Volume 2 wind energy 2 21 – trends prospects, and rd directions in wind turbine technology

2.21

Trends, Prospects, and R&D Directions in Wind Turbine Technology

JK Kaldellis and DP Zafirakis, Technological Education Institute of Piraeus, Athens, Greece
© 2012 Elsevier Ltd. All rights reserved.

2.21.1
Brief Description of Wind Power Time Evolution
2.21.2
The Current Wind Turbine Concept
2.21.3
Size Evolution of Wind Turbines
2.21.4
Pitch versus Stall and Active-Stall Wind Turbines
2.21.5
Direct-Drive versus Gearbox
2.21.6
Blade Design and Construction
2.21.7
Innovative Concepts
2.21.8
Environmental Impact Reduction
2.21.9
Offshore Wind Parks
2.21.10
Vertical-Axis Wind Turbines
2.21.11
Small Wind Turbines
2.21.12
Building-Integrated Wind Turbines

2.21.13
Wind Energy Cost Time Evolution
2.21.14
Research in the Wind Energy Sector
2.21.15
Wind Energy Technological Problems and R&D Directions
2.21.16
Financial Support of Wind Energy Research Efforts
2.21.16.1
1998–2002 (FP5)
2.21.16.2
2002–06 (FP6)
2.21.16.3
2007–Today (FP7)
2.21.17
Conclusions
References
Further Reading
Relevant Websites

Glossary
Capacity factor The capacity factor of a wind turbine refers
to the ratio of the actual energy production of the machine
for a given time period to the respective potential energy
production of the same machine if it had operated at its
rated power for the entire time period.
Embodied energy The energy consumed throughout the
various life cycle stages of a system, for example, a wind
turbine, equally well restricted to a single stage such as
manufacturing. Embodied energy amounts are usually

compared with the useful energy amounts produced by
the system in order to investigate whether they can be
compensated by the latter.
Feed-in tariff A policy mechanism developed for the
support of renewable energy technologies, through the
award of a certain payment per kilowatt hour for
electricity produced by a renewable resource and fed into
the grid. Feed-in tariffs may vary on the basis of
technology, geographical location, and installation size.
Framework programs Framework programs for research
and technological development, also abbreviated as FPs
on the basis of Framework Programmes alone, comprise

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funding programs that have been created by the European
Union so as to support and encourage research in various
sectors, including also wind energy.
Pitch control In pitch-controlled machines, the angle of
the blades is adjusted through signaling and the use of a
pitch actuator, so as to capture the energy from the wind in
the most efficient way.
Power (aerodynamic) coefficient A measure of the wind
turbine rotor’s ability to exploit the available kinetic
energy of wind. Its maximum theoretical value
corresponds to the Betz limit, being equal to 16/27.
R&D The term is used to describe research and
development, and refers to creative work undertaken on a
systematic basis in order to increase the stock of
knowledge and the use of this stock of knowledge to
devise new applications.
Stall control In stall-controlled machines, the angle of the
blades is fixed, while the blades are designed so that they
can increasingly stall the angle of attack with the increase
of wind speed.
Tip speed ratio The ratio of the linear speed at the tip of
the blade to the wind speed upstream of the rotor.

doi:10.1016/B978-0-08-087872-0.00224-9

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Trends, Prospects, and R&D Directions in Wind Turbine Technology

2.21.1 Brief Description of Wind Power Time Evolution
Wind energy development counts thousands of years, that is, from the starting point of the very first vertical-axis wind machines
operating on the basis of drag forces, up until the current time, during which wind turbines under development have reached the
scale of tens of MW (Figure 1).
Constant evolution of the wind power concept throughout this period may be reflected in the most straightforward way by the
fact that we are now arguably entering the time of fourth-generation wind power machines (Figure 2) [1]. From the early times of
wind power exploitation, when the first vertical-axis windmills were used for grinding, to the times that electricity power generation
lies on the rotation of huge epoxy-based blades reinforced with carbon fiber and the exploitation of offshore potential, humankind
has encountered numerous types of wind machines and designs, which have always found an important place in the puzzle of
technological development.
It was in fact centuries ago when the technology of wind energy made its first actual steps – although simpler wind devices date
back thousands of years – with the vertical-axis windmills found at the Persian–Afghan borders around 200 BC and the
horizontal-axis windmills of the Netherlands and the Mediterranean following much later (AD 1300–1875) (Figure 3) [2–4].
Further evolution and perfection of these systems was performed in the United States during the nineteenth century, when over six
million small machines were used for water pumping between 1850 and 1970 (Figure 4).

