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PHAROS4MPAS - Safeguarding marine protected areas in the growing Mediterranean blue economy. Capitalization report for the offshore wind energy sector.

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  • OSPAR Secretariat
  • BioConsult SH
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PHAROS4MPAs
A REVIEW OF SOLUTIONS TO AVOID AND
MITIGATE ENVIRONMENTAL IMPACTS OF
OFFSHORE WINDFARMS
Capitalization report
Maria Defingou
Franziska Bils
Britta Horchler
Thilo Liesenjohann
Georg Nehls
Citation: Defingou M; Bils F, Horchler B, Liesenjohann T & Nehls G (2019): PHAROS4MPAs- A
REVIEW OF SOLUTIONS TO AVOID AND MITIGATE ENVIRONMENTAL IMPACTS OF OFFSHORE
WINDFARMS. BioConsult SH on behalf of WWF France, p.264
24. June 2019
BioConsult SH report commissioned by WWF-France
PHAROS4MPAs - A REVIEW OF SOLUTIONS TO AVOID AND MITIGATE
ENVIRONMENTAL IMPACTS OF OFFSHORE WINDFARMS
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Contents
1 General introduction ................................................................................................................ 13
2 Characteristics of offshore windfarms (OWF) .......................................................................... 17
2.1 Components of OWF ........................................................................................................ 17
2.1.1 Foundation types (fixed) .......................................................................................... 17
2.1.2 Foundation types (floating) ...................................................................................... 22
2.1.3 Other OWF components .......................................................................................... 27
2.1.4 Electricity Collection and Transmission .................................................................... 30
2.1.5 Offshore substation .................................................................................................. 31
2.1.6 Associated components ........................................................................................... 32
2.2 Construction techniques .................................................................................................. 33
2.2.1 Assembling, transport and installation of offshore wind turbines .......................... 34
2.2.2 Construction of foundations .................................................................................... 34
2.2.3 Cable laying in the marine environment .................................................................. 37
2.2.4 Port facilities for assembly and storage ................................................................... 38
3 Current situation and trends .................................................................................................... 39
4 Mediterranean marine habitats & species and international conventions ............................. 46
5 Impacts of OWFs on the marine environment ......................................................................... 49
5.1 Introduction ..................................................................................................................... 49
5.1.1 Noise ......................................................................................................................... 50
5.1.2 Pollution and waste .................................................................................................. 52
5.1.3 Electromagnetic fields .............................................................................................. 53
5.1.4 Temperature ............................................................................................................ 54
5.1.5 Artificial light ............................................................................................................ 55
5.1.6 Collision risk .............................................................................................................. 56
5.1.7 Secondary impacts of OWF components ................................................................. 56
5.2 Impacts on abiotic environment ...................................................................................... 58
5.3 Impacts on benthic communities and habitats ................................................................ 59
5.3.1 Occupation of seabed areas and habitats ................................................................ 60
5.3.2 Physical disturbance, damage, displacement and removal of vegetation and fauna
60
5.3.3 Reef effect ................................................................................................................ 63
5.3.4 Electromagnetic fields (EMFs) .................................................................................. 64
5.3.5 Heat emissions ......................................................................................................... 64
5.3.6 Impact of noise on invertebrates ............................................................................. 64
5.3.7 Important marine habitats in the Mediterranean Sea ............................................. 65
5.3.8 Conclusion ................................................................................................................ 71
5.4 Impacts on fish/elasmobranchs ....................................................................................... 73
5.4.1 Noise ......................................................................................................................... 73
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5.4.2 Electromagnetic fields .............................................................................................. 74
5.4.3 Pollution and waste .................................................................................................. 75
5.4.4 Habitat loss/change .................................................................................................. 75
5.4.5 Secondary impacts ................................................................................................... 76
5.4.6 Situation in the Mediterranean Sea ......................................................................... 77
5.5 Impacts on sea turtles ...................................................................................................... 78
5.5.1 Potential noise impacts on sea turtles ..................................................................... 78
5.5.2 Ship traffic impacts ................................................................................................... 79
5.5.3 Electromagnetic fields .............................................................................................. 79
5.5.4 Artificial light impacts ............................................................................................... 79
5.5.5 Sea turtles in the Mediterranean Sea ...................................................................... 80
5.5.6 Conclusion ................................................................................................................ 81
5.6 Impacts on birds ............................................................................................................... 82
5.6.1 Collision .................................................................................................................... 82
5.6.2 Barrier effect ............................................................................................................ 86
5.6.3 Displacement/Habitat loss Attraction ................................................................... 87
5.6.4 Consequences of collisions and displacement ......................................................... 89
5.6.5 Mediterranean marine avifauna .............................................................................. 94
5.7 Impacts on marine mammals ......................................................................................... 105
5.7.1 Effects of noise on marine mammals ..................................................................... 106
5.7.2 Effects of anthropogenic sounds on marine mammals ......................................... 108
5.7.3 Impacts of noise in OWF during windfarm construction ....................................... 109
5.7.4 Impacts of noise during windfarm operation......................................................... 112
5.7.5 Further impacts of OWFs on marine mammals caused by other pressures than noise
114
5.7.6 Additional impacts on marine mammals present in the Mediterranean .............. 115
5.7.7 Marine mammals in the Mediterranean Sea ......................................................... 116
5.8 Socio-economic impacts ................................................................................................. 118
5.8.1 Fisheries and aquaculture ...................................................................................... 119
5.8.2 Tourism ................................................................................................................... 120
5.8.3 Transport ................................................................................................................ 120
5.8.4 Cultural heritage ..................................................................................................... 121
5.8.5 Seabed mining ........................................................................................................ 121
5.8.6 Military use ............................................................................................................. 121
5.9 Cumulative effects.......................................................................................................... 122
5.10 General conclusion on impacts ...................................................................................... 124
6 Mitigation measures and techniques ..................................................................................... 127
6.1 Site selection .................................................................................................................. 127
6.1.1 Marine spatial planning (MSP) ............................................................................... 127
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6.1.2 Strategic planning ................................................................................................... 131
6.1.3 Restrictions in terms of space and time ................................................................. 132
6.1.4 Overview of spatial mitigation approaches ........................................................... 133
6.1.5 Compensation ........................................................................................................ 134
6.2 Mitigation of underwater noise during construction .................................................... 134
6.2.1 Noise threshold values ........................................................................................... 135
6.2.2 Deterrence devices ................................................................................................. 135
6.2.3 Primary mitigation measures ................................................................................. 137
6.2.4 Secondary mitigations measures ........................................................................... 138
6.2.5 Surveillance of construction sites........................................................................... 144
6.2.6 Compensation ........................................................................................................ 145
6.2.7 Conclusion .............................................................................................................. 146
6.3 Mitigation of light ........................................................................................................... 146
6.4 Mitigation of impacts on habitats and benthic communities ........................................ 150
6.5 Mitigation of collision ..................................................................................................... 151
6.5.1 Ship strikes ............................................................................................................. 151
6.5.2 Collision with turbines ............................................................................................ 153
6.6 Mitigation of waste ........................................................................................................ 157
