MEP 451-Power Stations

Aya Diab

Power Plant Technology (Study Group)

for lecture notes & handouts

http://goo.gl/NeR7l

Alternative Energy Technology

Direct conversion of solar radiation to electricity

Requires an extremely energy intensive processing of sand to crystalline silicon

Photovoltaic

Indirect conversion of solar radiation to electricity/ or for heating purposes

Requires components that can gather and concentrate the solar radiation efficiently for conversion

Thermal

Solar Energy

An indirect form of solar energy induced by the uneven heating (and cooling)

of the earths crust by the sun combined with the rotation of the earth.

Wind Energy

Ocean waves are caused by winds which is in turn caused by uneven

solar heating (and subsequent cooling) of the earth's crust + the rotation

of the earth

Wave Energy

Feb Mar Apr May Jun Jul Aug Sep Nov Dec Jan

Surface Temperature

Temperature

Dept

h

summer

winter

Ocean Thermal Energy Conversion (OTEC)

Tides occur due to the imbalance of the gravitational forces between the moon and earth on one side and the sun and earth on the other side, both acting together to counteract the centrifugal force acting on the water as a result of the earth's rotation.

Tidal Energy

The result is the rhythmic rise and fall of the water surface.

Neap tide

Neap tide

Spring tide

Spring tide

Spring tide

Rela

tive

Heig

ht

The tidal schedule varies from day to day since the moon rotates around the earth every 24 hrs. & 50 min, with 2 neaps and 2 spring tides for every rotation.

Hydro-Electric Energy

Increasing Oil Prices ($/barrel)

Global Warming & Greenhouse Emissions

http://www.globalwarmingart.com/wiki/Image:Greenhouse_Gas_by_Sector.png

Energy Resources Potential Capacity

Challenges

Source: Solar photovoltaic Electricity, Empowering the World, EPIA 2011

An intermittent energy source is any source of energy that is not continuously available due to some factor outside direct control, i.e. cannot be dispatched to meet the demand of a power system.

In an electric power grid these resources are balanced by other dispatchablesources (fossil fuel nuclear, geothermal) or by storage in the form of (pumped hydro, compressed air or ice) for use when needed.

Global Renewable Resources

Diverse Mix = Energy Security

Sustainable Development"development that meets the needs of the present without compromising the ability of future generations to meet their own needs."

Regional development, by creation of local jobs. New employment levels in the sector ~ 1.5 million jobs by 2015, ~ 3.5 million by 2020 and ~ 4.5 million by 2030.

Clean electricity that contributes to international targets to cut emissions and mitigate climate change by avoiding up to ~ 4,000 million tonnes equivalent of CO2 every year by 2050. The cumulative total of avoided CO2 emissions from 2020 to 2050 would be ~ 65 billion tonnes.

The benefits of a paradigm shift towards renewable energy include:

Providing clean and sustainableelectricity to the world.

Production versus ConsumptionOil (million barrels/day)

Production versus ConsumptionCoal(million toe/day)

Nuclear & Hydroelectric Consumption(million toe)

Biofuels &Other Renewables Consumption (million toe)

World Consumption (million toe)

Diversification & Energy Security

Renewable Energy Capacity

Clean Energy Investment

RE Investment (Billion $)

Installed RE Capacity (GW)

Incentive Mechanisms

Feed-in-Tariff

Carbon Cap

Carbon Market

Renewable Energy Standard

Clean Energy Tax Incentives

Auto Efficiency Standards

Government Procurement

Green Bonds

Desertec Foundation

High-Voltage Direct Current (HVDC)To export renewable energy produced in the MENA desert region, a high-voltage direct current (HVDC) electric power transmission system is needed.

HVDC technology is a proven and economical method of power transmission over very long distances and also a trusted method to connect asynchronous grids or grids of different frequencies.

With HVDC energy can also be transported in both directions. For long-distance transmission HVDC suffers lower electrical losses (3% per 1,000 km) than alternating current (AC) transmission.

Existing Under construction Proposed

Obstacles to DesertecThere are also concerns that the water requirement for the solar plant to clean dust off panels and for turbine coolant may be detrimental to local populations in terms of the demand it will place on the local water supply. Opposed to this, studies point out the generation of fresh water by the solar thermal plants. Furthermore, no significant amount of water is needed for cleaning and cooling, since alternative technologies can be used (dry cleaning, dry cooling). However, dry cooling is more expensive, technologically challenging and less efficient than the water cooling currently planned. Plans for water desalination for cooling purposes are not part of the DESERTEC business plan or cost estimates as proposed.

