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Offshore wind energy 'The road to maturity' by oaw14128

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									Offshore wind energy:
‘The road to maturity’
 Dutch Offshore Wind Energy Converter (DOWEC) project

                      1997 – 2003




            I. Global offshore wind overview

                  II. DOWEC formation

      III. DOWEC achievements and future potential




                     January 2004




                           1
2
Preface
The successful completion of the DOWEC project is a milestone for us. Six
partners with totally different experience and backgrounds worked together on
fundamental scientific as well as industrial development tasks. The multi-
partner approach proved not always an easy one. It provided at the same time
excellent opportunities to grow into a new exiting business field with great
future promise, and to reflect on early offshore visions and expectations of
DOWEC ‘s founding fathers.

The booklet is subdivided into three closely interlinked parts.
Part I provides a global overview of offshore wind energy developments, and
installation targets set by leading wind nations. Also covered are subjects like
technology and market trends, offshore complexities, cost trends, installation
challenges, and clever maritime innovations.
Part II describes DOWEC ‘s formation period, plus a number of key objectives
and research considerations.
Part III evaluates achievements of the DOWEC project, and how results are
envisaged to positively affect offshore wind progress and international
competitiveness of all six parties involved.

We are pleased that partners judge positively about project achievements and
spin-offs for their individual organisations. One observed that DOWEC has
been the first Dutch project of this complexity and of this nature that was
successfully completed. A second partner praised the atmosphere of
openness in the group. We regard both statements as a compliment to the
whole group, as they together made things happen.
A combination of strengthened network and widened know-how base has no
doubt better equipped all DOWEC partners to successfully participate in other
challenging future offshore wind energy projects around the globe. In what
manner and at which pace this rapidly maturing technology can contribute
towards solving tomorrow ‘s energy needs for the benefit of next generations,
depends on real people and their drive to get things moving.

On behalf of the DOWEC group we do sincerely hope that you will enjoy
reading this booklet, and that some of our spirit and strong belief in the future
of offshore wind energy will be passed on.

December 2003
                                                 DOWEC Steering Committee




                                        3
Introduction
Plans for DOWEC date back to 1997, interrupted in 1998 by a turbulent period
with many changes for the Dutch wind industry. This combination of events
affected the pace of DOWEC ‘s formation and the group ‘s final composition.
When the project commenced, it comprised six partners from two distinct
business fields: offshore technology and wind energy. Key project objective
was to develop all know-how necessary for designing a competitive 6 MW
class offshore wind turbine, plus innovative erection, operating, and
maintenance methods best suited for the rough maritime environment.

One of the envisaged key project outcomes was a 3 MW + R&D demonstration
prototype, with a 100-metre rotor diameter. The erection of a 2.75 MW
Demonstrator prototype February 2003 at ECN ‘s new test site for multi-
megawatt class wind turbines in the Wieringermeer, NH-Province was a
project highlight. Product specifications of the turbine, with a 92-metre rotor
currently one of the world ‘s largest commercial prototypes, slightly differ from
earlier indicative figures for various reasons.

The Demonstrator itself
has been performing to
expectations and will
produce about nine
million kWh annually,
sufficient to cover the
electricity needs of
2,800 Dutch
households. Under
offshore conditions
annual energy
production will be even
higher. In addition within
weeks after
commissioning the
turbine, energy centre
ECN commenced with a
comprehensive
measuring and
validation programme.
DOWEC ‘s added value
for partners, project
developers, and other
stakeholders alike lies
in a balanced
combination of applied
and scientific know-
how, as will be
                                            Figure 1: The DOWEC demonstrator turbine in the
summarised in the                                          Wieringermeer (photo NEG Micon)
following chapters.



                                        4
Contents

Preface
Introduction
Contents
Partner views


Part I: Global offshore wind overview
   1. Offshore wind energy ambitions
   2. Kick-off projects
   3. Fast track to large turbines
   4. Market driven development
   5. Maturing technology
   6. Variable speed for superior control
   7. Costs structure trends
   8. Offshore complexities
   9. Foundation and installation challenges
   10. Maritime innovations


Part II: DOWEC formation
   11. DOWEC – from plans to project
   12. Pre-concept study
   13. DOWEC partners
   14. Partners in brief
   15. Project objectives
   16. Key focus wind farm optimisation
   17. DOWEC Demonstrator – R&D considerations


Part III: Partner achievements and future potential
   18. NEG Micon Holland: ‘DOWEC Demonstrator’
   19. LMGH: ‘World ‘s longest rotor blade from Heerhugowaard’
   20. Ballast Nedam: ‘DOWEC design installation method’
   21. Van Oord: ‘Cable related and scour protection tasks’
   22. ECN: ‘Measuring and validation programme’
   23. TU Delft: ‘Research and design focussed knowledge transfer’
   24. Future potential




                                     5
Partner views

All six DOWEC partners had their own motives and expectations when they decided
to participate into the project. Below is a random selection of their views and
statements:

‘Through our participation in DOWEC we came to know and understand the wind
energy market much better.’

‘For us the balance is positive, especially when viewed from an European perspective
and the advancement of wind energy and offshore technology in general.’

‘DOWEC fits well in the current phase of offshore wind energy development,
integration between wind technology and offshore is thereby highly essential.’

‘Through our participation in DOWEC we have as a relative outsider in the offshore
field learned a great deal about wind turbine installation methods.’

‘DOWEC has served as a fabric to strengthen our wind energy research base,
especially with regard to cost-effective and large-scale utilisation of offshore wind
turbines.’

‘This was the first Dutch wind project whereby multiple partners from research bodies
and industry worked closely together in a complex multi-year project.’

‘DOWEC was the first large Dutch project of this nature that was brought to a
successful completion.’

‘It was a great opportunity that we could work in a team with industrial partners,
which have the development of large commercial wind turbines and rotor blades for
onshore- and offshore application as their core business.’

‘This was the first Dutch wind project whereby the TU Delft and ECN worked closely
together with specialised offshore and civil-engineering parties.’

‘Our institute could experience first hand how internationally oriented offshore and
civil-engineering parties tackle specific challenges in their respective fields.’




                                           6
Part I: Global offshore wind overview

Chapters 1 – 10 provide an overall global overview of international wind
energy and offshore technology developments, and envisaged wind plant
Costs of Energy (CoE; €ct/kWh/20-years) trends.

