Design And Analysis Of Offshore Wind Power Platform.
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA
TAJUK: Design and Analysis of Offshore Wind Power Platform
SESI PENGA.JIAN: 2009/10 Semester 2
Saya KHOR HAN WEI
mengaku membenarkan Laporan PSM ini disimpan di Perpustakaan Universiti
Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut:
1. Laporan PSM adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis.
2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan
untuk tujuan pengajian sahaja dengan izin penulis.
3. Perpustakaan dibenarkan membuat salinan laporan PSM ini sebagai bahan
pertukaran antara institusi pengajian tinggi.
4. **Sila tandakan (..J)
D
D
D
SULIT
TERHAD
(Mengandungi maklumat yang berdarjah keselamatan
atau kepentingan Malaysia yang termaktub di dalam
AKTA RAHSIA RASMI 1972)
(Mengandungi maklumat TERHAD yang telah ditentukan
oleh organisasi/badan di mana penyelidikan dijalankan)
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Alamat Tetap:
Cop Rasmi:
NO. 18, Jalan TU 28,
TAUFIK
ｾｮ
Taman Tasik Utama, 75450,
Ayer Keroh, Melaka
Tarikh: _ _ _ _ _ _ _ _ __
ｾｕｮｬｶ･ｲｳｩｴ＠
ｳ ｹ｡
ｴ｡ｨ＠
-f'akulti Kejurutera•m Pembuatan
Teknikal Malaysia Melaka
Tarikh:
Jika Laporan PSM ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi
rkenaan dengan menyatakan sekali sebab dan tempoh laporan PSM ini perlu dikelaskan sebagai
ULIT atau TERHAD.
CHAPTER I
•
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Design and Analysis of Offshore Wind Power Platform
This report submitted in accordance with requirement of the Universiti Teknikal Malaysia
Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering (Manufacturing
Design) with Honours.
by
KHOR HAN WEI
FACULTY OF MANUFACTURING ENGINEERING
2010
DECLARATION
I hereby, declare this Final Year Project Report entitled “Design and Analysis of
Offshore Wind Power Floating Platform.” is the results of my own research except as
cited in the references.
Signature
:
…………………………………
Author‟s Name
:
KHOR HAN WEI
Date
:
9th APR 2010
ii
APPROVAL
Theis report submitted to the Faculty of Manufacturing Engineering of UTeM has
been accepted as partial fulfillment of the requirement for the degree of Bachelor of
Manufacturing Engineering (Manufacturing Design) with Honours. The members of
the supervisory committee are as follows:
………………………………………………
Supervisor: Mr. Taufik.
Date: ................................................
Stamp: ..............................................
iii
ABSTRACT
The title of this project is Design and Analysis of Offshore Wind Turbine. The
objective of this project is to gather the design data to competently design an
offshore wind turbine, which is composed of three main structures comprising of the
rotor/blades, the tower nacelle and finally the supporting structure. This project is
important because wind energy is the fastest growing renewable energy in the world
and major gains in terms of energy generation are achievable when turbines are
moved offshore. For the purposes of this Bachelor project, in-depth analysis of
rotor/blades will not be the focus. Design will focus on the nacelle and supporting
structure. The completed final design is analyzed using commercial finite-element
modeling tool ANSYS to obtain the structure‟s response towards loading conditions
and to ensure it complies with guidelines laid out by classification authority Det
Norske Veritas. Finally, a model of the structure will be fabricated using RapidPrototype technology.
Keywords: Offshore Wind Turbine, Design and Analysis, Computer Aided Design,
Computer Aided Engineering, Finite Element Analysis, ANSYS, Foundation,
Nacelle, Computational Fluid Dynamics.
iv
ABSTRAK
Tajuk projek ini adalah kajian tentang “Design and Analysis of Offshore Wind
Turbine”. Projek ini pada asasnya adalah untuk mentakrif pengesahan rekabentuk
pada “Offshore Wind Turbine” dan bermula dengan kajian untuk mendapatkan data
rekabentuk untuk struktur yang sedia ada. Struktur terdiri daripada tiga komponen
utama iaitu bilah mata turbin, “nacelle” dan juga struktur penyokong. Projek ini
penting kerana kuasa udara merupakan bidang yang sedang berkembang dengan
pesat antara kuasa alternatif dan perkembangan besar dari segi pengumpulan kuasa
dijangka apabila turbin ini didirikan luar laut. Untuk objektif projek sarjana muda ini,
bilah mata turbin tidak akan menjadi fokus, sebaliknya fokus akan kepada struktur
penyokong dan “nacelle”. Rekabentuk akhir akan dianalisis mengunakan software
ANSYS untuk menentukan respon struktur terhadap muatan yang dikenakan. Ini
juga untuk menentukan bahawa struktur mengikuti piawaian yang diluluskan oleh
Det Norske Veritas. Pada akhir projek, suatu modal Rapid Prototype akan dihasilkan.
v
ACKNOWLEDGEMENT
First and foremost, I would like to take this opportunity to express my gratitude and
appreciation to my knowledgeable supervisor, Mr. Taufik, for his full guidance and
the continuous support and help given to me allowing me to accomplish this project.
His willingness and eagerness to assist my project throughout these few months have
been invaluable and very timely.
Besides that, I also would like give special thanks to my friends and close associates
for being understanding and sharing their thoughts with me throughout the project.
Lastly, I would like to express my appreciation and gratitude to my parents for their
support given to me during the course of the project.
vi
TABLE OF CONTENTS
ABSTRACT ....................................................................................................................... iv
ABSTRAK .......................................................................................................................... v
ACKNOWLEDGEMENT ............................................................................................... vi
TABLE OF CONTENTS ................................................................................................ vii
List of Acronyms and Abbreviations ............................................................................... x
List of Figures ................................................................................................................... xi
List ofTables ................................................................................................................... xiy
CHAPTER 1: INTRODUCTION
1.1
BACKGROUND ................................................................................................. 3
1.2
OFFSHORE WIND TURBINE (OWT) TECHNOLOGY & DEVELOPMENT
.......................................................................................................................... 5
1.2.1
DESIGN STYLES .............................................................................................. 5
1.3
OFFSHORE WIND ENERGY ......................................................................... 10
1.3.1
DEVELOPMENTS IN MALAYSIA ................................................................ 10
1.3.2 DEVELOPMENTS OVERSEAS ..................................................................... 11
1.4
CHALLENGES FACED IN OFFSHORE WIND ............................................ 14
1.4.1
PROBLEM STATEMENT ............................................................................... 16
1.5
OBJECTIVES ................................................................................................... 17
1.6
SCOPE .............................................................................................................. 18
1.7
ORGANIZATION OF THE REPORT ............................................................. 18
1.8
ACTIVITY PLANNING FOR PSM I (PROPOSED AND ACTUAL) .............. .