Centralized solar energy plants and transmission lines may become a target of terrorist attacks.

DESERTEC would require extensive economic and political cooperation between Europe and North African/Middle Eastern countries (political unrest, corruption, etc)

Middle Eastern and African nations may need assurance of ownership of the project rather than it being imposed from Europe.

1. Wind Energy

Source of Wind Energy Uneven solar intensity causes the earth crust to heat unevenly. At the equator warmer air rises and cooler air from north and south to replace it.

The earths rotation causes a point on earth to have a velocity towards the east.

Global Wind AtlasAn enormous amount of power resides in wind (~ 1-2 %of the incident solar power is converted to wind) .

However wind is a diffuse source of energy and it is only possible to harness a very small fraction of this amount.

Winds are variable both in time and location.

Egyptian Wind Atlas

The Wind Atlas for the Gulf of Suez, published in March 2003, identified the areas of greatest suitability for wind farm projects.

Egyptian Wind ProjectsSince 1992, 5 MW wind capacity has been in service at Hurghada. By the end of 2008 there was 365 MW of installed capacity at Zafarana, developed in cooperation with Denmark, Germany and Spain producing 900 GWH annually totaling 545 MW by the end of 2010.

Recently, the area of Gabal El-Zayt on the Suez Gulf, some 150 km south of Zafarana, has been identified as being suitable for the installation of some 3000 MW of wind farms.

Feasibility studies have been undertaken for two plants - one of 80 MW with German assistance and another of 220 MW with Japanese assistance to realize Egypt's national energy planning which incorporates a target of 1050 MW wind capacity to be installed by the end of the Sixth Five-Year Plan period (2007-2012).

Types Wind TurbinesHorizontal Axis Vertical Axis

Off-shore

On-shore

HAWT vs. VAWTEnergy Conversion Efficiency

Since VAWTs turn parallel with the ground, half the time its rotor blades turn against the wind. This results in having lesser efficient energy conversion as compared to HAWTs.

Also, most VAWTs are located near the ground. Since wind speeds are generally faster in higher altitudes, VAWTs generate less power compared to HAWTs which are often erected high on top of a tower.

Land Area Requirement

HAWTs require a tower that can erect the rotor blades to a high enough location that would maximize wind speeds, whilst VAWTs would require guy cables to ensure that the machine remains stable. HAWTs require lesser land space compared to VAWTs since tower bases occupy minimal space whilst the need for guy cables for VAWTs would entail occupying a much larger land area.

HAWT vs. VAWTInstallationSince VAWTs can have rotor blades close to the ground, they are easier to install compared to HAWTs that often require the rotor blades to be at a high altitude depending on the blade length.

MaintenanceFor the same reason as above, VAWTs are easier to maintain since most of them are installed near the ground.HAWTs should also be checked constantly so that it faces against the wind, unlike VAWTs which require less maintenance. Automatic yaw-adjustment mechanisms have eliminated this need of constant maintenance on HAWTs though.

RecommendationsSince VAWTs are easy to maintain, installed near ground level, they are preferred over HAWTs for residential applications although the efficiency is lower, since they are just supplemental energy generators.

For large-scale power generation, HAWTs are the more efficient wind turbines. Since they can be situated on top of towers, very high wind speeds can be gathered, producing lots of electrical power. Also, since the land area taken up by HAWTs is small, they are ideal for large wind farms.

Wind Turbine Categorization

upwind downwind

single-bladed two-bladed three-bladed multi-bladed

vertical-axis(VAWT)

horizontal-axis(HAWT)

Wind Turbine

extracted power = change of KE of the air stream

22

2

2121

eo uum

umP

extracted power = thrust velocity

uuumuTP

eo

thrust = rate of change of momentum

eo uumumT

Wind Energy Principles"Disc Theory"

Note that wind power is proportional to u3, i.e. more power at higher wind speeds and fluctuations in wind speed cause significant variation in power output.

22

2

2121

eo uum

umP

uuumuTP

eo

oe

eo

eoeo

uuu

uuu

uuumuum

22121 22

22

222

2

uuuAuuuuA

uuumuuuum

uuumP

o

o

o

oo

eo

Question: Is there an upper limit to the power extraction? In other words, if the power output of the wind turbine depends on extracting KE of the flow, is it possible to convert all the KE to useful power?