6.7 Mitigation of electromagnetic fields and temperature ................................................. 157
6.7.1 Electromagnetic fields ............................................................................................ 157
6.7.2 Temperature .......................................................................................................... 159
6.8 Mitigation of socio-economic impacts ........................................................................... 159
6.8.1 Fisheries and aquaculture ...................................................................................... 160
6.8.2 Tourism ................................................................................................................... 161
6.8.3 Transport ................................................................................................................ 162
6.8.4 Cultural heritage ..................................................................................................... 162
6.9 General conclusion on mitigation measures .................................................................. 162
7 Monitoring methods and projects and conclusions for the Mediterranean ......................... 168
7.1 Introduction and overview ............................................................................................. 168
7.2 Monitoring methods & projects for abiotic environment ............................................. 170
7.3 Monitoring methods & projects for benthic communities and habitats ....................... 170
7.4 Monitoring methods & projects for fish/elasmobranchs .............................................. 173
7.5 Monitoring methods & projects for sea turtles ............................................................. 175
7.6 Monitoring methods & projects for birds ...................................................................... 175
7.7 Monitoring methods & projects for marine mammals .................................................. 178
7.8 Monitoring socio-economic sector ................................................................................ 182
7.9 Research and Development projects ............................................................................. 182
7.10 General conclusion on monitoring methods .................................................................. 183
8 Regulatory frameworks .......................................................................................................... 187
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8.1 EU frameworks ............................................................................................................... 187
8.1.1 Environmental Impact Assessment (EIA) Directive 85/337/EEC ............................ 187
8.1.2 SEA directive 2001/42/EC Strategic Environmental Assessment ........................ 188
8.1.3 Habitats 92/43/EEC and Birds 2009/147/EC Directives & Guideline documents .. 188
8.1.4 Marine Strategy Framework Directive (MSFD) ...................................................... 190
8.2 Examples from European countries on existing guidelines, regulations and standards 191
8.2.1 Germany ................................................................................................................. 191
8.2.2 United Kingdom (UK) .............................................................................................. 192
8.2.3 Denmark ................................................................................................................. 193
8.2.4 France ..................................................................................................................... 195
9 Discussion on MPAs and OWFs .............................................................................................. 195
9.1 MPAs in the Mediterranean Sea .................................................................................... 196
9.2 OWFs in MPAs? .............................................................................................................. 200
9.2.1 Avoidance mitigation - compensation approach ................................................ 201
9.2.2 Compatibility options for the co-location of OWFs and MPAs .............................. 202
9.2.3 Case studies regarding co-location of OWFs and MPAs ........................................ 204
9.3 Recommendations ......................................................................................................... 208
9.3.1 Recommendations to public authorities ................................................................ 209
9.3.2 Recommendations to MPA managers .................................................................... 212
9.3.3 Recommendations to the OWF business sector .................................................... 214
9.4 Apply lessons learned to the Mediterranean Sea .......................................................... 214
10 List of eu projects to capitalise upon ................................................................................. 220
11 Literature ............................................................................................................................ 228
ANNEX- DATA FROM 4COFFSHORE DATABASE ON WIND TURBINES
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List of figures
Figure 1.1 MPAs in the European Part of the Mediterranean Sea and planned OWFs. National
(dark green) as well as MPAs under the framework of Natura 2000 (bright green) are
displayed. (Source: WWF France, 2018) ...................................................................... 15
Figure 2.1 Types of foundations for offshore wind turbines (OH 2018). ..................................... 17
Figure 2.2 Comparisons of installed foundations for offshore wind energy conversion systems
(OWECs); symbols in figure (a) represent windfarms constructed with each foundation
type; bars in figure (b) represent the number of OWECs with respect to the capacity of
OWECs (Power Rating, PR) (OH 2018) ......................................................................... 18
Figure 2.3 Gravity foundations under construction for Thornton Bank (source: LUC VAN
BRAEKEL). ..................................................................................................................... 19
Figure 2.4 Components of a monopile foundation (KAISER & SNYDER 2012) ................................. 20
Figure 2.5 Installation of a suction bucket jacket at ‘Borkum Riffgrund 2’ in 2018 (copyright
Örstedt/Matthias Ibeler, source: https://orsted.de/presse-
media/news/2018/07/bkr02-letztes-sbj-installiert 06.12.2018). ............................... 21
Figure 2.6 Tripod foundations (left) and jacket foundation (right) (source: ‘Alpha Ventus’) ...... 22
Figure 2.7 Examples of floating wind turbine components and mooring systems (DNV GL 2018)
..................................................................................................................................... 24
Figure 2.8 An exemple of a spar type loating platform for offshore wind turbines (source:
https://www.equinor.com/en/what-we-do/hywind-where-the-wind-takes-us.html)
..................................................................................................................................... 25
Figure 2.9 Mooring systems for floating OWFs (RHODRI AND COSTA ROS 2015) .............................. 26
Figure 2.10 Anchoring systems for floating OWFs (RHODRI AND COSTA ROS 2015) ........................... 27
Figure 2.11 An assembled rotor being lifted onto a nacelle at Nysted windfarm (©DONG Energy)
..................................................................................................................................... 28
Figure 2.12 Percentage of Offshore Windfarm turbine types that are commercially available (n=90)
or installed as prototypes (n = 1) per various Power Rating (PR) categories (source:
Graph derived by processed data from 4coffshore database on wind turbines - October
2018, see Annex). ........................................................................................................ 29
Figure 2.13 Percentage of Offshore Windfarm turbine types that are commercially available (n=86)
per various rotor diameter (D) categories (source: Graph derived by processed data
from 4coffshore database on wind turbines - October 2018, see Annex). ................. 30
Figure 2.14 Export cable layout in the German EEZ collecting power of different OWF-Clusters and
landing the power at two main shore landing points (left ©BSH 2018) and inner-park
sub-station (right, at Gunfleet Sands © Offshore Wind Power MarineServices)........ 31
Figure 2.15 Substation at ‘Alpha Ventus’ (source: https://www.tennet.eu/our-grid/offshore-
projects-germany/alpha-ventus/). .............................................................................. 32
Figure 2.16 Met tower in the German EEZ (© BioConsult SH 2011) .............................................. 33
Figure 2.17 A typical gravity base caisson foundation for shallow depth (left © https://www.wind-
energy-the-facts.org/offshore-support-structures.html) A gravity foundation being
installed at Thornton Bank by the heavy lift vessel Rambiz (right, source & © LUC VAN
BRAEKEL) ...................................................................................................................... 34
Figure 2.18 A typical monopile foundation used in the offshore wind energy industry (source & ©
https://www.wind-energy-the-facts.org/offshore-support-structures.html) ............ 35
Figure 2.19 A tripod support structure for offshore wind turbines in transitional water depths. (left,
source & © https://www.wind-energy-the-facts.org/offshore-support-
structures.html). The Taklift 4 placing a tripod foundation at ‘Alpha Ventus’ (right,
source & © Alpha Ventus) ........................................................................................... 36
Figure 2.20 A typical jacket-tubular foundation structure (source: https://www.wind-energy-the-
facts.org/offshore-support-structures.html) ............................................................... 36
Figure 2.21 Different methods of burying cables into the seaground ........................................... 37
Figure 2.22 Different methods of protecting cables if layed onto the seabed .............................. 38
PHAROS4MPAs - A REVIEW OF SOLUTIONS TO AVOID AND MITIGATE
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Figure 3.1 Cumulative offshore wind energy capacity worldwide by country in 2016 and 2017.
Cumulative capacity is shown from 2011 2017. (GWEC, 2018)................................ 39
Figure 3.2 Average depth (m) and distance to coast of OWF under construction in 2017 in the
EU. The size of the bubbles represents the relative capacity of the OWF. (WIND EUROPE
2018). ........................................................................................................................... 40
Figure 3.3 Schematic view of the development of rotor diameter (m) and hub height (m)
worldwide of offshore turbines from 1991 2017. (OPEN OCEAN 2017) ................... 42
Figure 3.4 Comparative view of the size of the world’s biggest turbine Haliade-X and the floating
turbines of the WindFloat 2 pilot project, Portugal (source: modified after General
Electric Renewable Energy - https://www.ge.com/renewableenergy/wind-
energy/turbines/haliade-x-offshore-turbine).............................................................. 42
Figure 3.5 Average depth and distance to shore of bottom-fixed OWFs in Europe. The colour of
the bubbles represents the status of the OWF (blue = online, orange = under
construction, green = consented and yellow = application submitted). The size of the
bubbles indicates the overall capacity of the site. (WindEurope, 2018) ..................... 44
Figure 3.6 Global projections for development of worldwide offshore wind capacity. In green the
projected share of floating OWFs. (GWEC report, 2017) ............................................ 45
Figure 5.1 Relationship between pile diameter and noise immission expressed as SEL and Lpeak
from offshore pile driving (BELLMANN 2014). ............................................................ 52
Figure 5.2 Schematic presentation of the magnetic field (T) generated by an industry standard 13
kV subsea cable buried at 1 m depth. Blue line represents the seabed surface.