........................................................................................................................... 20
1.9
ACTIVITY PLANNING FOR PSM 11 ............................................................. 21
Vll
CHAPTER 2: LITERATURE REVIEW
2.1
CURRENT DESIGN ........................................................................................ 22
2.1 .1 FOUNDATION ................................................................................................. 22
2.1.2 NACELLE 30
2.1.3 ROTOR AND BLADES ................................................................................... 33
2.2
DESIGN PARAMETERS ................................................................................. 37
2.3
LOADING ......................................................................................................... 38
2.3.1 WEIGHT
38
2.3.2 WAVE FORCES ............................................................................................... 38
2.3.3 WIND FORCES ................................................................................................ 40
2.4
COMMERCIAL MODELLING APPROACHES ............................................ 41
2.4.1 DESIGN CODES .............................................................................................. 42
2.5
ANSYS .............................................................................................................. 46
2.5.1 CONCLUSION ................................................................................................. 47
CHAPTER3:METHODOLOGY
3.1
INTRODUCTION ............................................................................................. 49
3.2
FLOWCHART DESCRIPTION ....................................................................... 51
3.3
DESIGN STANDARDS ................................................................................... 52
3.4
CONCEPT GENERATION .............................................................................. 54
3.4.1 CONCEPT A ..................................................................................................... 54
3.4.2 CONCEPT B ..................................................................................................... 55
3.4.3 CONCEPT C ..................................................................................................... 56
3.5
CONCEPT SELECTION .................................................................................. 57
3.6
FINAL DESIGN ............................................................................................... 58
3.7
COMPLIANCE WITH OS-JIOI STANDARDS ............................................. 58
CHAPTER 4: DEVELOPMENT OF FINITE ELEMENT MODEL
Vlll
4.1
Solidworks Modelling ....................................................................................... 60
4.2
ANSYS Workbench (Hydrodynamic Diffraction) ............................................ 63
4.3
ANSYS Mechanical APDL (Classic) ............................................................... 67
4.3.1
Static Structural Analysis .................................................................................. 67
4.3.2 Modal Analysis ................................................................................................. 71
CHAPTERS: RESULTS
5.1
ANSYS AQWA Hydrodynamic Diffraction Results ........................................ 73
5.2
ANSYS Classis Static Structural Results .......................................................... 74
5.3
ANSYS Classis Modal Analysis Results .......................................................... 77
CHAPTER 6: DISCUSSION
6.1
Static Structural Results .................................................................................... 80
6.2
Resonance ......................................................................................................... 81
6.3
Optimizing for Solution Speed .......................................................................... 81
CHAPTER 7: CONCLUSION
7.1
Conclusion......................................................................................................... 85
7.2
Recommendations ............................................................................................. 86
REFERENCES ................................................................................................................ 87
APPENDIX A: Sample of DNV Certification Guidelines ............................................... 90
IX
List of Acronyms and Abbreviations
CAD
-
Computer Aided Design
CAE
-
Computer Aided Engineering
CNC
-
Computer Numerical Control
DNV
-
Det Norske Veritas
EPA
-
Environmental Protection Agency
IEO
-
International Energy Outlook
JONSWAP
-
Joint North Sea Wave Observation Program
NREL
-
National Renewable Energy Laboratory
OWT
-
Offshore Wind Turbine
RP
-
Rapid Prototyping
TLP
-
Tension Leg Platform
x
List of Figures
Figure 1-1: Energy consumption by country and fuel type 1998, USDOE (2009) ..... 1
Figure 1-2: Historical and projected price of oil in US Dollars per barrel, USDOE
(2009) .................................................................................................................... 2
Figure 1-3: Early examples of windmills which harness wind energy and converts it
into mechanical motion/energy. Picture courtesy of Darrel Dodge, Illustrated
History of Wind Energy ........................................................................................ 4
Figure 1-4: First large scale wind generator providing 12 kw of energy (Gardner, P)4
Figure 1-5: Darrieus-type VA WTs (Gardner, P) ........................................................ 5
Figure 1-6: Single and twin bladed rotor design (Gardner, P) .................................... 6
Figure 1-7: Part of the driveshaft connecting the rotor to the drivetrain, housed
inside the nacelle. (Gardner, P) ............................................................................. 8
Figure 1-8: Size ofwind turbine from 1980 to 2008 (Gardner. P.) ............................. 9
Figure 1-9: Wind energy growth rate from 1997 to 2010 predicted (8th World Wind
Energy Conference & Exhibition) ...................................................................... 12
Figure 1-10: Top installed wind turbine capacity and country share of new capacity
in 2008 (8th World Wind Energy Conference & Exhibition) ........................... 12
Figure 1-11: Number of jobs has doubled from 2005 to 2008 and is expected to
double again in 2010 ........................................................................................... 13
Figure 1-12: Blades of modem turbines are so large that they are transported in
sections ................................................................................................................ 14
Figure 2-1: Monopile foundation, consisting of a driven pile (Garder. P) ................ 23
Figure 2-2: Gravity based and tripod foundation concepts (U.S. DoE) .................... 23
Figure 2-3: Jacket structure ....................................................................................... 24
Figure 2-4: Suction Caisson foundation installation stages (HK EPA, 2009) .......... 25
Figure 2-5: Several structures proposed for transition water depths (U.S. DoE) ...... 26
Figure 2-6: The comers of the triangle represent idealized concepts, with actual
commercial designs overlaid to show the relationship to each (Butterfield) ...... 27
Figure 2-7: Dutch Tri-Floater ................................................................................... 27
Figure 2-8: WindFloat semi-submersible concept (Windfloat Energy) .................... 28
Xl
Figure 2-9: Typical components in a nacelle. (US. Dept. Of Energy, 2006) ............ 30
Figure 2-10: Components of a commercial turbine manufactured by Vestas ........... 31
Figure 2-11: Typical cost weightage in a nacelle (Morand, 2003) ........................... 32
Figure 2-12: Cross section view of a skin-spar-rib design (Richardson) .................. 34