Wind Energy Principles"Disc Theory"

Theoretical Maximum Power

aaAu

auauuAP

o

ooo

12

223

2

oauu

22 uuuAP o

In general u will be a fraction of uo , let

For maximum power, differentiate and equate to zero

So the power becomes:

32

a

(1-a): induction factor

Power Coefficient

ouu 32

For maximum power,

At which we get the maximum possible power coefficient

%3.592716

21

32

3214

21

3

23

max,

o

o

P

Au

Auc

3

2

3

21

2

21

o

o

o

P

Au

uuuA

u

Pc

Betz Limit

Pow

erWind Speed

actual power

max theoretical power

wind power

Wind Turbine OperationSevere fluctuations in power pose severe strain on the grid as well as the turbine hardware. Hence, the turbine has to follow a power curve as such:

Capacity FactorCapacity factor is the ratio of actual productivity in a year to productivity of the turbine

operated at the rated power is called the capacity factor.

Typical capacity factors are 2040%, with values at the upper end of the range in

particularly favorable sites.

rated

N

iiip

PT

vtcA

PowerRatedTimeTotalGeneratedEnergyCF

321

Overall Conversion EfficiencyThe Betz limit, Cp = 16/27, is the maximum theoretically possible rotor power coefficient. In practice three effects lead to a decrease in the maximum achievable power coefficient:

-Rotation of the wake behind the rotor

-Finite number of blades and associated tip losses

-Non-zero aerodynamic drag

3

21

o

outPelecmechoverall

Au

PC

Note the distinction between wind power & turbine output power

Wind DataThe viability of wind power in a given site depends on having sufficient wind speed

available at the height at which you intend to install the turbine.

It also depends on the frequency of different speeds which can either be empirically

measured or modeled using statistical function.

Long term data gathering at any site over a multiyear period provides sufficient data for

site assessment.

The data should provide the average and variance of wind speed which will only vary

within ~ 10% from year to year in most locations.

Wind RoseA wind rose is a graphic tool used by meteorologists to give a concise view of how wind speed and direction are typically distributed at a particular location.

Typical Site Data

Average vs. Energy Speeds

N

i

iiA T

VtV 33

N

i

iiE T

VtV

Classmarginal

fairgood

excellentoutstanding

4-55-66-77-8>8

Wind Speed (m/s)

Statistical Modeling

Using measured data provides a solid basis for calculating the available

energy at the proposed site. However, sometimes we only have an

average velocity with no information on the hourly distribution wind for

the year

Rayleigh Distribution Weibull Distribution

statistical modeling

Rayleigh Distribution

Weibull Distribution

SitingWind maps, meteorological data from met towers, models, and other criteria are used for selection of the wind farm locations. Other considerations for the wind farm developer are the type of terrain (complex to plains); wind shear; winddirection; spacing of the wind turbines, which then dependson predominant wind direction and availability and cost of the land; and other items, such as roads, turbine, and substation.

Terrain can be classified as complex, mesas, rolling, and plains. Passes may be primarily one type or a mixture.

In complex terrain, such as mountains and ridges, micro-siting is very important, whereas in the flat plains, the primary consideration is spacing between turbines in a row and spacing between rows.

On mesas, the highest wind speed is on the edge of the mesa facing the predominant wind direction, so there may be only one row of turbines.

In rolling terrain such as hills, the wind turbines will be placed on the higher elevations.

Site Topology

Wind Shear

Wind shear is the change of wind speed or direction over some distance. The

change in wind speed with height is an important factor in estimating the wind

turbine energy production.

s

RR HH

VV

Wind Shear

o

R

o

R

zHzH

VV

ln

ln

o

R

o

R

zHzH

VV

1ln

1lns

RR HH

VV

Terrain Zo (m/s)Urban areas 3-0.4

Farmland 0.3-0.002Open sea 0.001-0.0001

2.0

1021

oSz

Wake Effect

Wake Effect

In general, spacing is given in terms of the diameter, D, of the wind turbine, so larger turbines will be farther apart. This is called micro-siting

~8D

~5D

Micro-Siting

Capacity FactorCapacity factor is the ratio of actual productivity in a year to productivity of the turbine

operated at the rated power is called the capacity factor.

