The document discusses wind turbines and whether they will become economically feasible. It provides an overview of wind turbine costs, theoretical and empirical data on power output in relation to rotor diameter and wind speed, and how rotor diameter and other factors impact rated wind speed. It finds that while larger turbine sizes were once able to reduce costs, costs may now be rising due to the stronger materials needed for very large diameters. New materials development could potentially further reduce costs but significant improvements are uncertain. The future of wind power appearing unclear without new designs or materials breakthroughs.

1. Wind Turbines:
Will they ever become Economically
Feasible?
9th Session of MT5009
A/Prof Jeffrey Funk
Srikanth Narasimalu
Division of Engineering and Technology Management
National University of Singapore
For information on other technologies, see http://www.slideshare.net/Funk98/presentations

2. This is part of the Ninth Session of MT5009
Session Technology
1
Objectives and overview of course
2
3
Two types of improvements: 1) Creating materials that
better exploit physical phenomena; 2) Geometrical scaling
Semiconductors, ICs, electronic systems
4
5
6
7
MEMS and Bio-electronic ICs
Lighting and Displays (also roll-to roll printing)
Nanotechnology, 3D printing and DNA sequencing
Human-computer interfaces
8
Superconductivity, fusion, energy storage
9
10
Solar cells, wind turbines (also background on energy)
Telecommunications and Internet
2 | Presentation to PE forum, 18th Feb2011
N. Srikanth

3. Horizontal Axis Wind Turbines on Land and at Sea
Figure 1. Horizontal Axis Wind Turbine

4. Large Wind Farms in the
Ocean and on Land

5. Scale of Individual Wind Turbines are Being Increased

6. Wind Speed
meters per second
0.0
1.3
2.7
3.5
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
>12.0
0.0
2.9
6.0
7.8
10.0
11.2
12.3
13.4
14.5
15.7
16.8
17.9
19.0
20.1
>26.8
miles per hour

7. Wind Speed for U.S.

9. Wind Speed is not Constant!
Frequency of Wind Speed in a Ranch in Texas

10. Installed Global Capacity of Wind Power (MW)

11. Wind Capacity by Country
Nation
China
2006
2007
2008
2009
2010
2011
2012
2,599
5,912
12,210
25,104
44,733
62,733
75,564
11,603
16,819
25,170
35,159
40,200
46,919
60,007
Germany 20,622
22,247
23,903
25,777
27,214
29,060
31,332
Spain
11,630
15,145
16,740
19,149
20,676
21,674
22,796
India
6,270
7,850
9,587
10,925
13,064
16,084
18,421
UK
1,963
2,389
3,288
4,070
5,203
6,540
8,445
Italy
2,123
2,726
3,537
4,850
5,797
6,747
8,144
France
1,589
2,477
3,426
4,410
5,660
6,800
7,196
Canada
1,460
1,846
2,369
3,319
4,008
5,265
6,200
Portugal
1,716
2,130
2,862
3,535
3,702
4,083
4,525
Denmark
3,140
3,129
3,164
3,465
3,752
3,871
4,162
U.S.

12. But Wind Contributes Small % of Electricity Generation (1)
TWh: Tera Watt Hours

13. The Future of Wind Power
• Will wind power continue to diffuse?
• Advantages
• It has lower carbon and other environmental emissions
• Disadvantages
•
•
•
•
•
Wind doesn’t blow all the time (actual output about 1/4 of rated output)
Wind is far from large population centers, so high transmission costs
Wind turbines are considered ugly by many people
Sound of wind turbines causes health problems for some people
Wind power is still more expensive than fossil fuels
• But will wind power become cheaper than fossil fuels
• Will countries continue to subsidize wind power?
• Are wind turbines becoming cheaper on an cost per Watt basis?

14. Investment costs
per kWatt were falling
But now they are rising
in both Denmark (upper)
and U.S. (lower)
Source: http://srren.ipcc-wg3.de/report/srren-drafts-and-review/srren-sod-drafts/sod-chapter-07
14 | Presentation to PE forum, 18th Feb2011
N. Srikanth

15. Outline
• Overview of Wind Turbine Costs
• Theoretical Output from Wind Turbines (function of
diameter squared, wind speed cubed)
• Empirical Data
• Power output vs. rotor diameter
• Impact of rotor diameter and other factors on rated wind
speed
• Cost of wind turbines
• Implications of Analysis
• New materials are needed
• Are new designs needed?