1. Offshore wind energy ambitions
At the Madrid EWEC 2003 wind conference in June 2003, the European Wind
Energy Association (EWEA) announced an ambitious 10,000 MW offshore
wind energy target by 2010. This European offshore wind volume is
envisaged to reach 70,000 MW ten years later in 2020. By that time wind
capacity on land and offshore combined (180,000 MW), is expected to
generate sufficient energy to cover 13% of Europe ‘s electricity needs.
Background for the optimistic offshore forecasts is that an increasing number
of countries have set ambitious medium and long-term goals for harvesting
offshore wind energy in their territorial waters. In Europe wind energy
champion Germany has taken the lead with plans for an impressive 40,000
MW offshore wind capacity by 2030. The latest UK offshore target is 20,000
MW, and the Dutch government aims at 6,000 MW in 2020. Also on the other
side of the Atlantic offshore wind power is gaining interest. A number of
generally large US projects planned for the period 2004 – 2006 already add
up to 3,500 MW.

2. Kick-off projects
In The Netherlands, offshore wind
energy commenced with two
projects, both comprising ‘real
offshore characteristics’: wind farm
Lely (1994) and Dronten (1996).
Lely consists of four two-blade 500
kW NedWind turbines. The project
was built in the IJsselmeer near
Medemblik in water depths between
5 – 10 metres. Wind farm Dronten
is also positioned in the IJsselmeer,
some 30 metres from shore and
comprises 28 turbines of the 3-
blade Nordtank43/600 series.
Already at these projects later
Dowec partners like Rotorline/LM
Glasfiber, Nedwind/NEG-Micon,
and Ballast Nedam were the
selected parties that produced the
required blades and turbines, and           Figure 2: The Lely wind farm (photo Lex Salverda)
installed the purpose-designed
foundations.




                                        7
Optimistic plans build on successful recent fast-track development
experiences with a limited number of semi-commercial offshore wind projects.
The technology applied in these wind farms typically comprises offshore-
modified turbines in the 1.5 – 2.3 MW range. It is also noticeable that these
‘demonstration’ projects were accomplished in only three European pioneer
countries: Denmark, Sweden, and the UK (Table 1).
Autumn 2002 the huge Danish 160 MW Horns Rev North Sea project, widely
regarded the genuine kick-off for large-scale offshore wind utilisation in the
world, became operational.




Figure 3: The Horns Rev offshore wind farm (photo Vestas)



This year again a large (165 MW) offshore wind farm has been completed in
Denmark, this time near Nysted. And in the UK, Europe ‘s nation blessed with
the best (offshore) wind resource, the North Hoyle project (60 MW) recently
became operational. This sizable wind farm is regarded the UK ‘s first genuine
entrance in the offshore wind market, the Scroby Sands offshore wind farm
installation is underway and many more projects are in the pipeline for the
next years.




                                                 8
Figure 4: The Nysted offshore wind farm (photo Bonus)



Finally, in the Irish Sea south of Dublin (Ireland) a seven-turbine wind farm
was completed this autumn.

Table 1        European offshore wind projects 2000 – 2003
Name and location     Turbine make & type and         Project rated capacity   On-line
                      number                  [MW]

Blyth, UK                 2 x Vestas 2 MW                  4                   2000
Middelgrunden, DK         20 x Bonus 2 MW                  40                  2000
Utgrunden, SE             7 x GE Wind 1,42 MW              10                  2000

Yttre Stengrund, SE       5 x NEG Micon 2 MW               10                  2001

Horns Rev, DK             80 x Vestas 2 MW                 160                 2002
Samsø, DK                 10 x Bonus 2.3 MW                23                  2002

Frederikshavn, DK         2 x Vestas 3 MW                  6                   2003
                          1 x Bonus 2.3 MW                 2.3                 2003
                          1 x Nordex 2.3 MW ‘Offshore’     2.3                 2003
Nysted, DK                72 x Bonus 2.3 MW                165                 2003
North Hoyle, UK           30 x Vestas 2 MW                 60                  2003
Arklow Bank, IR           7 x GE Wind 3.6 MW Offshore      25.2                2003


Sources: Renewable Energy World, July-August 2003; Suppliers, 2000 - 2003




                                                 9
3. Fast track to large turbines
In the offshore wind industry 2003 will be remembered as the year when the 2
MW+ offshore size barrier was ‘smashed’ by the historic first-time installation
of much larger 3.6 MW size wind turbines (Table 1). In addition a 4.2 MW
NEG Micon NM 110/4200 prototype was erected early October at a new
onshore test field in Denmark. The latter comprises a 110-metre rotor
diameter and a top head mass (THM, nacelle plus rotor) of only 214 tonnes,
which is an industry record. For 2004 at least two new prototype installations
in the 4.0 - 5 MW range are expected (Table 2).




Figure 5: The NM110 prototype (photo NEG Micon)




                                              10
A genuine 2002 wind industry milestone formed the erection of the world ‘s
largest 4.5 MW prototype near Magdeburg (GE). This year a second Enercon
E-112 has become operational, and a third land prototype is under
construction.
Multi-megawatt wind turbine suppliers all aim at both land based and offshore
applications, for the single reason that there is still uncertainty about the pace
of offshore wind development. Pleasing is a favourable shift in visual
acceptance of larger wind turbines. And despite uncertainties reinforced by
continuously delayed planning permission procedures, a limited 4 – 5 MW
market takeoff is expected for 2005/6. Offshore wind projects with even larger
5 – 6 MW size turbines might according to some experts typically be
characterised by water depths of 30 – 40 metres, and a distance to shore in
the range of 40 kilometres and up. Others argue that there are lots of highly
suitable shallow water locations available, and that independent of water
depth and distance to shore site issues the arrival of new generations turbines
in the 8 – 12 MW class might become feasible within eight to ten years.


Table 2          Some multi-megawatt offshore wind turbine prototypes 2002 - 2004

Make & Type                      Capacity           rotor diameter Transmission   Prototype
                                 [MW]               [m.]           type
2002
                                                                     1
Enercon E-112                    4.5                112.8         DD              August
                                                                     2
GE 3.6 Offshore                  3.6                100.0         GD              May
NEG Micon NM92/2750              2.75               92.0          GD              June
Vestas V90                       3.0                90.0          GD              May

2003
ScanWind                         3.0                90            DD              n.a.
NEG Micon NM110/4200             4.2                110.0         GD              October

Expected 2004
Pfleiderer M5000                 5.0                116.0         HD              Spring
REpower 5M                       5.0                126.5         GD              Spring
                                                                    3
WinWind WWD-3                    3.0                90.0          HD              Spring

1.        Direct driven - slow running multi-pole ring generator
2.        Gear driven - multi-stage gearbox and fast running generator
3.        Hybrid drive - single-stage gearbox with medium speed generator
Sources: Wind industry, 2002 – 2003; Windkraftanlagenmarkt 2003



4. Market driven development
Market driven wind turbine development in general favours a gradual
evolutionary type of up scaling, and a commercial time scale in balance with
economically viable (offshore) wind site development progress. The bulk of
offshore wind farms now planned are typically projected in water depths
between 5 – 20 metres, perfect conditions for the latest 4 – 5 MW generation
turbines. An example is the 4.2 MW NM 110/4200 for which NEG Micon
foresees an optimising step for their current platform, increasing rotor size as
well as the power rating.