Typical capacity factors are 2040%, with values at the upper end of the range in

particularly favorable sites.

rated

N

iii

PT

vtA

PowerRatedTimeTotalGeneratedEnergyCF

321

How Does A Turbine Work?-a closer look

The thrust on the turbine is generated and translated into rotational energy by shaping

the turbine blades as aerofoils.

Aerodynamics Basics

Blade Aerodynamics

Aerodynamic Basics

cv

Llengthunitperforcedynamic

lengthunitperforceliftC

rel

L

22

1

Lift force - defined to be perpendicular to direction of the oncoming airflow. The lift force is a consequence of the unequal pressure on the upper and lower airfoil surfaces

cvCL relL 2

21

cvCf relLL 2

21

Aerodynamic Basics

cv

Dlengthunitperforcedynamic

lengthunitperforcedragC

rel

D

2

21

Drag force - defined to be parallel to the direction of oncoming airflow. The drag force is due both to viscous friction forces at the surface of the airfoil and to unequal pressure on the airfoil surfaces facing toward and away from the oncoming flow

cvCD relD 2

21

cvCf relDD 2

21

Aerodynamic BasicsAxial Thrust Force - which must be supported by the rotor, tower and foundation

sincos DLT

sincos DLT fff

sincos2

2

DLrel

T CCcvf

Aerodynamic BasicsTangential Force - develops a rotational torque that produces useful work

cossin DLQ

cossin DLQ fff

cossin2

2

DLrel

Q CCcvf

Blade AerodynamicsBetz limit is based on neglecting the effect of drag. Now that weve studied blade aerodynamics, we can include the effect of drag into the power coefficient

vu

vv

rot

axial tan

cotuv

Blade AerodynamicsBetz limit is based on neglecting the effect of drag. Now that weve studied blade aerodynamics, we can include the effect of drag into the power coefficient

uT

uLPNoDrag

cos

cotcot1sin

cot1sin

cossin

uCCL

rCCL

rDLrQTorquePower

L

D

L

D

cot1cos

L

DwithDrag C

CuLP

Revised Power CoefficientBetz limit is based on neglecting the effect of drag. Now that weve studied blade aerodynamics, we can include the effect of drag into the power coefficient

cot1

cot1

21cos21cos

3

3

L

DNoDrag

L

D

o

withDrag

o

NoDrag

CCCp

CC

Au

uLCp

Au

uLCp

aRrwhere cot Tip-Speed Ratio,

Tip-Speed Ratio,

o

tip

uv

Rrv

vRvrv tiptip ;

And notice that the rotational speed is a function of radial location,

raR

rvRua

Rrv

uvu

vv

tip

o

tip

rot

axial

tan

Revised Power Coefficient

CP,revised

Tip-Speed Ratio,

Pow

er C

oeffi

cien

t 0.59

max ~ 8-10

Betz Limit

0.4-0.48

Blade Aerodynamics

liftforce

dragforce

thrust

Lift Force

cv

Llengthunitperforcedynamic

lengthunitperforceliftC

rel

L

22

1

cvCL relL 2

21

cvCf relLL 2

21

Drag Force

cv

Dlengthunitperforcedynamic

lengthunitperforcedragC

rel

D

2

21

cvCD relD 2

21

cvCf relDD 2

21

Axial Thrust

sincos DLT

sincos DLT fff

sincos2

2

DLrel

T CCcvf

Tangential Force

cossin DLQ

cossin DLQ fff

cossin2

2

DLrel

Q CCcvf

Revised Blade PowerBetz limit is based on neglecting the effect of drag. Now that weve studied blade aerodynamics, we can include the effect of drag into the power coefficient

uT

uLPNoDrag

cos

cotcot1sin

cot1sin

cossin

uCCL

rCCL

rDLrQTorquePower

L

D

L

D

cot1cos

L

DwithDrag C

CuLP

Revised Power CoefficientBetz limit is based on neglecting the effect of drag. Now that weve studied blade aerodynamics, we can include the effect of drag into the power coefficient

cot1

cot1

21cos21cos

3

3

L

DNoDrag

L

D

o

withDrag

o

NoDrag

CCCp

CC

Au

uLCp

Au

uLCp

aRrwhere cot Tip-Speed Ratio,

Tip-Speed Ratio,

o

tip

uv

Rrv

vRvrv tiptip ;

And notice that the rotational speed is a function of radial location,

raR

rvRua

Rrv

uvu

vv

tip

o

tip

rot

axial

tan

Revised Power Coefficient

CP,revised

Tip-Speed Ratio,

Pow

er C

oeffi

cien

t 0.59

max ~ 8-10

Betz Limit

0.4-0.48

Rotor too slow, wind will pass through open areas, without interacting with the blade no energy transfer.