16. Wind Farm Investment Costs
Data source: EWEA for a 2MW Turbine.

17. Main Components in Terms of Costs

18. Outline
• Overview of Wind Turbine Costs
• Theoretical Output from Wind Turbines (function of
diameter squared, wind speed cubed)
• Empirical Data
• Power output vs. rotor diameter
• Impact of rotor diameter and other factors on rated wind
speed
• Cost of wind turbines
• Implications of Analysis
• New materials are needed
• Are new designs Needed?

19. Three Key Dimensions in Geometric Scaling: 1) rotor diameter;
2) swept area of blades; and 3) hub or tower height
Figure 1. Horizontal Axis Wind Turbine

20. Theoretical Output From Wind Turbine
Turbine power output by Rotor PR
3.229 D 2V 3
(Equation 1)
P = electric power (energy per second or watts)
D = rotor diameter (meters)
V = wind speed (meters/second)
• Output from rotor depends on square of rotor diameter; thus cost of electricity
from wind turbine might fall as diameter increases, as long as cost of wind
turbine rises at a rate less than diameter squared
• Cost of electricity from wind turbine might fall as diameter increases, if larger
diameter rotors enable a wind turbine to handle higher wind speeds.

21. Outline
• Overview of Wind Turbine Costs
• Theoretical Output from Wind Turbines (function of
diameter squared, wind speed cubed)
• Empirical Data
• Power output vs. rotor diameter
• Impact of rotor diameter and other factors on rated wind
speed
• Cost of wind turbines
• Implications of Analysis
• New materials are needed
• Are new designs Needed?

22. Empirical Data Finds Stronger Relationship
Equation (2)
Data source from Henderson et al.(2003) & manufacturer catalogue.

23. Reason for Discrepancy
• Equation in previous slide does not contain wind
velocity:
• which as noted above has large impact on output
• It does not contain wind velocity since the
turbines used for the collection of data on power
and rotor diameter for Figure 3
• operate under different wind speeds
• these wind conditions depend on the respective region
• But larger wind turbines can handle higher speeds
• The impact of larger rotor diameter and related
factors (e.g., tower height) on wind speed can be
investigated in four ways

24. First, relationship between diameter and
maximum rated wind speed
Best fit curve:
Rated wind speed (m/sec) = 9.403D0.081
Data source: Hau (2008).

25. Second, data on efficiency of wind turbines was
also collected
• Efficiency is the ratio of annual turbine power output
compared to the energy available in the wind
• Less of wind can be harnessed at tips of blades than near
center of the rotor
Average wind
speed (m/sec)
4
5
6
7
8
9
Maximum Power
density achievable
(W/m^2)
75
146
253
401
599
853
Small turbine
(<25 meters)
efficiency
19%
20%
18%
17%
15%
14%
Large turbine (>25
meters) efficiency
35%
37%
35%
31%
26%
21%

26. Third, Higher Towers, Higher Speeds
• Wind velocity is often lower near ground due to uneven terrain or
buildings
V
Vref
H
H ref
Equation (4)
• The factor alpha depends on the condition of the terrain and in
particular on the impact of the terrain on wind friction and is usually
about 0.32
• Combining equations (4) and (1) leads to equation (5). Since the
exponent for the ratio of the two heights is 3α, an α of 0.32 would
cause a doubling of the tower height to result in a 94% increase in
power output.
3
P
P
ref
H
H ref
Equation (5)

27. Comparison of Wind resource at different
altitudes (Indiana, USA)
Data source: EWEA

28. Outline
• Overview of Wind Turbine Costs
• Theoretical Output from Wind Turbines (function of
diameter squared, wind speed cubed)
• Empirical Data
• Power output vs. rotor diameter
• Impact of rotor diameter and other factors on rated wind
speed
• Cost of wind turbines
• Implications of Analysis
• New materials are needed
• Are new designs Needed?

29. Cost of Wind Turbines
• More than 2/3 the cost of electricity from wind turbine farms
comes from capital cost of wind turbine and almost half the
capital costs are in tower and blades (Krohn et al, 2009)
• Beginning with tower, WindPACT analysis (Malcom and
Hansen, 2006) found R-squared of 0.999
Tower cost (in $) = 0.85 (cD2H) – 1414
Equation (6)
c = cost of steel ($/Kg); H = tower height; D = rotor diameter
• Comparing equations (5) and (6), output from turbine
increases faster than costs as height is increased.
• For example, if alpha is 0.32 as was shown above and assuming a
constant rotor diameter,
• increasing height from 10 meters to 20 meters would cause output to
rise by 94% and costs to rise by 9 percent

30. CostRotor Cost
of the Rotor
D>50 meters (Purple):
Rotor cost = 96.7D2.3257
D<50 meters (dark blue):
Rotor cost = 434.D1.9258
Data source: Hau (2008) and EWEA (2010) .

