Wind)

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RENEWABLE

ENERGY(WIND)

Dr. Biswajit Basu


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Topics

1. Introduction Wind Turbine2. Wind Characteristics and Resources

General, Atmospheric Boundary Layer, Wind data

analysis, resource estimation, statistical techniques,measurement and instrumentation

3. Aerodynamics

1-D momentum and Betz limit, Ideal HAWT, Bladeelement theory, Blade shape, rotor design simplifiesHAWT rotor performance calculation, Drag, advancedtopics


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Introduction

Important factors for re-emergence of windenergy

NeedNeed; finiteness of fossil fuel

Potential; wind exists everywhere in the world TechnologyTechnology; other fields applied to wind turbine

VisionVision; a new way to use

Political willPolitical will; support research, testing, provideregulatory reform, interconnection withnetworks, incentive


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Modern Wind Turbines

Difference between wind mill are wind turbine capacity

small ~ 10 kW to ~ 50 kW to 2 MW

Aerodynamic force of lift => net positive torque on rotating

shaft => mechanical power => electricity in a generator

Not possible to store ~responds to wind immediately

available

Variability/Fluctuation

Not transportable


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Modern Wind Turbine

Horizontal Axis Wind Turbine ( HAWT)

HAWT ROTOR CONFIURATION

OptionsOptions

Number of Blades ( 2 or 3)

Rotor Orientation

Blade material, Profile

Hub Design Power Control =>Aerodynamic control ( STALL)

=> Variable Pitch Blade ( Pitch Control)

Fixed or Variable Rotor Speed Orientation by self aligning ( Free Yaw) or direct control

(Active Yaw)

Gearbox or Direct drive Generator

Synchronous or Induction Generator


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Rotor

Hub and Blades (important from performance

and cost)

Most turbines up wind with 3 blades

Fixed blade pitch with stall control ( intermediate

size), Increased pitch control ( larger size)

Materials; composites- fiber glass reinforcedplastics (GRP), wood/epoxy laminates


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Drive Train

Rotating parts

Low speed shaft (rotor side), gear box, high speed shaft

(generator side)

Supporting bearings, couplings, brakes, rotating parts ofgenerator

Types of gearbox: parallel shaft, planetary larger

machines (planetary gearbox) Unique loading: fluctuating wind and dynamics of large

rotors


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Generator

Induction or Synchronous

Induction more popular (50 Hz, 1500 rpm)

Induction: more rugged, inexpensive, easy toconnect to network

Variable speed wind turbine( less wear andtear, more efficiency)

Hardware: variable speed; power electronicscomponent; suitable power electronicconverters


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Nacelle and Yaw System Wind turbine housing, machine bed plate or maintenance

and yaw orientation system Mainframe: mounting and alignment

Nacelle: Protection from weather

Yaw system : align rotor with wind direction (bearingconnecting mainframe to tower)

Active: Contain motors which drive pinion gear against a bullgear attached to the yaw bearing

Sensor: On Nacelle

Yaw Brakes

Free yaw in down wind machine


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Tower and Foundation

Tower structure and foundation

Free standing; stand tubes; lattice or concrete

For smaller turbines, guyed towers

Tower height is typically 1 to 1.5 times rotordiameter

Possibility of coupled tower/rotor vibration

For down wind rotors, effect of tower shadow

causes complex tower dynamics, power

fluctuations, noise generation


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Controls

Sensor speed, position, temperature,flow, current

Controller mechanical, electrical,

computer Power amplifiers switches, electrical

amplifiers, hydraulic pumps, valves

Actuators motors, pistons, magnetsand solinoids


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Aim:

Upper bound on torque and power

experienced by drive train

Maximizing fatigue life of rotor drive train

and structural components

Maximize energy production


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Balance of Electrical Systems