                                               11
                                                   This ‘playing safe’ strategy
                                                   itself is typical for the wind
                                                   industry, as it helps
                                                   reducing development risks
                                                   and improves cost
                                                   effectiveness.

                                                   A limiting factor hampering
                                                   up scaling is that key
                                                   components for turbines of
                                                   this size, such as cast-iron
                                                   machine frames and rotor
                                                   hubs, are already very
                                                   bulky and heavy. Only a
                                                   handful of component
                                                   suppliers in the world is
                                                   currently capable of
                                                   manufacturing such huge
                                                   complex components in
                                                   sufficient quantities at the
                                                   required quality and for an
Figure 6: Production of a monopile for
offshore wind turbines (photo NEG Micon)           acceptable price.


This well-documented bottleneck could potentially slow down a fast entry into
the performance class of 6 MW and up. On the other hand a main supplier of
wind turbine gearboxes recently inaugurated testing facilities capable to
accommodate units up to 6 MW, while further steps up to even 12 MW are
envisaged. An unresolved question is whether the ongoing process of
continuously stretching technological and scientific boundaries, will in the end
also produce economically viable offshore wind turbines.


5. Maturing technology
While wind turbine up scaling is in full swing, rotor diameters tend to grow
even faster than installed power (MW). This positive trend results in an
increased energy production potential per megawatt installed capacity. It is a
fact that larger rotor sizes for a given generator capacity remains within limits
an economical investment in terms of energy yield potential, even under high-
speed offshore wind conditions. However, industry analysts initially predicted
that for offshore applications modified maritime versions of given land turbine
types would be fitted with substantially larger generators (+ 40 - 50%). That
proved wrong. Currently development of large relatively light rotor blades like
the 54-metre long LM54.0 P seems to keep pace with wind turbine up scaling.

With a global market share of about 80% grid connected state-of-the-art wind
turbine technology continues to be dominated by ‘conventional’ gear driven
systems with well-known manufacturers like NEG-Micon, Vestas, GE Wind,
Bonus, and Nordex.



                                           12
The grid connected direct drive segment has been an Enercon monopoly
since 1992. In addition a number of small international contenders like former
Lagerwey of the Netherlands have been trying for years to establish a position
into this ’minority’ market segment.

Hybrid drive (single step-up stage) was pioneered by engineering consultancy
aerodyn Energiesysteme of Germany, a patented compact drive solution they
named Multibrid®. Since 2001 licensee WinWind of Finland operates several
1 MW machines, a 3 MW prototype is planned early 2004. Pfleiderer of
Germany also plans a 5 MW Multibrid prototype for spring 2004. However,
hybrid Multibrid type concepts still have to prove what they are worth in the
short to medium term as the track record of this novel technology is very
limited.


6. Variable speed for superior control
For wind turbine systems from 1.5 - 2 MW and up, the combination variable
speed operation with full span rotor blade pitch control has rapidly become
state-of-the-art technology.

Key system features
include superior power
output control and
advanced grid support
functions. One distinct
control option is the
capability to operate a
wind farm like a peak-
power plant: in other
words a built-in capacity
to instantly reduce or
increase plant output on
demand. The only
limitation is that the
prevailing wind speed has
to be within operating
range.




Figure 7: Rotor hub with pitch
system, for connection of the
blades to a main shaft and for
turning the blades during
operation (picture NEG Micon)


                                     13
Variable speed operation also means superior gearbox torque control. For
example when a wind gust hits the rotor, drive train torque is more or less
kept constant by temporary accelerating the rotor (flywheel effect).

The majority of 1.5 – 1.65 MW and up gear driven wind turbines is fitted with a
double-fed induction type generator. Key advantage of this innovative variable
speed concept is that only 20 – 30% of the generated power has to be fed
through a frequency inverter. This represents a substantial investment cost
saving compared to identical systems fitted with a standard synchronous or
asynchronous generator, which both feed 100% of the power through an
inverter. The latter cost advantage is still valid today despite a substantial
drop in power electronics costs during the past 6 - 8 years.
In new direct drive wind turbine designs there appears a clear favour for
permanent magnet type synchronous generators (PMG). However, the
commercial wind market is currently dominated by ‘conventional’ synchronous
generator systems with external field excitation.


7. Costs structure trends
Land-based wind turbines investment percentages for foundation and
necessary infrastructure typically account for 25 –30% of total project costs.
Early studies indicate that this ratio is more or less reversed for offshore wind
farms, whereby the turbine (tower, nacelle, and rotor) typically caters for 30 –
35% of cumulated project costs. However, as a positive industry trend
foundation and infrastructure costs tend to drop structurally as a percentage
of total project investments, as the Nysted offshore wind farm cost overview
indicates (Table 3). Surprisingly fast learning curve advancements of
equipment manufacturers and offshore installation contractors is said to be a
major contributing factor explaining the positive phenomenon.


Table 3          165 MW Nysted investment cost structure

System component                                      % investment costs

Wind turbines (tower + nacelle + rotor)               49
Gravity-based foundations*                            18
Cable infrastructure wind farm                        6
Transformer station + 132 kV connection               12
Scada system                                          4
Miscellaneous                                         11

Note: Total investment € 245 million (€ 1,500/ kW)

* Water depth 9 metres, relatively heavy expensive concrete foundations
Source: Wind-kraft Journal & Natürliche Energien, Issue 4/2003


Future will tell whether power plants built in much deeper water and with full
exposure to rough North Sea conditions will be capable to produce
comparable investment cost-breakdown figures.



                                                 14
8. Offshore complexities
Due to the limited offshore ‘weather window’ wherein erection activities at sea
can be safe and economically performed, speed of work is crucial. It will
among others determine whether future wind farms of 500 MW and up can
still be completed in a single offshore season. The workable North Sea
weather window is typically restricted to the period April – September.
However, due to new generation jack-up barges this window can be
extended. Substantially longer windows are by comparison available in the
relatively calm Baltic Sea environment. When critical offshore activities are
performed outside the workable period, delays can be expected. For above
reasons and cost reduction purposes it is not surprising that wind developers
increasingly search for time saving offshore installation methods. The ultimate
aim is to lift and transport onshore assembled and pre-tested wind turbine
units in one single unit to their destination.