(BOEHLERT AND GILL, 2010) ........................................................................................ 53
Figure 5.3 Schematic overview of the fields associated with subsea power cables, whereas the
magnetic (B field) and induced electrical field (iE field) can potentially impact on the
marine environment. (GILL, 2005) ............................................................................... 54
Figure 5.4 Example of a modelled seabed temperature in the surrounding of a medium voltage
AC cable in an OWF buried at 1m depth. (IFAÖ 2006) ................................................ 55
Figure 5.5 Common starfish on scour protection of the Danish OWF “Horns Rev”. Photo: Maks
Klaustrup. Source: NIELSEN (2006) .............................................................................. 57
Figure 5.6 Exemplary photograph of the wind-wake effect at Horns Rev II after (HASAGER, 2017)
..................................................................................................................................... 59
Figure 5.7 Current distribution of Posidonia oceanica meadows. The current distribution of P.
oceanica (green areas) along the Mediterranean Sea coastline (TELESCA, 2015). ..... 66
Figure 5.8 Conservation status of fish in the Mediterranean Sea listed by the IUCN. (Datasource:
IUCN 2018, unpubl.) .................................................................................................... 77
Figure 5.9 Species richness of threatened marine fish in the Mediterranean Sea. (IUCN, 2010) 78
Figure 5.10 Major nesting sites (i.e. ≥10 clutches yr−1 and ≥2.5 clutches km−1 yr−1) of loggerhead
turtles Caretta caretta in the Mediterranean. Countries: AL: Albania; DZ: Algeria; BA:
Bosnia and Herzegovina; HR: Croatia; CY: Cyprus; EG: Egypt; FR: France; GR: Greece; IL:
Israel; IT: Italy; LB: Lebanon; LY: Libya; MT: Malta; ME: Montenegro; MA: Morocco; SI:
Slovenia; SP: Spain; SY: Syria; TN: Tunisia; TR: Turkey. Marine areas: Ad: Adriatic Sea;
Ae: Aegean Sea; Al: Alboran Sea; Io: Ionian Sea; Le: Levantine Basin; Si: Sicilian Strait;
Th: Tyrrhenian Sea; b: Balearic Islands (Spain) (CASALE et al. 2018 and references
therein). ....................................................................................................................... 81
Figure 5.11 Major nesting sites of green turtles Chelonia mydas. Classes of nesting activity: Very
high (>300 clutches yr1): yellow, High (100−300 clutches yr1): blue, Moderate-dense
(20−99 clutches yr1; ≥6.5 clutches km1 yr1): pink triangle, Moderate-not dense
(20−99 clutches yr1; 2.5−6.5 clutches km1 yr1) pink square, Low-not dense (10−19
clutches yr1; 2.5−6.5 clutches km1 yr1): green. CY: Cyprus; LB: Lebanon; SY: Syria; TR:
Turkey. Numbers represent nesting locations (CASALE et al. 2018 and references
therein). ....................................................................................................................... 81
Figure 5.12 Spatial density plots of the predicted diver distribution ‘before’ vs. ‘after’ the
construction of OWFs. Bold black lines: OWFs; thin black lines: 10 km distance buffer;
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dotted black lines: 20 km distance buffer; bold green line: Specially Protected Area
(SPA), (MENDEL 2019). ................................................................................................ 88
Figure 5.13 Effects that may influence marine mammals during the life of a windfarm (PERROW
2019) .......................................................................................................................... 106
Figure 5.14 Potential zones around the noise source divided in impact zones (POPPER & HAWKINS
2012) .......................................................................................................................... 106
Figure 5.15 The audiogram of 9 marine mammal families (POPPER & HAWKINS 2012) ................. 108
Figure 5.16 The tracks of a telemetry tagged harbour seal around Sheringham Shoal with the
turbines and sub-stations (circles) shown in red. Whilst tagged, the seal visited the
windfarm on each of its thirteen trips to sea (PERROW 2019). .................................. 115
Figure 5.17 The Mediterranean Sea and its areas (DEL MAR OTERO & CONIGLIARO 2012); blue ovals
added to the figure label the most productive and diverse areas regarding marine
mammals (HOYT 2005). .............................................................................................. 117
Figure 5.18 Schematic overview of human activities and interests taking place, interacting and
possibly competing for space in European Seas. (MUSES-PROJECT 2018) .................. 119
Figure 5.19 The process of the cumulative adverse effects of offshore wind energy development
on wildlife. Homotypic OWF hazards, as well as other heterotypic sources,
directly/indirectly adversely affect vulnerable receptors. These adverse effects
accumulate as vulnerable receptors are repeatedly exposed through time and space
to the OWF hazards via additive, synergistic, and countervailing pathways. The adverse
effects of the exposure of vulnerable receptors to OWED hazards can then accumulate
to a degree that a population threshold is passed (GOODALE & MILMAN 2016). ........ 123
Figure 5.20 Density of commercial vessels (2013) in the Mediterranean obtained via AIS data.
Potential OWF hotspot areas are displayed as black rectangles (BRAY et al. 2016) .. 125
Figure 6.1 Main sectors involved in Marine Spatial Planning. (UNESCO & INTERGOVERNMENTAL
OCEANOGRAPHIC COMMISSION 2009) ............................................................................. 128
Figure 6.2 Marine spatial plans for the German EEZ, developed since 2009. OWFs (operating,
constructed, approved or submitted for approval) are displayed in red. (MARIBUS et al.
2015) .......................................................................................................................... 129
Figure 6.3 Examples for marine spatial planning in the southwest of Great Britain (lower panel)
taking spatial requirements for OWFs (build, planned and/or approved), OWF related
grid connections, marine protected areas and shipping routes into account.
(VATTENFALL 2015) ................................................................................................... 129
Figure 6.4 Avoid - Mitigate - Compensate approach. The most effective way of reducing negative
impacts is always to avoid damage, and the preferred sequence of steps is to avoid
damage, followed by minimization of impacts, restoration, with compensation as the
last resort (NORWEGIAN MINISTRY OF CLIMATE AND ENVIRONMENT 2015) ......................... 132
Figure 6.5 Pinger (© BioConsult SH 2018). ................................................................................. 136
Figure 6.6 Seal scarer (© BioConsult SH 2018). .......................................................................... 137
Figure 6.7 Fauna Guard (FAUNAGUARD 2013) .............................................................................. 137
Figure 6.8 Schematic of a double ‚big bubble curtain(RUMES et al. 2016) ................................ 139
Figure 6.9 Projects, in which ‘big bubble curtains’ have been used (state 08.2016)(HYDROTECHNIK
LÜBECK SPEZIALWASSERBAU 2016) .................................................................................. 140
Figure 6.10 Schematic of the HSD single-net system (KOSCHINSKI & LÜDEMANN 2013) .................. 141
Figure 6.11 Illustration of the blue piling technology (FISTUCA 2018) ........................................... 142
Figure 6.12 Exemplary distribution of wireless marine mammal monitoring buoys with a detection
range of 400m (BIOCONSULT SH 2018) ..................................................................... 145
Figure 6.13 Overview of assessed „relevance of suggestions for good practice in the
environmentally sound development of OWFs“ (Delphi method by LÜDEKE 2017,
expert interviews via questionnaire) ......................................................................... 146
Figure 6.14 Map of the Cetacean Critical Habitats (CCH) and areas important for particular species
(ACCOBAMS 2016) ..................................................................................................... 152
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Figure 6.15 An example map of the western Mediterranean Sea, for potentially ship-fin-whale
collision risk areas (VAES et al. 2013). ........................................................................ 153
Figure 6.16 Magnetic field profiles at seabed level for an AC cable buried 0.5 m, 1 m, 1.5 m, or 2
m. X-axis displays the distance from the cable to the seabed. (TRICAS & GILL 2011) . 158
Figure 6.17 Mitigation measure classification (GARTMAN et al. 2016a) ....................................... 164
Figure 7.1 Observations of divers from HiDef digital flight monitoring surveys ........................ 176
Figure 7.2 Overview of remote sensing techniques operating in the vicinity of ‘Alpha Ventus 177
Figure 7.3 Schematic drawing camera orientation and set-up of HiDef digital aerial video surveys.