Rotor too fast, wind will deflect from the wind increased swirling losses

There is optimum tip-to-speed ratio for which the power coefficient is maximum

Actual Wind Turbine Performance

Tip-Speed Ratio,

Pow

er C

oeffi

cien

t

Blade AnglesWhile, is a static angle, depending only on the blade orientation, is a dynamic angle, which changes with operating condition: wind speed, rotational speed, blade twist (if there is), radial location from hub

Because any changes in affects the forces on the blade, the power changes hence the power coefficient changes as well during operation

When the wind speed changes, the angle of attack changes,

Angle of Attack & Operation

The power extracted by the turbine changes

This changes the forces on the blade (lift and drag, torque & thrust)

The power coefficient, Cp, changes

axialv

axialv

rotv

rotv

relv

relv

Reduced Power CoefficientPo

wer

Speed

cut-in speed

cut-out speed

rated power

rated speed

Pow

er C

oeff

icie

ntSpeed

Cp

Reduced Cp

At constant rotational speed, Cp changes when wind speed changes

Wind Turbine Performance

CP, max

Tip-Speed Ratio,

Pow

er C

oeff

icie

nt

0.59

max ~ 8-10

Betz Limit

0.4-0.48

If the wind turbine operates at constant rotational speed, for fixed r, the tip-speed ration will be large for a small wind speed and small for large wind speed

small wind speed

large wind speed

Wind Speed

Shaf

t Pow

er

Cp, max max

Cp, rated

CP, rated

Wind Turbine Performance

Cp is increasing & wind power is increasing

Wind Speed

Shaf

t Pow

er

Cp is decreased & wind power is

increasing

Cp, max max

Cp, rated

Cp, rated

Most wind turbines operate at fixed rotational speeds except when starting and stopping. This simplifies the system operation when using synchronous generators paralleled with the utility grid. Additionally it helps to prevent the turbine from being operated at a speed which will excite mechanical resonance that might destroy the turbine.

Variable SpeedHowever, fixed speed operation means that the maximum coefficient of performance is available only at one particular wind speed, with a lower coefficient for all other wind speeds which reduces the output power.

Some turbines operate at variable speed. That is if the turbine speed could be adjusted in relation to the wind speed, a higher average coefficient of performance and a higher average power output could be realized. Power electronics (inverters) is used for frequency decoupling.

Variable pitch operation at a fixed speed also improves performance but ads complexity and cost.

Some turbines employ both techniques

Fixed Speed Fixed Pitch

Fixed Speed Variable Pitch

Variable Speed Fixed Pitch

Variable Speed Variable Pitch

Principle of Pitch Control

axialv

axialv

rotv

rotv

relv

relv

Pitch controlled turbines can capture the power more effectively in moderate winds as the blades can be set to its optimum angle of attack by pitching.

Principle of Pitch Control

small wind speedlarge wind speed

Tip-Speed Ratio,

Pow

er C

oeffi

cien

t 0.59 Betz Limit

= 0

= 6

= 10

Principle of Stall Control

axialv

axialv

rotv

rotv

relv

relv

When the wind exceeds beyond the rated limit, the angle of attack increases. With thisincrease in angle of attack, the flow separates (whirling in an irregular vortex, causingturbulence). This kills the lift force on the blades, finally leading to blade stall. Thus theexcess power generated at high wind is regulated.

Pitch vs. Stall ControlBecause sometimes the wind blows stronger, a wind turbine must adapt itself to the prevailing wind speed to operate most efficiently. There are two basic approaches used to control a wind turbine in high wind speeds: pitch-control and stall-control.

In pitch-controlled turbines, an anemometer mounted atop the nacelle constantly checks the wind speed and sends signals to a pitch actuator, adjusting the angle of the blades to capture the energy from the wind most efficiently.

On a stall-regulated wind turbine, the blades are locked in place and do not adjust during operation. Instead the blades are designed and shaped to increasingly stall the blades angle of attack with the wind to both maximize power output and protect the turbine from excessive wind speeds.

There are relative advantages to both design approaches. A pitch-regulated wind turbine, for example, is generally considered to be slightly more efficient than a stall-regulated turbine. On the other hand, stall-regulated turbines are often considered more reliable because they do not have the same level of mechanical and operational complexity as pitch-regulated turbines.