Figure 8: The measurement mast as erected end of 2003 by NoordZeeWind (combination of NUON and
Shell) for the coast of Egmond aan Zee; used for wind and wave measurements (photo NoordZeeWind)



                                              15
A second key issue is operation and maintenance, by definition complex and
costly offshore activities. The main reason is that offshore wind turbine service
and maintenance access can be problematic during autumn and winter
periods. It is therefore a major challenge for the emerging offshore wind
industry to develop cost-effective, reliable, but above all safe all-weather
installation access methods. For wind turbine and auxiliary equipment
suppliers an equally challenging task is the development of much more
reliable ‘offshore design’ wind turbines requiring only one annual planned
service visit. This in contrast to a target twice a year service interval for state-
of-the-art land based units.


9. Foundation and installation challenges
The offshore industry quickly transforms itself into a competent and highly
valued partner to the global wind industry. Their joint aim is the rapid
development by the wind industry of state-of-the-art multi-megawatt class
wind turbines for future offshore power plants, which are in addition easy to
erect, connect to the grid, and maintain. The easy erection trend is reflected
by the increasing but still limited presence of purpose-built wind turbine
installation barges like Dutch Mammoet Van Oord’s Jack-up barge Jumping
Jack®, the Mayflower® Resolution [under construction, UK], and A2SEA ‘s
modified self-propelled freighter. Internationally active Dutch offshore, civil
engineering and steel construction specialists do play already a leading role in
the emerging offshore wind market. Their key involvement in Horns Rev
(2002) can serve as an example (Table 4).


Table 4           Key role Dutch companies in Horns Rev construction
Company                   Activity

Mammoet Van Oord          Foundation Installation, both monopiles and transition sections, using
                          the chartered jack-up barge “Buzzard” (owned by Ballast Nedam)

SIF                       Rolling and precision welding of all eighty thick-wall monopile and
                          transition piece tubes

Smulders Group            Detail design and production engineering of transition pieces in
                          cooperation with MT Hyjgaard (DK) en Techwise (DK)
                          Transition piece handling and construction; surface treatment
                          monopiles

HBG                       Engineering and construction offshore transformer station

Smit Heavy Lift           Offshore installation transformer station

Source: Dutch industry, 2002


This year Mammoet Van Oord (a company with two main shareholders,
Mammoet and DOWEC partner Van Oord), and the SIF/Smulders Group
carry out comparable tasks for Arklow Bank.



                                               16
A major difference is that Mammoet Van Oord is this time responsible for both
foundation and wind turbine installation works, activities for which it employs
the Jumping Jack.
Mammoet Van Oord is in addition member of the Dutch Q7-WP consortium,
which for 2005 aims at building a 120 MW (60 x 2 MW) North Sea wind farm
outside the 12-mile zone, in 20 – 25 metre deep water.
NEG Micon/DOWEC and Ballast Nedam are preferred EPC-contractors for
installing thirty-six 2.75 MW DOWEC offshore turbines as part of the 99 MW
Near Shore Windpark planned in 2005 near Egmond aan Zee.




Figure 9: The Jumping Jack of Mammoet van Oord (photo Mammoet van Oord)



10. Maritime innovations
Offshore wind turbine technology progress encourages the rapid development
of novel installation methods and the birth of completely new installation
vessel concepts. Some examples:

Civil engineering contractor and DOWEC partner Ballast Nedam developed a
special catamaran type installation vessel: the Svanen. The 103-metres long
and 90-metres wide self-propelled catamaran type Svanen is currently one of
the largest installation vessels available in the market. The vessel is very
stable in moderate wave height conditions, with standard wind compensation
technology fitted for lift activities performed at 80-metre elevations.


                                             17
The superstructure
is capable to hoist a
maximum load of
8,100-tonnes, more
than sufficient to lift,
transport, and install
complete 5 – 6 MW
wind turbines in one
single piece. The
Nieuwegein based
specialist will
probably utilize the
unique vessel for
NSW construction.             Figure 10: The Svanen of Ballast Nedam (picture Ballast Nedam)


Mammoet Van Oord ‘s new 91-metre long and 33-metres wide Jumping Jack
is equipped with four large steel legs, one at each corner. Main difference with
existing jack-up barges is that in conditions with water depths up to 32-
metres, and a sea states of up to around 2m significant wave height, the
Jumping Jack can raise itself out of the waves. The fixed positioning of the
legs onto the seabed secures a large, save and stable working platform for
installation crews. A clever systems innovation is that the barge lifts her self
up along the huge 49-metre long legs with the aid of steel cables and cable
winches. This lift solution works much faster compared to a common rack-
and-pinion drive. The less rigid cable connection between hull and legs in
addition reduces load impact on the barge in the treacherous transition period
between floating and standing position.
Finally, fitted on the deck is a rotating ringer type crane, capable to lift a
maximum load of 1,200 tons at 24m reach. This is more than sufficient to lift
complete 4 – 5 MW wind turbine assemblies (nacelle + rotor + tower) as well
as handle continuously in size growing foundation piles.




                                                                  Figure 11: The
                                                                  Jumping Jack of
                                                                  Mammoet van Oord
                                                                  (photo Mammoet
                                                                  van Oord)



                                        18
The Danish A2SEA Group developed an offshore wind turbine installation
method comprising a modified commercial freighter fitted with four spud-legs
and a crane system. For wind turbine construction purposes the hull is
elevated just sufficient to create a stable working platform.

Marine Structure Consultants of the Netherlands (MSC) finally presents with
the Trifloater® a completely different focussed offshore wind technology
innovation. Trifloater is essentially a floating wind turbine assembly destined
for future applications in water depths of 45 – 50m.


                                                          MSC designers
                                                          suggest that a
                                                          complete structure
                                                          comprising wind
                                                          turbine tower,
                                                          nacelle, and rotor,
                                                          can be assembled,
                                                          commissioned and
                                                          tested in a sheltered
                                                          place before being
                                                          towed to its final
                                                          destination. The
                                                          novel concept is a
                                                          spin-off
                                                          of a recent Dutch
                                                          feasibility study on
                                                          floating wind energy
                                                          named ‘Drijfwind’
                                                          [Floating wind]. The
                                                          latter study was
                                                          performed in
                                                          cooperation with
                                                          DOWEC partners
                                                          TU Delft and ECN,
                                                          Marin, TNO, and
                                                          former Lagerwey the
                                                          Windmaster.