Figure 2-13: Blade structure based on skin-spar-rib design (Rijswijk et al) ............ 34
Figure 2-14: Comparison between Pierson-Moskowitz and JONSWAP spectra
(Jonkman, 2007) ................................................................................................. 40
Figure 2-15: Interfacing modules to achieved a fully coupled simulation ............... 43
Figure 2-16: Screenshot ofGH Bladed software, courtesy ofGH Bladed .............. .45
Figure 2-17: ANSYS ASAS simulation flow (Pic courtesy of ANSYS Inc.) ........... 47
Figure 3-1- Reference Design, Monopile Wind Turbine (Courtesy ofExchange3D)
............................................................................................................................ 51
Figure 4-1: Dimensions for the suction caisson (meters) .......................................... 61
Figure 4-2: Structure geometry is imported using IGES format from Solidworks ... 63
Figure 4-3: Offsetting a plane to the level where it will split the model at the
waterline .............................................................................................................. 64
Figure 4-4: Split command issued, generating 3 new bodies ................................... 64
Figure 4-5: Properly grouping the body into 3 parts ................................................. 65
Figure 4-6: The green sphere indicates the C.O.G .................................................... 66
Figure 4-7: The meshed model. The caisson has been marked as inactive ............... 66
Figure 4-8: Meshed model inside ANSYS ................................................................ 67
Figure 4-9: Material Properties used (Jonkman 2007) .............................................. 69
Figure 4-10: Summary of ANSYS model. ................................................................ 70
Figure 4-11: Modal Analysis Settings ....................................................................... 72
Figure 5-1: Pressure force due to wave loading ........................................................ 73
Figure 5-2: Displacement Vector Sum (Nodal Solution) .......................................... 74
Figure 5-3: Y-Component of displacement ............................................................... 75
Figure 5-4: Stress Intensity (Nodal Solution) ........................................................... 76
Figure 5-5: Strain Intensity (Nodal Solution) ................................ ........................... 77
Figure 5-6: First Modal Shape Extraction ................................................................. 78
Figure 5-7: Second Modal Shape .............................................................................. 78
Xll
Figure 5-8: Third Modal Shape ................................................................................. 79
Figure 6-1: Configuring for SMP .............................................................................. 83
xiii
List of Tables
Table 2-1: Comparison of common foundations ....................................................... 29
Table 3-1: Gross properties chosen for the NREL 5MW Baseline Wind Turbine ... 53
Table 3-2: Concept Selection using Pugh Selection Method .................................... 58
Table 4-1: Material specifications for Steel355D .................................................... 62
Table 4-2: Auto-generated mass information based on dimension and material spec .
............................................................................................................................ 62
Table 4-3: List of elements used ............................................................................... 68
Figure 5-l: Modal Frequencies ................................................................................. 77
XlV
Chapter 1
INTRODUCTION
1
BACKGROUND
The energy industry have been experiencing a period of massive growth as
consumption of energy rose and are rising higher, driven mostly by developments in
industrial growth in countries such as China and India and also developed countries
such as Germany and the United States.
Figure 1-1: Energy consumption by country and fuel type 1998, USDOE (2009)
The chart to the left is sourced from the US Department of Energy and shows the
trend of energy consumption as a linear growth. Industrial and developed countries
lead the consumption but are expected to be overtaken by developing countries by
2015.
As for the energy by consumption type, it is obvious that fossil fuels, which are oil,
natural gas and coal contribute some 80% of the total energy requirements of our
1
world and although it is expected to grow linearly, production is a different matter as
fossil fuels are getting more and more scarce.
Russian Prime Minister Vladimir Putin recently announced that the era of cheap
energy is over and that the rising cost of extracting energy means the price of energy
will only continue to increase. This was demonstrated briefly in mid-July of 2008
when oil prices hit $147 per barrel, the highest on record since oil was first drilled.
The petroleum problem, or as President Bush calls it the „addiction to petroleum‟ is
becoming a problem as economies become dependent on oil producing countries
supplying them with enough cheap energy to keep their economies growing.
However the price spike showed that this dependence can have serious
consequences.
Based on the historical figures, the latest International Energy Outlook released by
the US Department of Energy shows a prediction of the price of oil rising steadily up
to $130 by 2030.
Figure 1-2: Historical and projected price of oil in US Dollars per barrel, USDOE (2009)
The revision from IEO2008 to IEO2009 is caused mainly by the unexpected
recovery of oil prices and a faster-than-expected recovery of the global economy
which saw oil prices swing back to the high $60s to low $70s.
2
The demand of energy will see renewable energy play an increasingly important role
as fossil fuels become more and more expensive and harder to justify in expenses. It
is expected that wind energy will contribute 1.1 trillion kilowatt-hours of the total 3.3
trillion kilowatt-hours of renewable energy predicted to be supplied by 2030.
Furthermore, it is expected that only solar and wind can provide economical
alternative energy sources, as other exotic renewable energy sources remain
expensive and unproven.
Thus it is apparent that wind and solar are going to be the focus for future
engineering efforts as we try to cope with this thirst for energy. Solar energy is
expected to become dominant as Arab countries with vast swaths deserts have
already started investigating the prospect of generating solar power to continue
developing their countries.
For wind energy, the future lies in developing offshore wind turbines that are capable
of harnessing the much higher wind speeds available offshore while avoiding the
problem of skyline pollution. A more detailed investigation of the current and future
wind energy outlook will be presented in the next section.
1.1 BACKGROUND
Wind power have been present in the history of man helping to do work such as
moving ships using sails and also with milling grains to create flour. It is also
harnessed for entertainment (kites) as well as providing a means for moving water
using water mills. All these are early examples of humanity harnessing the natural
power of wind in order to do work.
3
Figure 1-3: Early examples of windmills which harness wind energy and converts it into mechanical
motion/energy. Picture courtesy of Darrel Dodge, Illustrated History of Wind Energy
It wasn‟t before the 20th century that wind energy is harnessed to generate electricity.
As electricity was discovered and the motor invented, the first large electric windmill
was constructed in Cleveland, Ohio by Charles F. Brush, which had a rotor of 17
meters and turned a direct current generator producing 12 kilowatts of energy.