................................................................................................................................... 180
Figure 9.1 MPAs under the Natura 2000 network in the Mediterranean Sea. SPAs are displayed in
red, areas protected under the EU Habitats directive in blue. (EUROPEAN
ENVIRONMENT AGENCY, 2018b) ............................................................................... 197
Figure 9.2 MPAs in the Mediterranean. The different designation types are colour coded.
(MedPAN, UNEP/MAP/SPA-RAC, 2017) .................................................................... 198
Figure 9.3: Development of MPAs in the Mediterranean Sea since 1950s. Bars show the number
of newly designated MPAs per year. The black line indicates the cumulative surface of
protected area. Source: MedPAN & UNEP-MAP-SPA/RAC (MEDPAN, UN
ENVIRONMENT/MAP & SPA/RAC, 2016). ...................................................................... 199
Figure 9.4 Matrix of marine activities that may be appropriate for each IUCN management
category (IUCN 2012)................................................................................................. 203
Figure 9.5 Area favourable (in red) to the development of a pilot OWF project in the NMPGL. The
different zones of the Park are shaded in green (AGENCE FRANCAISE POUR LA
BIODIVERSITE, 2018). ................................................................................................. 206
Figure 9.6 National MPAs (Natural parks), marine Natura 2000 sites and planned OWFs
overlapping with MPAs in Greece (GREEK REGULATORY AUTHORITY FOR ENERGY &
GREEK MINISTRY 2017). ............................................................................................. 207
Figure 9.7 Map of the Belgian zone for offshore renewable energy, the Dutch Borssele offshore
wind area and Natura 2000 areas in the vicinity. Already constructed wind farms are
indicated in blue (CP:C-Power, NT: Northwind and B: Belwind), wind farms under
construction in 2016 in yellow (NB: Nobelwind), 2017 in orange (R: Rentel), 2018 pink
(N: Norther, 1 and 2: Borssele 1 and 2) and 2019 in purple (S: Seastar, NW2:
Northwester2, M: Mermaid, 3 and 4: Borssele 3 and 4) (DEGRAER et al. 2016) ......... 208
Figure 9.8 The localization of the four macro-zones identified to potentially host the development
of commercial windfarms. The pilot OWF are depicted in red dots and give an idea of
sites preferences. Natura 2000 sites and marine protected areas designated in the Gulf
of Lion are depitected in green and blue (AGENCE FRANCAISE POUR LA BIODIVERSITE,
2018). ......................................................................................................................... 211
Figure 9.9 Overview of the decision process for the development of the OWF in the NMPGL. The
process consisted of two mandates of the OWF working group prior to and after the
designation of the OWF project and resulted in the acceptance of most of the working
group’s recommendations and an approval of the MPA management board. ........ 213
Figure 9.10 Schematic view of an integrated approach for the development of OWF in the
Mediterranean. (BOERO et al. 2016) ......................................................................... 219
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List of tables
Table 3.1 Number of offshore windfarms, turbines, installed capacity per European country.
Modified after WindEurope (2018). Besides “Hywind” OWF in the UK and one turbine
in France, there is no floating OWF operating and grid connected in the countries
included in the table. ................................................................................................... 41
Table 5.1 Overview of sound levels underwater of common events.......................................... 51
Table 5.2 Response of seabirds to the presence of operating offshore windfarms according to
results of post-construction studies. Windfarms are listed from west to east. Numbers
and colours indicate the allocated class of response from strong avoidance (1, red) to
strong attraction (5, dark green), with letter codes indicating the criteria used (see
Table 5.3 for details). The second column gives the calculated arithmetic mean of the
studies, but note that the final classification (colour) can slightly deviate owing to
species-specific considerations. Regions: CS Celtic Seas, NS North Sea, BS Baltic Sea
(DIERSCHKE 2016). ....................................................................................................... 91
Table 5.3 Definition of classes regarding spatial behaviour of seabirds in response to offshore
windfarms (DIERSCHKE 2016). ..................................................................................... 92
Table 5.4 Response of seabirds to offshore windfarms and estimated response distance (i.e.
distance from the windfarm to which birds are affected). ‘−’ and ‘+’ signs indicate
statistically significant negative and positive effects on abundance, respectively; ‘0’
indicates no detected effect. Symbols in parentheses indicate no statistical effect, but
response suggested by the authors (WELCKER & NEHLS, 2016). ................................ 93
Table 5.5 Seabird species present in Mediterranean with Global, European and EU27 IUCN Red
list status, Annex I category according to EU Birds Directive 2009/147/EC, the updated
list of endangered or threatened species found in the Mediterranean established
under the Specially Protected Areas and Biological Diversity Protocol (SPA/BD
Protocol) of the Barcelona Convention, and indicative percentage of the global
population of each species situated in Europe25. Bird species considered to be
particularly vulnerable to windfarms. XXX = Evidence on substantial risk of impact, XX
= Evidence or indications of risk or impact, X = Potential risk or impact, x = small or
non-significant risk or impact, but still to be considered in assessments. This is an
indicative list for guidance, and any potential impacts will be site-specific (source). 95
Table 5.6 Overview of anthropogenic pressures with the type of impacts and the species being
affected the most in the Mediterranean. .................................................................. 115
Table 5.7 Overview of the 12 resident marine mammals to the Mediterranean Sea with one
pinnipedand 11 cetaceans (NOTARBARTOLO DI SCIARA 2016). ....................................... 117
Table 5.8 Potential impacts, positive and negative, of OWF on tourism in the Baltic Sea region.
(STIFTUNG OFFSHORE-WINDENERGIE, 2013) ........................................................... 120
Table 6.1 Examples of OWFs as tourist attractions and specifications of the type of tourist
activity. (STIFTUNG OFFSHORE-WINDENERGIE, 2013) .............................................. 161
Table 6.2 Taxonomic groups / habitats, pressures, resulting impacts, ranking of impacts and
suggested mitigation measure is presented below; Mitigation measures with proved
efficacy are highlighted by bold letters while the rest either contribute additively or
need to be further investigated. ................................................................................ 165
Table 7.1 Monitoring concepts already applied to OWFs and the applicability to the
Mediterranean marine environment ........................................................................ 185
Table 9.1 Types of MPAs in the Mediterranean Sea. Types of legislation and examples for
designations are given. Sources: (MEDPAN et al. 2016) ............................................ 198
Table 9.2 Compatibility with OWFs and the different MPA categories according to French
legislation (Source: AGENCE FRANÇAISE pour la BIODIVERSITÉ, http://www.aires-
marines.fr/Concilier/Energies-marines-renouvelables-et-AMP). .............................. 205
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List of abbreviations
ACCOBAMS
Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and
contiguous Atlantic area
AC
Altering electric currents
ADD
Acoustic Deterrent Devices
AHD
Acoustic Harassment Devices
AIS
Automatic Identification System
BACI
Before-After/Control-Impact, a monitoring approach
(D)BBC
(double) Big Bubble Curtain
BfN
Bundesamt für Naturschutz, Federal Agency for Nature Conservation
BioConsult SH
Independent, ecological/ environmental research and consulting office in Schleswig-
Holstein (Northern Germany)
BMU
Bundesministerium für Umwelt, Federal Ministry for the Environment
BSH
Bundesamt für Seeschifffahrt und Hydrographie, Federal Maritime and Shipping
Authority, Germany
CAE
Cumulative Adverse Effects
CRM
Collision Risk Models
C-POD
Cetacean-Porpoise Detector
dB
Decibel, used within the acoustics as a ratio to describe the sound pressure level
DC
Direct electric currents
EEZ
Exclusive Economic Zone
EIA
Environmental Impact Assessment
EMF
Electromagnetic Field
EU
European Union
FAO
Food and Agriculture Organisation
FFH
Fauna-Flora-Habitat. Areas which were selected for the European protected areas system
Natura2000
FINO
Forschungsplattformen In Nord- und Ostsee, Research platforms in North and Baltic Sea
GES
Good Environmental Status
GW
Gigawatt
HDD
Horizontal Directional Drilling
HELCOM
HELsinki COMmission, monitoring concept for the Baltic Sea
HiDef
High-Definition digital flight monitoring surveys
HRA
Habitats Regulations Assessment
HSD
Hydro Sound Damper
HVDC
High-Voltage Direct-Current
IAC
Inner-Array Cables
IBA
Important Bird Area
ICCAT
International Commission for the Conservation of Atlantic Tunas
ICCP
Impressed Current Cathodic Protection
IfAÖ
Institut für Angewandte Ökosystemforschung, Institute for Applied Ecosystem Research
IHC-NMS
Noise Mitigation System of the company IHC B.V.