Figure 1 Wind power evolution: From the very first vertical-axis machines to large-scale contemporary wind turbines.

Uses: Power generation
Type: Electric, geared or gearless
generators, auxiliary excitation,
Wind blades: Plastics, pitch control
Towers: Steel or concrete
Erection: High-rise crane
Twentieth century
Uses:Power generation−grinding mills

Type: Electric/mechanical
Wind blades: Wood/metal, stalled
Towers: Wood (handycraft)
Erection: Manual
Nineteenth century
Uses: Water pumping−grinding mills
Type: Mechanical
Wind blades: Wood and cloth, hand
adjusted or stalled
Towers: Wood (carpentry)
Erection: Manual
From BCE to 1800

Third generation

Second generation

First generation
Figure 2 Wind power evolution: From the first to the fourth generation of wind power machines.

Uses: Power generation
Type: Electric, gearless generators, permanent
magnets, no slip rings
Wind blades: Plastics (epoxy) or bioplastics, fail
safe pitch control
Towers: Extruded concrete (selfmounting)
Erection: self erecting
Twenty-first century

Fourth generation

Trends, Prospects, and R&D Directions in Wind Turbine Technology

673

Figure 3 The vertical-axis grain machines of the Persians and the horizontal-axis windmills of the Netherlands.

Figure 4 From water pumping to the California outbreak.

On the other hand, the first ‘large’ wind machine to generate electricity (a low-speed and high-solidity wind turbine of 12 kW)
was installed in Cleveland, Ohio, in 1888, while during the late stages of World War I, the use of 25 kW machines throughout
Denmark was widespread. Much later, the first wind turbine feeding a local grid was installed in 1931 in the USSR in Balaklava, with
the electricity generated being fed into a small grid that was supplied by a 20 MW steam power station. Further development of wind
generators in the United States was inspired by the design of airplane propellers and monoplane wings, while subsequent efforts in
Denmark, France, Germany, and the United Kingdom during the period between 1935 and 1970 showed that large-scale wind
turbines could work. Note that during this period, emphasis was mainly given to the development of horizontal-axis wind machines
(i.e., the shaft of rotation is parallel to the ground) operating on the top of adequately high towers and using a small number of
blades (normally two or three).
Meanwhile, it was in 1931 that Georges Darrieus invented the vertical-axis wind turbine known as the ‘eggbeater’ windmill,
introducing a new power generation concept for wind machines (Figure 5). European developments continued after World War II.
In Denmark, the Gedser mill 200 kW three-bladed upwind rotor wind turbine operated successfully until the early 1960s [5], while
in Germany, a series of advanced horizontal-axis designs were developed, with both of the aforementioned concepts dictating the
future horizontal-axis design approaches later emerging in the 1970s.
One of the most important milestones of wind energy history coincides with the US government involvement in wind energy
R&D after the oil crisis of 1973 [6–8]. Following this, in the years between 1973 and 1986, the commercial wind turbine market
evolved from domestic and agricultural (1–25 kW) to utility-interconnected wind farm applications (50–600 kW). In this context,
the first large-scale wind energy penetration outbreak was encountered in California [9], where over 16 000 machines ranging from
20 to 350 kW (a total of 1.7 GW) were installed between 1981 and 1990, as a result of the incentives (such as the federal investment
and energy credits) given by the US government (Figure 4). In northern Europe, wind farm installations increased steadily through

the 1980s and 1990s (Figure 6), with the higher cost of electricity and the excellent wind resources leading to the creation of a small
but stable market.
After 1990, most market activity shifted to Europe [10], with the last 20 years bringing wind energy to the front line of the
global scene, with major players from all world regions. Nevertheless, both the revival of interest in the United States and the
recent dynamic introduction of the Chinese in the wind energy sector have much altered the up-to-now wind energy market
situation.
In summary, during these past 20 years, the wind energy sector has met tremendous growth, not only in terms of market share
but also in terms of technological developments, with the latest achievements bringing about the era of offshore wind power


674

Trends, Prospects, and R&D Directions in Wind Turbine Technology

Figure 5 Aspects of Darrieus vertical-axis wind machines.