Figure 1-4: First large scale wind generator providing 12 kw of energy (Gardner, P)
Developments of wind energy continued rather slowly, although progress is made in
the preceding years increasing the efficiency as well as size of the wind turbines. The
US Government took an interest and invested into wind energy a few years after the
Arab Oil Crisis of 1973, but despite the amount of money and activity involved, the
program eventually died down due to the withdrawal of financial support and
political intervention, as well as falling oil prices which rendered wind energy
uneconomical.
4
1.2 OFFSHORE
WIND
TURBINE
(OWT)
TECHNOLOGY
&
DEVELOPMENT
Wind turbines have progressed vastly since the Dutch first used it to grind their mills
and have grown in power, from 25kw to 2500kw and more. With the growth of wind
turbine size, the tools and engineering expertise used to overcome the challenges of
harnessing wind power have also grown and expanded, with computer-aided tools
becoming more and more prolific and colleges and universities that have started to
offer courses on wind technology.
Modern offshore wind turbines are now required to generate high-quality, network
frequency electricity in an independent and automatic manner and do so for 20 years
or more continuously with low to no maintenance in some of the harshest
environments in our planet. That will be the challenges facing engineers today.
1.2.1
DESIGN STYLES
Vertical Axis Wind Turbine (Darrieus)
Figure 1-5: Darrieus-type VAWTs (Gardner, P)
5
Initially, wind turbines which rotates on the vertical axis were considered as a design
as the expected advantages are omni-directionality and having gears and power
generating equipment located at the base of the tower to lower loads. The shape of
the turbine is like an onion, also called the „troposkein curve‟. The design failed due
to the inherent inefficiencies of the rotor, extra weight in construction as well as
serious metal-fatigue problems due to the tension-loaded rotors (Gardner. P., 2002).
However, the design is still viable in low-power applications and can be mounted on
the rooftops of buildings.
Number of Blades
Figure 1-6: Single and twin bladed rotor design (Gardner, P)
The one bladed design is structurally the most efficient as all the blade area is
concentrated on one blade. However, the design needs to spin at a higher speed
(relative to multibladed designs) to generate power and this leads to higher blade and
tower loads. This high speed often generates a lot of noise which can be undesirable
in onshore designs. The use of a counterbalance to give the structure static balance is
also inefficient use of weight. Hence commercially, one bladed design has been
mostly eliminated.
Two bladed rotor designs is the next design that improves upon the single blade and
has a teeter hinge which allows the two blades to move as a single beam, with a +/7° of out-of-plane rotation designed to relieve the high loads experienced. However,
6
the apparently unsteady passage of blades through a cycle of rotation has caused it to
be almost eliminated from commercial consideration.
Three bladed designs are now the dominant as it offers the best characteristics in
terms of lower rotational speeds and more even loads. Most, if not all, modern
commercial designs are based on this Dutch three-bladed design.
Pitch vs Stall
According to Gardner in Wind Energy – The Facts, wind turbines utilize stall and
pitch regulation in order to limit the rotor power when experiencing high operational
wind speeds. Stall regulation is where the speed of the rotor is held constant or
approximately constant even under increasing wind speeds. This causes the angle of
flow over the blade sections to steepen. In effect, the blades become increasingly
stalled and thus limit the power to acceptable levels, without requiring any additional
active control.
Aerodynamicists were initially shocked at the idea of using stall as a form of limiting
power because in flight aerodynamics, stall is often fatal and can cause planes and
helicopters to crash. However, it proved to be effective to control overspeeding and
the solution is unique to the wind energy industry.
The limiting of rotor speed is done by connection of the electric generator to the grid;
the grid behaves like a giant flywheel, storing energy for the turbine.
Another alternative to stall regulation is pitch regulation. Here, the rotor is turned
about its long axis, regulating the power extracted by the rotor. This system requires
active rotor control comprising of blade position sensors, power output measurement
and a control system which adjusts the rotor angle.
The systems of speed regulation are necessary and crucial because wind gusts
happen quickly and suddenly and may cause damage to the turbine due to
overspeeding of the turbine blades.
7
Variable Speed Designs
Initially, the wind industry used fixed speed turbines which were simpler to design
and manufacture. However newer designs have started to adopt variable turbine
speeds for reasons of improved capture of energy from the wind and because the
turbine can be optimally matched to the wind flow for maximum efficiency
(Gardner. P., 2002).
Another reason variable speed was introduced is the problem of maintaining smooth
electricity generation at high wind speeds (15-20 m/s) on wind turbines that employ
pitch regulation. The high speeds introduce very turbulent flows that force the pitch
regulation system to constantly change the pitch angle of the blade. Sometimes, the
system does not respond quickly enough to the fast-changing flow and the result is
excessive power variation. The variation in power put tremendous strains for the
electrical system and also to the grid it is connected to.
The costs are higher than fixed speed design but the newer generation of turbines
have started to utilize variable speed design widely as it offers more flexibility for
the design.
Nacelle Designs
Figure 1-7: Part of the driveshaft connecting the rotor to the drivetrain, housed inside the nacelle.
(Gardner, P)
The nacelle of a wind turbine houses the generator, gearbox and drive train which are
then connected to the rotors. There are a large variety of nacelle arrangement, from
8
direct drive systems, multi-stage gearing systems and multi-pole generators (as
opposed to the more common 2 and 4 pole generators being fitted today). There is
still high competition and a clear, efficient design has yet to emerge, if indeed such a
thing exists.
Size Trends
Wind turbines have been growing in size/hub diameter. The reason for this is simply
because of the economics of scale. Smaller turbines require more maintenance and
when compared to large turbines, the cost-per-kilowatt for large turbine is much
cheaper. Furthermore, the developments of offshore wind turbines necessitates even
larger turbines as it would mean reducing the number of turbines required to be
installed offshore and reduce maintenance costs as well. The expensive foundations
for offshore turbines also mean it is cheaper to install one very large turbine rather
than several smaller ones.
Figure 1-8: Size of wind turbine from 1980 to 2008 (Gardner. P.)
However, there has been no significant growth in terms of turbine size since 2004, as
shown in the chart above. Although there are many theoretical works in progress for
turbines that are much larger than the current 120m limit, the engineering challenges
are still tremendous. With rising oil prices, it is expected that a renewed interest in
wind technology will see development of turbines that are rated 10MW and beyond.