IMMA
Important Marine Mammal Areas
IUCN
International Union for Conservation of Nature
IWC
International Whaling Commission
kHz
Kilohertz
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kJ
Kilojoule
kV
KiloVolt
LED
Light Emitting Diode
MAP
Mediterranean Action Plan
MedPAN
Network of Marine Protected Areas managers in the Mediterranean
MMO
Marine Mammal Observer
MPA
Marine Protected Area
MSFD
Marine Strategy Framework Directive
MSP
Marine spatial planning
MW
Megawatt
NGO
Non-Governmental Organisation
NM
Nautical Miles
NMS
Noise Mitigation System
NW
Northwest
ORJIP
Offshore Renewables Joint Industry Programme
OSPAR
OSlo-PARis Convention, monitoring concept for the North Sea
OWECS
Offshore Wind Energy Conversion Systems
OWF
Offshore Windfarm
PAM
Passive-Acoustic-Monitoring
PHAROS4MPAs
Lighthouse project for Offshore Windfarms in Marine Protected Areas
POD
POrpoise Detector
PTS
Permanent Threshold Shift
R&D
Research and Development project
SAC
Special Area of Conservation
SBC
Small Bubble Curtain
SCADA
Supervisory Control and Data Acquisition
SCI
Site of Community Importance
SCUBA
Self-Contained Underwater Breathing Apparatus
SEA
Strategic Environmental Assessment
SEL / S-SEL
Sound Exposure Level
SPA
Special Protected Area
SPAMIs
Specially Protected Areas of Mediterranean Importance
SPL
Sound Pressure Level
StUK4
4th version of the German Standard Investigation concept of the BSH (standard
Investigation of the Impacts of Offshore Wind Turbines on the Marine Environment),
Standard UntersuchungsKonzept
SW
Southwest
T-POD
Timing Porpoise Detector
TTS
Temporal/ Temporary Threshold Shift
UAV
Unmanned Aerial Vehicle (drone)
UK
United Kingdom
UN
United Nations
UNEP
United Nations Environment Programme
V
Volt
VWS
Vessel Monitoring System
WWF
World Wide Fund for Nature
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1 GENERAL INTRODUCTION
Purpose and methodology of the Capitalisation report - Background
The steadily rising concentration of Greenhouse Gases (GHG) in the Earth’s atmosphere is a
consequence of the increased emission by anthropogenic activities. These emissions and the
consequential climate change have caused and are continuously causing serious threats to
ecosystems, single species as well as human health. To reduce these emissions and hence diminish
the consequences of climate change, several international (e.g. UNEP) and national institutions
have established programs and projects to mitigate, reduce, or integrate effects of climate change.
Among others, the European Union has developed programs and targets to replace energy from
fossil sources by energy from renewable sources. The renewable energy targets developed by the
EU in 2008 and renewed in 2014, aim for
a 40% cut in greenhouse gas emissions compared to 1990 levels
at least a 27% share of renewable energy consumption by 2030
Energy generated from wind power is one of the most promising tools to reach this EU targets and
make energy production more sustainable. Besides generating energy from wind with land-based
turbines, the field of offshore windfarms located in the oceans is developing since more than 25
years and gains raising awareness. Windfarms located offshore benefit from favourable wind
conditions for efficient energy production and seem to profit from almost “infinite” space.
However, OWFs impact on the surrounding environment and the more OWFs are developed, the
greater the competition for space with the environment and other anthropogenic activities is
becoming.
Since 1991, when Denmark built the first OWF, 17 countries have constructed OWFs, most of them
located in Northern Europe (GLOBAL WIND ENERGY COUNCIL 2018). In the Mediterranean there is no
OWF present so far. Turbines of OWFs usually have greater dimensions compared to the turbines
onshore, and reach higher efficiency and yielding more energy per installation. Across Europe there
have been about 4000 turbines installed so far (WIND EUROPE 2018). The present turbines are
designed for relatively shallow waters (±40 m), as can be found in the North Sea and the Baltic Sea.
To ensure resistance to severe weather conditions the foundations of those turbines are piled 30 m
and more into the sea bed. Recent projects and developments also take possible locations further
offshore, in deeper waters or on ground not suitable for piling, into account. However, major
constraints, like the efficient transmission of the produced energy to the shore, are still under
research and development. Floating turbines have been developed, which do not require a solid
foundation, but are instead anchored in the ground. Until now several test sites and pilot projects
have been constructed (e.g. OWF ‘Hywind’ in Scotland). Nevertheless, there are several projects in
the early or advanced planning phase, for instance in the Mediterranean, where this construction
technique is seen as most promising for the prevailing conditions (e.g. ‘Les éoliennes flottantes du
Golfe du Lion” in France) (4C OFFSHORE LTD 2018).
The construction, operation and decommissioning of OWF are impacting on the surrounding marine
environment and also have consequences on a socio-economic level. It is proven that OWFs impact
on the hydrographic conditions in their vicinity and that certain animal groups and habitats can
severely be affected by an OWF. Potential impacts of OWF are investigated for instance for benthic
communities, fishes, birds and marine mammals. Chemical pollutants, e.g. from sacrificial anodes
can accumulate in the sediment with currently unknown consequences for the marine
environment. Benthic communities can suffer from habitat loss due to the space the OWF requires
and the seabed that is moved during construction of the turbines and associated constructions (e.g.
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cables) (HUDDLESTON 2010). The impact of electromagnetic fields emitted by the cables transporting
the energy from the turbines to the shore on benthic animals and invertebrates in general is not
very well known. On the other hand benthic communities can use the newly introduced structures
as additional habitat and this way contribute to generating an artificial reef (LINLEY et al. 2007). Such
an artificial reef may be attractive for mobile animals, such as fish or marine mammals, which may
use the reef as a feeding ground or, in case fishing is prohibited in the OWF, as a refuge (DEGRAER et
al. 2013). Whether these secondary impacts of an OWF are beneficial for an ecosystem depends on
several factors, such as the native habitat structure or the organisms, mainly colonizing the artificial
reef. As some fish species have excellent hearing capabilities fish may also be harmed by the noise
introduced to the marine realm by the piling of the foundations into the ground or by the pressure
associated with the piling events (MUELLER-BLENKLE et al. 2010).
Marine mammals are known to respond at large distances to noise levels generated during
construction. The main concern is that the sensitive auditory systems can be seriously harmed by
pulsed noise generated during piling activities (e.g., eliciting a temporary or permanent threshold
shift (BRANDT et al. 2014)). Also temporary or permanent displacement (habitat loss) is seen as a
major pressure on marine mammals, because it can be followed by negative effects on the
individual as well as on the population level. For birds several negative impacts are known. The
physical presence of the OWF can lead to habitat loss as some species tend to avoid the windfarm
area (Garthe et al. 2018). Furthermore the OWF can act as a barrier on migration routes of migrating
birds and force the birds to change their original route. Furthermore birds face a potential risk of
mortality due to an elevated collision risk with the turbines (DEGRAER et al. 2013).
In order to minimize negative impacts of OWF on the marine environment, it is recommended to
follow the principles of 1. Avoidance 2.Mitigation and 3.Compensation. Negative impacts should be
generally avoided. If this is not possible, these impacts should be mitigated following best-practice
strategies and, as the least preferred option, the impacts should be compensated adequately.
Possible strategies for avoidance and mitigation of negative pressures of most concern are
presented in this report, including case studies of OWF, where these methods have been applied.
Furthermore monitoring methods and research projects are highlighted, focussing on Northern
European countries and how those can be adapted to future projects in the Mediterranean Sea.