Figure 6 Danish stamp of 1989 and a present-day offshore wind farm.

generation (Figure 6) [11]. At this point, it should be noted that important advancements met in the field comprise the result of
constant and unceasing research efforts, aiming at the development of innovative clean energy technologies.
In fact, according to the latest figures, systematic efforts recorded throughout this period of growth correspond to a
galloping global wind power capacity that recently managed to exceed 200 GW (Figure 7) and that is, according to market
experts, anticipated to reach 450 GW by 2015 [12]. As already implied (Figure 7), the cumulative installed wind power is

(a)

(b)


Installed capacity (GW)

210

180
4.0
5.2

150
120

3.8

44.7

26.7

5.7

90

5.8

60

13.1

40.2

30
20.7

19
9
19 6
97
19
9
19 8
99
20
0
20 0
0
20 1
02
20
0
20 3
04
20
0
20 5
06
20
0
20 7
08
20
09
20

10

0

Year

Figure 7 (a) Time evolution of installed wind power and (b) 2010 cumulative wind capacity distribution.

27.2

China
Spain
France
Denmark

USA
India
UK
Rest

Germany
Italy
Canada


Trends, Prospects, and R&D Directions in Wind Turbine Technology

675

nowadays mainly concentrated in the European Union, the United States, China, and India, while what should also be noted is

that there is aremarkable activity recently recorded in offshore installations, with contemporary machines now reaching or even
exceeding 5 MW.

2.21.2 The Current Wind Turbine Concept
Being the result of strong competition among different design schools, techniques and manufacturers from all around the world, the
vast majority of today’s wind turbines comprise the following main parts [13] (Figure 8):
A ‘rotor’ of diameter D, using three relatively thin blades placed upstream of the tower and rotating on the basis of a horizontal
axis that is almost parallel to both the ground and the wind direction. Rotational speed of the rotor nR is kept relatively low in order
to limit development of strong centrifugal stresses upon the blades [14], while it is the rotor that at the same time determines the
power of wind to be exploited Pw (see also eqn [1]):
Pw ¼ 0:5⋅ρ⋅

π⋅D2 3
⋅V
4

½1Š

where ρ is the air density passing through the rotor and V is the vertical to the rotor component of wind speed upstream of the rotor
(normally at a distance approximately equal to the rotor diameter D).
A ‘tower’, being normally of solid geometry and determined by a height H that is related to the rotor diameter (usually Η ≈ D). ine Design
Project acronym: UPWIND
EC contribution: €14.56 million
Duration: March 2006 to February 2011 (60 months)
Abstract: UPWIND looks toward wind power tomorrow, toward the design of very large turbines (8–10 MW) standing in wind
farms of several hundred megawatts, both on- and offshore. It will develop the accurate, verified tools, and component concepts the
industry needs to design and manufacture this new breed of turbine. It will focus on design tools for the complete range of turbine
components. It will address the aerodynamic, aeroelastic, structural, and material design of rotors. Critical analysis of drivetrain
components will be carried out in the search for breakthrough solutions.

Prediction of Waves, Wakes and Offshore Wind
Project acronym: POWWOW
EC contribution: €1.05 million
Duration: October 2005 to September 2008 (36 months)
Abstract: Currently, a good number of research projects are underway on the European and national level in the fields of short-term
forecasting of wind power, offshore wind and wave resource prediction, and offshore wakes in large wind farms. The purpose of this
action is to coordinate the activities in these related fields, to spread the knowledge gained from these projects among the partners
and colleagues, and to start the work on some roadmaps for the future.


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Trends, Prospects, and R&D Directions in Wind Turbine Technology

Dissemination Strategy on Electricity Balancing for large Scale Integration of Renewable Energy
Project acronym: DESIRE
EC contribution: €1.2 million
Duration: June 2005 to May 2007 (24 months)
Abstract: DESIRE will disseminate practices that will integrate fluctuating renewable electricity supplies, such as wind power, into
electricity systems using combined heat and power. This will allow an increase in pan-European trade in electricity, improve the
economic competitiveness of both combined heat and power production (CHP) and wind power, and allow the proportion of
renewable electricity that can be absorbed by the system to increase.