Constant Speed, Fixed Pitch

The power available from the wind is proportional to the cube of the wind speed. Therefore, in order to regulate power as the wind speed increases, there must be somemechanism to reduce the efficiency of the rotor blades.

Constant-speed, fixed-pitch wind turbines accomplish this automatically, because in high winds their blades stall. The resulting reduction in lift and increase in drag dramatically reduces the ability of the blades to extract power from the wind. It is important to note that this will be the case only if the generator (and power converter, in our case) can limit the rotor RPM, thereby forcing the blades to stall. It is also desirable that the blades stall gently, so that mechanical loading on the wind turbine components is not significantly increased

Turbine ControlEnergy Capture

Fixed Speed Fixed Pitch

Fixed Speed Variable Pitch

Variable Speed Fixed Pitch

Variable Speed Variable Pitch

Mechanical Load Power Quality

Wind Turbine Control Schemes

Fixed speed operation simplifies system but deteriorates performanceVariable pitch operation at fixed speed can improve performance but adds complexity and cost.

Variable speed operation enhances performance, but complicates systemVariable pitch operation at variable speed offers flexibility and improve performance but adds complexity and cost

Wind turbines employ can fall into any of these four categories depending on a compromise between cost & performance

Fixed Speed Fixed Pitch

Fixed Speed Variable Pitch

Variable Speed Fixed Pitch

Variable Speed Variable Pitch

Wind Turbine Technologiesvariable speedfixed speed

rotor speed is determined by frequency of supply grid, gear ratio & generator design-designed to achieve maximum efficiency at one particular wind speed.

-to increase power production, twowinding sets: one for low wind speeds (typically 8 poles) another for mediumand high wind speeds (typically 46 poles).

-simple, robust, reliable & low cost.

-uncontrollable reactive power consumption, mechanical stress and limited power quality control.

-fluctuations in wind speed are transmitted as fluctuations in mechanical torque and then as fluctuations in electrical power on grid

Currently dominant type due to advances in power electronics & use of inverters-designed to achieve maximum aerodynamic efficiency over a wide range of wind speeds.

-possible to continuously adapt (accelerate or decelerate) the rotational speedof the wind turbine to the wind speed.

-tip speed ratio is kept constant at a predefined value corresponding to maximum power coefficient

-keeps the generator torque fairly constant and variations in wind are absorbed by changes in the generator speed

-improved power quality, reduced mechanical stresses, but more complex system

Power RegulationThe cut-in and cut-out speeds are the operating limits of the turbine. By staying in this range, you ensure that the available energy is above the minimum threshold and structural integrity is maintained.

The rated power, a point provided by the manufacturer, takes both energy and cost into consideration. Also, the rated wind speed is chosen because speeds above this point are rare. Typically, you can assume that a turbine design that extracts the bulk of energy above the rated wind speed is not cost-effective.

PitchingThe purpose of pitch control is to maintain the optimum blade angle to achieve certain rotor speeds or power output. Pitch angle adjustment is the most effective way to limit output power by changing aerodynamic force on the blade at high wind speeds.

By either stalling the wind turbine, by increasing the angle of attack, which causes the flat side of the blade to face further into the wind.

Or feathering the wind turbine, by decreasing the angle of attack, causing the edge of the blade to face the oncoming wind.

Yaw & FurlingPrinciple: Moving the axis out of the direction of the wind decreases angle of attack and cross-section

Standard modern turbines all furl in high wind. Requires active pitch control: pitch angle of the blades needs to be minimized first, otherwise the torque on the rotor would be to big for furling.

Yaw control refers to the rotation of the entire wind turbine in the horizontal axis. Yaw control ensures that the turbine is constantly facing into the wind to maximize the effective rotor area and, as a result, power. Yaw control can be achieved passively (for small wind turbines) with a fin attached to the nacelle on the opposite side of the rotor, or actively via a motor.

Emergency Break

aerodynamic break

All wind turbines should have some mechanical or electrical way to shut them down during severe weather events:

-shorting the alternator phases,

-a mechanical brake,

-a crank that turns the tail into fully-furled position.

The problem with this method is that when the machine is spinning at high RPMs during a windstorm, the shutdown may be either impossible electrically, or too damaging to the alternator ( too much heat produced in the stator coils by shutdown at high speeds)

Usually, this is done first to slow down the turbine, ten either electrical or mechanical emergency shutdown is applied.