Rising anthropogenic activities by increasing offshore wind developments will also cause spatial
competition with other economic sectors (e.g., fisheries or tourism) as well as ecologic interests
and targets, such as existing/planned Marine Protected Areas (MPAs) or sites of special ecological
value. Since the 1950 there has been consistent progress in establishing protected areas in the
Mediterranean Sea and in 2016 there were 1231 sites designated as MPAs, which equals 7.14% of
the area of the Mediterranean Sea (MedPAN et al. 2016) (Figure 1.1).
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Figure 1.1 MPAs in the European Part of the Mediterranean Sea and planned OWFs. National (dark green)
as well as MPAs under the framework of Natura 2000 (bright green) are displayed. (Source:
WWF France, 2018)
According to the Aichi targets of the ‘Convention on Biological Diversity’ and ‘Sustainable
Developments Goals’ of the United Nations (UN) the overall goal is to have at least 10% of coastal
and marine areas conserved “consistent with national and international law” (MEDPAN et al. 2016)
by 2020. There is no clear definition of the term ‘Marine Protected Area’ and thus there are various
different types of MPAs with varying protection status in the Mediterranean Sea. Only 0.04% of the
Mediterranean belongs to no-take zones, where e.g. fishing is strictly prohibited. In the
Mediterranean there are national or regional designated MPAs, e.g. within the Natura2000 network
and Specially Protected Areas of Mediterranean Importance (SPAMIs). Internationally designations
exist for instance from the UNESCO (UNESCO World Heritage Sites). The actual management of
these MPAs is often not fully developed and knowledge about the existing management measures
and their effectiveness is scarce. In addition the legislation is often not adequately defined to deal
with existing pressures and provide mitigation or compensations measures or to initiate research
projects (questionnaire within the MedPAN framework). It is assumed that doubling the share of
renewable energy in general on a global scale to 36% by 2030, would give the opportunity to keep
global warming from failing the 2°C threshold (IRENA 2019). Offshore wind power is seen as one of
the most promising tools of producing renewable energy to reach these goals. At the same time
the Aichi targets are crucial to be fulfilled to maintain and/or recover biological diversity in the
marine realm and sustain a functioning and healthy marine environment. To ensure that these two
important goals of the near future can be successfully fulfilled, a discussion on whether and how
these goals can co-exist is inevitable.
Ecologic interests, for renewable energy production on the one hand and conservation goals on the
other hand, may compete for space and most suitable locations, but are also seen as areas of
potential co-use, if managed sustainably (LACROIX & PIOCH 2011). In order to establish future
guidelines if and how anthropogenic activities and MPAs can co-exist, this report aims to review the
best available knowledge on the impacts, mitigation and monitoring methods of different types and
phases of OWF to enable stakeholders and decision makers in the MPA sector as well as in the
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offshore wind industry and politics to establish regulations or recommendations for sustainable
OWF projects in the Mediterranean Sea. Within the framework of the PHAROS4MPAs projects
BioConsult SH was assigned to draft a Capitalization report reviewing literature assessing marine
environmental issues related to the developing offshore windfarm industry. According to the
guidelines given by WWF France within the PHAROS4MPAs project the present report is “[…] based
on methodologies, practices, intervention tools already tested and implemented by stakeholders
at local or regional level that represent a strong interest for wider targeted dissemination in the
Mediterranean area”. The capitalization report focuses on impacts of the offshore windfarm sector
on the marine environment and relevant mitigation and monitoring techniques. Due to the existing
experiences and research projects dating back to the early 1990s, the present report focuses mainly
on knowledge gained in the North Sea, Baltic Sea and North-East Atlantic. It is based on an extensive
and thorough literature research, only considering scientifically sound research, databases and
literature. The detailed aims and objectives targeted by this report are as follows.
Aims & Objectives
Overview of techniques and trends in the Offshore Windfarm (OWF) sector with focus on
Northern Europe
Review and consolidate existing information about impacts of OWFs on marine
environment
Define the most important threats and review and consolidate existing information about
mitigation techniques
Review and consolidate existing information about monitoring techniques and programs
Extrapolate existing knowledge to the situation in the Mediterranean Sea
Describe examples of currently existing regulations, guidance and advice that is applicable
to the marine environment and OWF development
Review and list existing legal regulations and regulatory frameworks that could be used to
support recommendations for the sector in the Mediterranean Sea
Discuss how the current knowledge, experiences, mitigation and monitoring methods can
be used in the light of increasing OWF development in the Mediterranean Sea with the
emphasis on marine protected areas.
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2 CHARACTERISTICS OF OFFSHORE WINDFARMS (OWF)
2.1 Components of OWF
In this chapter relevant components are outlined and procedures for the construction are
highlighted.
2.1.1 Foundation types (fixed)
For offshore construction works, the water depth is generally divided into three classes: Shallow
waters (030 m), transitional waters (30-50 m), and deep waters (50200m) (MUSIAL & BUTTERFIELD
2004). The sea depth is the most important factor for the capital market viability of offshore
winfarms because the cost for foundations significantly increases with increasing depth. Hence,
several types of foundations are already developed, and some types are under development
considering varying factors such as sea depth and e.g., soil conditions (Figure 2.1) (OH et al. 2018).
Figure 2.1 Types of foundations for offshore wind turbines (OH 2018).
Figure 2.2a shows the current types of foundations used in commercial OWF with respect to the
sea depth and the distance from shore. This figure provides insights into trends for foundation types
with respect to the sea depth and the distance from shore. Figure 2.2b also shows the trend of
foundations for OWF over the sea depth and the capacity: gravity monopile multipod. As the
site is deeper and is farther from shore, multipod is more widely used than gravity and monopile
foundations.
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Figure 2.2 Comparisons of installed foundations for offshore wind energy conversion systems (OWECs);
symbols in figure (a) represent windfarms constructed with each foundation type; bars in
figure (b) represent the number of OWECs with respect to the capacity of OWECs (Power
Rating, PR) (OH 2018)
In shallow waters, gravity type (Figure 2.2 a) and monopile type foundations (Figure 2.2 b) are
mainly used. Especially, monopiles are most frequently used because of the suitable sea depth at
available locations and a quick and safe construction sequence including market-ready equipment
and installation vessels. Gravity basements have been used seldom and experience is limited to a
few locations. However plans for future OWF include gravity basement structures in water depth
up to 60m with base slab diameters around 40m and a capacity to carry generators of maximal 8-
10 MW and more. Gravity basements have been used e.g., for the Danish windfarm ‘Rodsand 2’
(2.3 MW turbine capacity) and the Swedish windfarm ‘Karehamn’ (3,0 MW turbine capacity). In
transitional and deep waters, monopiles, tripods and jacket foundations are mainly deployed until
water depths are too high for grounded foundations.
The current status of applications for different fixed foundations are discussed in the following sub-
sections
Gravity based support structures
A gravity-type foundation consists of a large circular pile with a concrete plate structure resting on
the seabed (Figure 2.3). Initial offshore windfarms in Denmark were installed by using this type of
foundation close to shore, where the water depth is very shallow. Moreover, several demonstration
projects such as the ‘Avedøre Holme’, ‘Breitling’, ‘Thornton Bank (Phase I)’ offshore windfarms used
this type of foundation because this type of support structure combines some essential advantages
such as production on-shore, lowering on the seaground instead of piling, filling with ballast from
the seaground, durability in marine environments and structures can be easily removed by
replacing the ballast with air. The deepest gravity foundations in operation are in Thornton Bank
(27 m). In Europe, gravity foundations will likely continue to fill an important niche for shallow to
moderate water depth regions where drivability is a concern (including plans for offshore
windfarms in the French channel waters).
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Figure 2.3 Gravity foundations under construction for Thornton Bank (source: LUC VAN BRAEKEL).
Monopile
Monopiles are typically large diameter, steel cylinders that are piled or drilled into the seabed
(Figure 2.4). Outer diameters usually range from 3 to 10 m, their length, of which about 50% is
driven into the seabed, varies between 30-80 meters.
Monopile foundations are the most commonly deployed foundation structure used in the offshore
wind energy industry to date and especially in European offshore windfarms. Most European
offshore windfarms have been constructed in shallow waters with less than or around 40 m depth,
with soil mainly consisting of sand and gravel, which requires relatively low effort on piling of piles.