                                                          Figure 12: The Trifloater
                                                          concept




                                       19
Part II: DOWEC formation

The following chapters 11 – 17 contain an overview of project formation
stages, provide an introduction to the six DOWEC partners, and state
objectives and key R&D considerations.


11. DOWEC – from plans to project
Driving force behind plans for a high-profile Dutch offshore wind turbine
development group in 1997 were three companies: ECN, Rotorline and
Aerpac. Their joint initiative led to the formation of the Dutch Offshore Wind
Energy Converter (DOWEC) group. Background was a sobering analysis that
a once leading national wind industry had largely lost the world market to
more successful Danish and German competitors. A dedicated effort by
determined Dutch wind energy and offshore technology players, supported by
the government, had to reverse the tide by creating ‘last chance’ high-growth
opportunities within an emerging offshore wind sector.

Late 1997 DOWEC plans evolved into a research proposal. Next step was a
pre-feasibility subsidy application to the government sponsored EET program
(Economy, Ecology, Technology). Awaiting the outcome a pre-concept study
funded by the Netherlands Organisation for Energy and the Environment
(Novem) commenced early 1999. This study was executed by a group
comprising turbine manufacturer NedWind, rotorblade manufacturers
Rotorline and Aerpac, offshore specialist Van Oord, technology research
institutes Delft University and ECN, and engineering consultancy SPE. A
major project change occurred when NEG Micon of Denmark took over
NedWind, and Danish rotor blade supplier LM Glasfiber became Rotorline ‘s
new owner.
In the new setting NEG Micon Holland took over the position of DOWEC
project leader.


12. Pre-concept study
 Starting point for the pre-concept study was a clean sheet of paper, leaving
all conceptual design options open. This approach resulted in six different
concepts (Table 5), for which a comparative analysis was conducted, covering
criteria like expected yearly failure frequencies, availability, and calculated
annual energy yield. In addition covered were indicative energy production
potential, and operation & maintenance (O&M) costs in €/kWh.




                                      20
Table 5        Operational data six pre-concepts

Concept        Drive system   Rotor blades        Operation

Base Line      GD             3                   FS & Active Stall
Advanced*      GD             3                   VS & Active Pitch
Robust         GD             2                   FS & ‘Classic’ Stall
Stall-teeter   GD             2                   VS & ‘Classic’ Stall
Smart Stall    GD             3                   VS & Stall & blade tip control
Advanced DD    DD             3                   VS & Active Pitch

DD     = Direct drive
GD     = Gear drive
FS     = Fixed Speed
VS     = Variable Speed

* Current DOWEC technology
Source: DOWEC, 2000


But despite accumulation of substantial know-how during the study, qualitative
and quantitative inputs did not justify hard and decisive conclusions favouring
one of the pre-selected concepts. Specific recommendations for continued
investigation in the DOWEC project were formulated.
Finally, all preparatory project tasks were completed in 1999. Partners used
this ‘spare’ time also for necessary teambuilding and the development of a set
of shared principles. January 1, 2000 marked DOWEC ‘s formal take-off.


13. DOWEC partners
DOWEC ‘s six partners can be subdivided into three different categories on
the basis of specific competence fields. Each group comprising two partners
was responsible for conducting specific tasks within the DOWEC project:

Industrial and Product Development




NEG Micon Holland                                         LM Glasfiber Holland (LMGH)



Offshore & Civil Engineering




Ballast Nedam                                             Van Oord


                                             21
Fundamental and Applied Research




Energy research centre ECN                                  TU Delft


14. Partners in brief
DOWEC leader NEG Micon Holland is a 100% subsidiary of NEG Micon A/S.
This world ‘s third largest (2002) manufacturer has a presence in all key wind
markets. It offers a range of products from 600 kW (fixed speed, stall control)
to the latest 2.75 MW (variable speed, pitch control) onshore/offshore wind
turbine. The fifteen person strong Bunnik based DOWEC team serves as the
Group ‘s global offshore competence centre.
With regard to offshore wind track record, formerly two small projects
consisting of 500 and 550 kW turbines were built in The Netherlands
(Medemblik) and Sweden (Bockstigen). A major technological and logistical
leap forward was the 10 MW Swedish Yttre Stengrund wind farm (5 x 2 MW).
Again a step forward is that NEG Micon has now been selected to supply 2.75
MW DOWEC wind turbines for NSW.




Figure 13: The Yttre Stengrund offshore project of NEG Micon (photo NEG Micon)




                                                22
LM Glasfiber Holland is a full subsidiary of LM Glasfiber A/S, the world‘s
leading rotor blade manufacturer. Heerhugowaard based LMGH is part of LM
Glasfiber ‘s rotor blade development organisation, employing seven design
specialists. LM Glasfiber bases its offshore know-how on a broad experience
with supplying blades to more than 50% of all offshore wind farms in operation
by the end of 2002. In addition twelve years of operational experience have
been gained from monitoring rotor blades of the world ‘s first offshore wind
farm. LM is in addition one of the few manufacturers with in-house blade
testing facilities and the only true global manufacturer of rotor blades for wind
turbines.

                                              A recent company milestone
                                              was the completion of an
                                              ambitious Future Blade
                                              Technology research
                                              programme, aimed at setting
                                              new standards with advanced
                                              lightweight rotor blades.




                                              Figure 14: The blade test of the LM54
                                              blade, in which the extreme strength and
                                              the lifetime of the blade is verified (photo
                                              LM)



Ballast Nedam is Europe-wide active in civil engineering contracting works
like utility buildings, harbours, tunnels and bridges. A prestigious project
Ballast Nedam took part in was the world famous Størebelt bridge connection
between Denmark and Sweden.
For lifting and exact positioning of piers and superstructure elements for this
major project Ballast Nedam developed the Svanen initially.




                                                          Figure 15: The Svanen
                                                          installation vessel during
                                                          the Størebelt bridge
                                                          construction (photo Ballast
                                                          Nedam)

                                       23
Van Oord is a specialist marine contractor with over 50 years of experience
and a proven track record in three areas: dredging, offshore works and
coastal construction.

Van Oord is one of the
internationally leading
contractors for dredging
works, with a substantial
fleet of dredging vessels.
It is also market leader in
offshore rock placement
activities boasting the
world ‘s largest fleet of
flexible fall-pipe vessels.
Furthermore, through a fleet of dedicated vessels and equipment Van Oord is
a leading contractor for landfalls aimed at cable and pipeline installations. In
June 2002 Mammoet Van Oord, officially inaugurated the Jumping Jack,
marking a new and challenging offshore wind turbine installation era for both
companies.