9
BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA
TAJUK: Design and Analysis of Offshore Wind Power Platform
SESI PENGA.JIAN: 2009/10 Semester 2
Saya KHOR HAN WEI
mengaku membenarkan Laporan PSM ini disimpan di Perpustakaan Universiti
Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut:
1. Laporan PSM adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis.
2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan
untuk tujuan pengajian sahaja dengan izin penulis.
3. Perpustakaan dibenarkan membuat salinan laporan PSM ini sebagai bahan
pertukaran antara institusi pengajian tinggi.
4. **Sila tandakan (..J)
D
D
D
SULIT
TERHAD
(Mengandungi maklumat yang berdarjah keselamatan
atau kepentingan Malaysia yang termaktub di dalam
AKTA RAHSIA RASMI 1972)
(Mengandungi maklumat TERHAD yang telah ditentukan
oleh organisasi/badan di mana penyelidikan dijalankan)
TIDAK TERHAD
Disahkan oleh:
ＨｔａｎｄｾｙｅｌｉＩ＠
Alamat Tetap:
Cop Rasmi:
NO. 18, Jalan TU 28,
TAUFIK
ｾｮ
Taman Tasik Utama, 75450,
Ayer Keroh, Melaka
Tarikh: _ _ _ _ _ _ _ _ __
ｾｕｮｬｶ･ｲｳｩｴ＠
ｳ ｹ｡
ｴ｡ｨ＠
-f'akulti Kejurutera•m Pembuatan
Teknikal Malaysia Melaka
Tarikh:
Jika Laporan PSM ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi
rkenaan dengan menyatakan sekali sebab dan tempoh laporan PSM ini perlu dikelaskan sebagai
ULIT atau TERHAD.
CHAPTER I
•
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Design and Analysis of Offshore Wind Power Platform
This report submitted in accordance with requirement of the Universiti Teknikal Malaysia
Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering (Manufacturing
Design) with Honours.
by
KHOR HAN WEI
FACULTY OF MANUFACTURING ENGINEERING
2010
DECLARATION
I hereby, declare this Final Year Project Report entitled “Design and Analysis of
Offshore Wind Power Floating Platform.” is the results of my own research except as
cited in the references.
Signature
:
…………………………………
Author‟s Name
:
KHOR HAN WEI
Date
:
9th APR 2010
ii
APPROVAL
Theis report submitted to the Faculty of Manufacturing Engineering of UTeM has
been accepted as partial fulfillment of the requirement for the degree of Bachelor of
Manufacturing Engineering (Manufacturing Design) with Honours. The members of
the supervisory committee are as follows:
………………………………………………
Supervisor: Mr. Taufik.
Date: ................................................
Stamp: ..............................................
iii
ABSTRACT
The title of this project is Design and Analysis of Offshore Wind Turbine. The
objective of this project is to gather the design data to competently design an
offshore wind turbine, which is composed of three main structures comprising of the
rotor/blades, the tower nacelle and finally the supporting structure. This project is
important because wind energy is the fastest growing renewable energy in the world
and major gains in terms of energy generation are achievable when turbines are
moved offshore. For the purposes of this Bachelor project, in-depth analysis of
rotor/blades will not be the focus. Design will focus on the nacelle and supporting
structure. The completed final design is analyzed using commercial finite-element
modeling tool ANSYS to obtain the structure‟s response towards loading conditions
and to ensure it complies with guidelines laid out by classification authority Det
Norske Veritas. Finally, a model of the structure will be fabricated using RapidPrototype technology.
Keywords: Offshore Wind Turbine, Design and Analysis, Computer Aided Design,
Computer Aided Engineering, Finite Element Analysis, ANSYS, Foundation,
Nacelle, Computational Fluid Dynamics.
iv
ABSTRAK
Tajuk projek ini adalah kajian tentang “Design and Analysis of Offshore Wind
Turbine”. Projek ini pada asasnya adalah untuk mentakrif pengesahan rekabentuk
pada “Offshore Wind Turbine” dan bermula dengan kajian untuk mendapatkan data
rekabentuk untuk struktur yang sedia ada. Struktur terdiri daripada tiga komponen
utama iaitu bilah mata turbin, “nacelle” dan juga struktur penyokong. Projek ini
penting kerana kuasa udara merupakan bidang yang sedang berkembang dengan
pesat antara kuasa alternatif dan perkembangan besar dari segi pengumpulan kuasa
dijangka apabila turbin ini didirikan luar laut. Untuk objektif projek sarjana muda ini,
bilah mata turbin tidak akan menjadi fokus, sebaliknya fokus akan kepada struktur
penyokong dan “nacelle”. Rekabentuk akhir akan dianalisis mengunakan software
ANSYS untuk menentukan respon struktur terhadap muatan yang dikenakan. Ini
juga untuk menentukan bahawa struktur mengikuti piawaian yang diluluskan oleh
Det Norske Veritas. Pada akhir projek, suatu modal Rapid Prototype akan dihasilkan.
v
ACKNOWLEDGEMENT
First and foremost, I would like to take this opportunity to express my gratitude and
appreciation to my knowledgeable supervisor, Mr. Taufik, for his full guidance and
the continuous support and help given to me allowing me to accomplish this project.
His willingness and eagerness to assist my project throughout these few months have
been invaluable and very timely.
Besides that, I also would like give special thanks to my friends and close associates
for being understanding and sharing their thoughts with me throughout the project.
Lastly, I would like to express my appreciation and gratitude to my parents for their
support given to me during the course of the project.
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TABLE OF CONTENTS
ABSTRACT ....................................................................................................................... iv
ABSTRAK .......................................................................................................................... v
ACKNOWLEDGEMENT ............................................................................................... vi
TABLE OF CONTENTS ................................................................................................ vii
List of Acronyms and Abbreviations ............................................................................... x
List of Figures ................................................................................................................... xi
List ofTables ................................................................................................................... xiy
CHAPTER 1: INTRODUCTION
1.1
BACKGROUND ................................................................................................. 3
1.2
OFFSHORE WIND TURBINE (OWT) TECHNOLOGY & DEVELOPMENT
.......................................................................................................................... 5
1.2.1
DESIGN STYLES .............................................................................................. 5
1.3
OFFSHORE WIND ENERGY ......................................................................... 10
1.3.1
DEVELOPMENTS IN MALAYSIA ................................................................ 10
1.3.2 DEVELOPMENTS OVERSEAS ..................................................................... 11
1.4
CHALLENGES FACED IN OFFSHORE WIND ............................................ 14
1.4.1
PROBLEM STATEMENT ............................................................................... 16
1.5
OBJECTIVES ................................................................................................... 17
1.6
SCOPE .............................................................................................................. 18
1.7
ORGANIZATION OF THE REPORT ............................................................. 18
1.8
ACTIVITY PLANNING FOR PSM I (PROPOSED AND ACTUAL) .............. .