Nevertheless, this technology requires heavy duty equipment like jack-up barges or moon-bay
barges for installation, which cause considerable footprints, piling noise, and suspended sediment.
Hence, marine mammals are exposed to high noise levels and in addition. Fisheries and other
environmental issues must be considered for installing offshore windfarms with this substructure.
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Figure 2.4 Components of a monopile foundation (KAISER & SNYDER 2012)
Suction bucket
Suction buckets are steel fabrications that look like upturned buckets embedded in the marine
sediment (Figure 2.5). The installation is relatively quick with low level of vibration, noise, and
suspended sediment. Moreover, this type of foundations is economic because of the simple and
fast installation procedure (MUSIAL et al. 2006).
Several North Sea trial installations were performed including a full scale test of a wind turbine at
the German ‘Borkum Riffgrund I’ site, carrying a Siemens SWT-4.0. This trial was carried out by Dong
energy in water depth of 25m with dense sand beds as installation ground. Footprint of the buckets
was 8x8m, with a total installation weight of more than 700 tons. At the ‘Borkum Riffgrund 2’ site,
20 Suction Bucket Jackets were installed in 2018 carrying 8 MW generators.
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Figure 2.5 Installation of a suction bucket jacket at ‘Borkum Riffgrund 2’ in 2018 (copyright
Örstedt/Matthias Ibeler, source: https://orsted.de/presse-media/news/2018/07/bkr02-
letztes-sbj-installiert 06.12.2018).
Multipod (tripod and jacket)
Space frame substructures such as tripod and jacket structures can provide the required strength
and stiffness for transitional water depths (Figure 2.1(d) and (e)).
Tripods consist of a central steel shaft connected to three cylindrical steel tubes through which piles
are driven into the seabed (Figure 2.6).Tripods are heavier and more expensive to manufacture
than monopiles, but can be more reliable in deep water.
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Figure 2.6 Tripod foundations (left) and jacket foundation (right) (source: ‘Alpha Ventus’)
A jacket foundation is a very large multi-chord base formed of multiple sections of structural tubing
or pipe that are welded together. Jacket foundations are an open lattice steel truss template
consisting of a welded frame of tubular members extending from the mudline to above the water
surface (Figure 2.6). Jacket structures have gone under intense modelling and testing and can be
installed in waters as far as 60 meters deep. Tripod and jacket structures provide sufficient bearing
capacity in transitional water depths with relative short penetration length.
2.1.2 Foundation types (floating)
Most OWFs with floating type foundations are demo and test versions. The test floating OWF
foundations target very deep sites (e.g., 100200 m) and have high rated capacity (e.g., 58 MW).
Floating support structures can be classified into three main classes (CENTER OF WIND ENERGY AT JAMES
MADISON UNIVERSITY 2012, RHODRI AND COSTA ROS, 2015) each having their advantages and
disadvantages:
Semi-submersible platform: uses the water plane area to achieve stability, similar to tway
a barge does. Simple moorings are used to keep the structure in place. Buoyancy stabilised
platform which floats semi-submerged on the surface of the ocean whilst anchored to the
seabed with catenary mooring lines. Often requires a large and heavy structure to maintain
stability, but a low draft allows for more flexible application and simpler installation.
Examples: WindFloat (by Principle Power); Damping Pool (by IDEOL); SeaReed (by DCNS).
Spar-buoy: Ballast stabilized uses a very large weight deep under water, providing a
counterbalance to the loads. Simple moorings are used to keep the structure in place. A
cylindrical ballast-stabilised structure which gains its stability from having the centre of
gravity lower in the water than the centre of buoyancy. Thus, while the lower parts of the
structure are heavy, the upper parts are usually lighter, thereby raising the centre of
buoyancy. The simple structure of the spar-buoy is typically fairy easy to fabricate and
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provides good stability, but the large draft requirement can create logistical challenges
during assembly, transportation, and installation, and can constrain deployment to waters
>100m depth. Examples: Hywind (by Statoil); Sway (by Sway); Advanced Spar (by Japan
Marine United).
Tension leg platform (TLP): uses tensioned mooring arrangements to keep the structure
stable. A semi-submerged buoyant structure, anchored to the seabed with tensioned
mooring lines, which provide stability. The shallow draft and tension stability allows for a
smaller and lighter structure, but this design increases stresses on the tendon and anchor
system. There are also challenges with the installation process and increased operational
risks if a tendon fails. Examples: PelaStar (by Glosten)
In most types (spar-buoy, barge and semi-submerged) the mooring chains are not under tension
but consist of steel of high tenacity and 4-6 times the water depth in length. This needs stable or
heavy anchorages, also in high water depth. On the other hand, mooring structures under tension
exist, anchoring the floater directly to the ground (tension leg platform, or “TLP”) (Figure 2.7 and
Figure 2.8). Floating foundation types include floating steel structures that can be imported as well
as concrete structures (floating barge FLOATGEN) that can be manufactured close to the
deployment site.
Floating windfarms have the potential to significantly increase the sea area available for offshore
windfarms, especially in countries with limited shallow waters, such as Mediterranean countries
which face bathymetry restrictions for installation of fixed foundations due to the rapid drop off of
the continental shelf. Another beneficial aspect of floating offshore windfarms is that they can be
placed farther offshore and minimize landscape alteration. Also they can potentially reduce the
conflicts with other marine activities (such as fishing, recreation and coastal navigation) and can
reach stronger and more consistent wind resources. In case of the offshore windfarm development
in France this type of foundations was proposed as most appropriate considering that near the
coast there are dense marine human activities (trawling, small coastal fishing, nautical activities,
seaside tourism etc.), relatively modest wind fields compared to ones further offshore as well as
water depths reaching more than 40 m near the shore that do not allow the installation of fixed
offshore windfarms (DIRECTION INTERRÉGIONALE DE LA MER MÉDITERRANÉE 2015). All structures have the
advantage of a high degree of prefabrication (if deep sea harbours are at hand) and quick and easy
transport to the construction site. Impact on the marine environment is reduced because the
practices for floating OWFs in Europe so far use techniches without piling of foundations. Floating
foundations and wind turbines are built on land then towed offshore to be anchored at the selected
site. A good example is the ‘Hywind’ concept. Many parts of the five floaters were prefabricated in
Spain, and then placed in waters off Norway for assembly and transport horizontally to Scotland.
The foundation consists of an 8.3 m diameter, 100 m long submerged cylinder secured to the
seabed by three mooring cables.in 95 to 120 m water depth.
Although pioneer countries have focused on fixed bottom foundations taking advantage of the mild
bathymetry of the North and Baltic Sea, floating designs, although promising, constitute a recent
development and so far few cases of floating OWFs have been documented in Europe:
Hywind: Hywind Scotland is the world's first commercial windfarm using floating wind turbines,
situated 29 km off Peterhead, Scotland. The farm has 5 Hywind floating turbines with a total
capacity of 30 MW. Equinor (then: Statoil) launched the world's first operational deep-water
floating large-capacity wind turbine, Hywind, in 2009. The pilot windturbine (tower: 120 m, 2.3
MW) turbine was towed 10 km offshore into the Amoy Fjord in 220 m deep water, off of Stavanger,
Norway on 9 June 2009 for a two-year test run (mooring with drag embedded anchor). In 2015, the
company received permission to install the windfarm in Scotland. Three suction cup anchors hold
each turbine. Hywind Scotland was commissioned in October 2017. Hywind is a floating wind
turbine design based on a single floating cylindrical spar buoy moored by cables or chains to the
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sea bed. Its substructure is ballasted so that the entire construction floats upright. Hywind uses a
ballasted catenary layout with three mooring cables with 60 t weights hanging from the midpoint
of each anchor cable to provide additional tension
1
.
Windfloat: In October, 2011, Principle Power deployed a full-scale 2 MW WindFloat prototype
(WF1) 5km off the coast of Aguçadoura, Portugal
2
. The Windfloat stability system (also known as
active ballast) distributes water ballast between the three columns of the semi-submerged floating
structure to compensate for variable turbine thrust due to low frequency changes in wind velocity
and direction. The system is closed-loop (no water moves in or out of the system. Drag embedment
anchors were used, a mooring configuration similar to those on Oil and Gas platforms and
permanently moored maritime structures. Decommissioning started in 2016 after a successful 5-
year deployment.