                                                            The combination is
                                                            capable to offer a
                                                            complete installation
                                                            package, including
                                                            quayside logistics
                                                            (Mammoet), and
                                                            offshore cable
                                                            installation plus scour
                                                            protection installation
                                                            (Van Oord).


                                                            Figure 16: Equipment of Van
                                                            Oord: a dredging vessel
                                                            and a stone placement vessel
                                                            (photos Van Oord)



Energy research centre ECN is an independent market-oriented organisation
for research, development, consultancy, and knowledge transfer in energy
and related fields. With sustainable development as a guiding principle ECN ’s
R&D effort is focused on seven priority fields: solar energy, wind energy,
energy from biomass, energy policy studies, efficient use of energy and
materials in industry and the built environment, and clean use of fossil fuels.
Wind energy is one of the seven ECN sustainable energy priority areas.




                                       24
The 45-person strong
wind energy unit ECN
Wind Energy (established
in 1975) covers all
relevant disciplines,
including offshore wind.
Key activities comprise
among others integral
design of offshore and
onshore wind power
farms, resource
assessment studies,
aerodynamic and aero-
elastic diagnosis, and
rotor design. Finally, ECN
develops and evaluates
‘first of a kind projects’                      Figure 17: Investigation on the development of vortices
and offers specialist wind                           (i.e. the aerodynamic flow) behind a wind turbine)
energy training courses.                                                                  (photo ECN)



The TU Delft has a rich history in wind energy research, which commenced in
1975 with rotor aerodynamics and rotor blade tip vane behaviour. This was in
1985 reinforced by new subjects like fundamentals of rotor blade fatigue,
control technology and power electronics.

                                                                   A milestone in the early
                                                                   1990s was a new
                                                                   professorship in wind
                                                                   energy & technology and
                                                                   the founding of DUWIND
                                                                   (1999), a multi-
                                                                   disciplinary organisation
                                                                   and cooperation between
                                                                   various engineering
                                                                   departments. Key
                                                                   objectives were
                                                                   strengthening internal
                                                                   and external networks,
                                                                   and conducting joint
                                                                   projects. With a student
                                                                   population of 13,000 the
Figure 18: Wind tunnel test on airfoil DU96W180,
which is used on wind turbine blades (photo TU Delft)
                                                                   TU Delft is the largest
                                                                   technical university in the
                                                                   Netherlands.




                                                  25
15. Project objectives
DOWEC ‘s key industrial objective (2000 – 2003) was to develop all
necessary knowledge, design tools, competences, and related facilities to
build reliable commercially attractive multi-megawatt class offshore wind
turbines. In a broader perspective, the DOWEC project aimed at contributing
to an overall increase of wind energy capacity to the national Dutch power
supply. Being a nationally funded project with local partners, competitiveness
of the local industry at the world market should also be substantially improved
with clearly measurable end results.
Another more scientific focussed part of DOWEC activities aimed at acquiring
generic knowledge of offshore wind energy application, subdivided in
fundamental and applied research. Some activities specifically focused at
obtaining knowledge required for the offshore wind system design process,
supplemented by applied industrial research aimed at specific product and
process design solutions. Part of the scientific package was to evaluate the
economics of different wind turbine concepts. The systems evaluation
encompassed turbine scale effects, CoE and cost breakdown aspects,
technological and related challenges. These and additional external design
drivers logically resulted - compared with better-known onshore conditions -
into a need for a fundamental concept evaluation, rather than simply up
scaling existing onshore technology.


16. Key focus wind farm optimisation
Initially science-driven DOWEC research indicated that 5 - 6 MW class wind
turbines developed for offshore wind power plants of about 500 MW, would be
a prerequisite for competitive industrial-scale maritime wind application. It is
already a fact that several offshore wind plants of this size and even
substantially larger have been planned in Germany.
With this background intelligence the DOWEC group engaged in a baseline
design for a 500 MW reference wind plant, comprising installation, operation
and maintenance strategy, grid connection, and wind turbine pre-design. This
design has been partly optimised, and contains a detailed cost analysis plus a
CoE calculation. In addition a substantial number of design variations was
predefined and evaluated. This evaluation had a key focus at influences of
specific design variations on CoE. The evaluation comprised conceptual and
parametric design factors like changes in water depth and distance to shore.
Possibilities for significant cost optimisation have been pinpointed at in the
operation and maintenance strategy, reliability of the machine design,
installation procedures, and load reducing control strategies. What size and
type of wind installations will finally become winning concepts for these future
mega projects therefore depends on many preconditions. Certain is that
besides water depth and distance to shore, one of the most crucial factors will
be the timely availability of economic reliable state-of-the-art wind turbines
with sufficient track record.




                                      26
                                        Break-down of Generating Costs



                     Retrofit & Overh aul    De comm is sioni ng                         To wer
                                                                          Fo undatio n
                              6%                   1%                                     9%
                                                                              9%

 Y early Operatio n &
    Maint enanc e
         2 7%




                                                                                                     W ind t urbine
                                                                                                         24%




     As sem b ly, Trans po rt                                                             El ec tric Col lec tion
                                     Other
        a nd Installa tion                                   Trans mi ss ion Sy ste m            Sys tem
                                      5%
              11%                                                   to Shore                        2%
                                                                       6%


Figure 19: The beak-down of generating costs for the reference wind farm (calculation and graph by
ECN)



17. DOWEC Demonstrator - R&D considerations
DOWEC ‘s research package comprised the development of a 3 MW (D = 100
m.) demonstrator prototype, aimed at evaluating load patterns and
behavioural aspects on both individual component and systems level.
Another key research topic was improved understanding of the complex
offshore environment, and how this affects commercial application of wind
energy. Examples of external influences are hydrodynamic loading (tides,
waves and current), the corrosive offshore environment, and preventing
seabed erosion around foundation structures. Related issues encompassed
power transmission, support structure alternatives, and offshore maintenance.
Freedom in design is much a much more favourable condition for offshore
installations compared to land-based systems. Also transport logistics,
structural and visual aspects, noise, and safety related issues differ
considerably from the onshore situation, and are usually characterised by
(potentially) far fewer restrictions. DOWEC research activities with reason had
a major focus on exploring design related opportunities provided by the
challenging operational offshore environment.
And while the search for an optimal offshore wind turbine was initially
envisaged to commence with a clean sheet of paper, it became in practice
soon embedded into a more market oriented industrial product development
effort. This shift in focus was a consequence of the anticipated boom in
commercial scale offshore wind power projects, which substantially reduces
the available Time-to-Market. These commercial projects in turn are planned
by risk avoiding developers interested in the well functioning of their
investment for at least twenty years. They therefore demand products and
procedures based on well-known technology concepts and proven principles.