Cables, switchgear, transformer

Power electronic converters, power

factor correction capacitors

Yaw, pitch motors

Interconnection with network


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Wind Characteristics

Mechanics of wind motion

Spatial variation in heat transfer to the earths atmosphere

create variations in the atmospheric pressure field

Cause: Air movement from high to low pressureFour atmospheric forces

1. Pressure forces

2. Coriolis force (rotation)

3. Inertial forces (large scale circular motion)

4. Frictional forces


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Wind Characteristics (contd)

Pressure force 1p

p

F n

=

= density of air, p = pressure ( n is the direction

normal to the lines of constant pressure)

Coriolis Force Fc= fu, u = wind speed,

f = Coriolis parameter = 2 sinw

= Latitude, = angular rotation of earthw


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Variation in time

Inter-annual:> 1 year, long term

30 years data required, average (annual) over 5years

Prediction at 90% confidence levelAnnual: Significant seasoned variations;

monthly average wind speeds

Diurnal: Large wind variations on a daily scaledue to differential heating of earths surfaceduring the daily radiation cycle


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Short-term:

Short term wind speed variation induce

turbulence and gust over mean

Usually mean variation over 10 min or

less sampled at 1 sec. Stochastic character represent

turbulence Gust is a discrete event


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Atmospheric boundary layer

Lapse rate dp = -gdzp = pressure, = density,z = elevation measured positive upward

1st Law of ThermodynamicsHeat transferred, dq = du + pdv

= dh dp

=CpdT 1/ dpT = temperature, u = internal energy, h = enthalpy,= Specific heat, Cp =constant pressure specific heat


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Atmospheric boundary layer

(contd)

For adiabatic pressure, dq = 0

Therefore, CpdT = 1/ dp = -g/Cpwhich gives

g = 9.81 m/s2; Cp= 1.005 KJ/kgKThis is important for atmospheric stability and generation of

turbulence

0 . 0 0 9 8

a d i a b a t i c

d T K

d z m

=


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Turbulence

Turbulence Intensity ( TI)

Velocity,_

u U U= +

0

1, 10min

t

U udt t

t

= =

_

U=mean, U =fluctuating

Sampled form,1

1i

is

U uN =

= sN

, . ,s st N t N No of samples t Sampling time = = =

uTI

U

=


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Turbulence (contd)

where, standard deviation

( )2

1

1

1

sN

u i

is

u UN

=

=

Normally, TI = 0.1 to 0.4, depends on site terrain

features and surface conditions


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Wind Velocity Profile

Log law

( )*

0

lnU zU zk z

=

z0= Surface roughness, K = Von Karman constant = 0.4U*=friction velocity

0*ln( ) ( ) ln( )

K

z U z zU

= + Also,

Z0 is a function of terrain


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Wind Velocity Profile (contd)

Power law (simple)0

0

ln

( )( ) ln rr

z

zU zzU z

z

=

( )( )r r

U z zU z z

=

= function of elevation, time of day, season, terrain, temperature

( )( )

0.37 0.088ln,

1 0.088 ln 10

ref

ref

Uvelocity height

z

=

( )2

10 0 10 00.096log 0.016 log 0.24z z= + +(surface

roughness)


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Wind Speed Measurement

Cup anemometers: Based on rotation

Propeller anemometers: Three

dimensional measurement of velocity

components Kite anemometers: At heights greater

than towers; at areas of high turbulenceAcoustic Doppler sensors (SODAR)


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Advanced Topics

Application of stochastic processes

Fatigue Model field data with historical datae

Turbulence

Load Structured excitation

Fatigue

Control Power Quality


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Advanced Topics (contd)

CFD for flow characterization

Numerical modelling of complex flow Micrositing

Resource assessment tool to determine exactposition

CFD models or micrositing models

Statistically based resource assessment Alternative of physical models

MCP approach (Measure-Correlate-Predict)


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1-D Momentum Theory and Betz

Limit

Idealized rotor turbine

Actuator disk model of WT

Assumptions: Homogeneous, incompressible, steady state flow

No frictional drag

Infinite number of blades

Uniform thrust over disk

A non rotating wake

Static pressure for upstream and for downstream of the

rotor is equal to the undisturbed air pressure


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Renewable Energy(Wind)