........................................................................................................................... 20
1.9
ACTIVITY PLANNING FOR PSM 11 ............................................................. 21
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CHAPTER 2: LITERATURE REVIEW
2.1
CURRENT DESIGN ........................................................................................ 22
2.1 .1 FOUNDATION ................................................................................................. 22
2.1.2 NACELLE 30
2.1.3 ROTOR AND BLADES ................................................................................... 33
2.2
DESIGN PARAMETERS ................................................................................. 37
2.3
LOADING ......................................................................................................... 38
2.3.1 WEIGHT
38
2.3.2 WAVE FORCES ............................................................................................... 38
2.3.3 WIND FORCES ................................................................................................ 40
2.4
COMMERCIAL MODELLING APPROACHES ............................................ 41
2.4.1 DESIGN CODES .............................................................................................. 42
2.5
ANSYS .............................................................................................................. 46
2.5.1 CONCLUSION ................................................................................................. 47
CHAPTER3:METHODOLOGY
3.1
INTRODUCTION ............................................................................................. 49
3.2
FLOWCHART DESCRIPTION ....................................................................... 51
3.3
DESIGN STANDARDS ................................................................................... 52
3.4
CONCEPT GENERATION .............................................................................. 54
3.4.1 CONCEPT A ..................................................................................................... 54
3.4.2 CONCEPT B ..................................................................................................... 55
3.4.3 CONCEPT C ..................................................................................................... 56
3.5
CONCEPT SELECTION .................................................................................. 57
3.6
FINAL DESIGN ............................................................................................... 58
3.7
COMPLIANCE WITH OS-JIOI STANDARDS ............................................. 58
CHAPTER 4: DEVELOPMENT OF FINITE ELEMENT MODEL
Vlll
4.1
Solidworks Modelling ....................................................................................... 60
4.2
ANSYS Workbench (Hydrodynamic Diffraction) ............................................ 63
4.3
ANSYS Mechanical APDL (Classic) ............................................................... 67
4.3.1
Static Structural Analysis .................................................................................. 67
4.3.2 Modal Analysis ................................................................................................. 71
CHAPTERS: RESULTS
5.1
ANSYS AQWA Hydrodynamic Diffraction Results ........................................ 73
5.2
ANSYS Classis Static Structural Results .......................................................... 74
5.3
ANSYS Classis Modal Analysis Results .......................................................... 77
CHAPTER 6: DISCUSSION
6.1
Static Structural Results .................................................................................... 80
6.2
Resonance ......................................................................................................... 81
6.3
Optimizing for Solution Speed .......................................................................... 81
CHAPTER 7: CONCLUSION
7.1
Conclusion......................................................................................................... 85
7.2
Recommendations ............................................................................................. 86
REFERENCES ................................................................................................................ 87
APPENDIX A: Sample of DNV Certification Guidelines ............................................... 90
IX
List of Acronyms and Abbreviations
CAD
-
Computer Aided Design
CAE
-
Computer Aided Engineering
CNC
-
Computer Numerical Control
DNV
-
Det Norske Veritas
EPA
-
Environmental Protection Agency
IEO
-
International Energy Outlook
JONSWAP
-
Joint North Sea Wave Observation Program
NREL
-
National Renewable Energy Laboratory
OWT
-
Offshore Wind Turbine
RP
-
Rapid Prototyping
TLP
-
Tension Leg Platform
x
List of Figures
Figure 1-1: Energy consumption by country and fuel type 1998, USDOE (2009) ..... 1
Figure 1-2: Historical and projected price of oil in US Dollars per barrel, USDOE
(2009) .................................................................................................................... 2
Figure 1-3: Early examples of windmills which harness wind energy and converts it
into mechanical motion/energy. Picture courtesy of Darrel Dodge, Illustrated
History of Wind Energy ........................................................................................ 4
Figure 1-4: First large scale wind generator providing 12 kw of energy (Gardner, P)4
Figure 1-5: Darrieus-type VA WTs (Gardner, P) ........................................................ 5
Figure 1-6: Single and twin bladed rotor design (Gardner, P) .................................... 6
Figure 1-7: Part of the driveshaft connecting the rotor to the drivetrain, housed
inside the nacelle. (Gardner, P) ............................................................................. 8
Figure 1-8: Size ofwind turbine from 1980 to 2008 (Gardner. P.) ............................. 9
Figure 1-9: Wind energy growth rate from 1997 to 2010 predicted (8th World Wind
Energy Conference & Exhibition) ...................................................................... 12
Figure 1-10: Top installed wind turbine capacity and country share of new capacity
in 2008 (8th World Wind Energy Conference & Exhibition) ........................... 12
Figure 1-11: Number of jobs has doubled from 2005 to 2008 and is expected to
double again in 2010 ........................................................................................... 13
Figure 1-12: Blades of modem turbines are so large that they are transported in
sections ................................................................................................................ 14
Figure 2-1: Monopile foundation, consisting of a driven pile (Garder. P) ................ 23
Figure 2-2: Gravity based and tripod foundation concepts (U.S. DoE) .................... 23
Figure 2-3: Jacket structure ....................................................................................... 24
Figure 2-4: Suction Caisson foundation installation stages (HK EPA, 2009) .......... 25
Figure 2-5: Several structures proposed for transition water depths (U.S. DoE) ...... 26
Figure 2-6: The comers of the triangle represent idealized concepts, with actual
commercial designs overlaid to show the relationship to each (Butterfield) ...... 27
Figure 2-7: Dutch Tri-Floater ................................................................................... 27
Figure 2-8: WindFloat semi-submersible concept (Windfloat Energy) .................... 28
Xl
Figure 2-9: Typical components in a nacelle. (US. Dept. Of Energy, 2006) ............ 30
Figure 2-10: Components of a commercial turbine manufactured by Vestas ........... 31
Figure 2-11: Typical cost weightage in a nacelle (Morand, 2003) ........................... 32
Figure 2-12: Cross section view of a skin-spar-rib design (Richardson) .................. 34