                                                             27
Part III: Partner achievements and future potential

The last seven chapters of this booklet contain a summary of DOWEC partner
key achievements, followed by a closing chapter on the future potential with
key challenges to commercial offshore wind energy application.


18. NEG Micon Holland: ‘DOWEC Demonstrator’
Besides conducting product design, development, and coordinating tasks for
the 2.75 MW NM 92/2750 and DOWEC Demonstrator spin-offs, the Dutch
specialists are engaged in many other future oriented Group activities. They
played among others a key role in the structural design of the 4.2 MW NM
110/4200 offshore wind turbine, and several smaller 1.5 - 2 MW class
machines.

                                        The DOWEC NM 92/2750 Demonstrator
                                        operates with an optimized variable speed
                                        and functionally integrated blade pitching
                                        system called Pitch Regulated Variable
                                        Speed (PRVS). This proven technology
                                        dates back to the beginning of 2002. The
                                        huge three-blade rotor itself is optimized
                                        for cost-effective and reliable offshore
                                        operation. For the Demonstrator drive train
                                        a deliberate choice was made for a state-
                                        of the-art three-point gearbox support
                                        assembly and a non-integrated generator
                                        system. This design concept builds on
                                        experiences with hundreds of smaller NEG
                                        Micon turbines types in the 1.5 – 2 MW
                                        capacity class. It is also the semi-standard
                                        state-of-the-art engineering solution for a
                                        majority of gear driven systems now
                                        applied in the wind industry.

                                        Figure 20: The DOWEC NM92/2750 wind turbine (picture
                                        NEG Micon)




Benefits of proven technology and a strong multi-year track record clear:
reduced risks, optimized system costs plus improved quality, and a
substantially shortened ‘Time to Market’. This evolutionary rather than
revolutionary design strategy offers the best guarantees for substantial kWh
cost price reduction, even when measured during a twenty-year operational
period. And as grid power quality requirements are becoming more stringent
all the time, a lot of emphasis has been given to wind turbine grid integration
capabilities of the system. Among advanced PRVS features are active grid
support and stabilization of weak grids, and a built-in capacity to operate wind
turbines if required as a peak power plant.


                                       28
Flexibility
As the Demonstrator was specifically designed for offshore operation, the
system has a built-in flexibility to cope with different support structures, grid
connection and installation methods. One distinct Demonstrator system
feature is a modest Top Head Mass (THM) aimed at easier (offshore)
installation as well as reduced structural loads on the foundation structure.
Finally, the machine is equipped with an internal crane system consisting of a
permanent so-called column and beam assembly in the nacelle. Two different
hoisting system types are available for service and maintenance visits:
    - a permanent winch with a 1-tonne capacity;
    - a temporary winch assembly for larger lift jobs, like interchanging a
        blade, gearbox, or generator.

The permanent winch is
used during ‘normal’
once-a-year planned
service visits, and as an
assistance tool during
assembly of the
temporary hoisting
system. The 1-tonne
hoisting winch itself
operates with a ‘crab
type’ transport
movement mechanism
enabling it to cover the
entire nacelle area in
longitudinal as well as
transverse directions.




Figure 21: The wind turbine with
the internal crane construction
mounted (picture NEG Micon)



The combination of the above crane systems in place, and a stringent design-
for-easy-maintenance strategy, offers the best guarantees that turbine
downtime is reduced to an absolute minimum. The outcome is increased
availability, and substantial CoE advantages that apply both for offshore as
well as demanding land based applications.




                                       29
19. LMGH: ‘World ‘s longest rotor blade from Heerhugowaard’
During 1999 - 2001 LMGH made substantial design contributions to the 44.8-
metre long LM 44.8 P, a rotor blade used on the DOWEC Demonstrator
The longer LM 54.0 P blade is specifically designed for the NM110/4200. The
design itself is a result of close cooperation between specialist teams of LM
Glasfiber Holland and NEG Micon Holland.

When the test blade and
prototype set of the LM 54.0 P
blade were produced in 2003 it
was the longest commercial
blade in the world. LM
Glasfiber Holland specialists
performed all blade design and
management tasks of this
ambitious project.

The LM 54.0 P is a glass fibre reinforced epoxy (GFRE) blade for which
extensive use is made of the Future Blade Technology, resulting in a total
mass of only 13.5 tonnes. Consequently, this blade is 20-50% lighter
compared to competing blades with sizes above 50-metre length.
Furthermore the automated Future Blade Technology has resulted in a blade,
which is highly competitive and well suited for mass production. The blade
has already been successfully tested statically. Dynamic fatigue tests will be
finished by mid 2004.
                                                               Finally, the LM 54.0 P
                                                               blade is equipped with
                                                               LM ’s well-tested and
                                                               documented Multi
                                                               Receptor Lightning
                                                               Protection System. This
                                                               lightning protection
                                                               system, the use of well-
                                                               tested proven materials,
                                                               new aerodynamic
                                                               profiles, and novel
                                                               working procedures all
                                                               contribute to the blade
Figure 22: Transport of the LM54.0 P blade by LM (photos LM)
                                                               ‘s reliability.
The combination with built-in damage tolerance capacity and low
maintenance requirements finally results into trend setting availability
standards, all essential preconditions and key success factors for the
upcoming offshore wind industry.




                                                30
20. Ballast Nedam: ‘DOWEC design installation method’
Within the DOWEC project Ballast Nedam focussed at the development and
engineering of state-of-the-art foundations, and new installation methods for
foundations as well as turbines. As part of the project the group developed an
innovative offshore installation method for the Svanen. During start-up the
Svanen will take a monopile, transition piece and piling hammer on board in
IJmuiden harbour. Each monopile typically has a length between 45 and 56-
metres, a diameter of approximately 4.5-metres, and a mass between 270 -
360 tonnes. Transition pieces slide over the top of the monopiles. Their
function is to correct misalignment with a maximum of 0.5 degrees.
Misalignment occurs when a monopile is not hammered exactly vertical into
the seabed, but the tower position has to be level.
After loading the Svanen sets sail to its destination, hammer in the monopile
and install a corresponding transition piece. When the vessel returns to
IJmuiden a next corresponding monopile and transition piece set are being
loaded. This time transport also incorporates a complete superstructure
comprising tower, nacelle, and rotor. But even with a complete installation on
deck, the additional 800-tonne payload for 6 MW scale wind systems is minor
compared to the 8,000-tonne cargo capacity.