These systems physically brake the wind generator, or force it out of the wind by turning the tail parallel to the blades.

Fixed-Speed Fixed-PitchImpossible to improve performance with active control, only stall control at high wind speeds is possible.

In this design, the turbines generator is directly coupled to the power grid, causing the generator speed to lock to the power line frequency and fix the rotational speed.

From the figure, it is apparent that the actual power does not match the ideal power, implying that there is lower energy capture. Notice that the turbine operates at maximum efficiency only at one wind speed in the low-speed region. The rated power of the turbine is achieved only at one wind speed as well. This implies poor power regulation as a result of constrained operations.

Fixed-Speed Variable-Pitch

Below the rated wind speed, the FS-VP turbine has a near optimum efficiency around Region II. Exceeding the rated wind speed, the pitch angles are continuously changed, providing little to no loss in power.

Operates at a fixed pitch angle below the rated wind speed and continuously adjusts the angle above the rated wind speed.

Here both feather and stall pitch control methods can be used to limit power. Keep in mind that feathering takes a significant amount of control design and stalling increases unwanted thrust force as stall increases.

Variable-Speed Fixed-PitchContinuously adjusts the rotor speed relative to the wind speed through power electronics controlling the synchronous speed of the generator.; i.e. the generator is isolated from the grid so that it is free to rotate independently of grid frequency.

Fixed-pitch relies heavily on the blade design to limit power through passive stall.

The power efficiency is maximized at low wind speeds, and you can achieve rated turbine power only at one wind speed. Passive stall regulation plays a major role in not achieving the rated power and can be attributed to poor power regulation above the rated wind speed. In lower wind speed cases, VS-FP can capture more energy and improve power quality.

Variable-Speed Variable-Pitch

Operating below the rated wind speed, variable speed and fixed pitch are used to maximize energy capture and increase power quality.

Operating above the rated wind speed, fixed speed and variable pitch permit efficient power regulation at the rated power.

VS-VP is the only control strategy that theoretically achieves the ideal power curve.

Mechanical Loads

Wind Turbine Losses

Generator losses are primarily due to hysteresis and eddy currents, windage and bearing friction.

Transmission losses are primarily due to friction and viscous losses.

Wind Turbine Losses

wpgme PCP

Hence the delivered power should take all these losses into consideration

Wind Turbine Clusters

Wind Turbine Technology

http://gulzar05.blogspot.com/2011/08/20-mw-wind-turbine.html

Blade Manufacturing

http://www.gurit.com/breakdown-of-a-turbine-blade.aspx

Blade Manufacturing

Blade Construction Design

Spar Shell Construction

Stressed Shell Construction

Aerofoil Templates

Smoothing of Blade Pattern

Laminating Over Finished Pattern

Molds, Fixtures & Assembly

Cured Sections Demolding

Blade Assembly

Blade Testing & Balancing

Barrel Testing

Fatigue Testing

Balancing

Wind Turbine Manufacturing

Cost of Wind Energy

Economics of Scale

Cost-Lifetime Relationship

Major Companies

Vestas

GE Wind Energy

Sinovel

Enercon

Goldwind

Gamesa

Dongfang Electric

Suzlon

Siemens Wind Power

REpower

8.5%

GE

GoldWind

DongfangElectric

Suzlon

SiemensREpower

Companies Market Share

http://en.wikipedia.org/wiki/List_of_wind_turbine_manufacturers

12.5%

12.4%

9.2%7.2%

6.7%

6.5%

6.4%

5.9%3.4%

Enercon

Sinovel

Vestas

Gamesa

Cost-Material Allocation

Labor

Materials

Profit & Overheads

Transportation

Other

Fiberglass

Core

Resign

Adhesive

Root Studs9% Core

61% Fiberglass

19% Resign

3% Adhesive8% Root Studs

36% Materials

31% Labor

21% Profit & Overhead

7% Transportation5% Other

Expected Outages

)dB (Noise Level Noise140Threshold of pain

95Pneumatic drill at 7 m60Busy general office

35-45Wind farm at 350 m20-40Rural night-time background

0Threshold of hearing

Public Acceptance

Over a period of two years:

~ 200 birds killed in a wind farm in California

~ 0.1 birds (on average) killed in 18 wind farms in Spain

~ 120106 birds killed by cars

~100106 birds killed by flying into glass windows

~ 50106 birds killed by cats in the UK