Figure 2-13: Blade structure based on skin-spar-rib design (Rijswijk et al) ............ 34
Figure 2-14: Comparison between Pierson-Moskowitz and JONSWAP spectra
(Jonkman, 2007) ................................................................................................. 40
Figure 2-15: Interfacing modules to achieved a fully coupled simulation ............... 43
Figure 2-16: Screenshot ofGH Bladed software, courtesy ofGH Bladed .............. .45
Figure 2-17: ANSYS ASAS simulation flow (Pic courtesy of ANSYS Inc.) ........... 47
Figure 3-1- Reference Design, Monopile Wind Turbine (Courtesy ofExchange3D)
............................................................................................................................ 51
Figure 4-1: Dimensions for the suction caisson (meters) .......................................... 61
Figure 4-2: Structure geometry is imported using IGES format from Solidworks ... 63
Figure 4-3: Offsetting a plane to the level where it will split the model at the
waterline .............................................................................................................. 64
Figure 4-4: Split command issued, generating 3 new bodies ................................... 64
Figure 4-5: Properly grouping the body into 3 parts ................................................. 65
Figure 4-6: The green sphere indicates the C.O.G .................................................... 66
Figure 4-7: The meshed model. The caisson has been marked as inactive ............... 66
Figure 4-8: Meshed model inside ANSYS ................................................................ 67
Figure 4-9: Material Properties used (Jonkman 2007) .............................................. 69
Figure 4-10: Summary of ANSYS model. ................................................................ 70
Figure 4-11: Modal Analysis Settings ....................................................................... 72
Figure 5-1: Pressure force due to wave loading ........................................................ 73
Figure 5-2: Displacement Vector Sum (Nodal Solution) .......................................... 74
Figure 5-3: Y-Component of displacement ............................................................... 75
Figure 5-4: Stress Intensity (Nodal Solution) ........................................................... 76
Figure 5-5: Strain Intensity (Nodal Solution) ................................ ........................... 77
Figure 5-6: First Modal Shape Extraction ................................................................. 78
Figure 5-7: Second Modal Shape .............................................................................. 78
Xll
Figure 5-8: Third Modal Shape ................................................................................. 79
Figure 6-1: Configuring for SMP .............................................................................. 83
xiii
List of Tables
Table 2-1: Comparison of common foundations ....................................................... 29
Table 3-1: Gross properties chosen for the NREL 5MW Baseline Wind Turbine ... 53
Table 3-2: Concept Selection using Pugh Selection Method .................................... 58
Table 4-1: Material specifications for Steel355D .................................................... 62
Table 4-2: Auto-generated mass information based on dimension and material spec .
............................................................................................................................ 62
Table 4-3: List of elements used ............................................................................... 68
Figure 5-l: Modal Frequencies ................................................................................. 77
XlV
Chapter 1
INTRODUCTION
1
BACKGROUND
The energy industry have been experiencing a period of massive growth as
consumption of energy rose and are rising higher, driven mostly by developments in
industrial growth in countries such as China and India and also developed countries
such as Germany and the United States.
Figure 1-1: Energy consumption by country and fuel type 1998, USDOE (2009)
The chart to the left is sourced from the US Department of Energy and shows the
trend of energy consumption as a linear growth. Industrial and developed countries
lead the consumption but are expected to be overtaken by developing countries by
2015.
As for the energy by consumption type, it is obvious that fossil fuels, which are oil,
natural gas and coal contribute some 80% of the total energy requirements of our
1
world and although it is expected to grow linearly, production is a different matter as
fossil fuels are getting more and more scarce.
Russian Prime Minister Vladimir Putin recently announced that the era of cheap
energy is over and that the rising cost of extracting energy means the price of energy
will only continue to increase. This was demonstrated briefly in mid-July of 2008
when oil prices hit $147 per barrel, the highest on record since oil was first drilled.
The petroleum problem, or as President Bush calls it the „addiction to petroleum‟ is
becoming a problem as economies become dependent on oil producing countries
supplying them with enough cheap energy to keep their economies growing.
However the price spike showed that this dependence can have serious
consequences.
Based on the historical figures, the latest International Energy Outlook released by
the US Department of Energy shows a prediction of the price of oil rising steadily up
to $130 by 2030.
Figure 1-2: Historical and projected price of oil in US Dollars per barrel, USDOE (2009)
The revision from IEO2008 to IEO2009 is caused mainly by the unexpected
recovery of oil prices and a faster-than-expected recovery of the global economy
which saw oil prices swing back to the high $60s to low $70s.
2
The demand of energy will see renewable energy play an increasingly important role
as fossil fuels become more and more expensive and harder to justify in expenses. It
is expected that wind energy will contribute 1.1 trillion kilowatt-hours of the total 3.3
trillion kilowatt-hours of renewable energy predicted to be supplied by 2030.
Furthermore, it is expected that only solar and wind can provide economical
alternative energy sources, as other exotic renewable energy sources remain
expensive and unproven.
Thus it is apparent that wind and solar are going to be the focus for future
engineering efforts as we try to cope with this thirst for energy. Solar energy is
expected to become dominant as Arab countries with vast swaths deserts have
already started investigating the prospect of generating solar power to continue
developing their countries.
For wind energy, the future lies in developing offshore wind turbines that are capable
of harnessing the much higher wind speeds available offshore while avoiding the
problem of skyline pollution. A more detailed investigation of the current and future
wind energy outlook will be presented in the next section.
1.1 BACKGROUND
Wind power have been present in the history of man helping to do work such as
moving ships using sails and also with milling grains to create flour. It is also
harnessed for entertainment (kites) as well as providing a means for moving water
using water mills. All these are early examples of humanity harnessing the natural
power of wind in order to do work.
3
Figure 1-3: Early examples of windmills which harness wind energy and converts it into mechanical
motion/energy. Picture courtesy of Darrel Dodge, Illustrated History of Wind Energy
It wasn‟t before the 20th century that wind energy is harnessed to generate electricity.
As electricity was discovered and the motor invented, the first large electric windmill
was constructed in Cleveland, Ohio by Charles F. Brush, which had a rotor of 17
meters and turned a direct current generator producing 12 kilowatts of energy.