Distant Offshore Wind Farms with No Visual Impact in Deepwater
Project acronym: DOWNVIND
EC contribution: €6.0 million
Duration: September 2004 to September 2009 (60 months)
Abstract: The R&D program will conduct research into the factors of environmental, electrical, operations and maintenance and
wind turbine substructure pertinent to the installation and operation of large-capacity wind farms offshore in deepwater. The
Demonstrator Project will install two 5 MW wind turbine generators (WTGs) in deep water near the Beatrice Alpha oil production

platform in the Moray Firth, offshore north-east Scotland, then monitor their operation for an extended period to gather data on the
WTG and substructure performance.

Standardization of Ice Forces on Offshore Structures Design
Project acronym: STANDICE
EC contribution: €0.24 million
Duration: June 2004 to December 2007 (43 months)
Abstract: The main objective of this project is to contribute to the development of an international standard for the design
of marine structures such as offshore wind energy converters (OWECs) against ice loads with special emphasis on
European subarctic ice conditions. To achieve this objective, the project will take advantage of an international standardi­
zation effort.

Hogsara Island Demonstration Project
Project acronym: HISP
EC contribution: €1.7 million
Duration: April 2004 to July 2007 (39 months)
Abstract: The objective of the project is to gain experience and to build up a track record of a small wind farm with
multi-megawatt wind turbines built on an island, to demonstrate high availability, and to verify the low-cost foundation design
with as little alteration on the nature and inhabitants of the islands as possible. The electrical conversion system will be designed
for a cluster of turbines in order to minimize the number of components and to optimize costs, thus contributing to the
objectives mentioned.

Appendix C

Wind Energy Projects Funded by FP7 (Since 2007)

Off-Shore Renewable Energy Conversion Platforms – Coordination Action
Project acronym: ORECCA
EC contribution: €1.6 million
Duration: March 2010 to August 2011 (18 months)

Abstract: The objectives of the projects are to create a framework for knowledge sharing and to develop a research roadmap for
activities in the context of offshore renewable energy (RE). In particular, the project will stimulate collaboration in research activities
leading toward innovative, cost-efficient, and environmentally benign offshore RE conversion platforms for wind, wave, and other
ocean energy resources, for their combined use, as well as for the complementary uses.


Trends, Prospects, and R&D Directions in Wind Turbine Technology

719

Marine Renewable Integrated Application Platform
Project acronym: MARINA PLATFORM
EC contribution: €8.7 million
Duration: January 2010 to June 2014 (54 months)
Abstract: MARINA is a European project dedicated to bringing offshore renewable energy applications closer to the market by
creating new infrastructures for both offshore wind and ocean energy converters. It addresses the need for creating a cost-efficient
technology development basis to kick-start growth of the nascent European marine renewable energy (MRE) industry in the deep
offshore.

Multi-Scale Data Assimilation, Advanced Wind Modeling and Forecasting with Emphasis to Extreme Weather Situations
for a Secure Large-Scale Wind Power Integration
Project acronym: SAFEWIND
EC contribution: €3.99 million
Duration: September 2008 to August 2012 (48 months)
Abstract: The aim of this project is to substantially improve wind power predictability in challenging or extreme situations and at
different temporal and spatial scales. Going beyond this, wind predictability is considered as a system design parameter linked to
the resource assessment phase, where the aim is to take optimal decisions for the installation of a new wind farm.

Pilot Demonstration of Eleven 7 MW-Class WEC at Estinnes in Belgium
Project acronym: 7 MW-WEC-BY-11

EC contribution: €3.27 million
Duration: August 2008 to August 2012 (48 months)
Abstract: This action focuses on demonstrating the development of a cost-effective, large-scale, high-capacity wind park using new
state-of-the-art multi-megawatt turbines coupled with innovative technology used to stabilize the grid. A key objective of the ‘7­
MW-WEC-by-11’ project is to introduce a new power class of large-scale wind energy converters, the 7 MW WEC, into the market.
The new 7 MW WEC will be designed and demonstrated at a large scale: 11 such WECs will be demonstrated in a 77 MW wind park
close to Estinnes (Belgium).

Northern Seas Wind Index Database
Project acronym: NORSEWIND
EC contribution: €3.95 million
Duration: August 2008 to August 2012 (48 months)
Abstract: NORSEWIND is a program designed to provide a wind resource map covering the Baltic, Irish, and North Sea areas. The
project will acquire highly accurate, cost-effective, physical data using a combination of traditional meteorological masts,
ground-based remote sensing instruments (LiDAR and SoDAR), and satellite-acquired synthetic aperture radar (SAR) winds. The
resultant wind map will be the first stop for all potential developers in the regions being examined, and as such represents an
important step forward in quantifying the quality of the wind resource available offshore.