31. Compared with Output
Cost of the Rotor
Theoretical Output:
3.229D2V3 (Equation 1)
Empirical Output:
0.1034D2.2538 (Equation 2)
D>50 meters
(Purple):
Rotor cost =
96.7D2.3257
D<50 meters (dark blue):
Rotor cost = 434.D1.9258

32. Rotor Cost Per Swept Area of Turbine
Blades (1)
• Compare last two slides’ regression equations with
theoretical cost curve (equation 1)
D<50 meters: Rotor cost/output = 434.D-0.0742
D>50 meters: Rotor cost/output = 96.7D0.3257
• Compare last two slides’ regression equations with
empirical cost curve (equation 2)
D<50 meters: Rotor cost/output = 96.7D-0.2280
D>50 meters: Rotor cost/output = 434.D0.0719

33. Rotor Cost Per “Swept Area” of Turbine Blades (2)
• Benefits from increasing scale
• diameters < 50 meters; Some
• diameters > 50 meters; Hard to say, Maybe Not
• “Maybe” because equation (2) does not take into account
• the impact of increased tower height or rotor diameter on maximum
rated wind speeds or increased efficiencies.
• Including the increased efficiencies, maximum rated wind
speeds, and greater tower heights, which are partly
represented by equations (3) and (5)
• would provide a further improvements in our understanding of scaling
• would probably show some benefits to increases in scale

34. The previous slides are
consistent with other sources
(IPCC, Chapter 7)
that say investment costs per
output are now rising!!
Source: http://srren.ipcc-wg3.de/report/srren-drafts-and-review/srren-sod-drafts/sod-chapter-07

35. Why? Cost of Blades Rise
• The reason for the change in slopes for < and > than 50
meters is that lighter, thus higher cost materials are needed:
• for diameters > 50 meters (carbon fiber-based blades).
• than for diameters < 50 meters (aluminum, glass fiber reinforced
composites, and wood/epoxy).
• Early blades can be manufactured with methods borrowed
from pleasure boats such as “hand lay up” of fiber-glass
reinforced with polyester resin.
• Carbon-based blades require better manufacturing methods
such as vacuum bagging process and resin infusion method
that have been borrowed from the aerospace industry
(Ashwill, 2004)

36. Outline
• Overview of Wind Turbine Costs
• Theoretical Output from Wind Turbines (function of
diameter squared, wind speed cubed)
• Empirical Data
• Power output vs. rotor diameter
• Impact of rotor diameter and other factors on rated wind
speed
• Cost of wind turbines
• Implications of Analysis
• New materials are needed
• Are new designs needed?

37. New Materials are Needed
• Stronger and lighter materials are needed for
further increases in scaling
• Lighter materials are needed in order to reduce
inertia of large rotors
• Stronger materials are needed to withstand high
wind speeds
• Without new materials, there will be few (or
no) benefits from further scaling
• Perhaps too large of wind turbines have
already been installed

38. Source: Eric Hau
Wind turbines:
fundamentals,
technologies,
application,
economics, 2006
Note: meter
squared is for
rotor area
38 | Presentation to PE forum, 18th Feb2011
N. Srikanth

39. Material Technology Choice for Blades
Note: Squared meters is for swept area of rotor
Source Eric Hau (2006) and analysis by Srikanth Narasimalu)

40. Outline
• Overview of Wind Turbine Costs
• Theoretical Output from Wind Turbines (function of
diameter squared, wind speed cubed)
• Empirical Data
• Power output vs. rotor diameter
• Impact of rotor diameter and other factors on rated wind
speed
• Cost of wind turbines
• Implications of Analysis
• New materials are needed
• Are new designs needed

43. The “Aerogenerator:” Implementation of 275 meter diameter turbine by 2014?

44. Tethered Wind Turbine

45. Tethered Wind Turbine
What about increasing size of fins?

47. Final Words
• Costs of electricity of wind turbines were slowly
falling
• Now cost reductions have stopped and the costs
may be rising
• New materials may enable further cost reductions
• But will these improvements be significant, even if
the materials can be developed?
• New designs are needed, but even their benefits
are unclear
• The future of wind power doesn’t look good….

48. Appendix