Figure 1-4: First large scale wind generator providing 12 kw of energy (Gardner, P)
Developments of wind energy continued rather slowly, although progress is made in
the preceding years increasing the efficiency as well as size of the wind turbines. The
US Government took an interest and invested into wind energy a few years after the
Arab Oil Crisis of 1973, but despite the amount of money and activity involved, the
program eventually died down due to the withdrawal of financial support and
political intervention, as well as falling oil prices which rendered wind energy
uneconomical.
4
1.2 OFFSHORE
WIND
TURBINE
(OWT)
TECHNOLOGY
&
DEVELOPMENT
Wind turbines have progressed vastly since the Dutch first used it to grind their mills
and have grown in power, from 25kw to 2500kw and more. With the growth of wind
turbine size, the tools and engineering expertise used to overcome the challenges of
harnessing wind power have also grown and expanded, with computer-aided tools
becoming more and more prolific and colleges and universities that have started to
offer courses on wind technology.
Modern offshore wind turbines are now required to generate high-quality, network
frequency electricity in an independent and automatic manner and do so for 20 years
or more continuously with low to no maintenance in some of the harshest
environments in our planet. That will be the challenges facing engineers today.
1.2.1
DESIGN STYLES
Vertical Axis Wind Turbine (Darrieus)
Figure 1-5: Darrieus-type VAWTs (Gardner, P)
5
Initially, wind turbines which rotates on the vertical axis were considered as a design
as the expected advantages are omni-directionality and having gears and power
generating equipment located at the base of the tower to lower loads. The shape of
the turbine is like an onion, also called the „troposkein curve‟. The design failed due
to the inherent inefficiencies of the rotor, extra weight in construction as well as
serious metal-fatigue problems due to the tension-loaded rotors (Gardner. P., 2002).
However, the design is still viable in low-power applications and can be mounted on
the rooftops of buildings.
Number of Blades
Figure 1-6: Single and twin bladed rotor design (Gardner, P)
The one bladed design is structurally the most efficient as all the blade area is
concentrated on one blade. However, the design needs to spin at a higher speed
(relative to multibladed designs) to generate power and this leads to higher blade and
tower loads. This high speed often generates a lot of noise which can be undesirable
in onshore designs. The use of a counterbalance to give the structure static balance is
also inefficient use of weight. Hence commercially, one bladed design has been
mostly eliminated.
Two bladed rotor designs is the next design that improves upon the single blade and
has a teeter hinge which allows the two blades to move as a single beam, with a +/7° of out-of-plane rotation designed to relieve the high loads experienced. However,
6
the apparently unsteady passage of blades through a cycle of rotation has caused it to
be almost eliminated from commercial consideration.
Three bladed designs are now the dominant as it offers the best characteristics in
terms of lower rotational speeds and more even loads. Most, if not all, modern
commercial designs are based on this Dutch three-bladed design.
Pitch vs Stall
According to Gardner in Wind Energy – The Facts, wind turbines utilize stall and
pitch regulation in order to limit the rotor power when experiencing high operational
wind speeds. Stall regulation is where the speed of the rotor is held constant or
approximately constant even under increasing wind speeds. This causes the angle of
flow over the blade sections to steepen. In effect, the blades become increasingly
stalled and thus limit the power to acceptable levels, without requiring any additional
active control.
Aerodynamicists were initially shocked at the idea of using stall as a form of limiting
power because in flight aerodynamics, stall is often fatal and can cause planes and
helicopters to crash. However, it proved to be effective to control overspeeding and
the solution is unique to the wind energy industry.
The limiting of rotor speed is done by connection of the electric generator to the grid;
the grid behaves like a giant flywheel, storing energy for the turbine.
Another alternative to stall regulation is pitch regulation. Here, the rotor is turned
about its long axis, regulating the power extracted by the rotor. This system requires
active rotor control comprising of blade position sensors, power output measurement
and a control system which adjusts the rotor angle.
The systems of speed regulation are necessary and crucial because wind gusts
happen quickly and suddenly and may cause damage to the turbine due to
overspeeding of the turbine blades.
7
Variable Speed Designs
Initially, the wind industry used fixed speed turbines which were simpler to design
and manufacture. However newer designs have started to adopt variable turbine
speeds for reasons of improved capture of energy from the wind and because the
turbine can be optimally matched to the wind flow for maximum efficiency
(Gardner. P., 2002).
Another reason variable speed was introduced is the problem of maintaining smooth
electricity generation at high wind speeds (15-20 m/s) on wind turbines that employ
pitch regulation. The high speeds introduce very turbulent flows that force the pitch
regulation system to constantly change the pitch angle of the blade. Sometimes, the
system does not respond quickly enough to the fast-changing flow and the result is
excessive power variation. The variation in power put tremendous strains for the
electrical system and also to the grid it is connected to.
The costs are higher than fixed speed design but the newer generation of turbines
have started to utilize variable speed design widely as it offers more flexibility for
the design.
Nacelle Designs
Figure 1-7: Part of the driveshaft connecting the rotor to the drivetrain, housed inside the nacelle.
(Gardner, P)
The nacelle of a wind turbine houses the generator, gearbox and drive train which are
then connected to the rotors. There are a large variety of nacelle arrangement, from
8
direct drive systems, multi-stage gearing systems and multi-pole generators (as
opposed to the more common 2 and 4 pole generators being fitted today). There is
still high competition and a clear, efficient design has yet to emerge, if indeed such a
thing exists.
Size Trends
Wind turbines have been growing in size/hub diameter. The reason for this is simply
because of the economics of scale. Smaller turbines require more maintenance and
when compared to large turbines, the cost-per-kilowatt for large turbine is much
cheaper. Furthermore, the developments of offshore wind turbines necessitates even
larger turbines as it would mean reducing the number of turbines required to be
installed offshore and reduce maintenance costs as well. The expensive foundations
for offshore turbines also mean it is cheaper to install one very large turbine rather
than several smaller ones.
Figure 1-8: Size of wind turbine from 1980 to 2008 (Gardner. P.)
However, there has been no significant growth in terms of turbine size since 2004, as
shown in the chart above. Although there are many theoretical works in progress for
turbines that are much larger than the current 120m limit, the engineering challenges
are still tremendous. With rising oil prices, it is expected that a renewed interest in
wind technology will see development of turbines that are rated 10MW and beyond.
9