PROcedures for TESTing and Measuring Wind Energy Systems
Project acronym: PROTEST
EC contribution: €1.98 million
Duration: March 2008 to December 2010 (30 months)
Abstract: The objective of this pre-normative project is to set up a methodology that enables better specification of design loads for
the mechanical components. The design loads will be specified at the interconnection points where the component can be isolated
from the entire wind turbine structure (for gearboxes, for instance, the interconnection points are the shafts and the attachments to
the nacelle frame). The focus will be on developing guidelines for measuring load spectra at the interconnection points during
prototype measurements and to compare them with the initial design loads.


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Trends, Prospects, and R&D Directions in Wind Turbine Technology

Reliability Focused Research on Optimizing Wind Energy Systems Design, Operation and Maintenance: Tools, Proof of Concepts,
Guidelines & Methodologies for a New Generation
Project acronym: RELIAWIND
EC contribution: €5.18 million
Duration: March 2008 to March 2011 (36 months)
Abstract: The RELIAWIND consortium, for the first time in the European wind energy sector, and based on successful experiences
from other sectors (e.g., aeronautics) will jointly and scientifically study the impact of reliability, changing the paradigm of how
wind turbines are designed, operated, and maintained. This will lead to a new generation of offshore (and onshore) wind energy
systems that will hit the market in 2015.

Future Deep Sea Wind Turbine Technologies
Project acronym: DEEPWIND
EC contribution: €2.99 million
Duration: October 2010 to October 2014 (48 months)
Abstract: The objectives of this project for new wind turbines are (1) to explore the technologies needed for development of a new
and simple floating offshore concept with a vertical-axis rotor and a floating and rotating foundation, (2) to develop calculation and
design tools for development and evaluation of very large wind turbines based on this concept, and (3) to evaluate the overall
concept with floating offshore horizontal-axis wind turbines.

High Altitude Wind Energy
Project acronym: HAWE
EC contribution: €1.92 million
Duration: October 2010 to April 2014 (42 months)
Abstract: The aim of this project is to develop a wind power system capable of harnessing the energy potential of high-altitude wind
(actually wind towers mainly use low-altitude wind, which is slow and intermittent and means that most wind farms operate at only
25–35% of their capacity) through R&D in technology fields such as materials, aerodynamics, and control.

High Power, High Reliability Offshore Wind Technology
Project acronym: HIPRWIND
EC contribution: €11.0 million
Duration: November 2010 to November 2015 (60 months)
Abstract: The aim of the HIPRWIND project is to develop and test new solutions for very large offshore wind turbines at an industrial
scale. The project addresses critical issues such as extreme reliability, remote maintenance, and grid integration, with particular
emphasis on floating wind turbines, where weight and size limitations of onshore designs can be overcome.

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Further Reading
Asmus P (2000) Reaping the Wind: How Mechanical Wizards, Visionaries, and Profiteers Helped Shape Our Energy Future, 1st edn. Washington, DC: Island Press.

Gipe P (1995) Wind Energy Comes of Age, 1st edn. New York: John Wiley & Sons.

Mathew S and Philip GS (2011) Advances in Wind Energy Conversion Technology, 1st edn. Berlin; Heidelberg; New York: Springer.

Stankovicˇ S, Campbell N, and Harries A (2009) Urban Wind Energy, 1st edn. London, UK: Earthscan.

Twidell J and Gaudiosi G (2009) Offshore Wind Power, 1st edn. Brentwood, Essex, UK: Multi-Science Publications.

Wood D (2011) Small Wind Turbines. Analysis, Design and Application, 1st edn. Berlin; Heidelberg; New York: Springer (due August 2011).

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Relevant Websites
– Acciona.

– DEWI GmbH.

– ECN: Energy Research Centre of the Netherlands.

– Enercon.

– European Commission: Research & Innovation.

– EWEA (The European Wind Energy Association).

– Gamesa.

– GE Energy.

– Goldwind.

– IEA Wind.

– Nordex: We’ve got the power.

– NREL (National Renewable Energy Laboratory).

– OECD.StatExtracts.

– Repower Systems.

– Risø DTU: National Laboratory for Sustainable Energy.

– Sandia National Laboratories.

– Siemens.

– Suzlon: Powering a greener tomorrow.

– Vestas.

– Wind Energy: The Facts