A special support
vessel meanwhile
positions anchors
for the Svanen in a
predefined pattern.
Immediately after
arrival, cables will
be attached to the
anchors and the
vessel can
manoeuvre itself in
a predefined
position for placing
the superstructure.
                                           Figure 23: The Svanen (picture Ballast Nedam)

To minimize wave motion influence the Svanen is also positioned at a
predefined angle relative to the prevailing wave direction. The hoisting system
itself is fitted with a surge-compensator (constant tensioning technology).
Under favourable conditions up to 3 - 4 turbines can be loaded in a single
voyage. This is from a time and costs saving point of view especially attractive
for large wind farm construction jobs, but depends in practice to a large
extend on weather conditions. A major uncertainty is for instance that
installation activities can only take place during moderate wave heights, while
weather predictions are normally reliable for a time span of two to three days
at a maximum.




                                      31
21. Van Oord: ‘Cable related and scour protection tasks’
Van Oord’s tasks within DOWEC were twofold: cable related, and scour
protection works around turbine foundations. The pull-in of a cable into each
individual wind turbine unit is by itself a highly complex operation. It comprises
cable transition from a static wind turbine into the dynamic and continuously
moving surrounding seabed. Long-term cable protection and securing the
turbine foundation’s integrity in the eroding seabed environment were both
specialised Van Oord inputs into the DOWEC project.

In June 2002 Mammoet
Van Oord, officially
inaugurated the Jumping
Jack, marking a new and
challenging offshore wind
turbine installation era for
both companies: Mammoet
and Van Oord. The
combination is capable to
offer a complete installation
package. This
encompasses quayside
logistics (Mammoet), and
offshore cable installation
plus scour protection                    Figure 24: Jumping Jack working on the installation
installation (Van Oord).                                   of foundations (photo Van Oord)



22. ECN: ‘Measuring and validation programme’
ECN coordinates DOWEC ‘s R&D programme. Key research basis is an
integrated wind farm concept, focussed primarily at price-performance
improvement issues. The research effort included a comparative wind turbine
concept evaluation, and cost-modelling studies focussed at interactions
between cost parameters versus performance characteristics. Related
questions were how these interactions affect CoE of large future offshore wind
plants (>500 MW) during a twenty-year operational lifetime. ECN finally
conducted among others rotor blade aerodynamics calculations in close
cooperation with NEG Micon and LM Glasfiber, and engaged in developing
advanced control strategies.

Soon after the Demonstrator became operational, ECN commenced with a
comprehensive measuring and validation programme comprising three main
objectives: testing all main mechanical components like the gearbox,
validation of aero-elastic and aerodynamic turbine behaviour, and the
application of new measurement techniques especially suited for offshore
use.




                                       32
As part of the program
strain gauges have been
attached at different
sections of the blade length
measured from each tip.
The use of strain gauges
based on glass-fibre
technology is new and
offers specific advantages.
With this novel technology
solution and a large 92-
metre rotor fitted on the
Demonstrator, the risk of
lightning strikes at critical               Figure 25: Simulation of the dynamic behaviour
rotor sections can be                                  of a rotor construction (picture ECN)
substantially reduced.
The technology offers in addition new and exiting opportunities for better
dynamic loads monitoring and turbine control on the basis of these measured
results. Equally new is a Sodar-type wind measuring system that enables
wind measurements up to a height of 250 metres, without having to invest into
an expensive wind measuring mast.


23. TU Delft: ‘Research and design focussed knowledge transfer’
A number of DUWIND specialists have been assigned to the DOWEC project,
with research priorities mainly concentrating on two key subjects: operation &
maintenance (O&M), and life cycle cost analysis research focussed on future
large scale (> 500 MW) wind power plants.
A key research question was the actual performance of current state-of-the-
art (semi) offshore turbines in the 2 – 3 MW capacity class with respect to
maintenance requirements and availability. Related issues include among
others (potential) measures that reduce the need for service and maintenance
from the current twice a year interval to only one annual visit. Equally
important is whether these results can serve as relevant design criteria for
future offshore wind plants, consisting of much larger custom designed
offshore wind turbines in the 4 - 6 MW range.
DOWEC provided an excellent opportunity for the TU Delft to implement
lessons learnt in previous research studies on offshore wind energy in a
result-oriented design-focussed project environment. In the margin of the
project, knowledge could be transferred to the other five partners. The latter is
at the same time one of the TU Delft ‘s main objectives. In return, experience
and knowledge from industry has provided valuable feedback on practical
issues involved. Knowledge obtained during the DOWEC project has in
addition been integrated in courses developed for master students, and
serves to the general benefit of the Dutch industry.




                                       33
One practical idea picked up during project execution is fitting tower segments
with a slip-joint, a proven solution applied before at some smaller onshore
turbines. Instead of a grouted or flanged connection the tower slides over the
somewhat conical top of the foundation pile.

                                                         The method appears to
                                                         be feasible for current
                                                         state-of-the-art offshore
                                                         wind turbines. It might
                                                         offer substantial
                                                         advantages like
                                                         eliminating the costs of a
                                                         transition piece and
                                                         accompanying
                                                         cumbersome installation
Figure 26: A family of DU profiles which are used        process.
on wind turbine blades (picture TU Delft)



24. Future potential
DOWEC partners today stand at the forefront of wind energy and offshore
technology development. This is an excellent starting point for further
strengthening that strong position in future. Group experiences of today will
make it easier for individual DOWEC partners to face challenges offered by
tomorrows demanding offshore wind markets. These challenge turned
opportunities are clearly reinforced by joint network benefits built since 2000.

What offshore wind energy will bring in future challenges our imagination. One
thing seems certain: developments will accelerate even faster than anticipated
and thought possible today. This fast offshore wind development track is also
envisaged to result into even more reliable wind turbines, technologically
superior cost-effective installation methods, and CoE levels far below than
what can currently be imagined. From a wind technology point of view a rotor
diameter in the range of 110 – 125 metres, and a 4 – 4.5 MW installed
capacity is at present regarded top of the market. In this highly dynamic
market environment discussions about turbine capacities of 8 – 12 MW and
rotor sizes in the range of 155 – 160 metres have evolved already into
feasibility studies and beyond. Some visionaries envisage such huge
installations to become operational within 8 – 10 years from today, but their
technological and economic feasibility still awaits hard answers.
DOWEC partners are confident that the positive outcomes of their project will
serve as a catalyst for a professional and successful Dutch offshore wind
energy sector, potentially providing highly skilled well-paid jobs for thousands
of professionals. They also believe that with the right approach and dedicated
support offshore wind will turn into a formidable powerhouse, serving an
increasingly power hungry world with competitive and inexhaustible supplies
of clean energy.

Editor: Eize de Vries.



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