Floatgen: In France the first pilot floating offshore wind turbine ‘Floatgen’ with a capacity of 2 MW
located in the Bay of Biscay (Atlantic Ocean) was grid connected in 2018. The floating structure
consists of concrete and the mooring systems include 6 anchors and mooring lines made from
synthetic fiber (Nylon)
3
.
Figure 2.7 Examples of floating wind turbine components and mooring systems (DNV GL 2018)
1
https://www.equinor.com/en/what-we-do/hywind-where-the-wind-takes-us.html
2
http://www.principlepowerinc.com/en/windfloat
3
https://floatgen.eu/en/demonstration-and-benchmarking-floating-wind-turbine-system-power-
generation-atlantic-deep-waters
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Figure 2.8 An exemple of a spar type loating platform for offshore wind turbines (source:
https://www.equinor.com/en/what-we-do/hywind-where-the-wind-takes-us.html)
Mooring systems
According to RHODRI AND COSTA ROS, (2015) the most common mooring configurations are either
taut-leg mooring systems, which are used with TLP concepts, or catenary mooring systems, which
are used with spar-buoy and semi-submersible concepts. Some concepts will also adopt a semi-taut
mooring system, which is a mix between both characteristics, though this is less common. An
overview of these configurations is showed below (Figure 2.9).
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Figure 2.9 Mooring systems for floating OWFs (RHODRI AND COSTA ROS 2015)
Anchoring systems
According to RHODRI AND COSTA ROS, (2015) there are a number of anchoring solutions available,
depending on the mooring configuration, seabed conditions, and holding capacity required.
Catenary mooring configurations will often use drag-embedded anchors to handle the horizontal
loading, though piled and gravity anchors are still applicable, while taut-leg moorings will typically
use either drive piles, suction piles, or gravity anchors to cope with the large vertical loads placed
on the mooring and anchoring system. The size of the anchor is also variable, with larger and heavier
anchors able to generate a greater holding capacity.
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Ultimately, anchor choice will be project and site specific, often dictated by the seabed conditions.
Higher holding capacities are usually generated in sands and hard clays than in soft clays, although
where penetration is difficult in firm soils, gravity base or piled solutions might be required. A
summary of the main anchor types is detailed below, but there is great variety even within these
typologies (Figure 2.10). All are proven concepts which have been used extensively in the marine
and oil & gas industries.
Figure 2.10 Anchoring systems for floating OWFs (RHODRI AND COSTA ROS 2015)
2.1.3 Other OWF components
Turbines
The wind turbine is composed of a tower (usually starting from a transition piece at sea level),
nacelle, hub, and blades (Figure 2.7). Offshore turbines range from 3 to 8 MW with 12 MW under
research and prototype construction (for example the Haliade 12X of GE that could be tested in
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Cherbourg in 2020/2021). Turbine’ suppliers work also on 15 MW turbine development, that could
be ready for projects installed before 2030
4
.
Tower
Towers are tubular structures consisting of steel plate cut, rolled, and welded together into large
sections. The tower provides support to the turbine assembly and the balance of plant components,
including a transformer located in the base, and communication and power cables. Tower height is
determined by the diameter of the rotor star and the clearance above the water level. Typical tower
heights are 6080 m giving a total hub height of 7090 m when added to the foundation height
above the water line. Tower diameter and strength depend on the weight of the nacelle and
expected wind loads.
Figure 2.11 An assembled rotor being lifted onto a nacelle at Nysted windfarm (©DONG Energy)
Nacelle
The nacelle houses the generator and the gearbox. Nacelles are large prefabricated units and need
the heaviest and highest lift. Thus their installation offshore has together with the rotor stars the
highest constraints regarding wind and wave limits and thus plays a major role in the time-line of
construction works (Figure 2.11).
Blades
Blades are airfoils made of composite material, usually reinforced glass-fibre composites. The
blades are bolted to the hub either onshore or offshore.
4
http://newbedfordwindenergycenter.org/2017/09/dong-energy-predicts-13-15mw-wind-
turbines-by-2024/
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Generators
A wide range of turbines and generators regarding their power rating and their suitability to a
certain rotor diameter is commercially available. Due to the technical development in the last years,
many versions of a power rating of 2-4 MW are available, but recent trends enlarge as well rotor
stars as nacelles with generators, making 6-8 MW turbines state of the art and up to 12 or 15 MW
can be expected to be available in the near future (Figure 2.12 and Figure 2.13).
Figure 2.12 Percentage of Offshore Windfarm turbine types that are commercially available (n=90) or
installed as prototypes (n = 1) per various Power Rating (PR) categories (source: Graph derived
by processed data from 4coffshore database on wind turbines - October 2018, see Annex).
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Figure 2.13 Percentage of Offshore Windfarm turbine types that are commercially available (n=86) per
various rotor diameter (D) categories (source: Graph derived by processed data from
4coffshore database on wind turbines - October 2018, see Annex).
2.1.4 Electricity Collection and Transmission
Cables
Cables are needed to connect the offshore components starting from energy production at the
wind turbines over the sub-stations to the final destination at the consumption points (Households,
industry, infrastructure, transportation etc.). Cables connect the turbines and the windfarm to the
electrical grid. Collection cables connect the output of strings (rows) of turbines depending on the
configuration and layout of the windfarm. The output of multiple collection cables is combined at
a common collection point or substation for transmission to shore.
Inner-Array Cables
The inner-array cables (IAC) connect the wind turbines within the array to each other and to an
offshore substation. The turbine generator is low voltage (usually less than 1 kV, often 500600 V)
which is not high enough for direct interconnection to other turbines. A turbine transformer steps
up the voltage to 1036 kV for cable connection. Inner-array cables are connected to the turbine
transformer and exit the foundation near the mudline. Cables are buried 12 m below the mudline
and connected to the transformer of the next turbine in the string. The power carried by cables
increases as more turbines are connected and the cable size or voltage may increase to handle the
increased load: actually, 66 kV is becoming the base case for IAC voltage (EOLFI, WPD pers.
communication). The amount of cabling required depends on the layout of the farm, the distance
between turbines, and the number of turbines.
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Export Cable
Export cables connect the windfarm to the onshore transmission system and are typically installed
in one continuous operation. Export cables are buried to prevent exposure, and in some places,
may require scour protection. At the shore, cables come onshore and may be spliced to a similar
cable and/or connected to an onshore substation. Water depths along the cable route, soil type,
coastline types, and many other factors determine the cable route, installation time, and cost. At
the onshore substation or switchyard, energy from the offshore windfarm is delivered to the power
grid.
Export cables are composed of three insulated conductors protected by galvanized steel wire.
Medium voltage cables are used when no offshore substation is installed and usually range
between 24 and 36 kV. High voltage cables are typically 110225 kV (EOLFI, WPD pers.
communication and are used with offshore substations. High voltage cables have the capacity to
carry more power than a medium voltage cable but are heavier and wider in diameter (Figure 2.14).
Figure 2.14 Export cable layout in the German EEZ collecting power of different OWF-Clusters and landing
the power at two main shore landing points (left ©BSH 2018) and inner-park sub-station
(right, at Gunfleet Sands © Offshore Wind Power MarineServices)
Due to the high distances of some offshore windfarms e.g., in the German EEZ (Exclusive Ecopnomic
Zone) to the onshore interconnectors, a high-voltage direct-current (HVDC) transmission link is
often installed to minimize transmission loss.
2.1.5 Offshore substation
The purpose of an offshore substation is to increase the voltage of the electricity generated at the
wind turbine to minimize transmission losses. The substation is sized with the appropriate power
rating (MVA) for the project capacity, and steps up the line voltage from the collection system
voltage to a higher voltage level, usually that of the POI.
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All offshore windfarms require substations but not all substations are located offshore. The need
for offshore substations depends upon the power generated and the distance to shore which
determines the tradeoffs between capital expenditures and transmission losses (KAISER & SNYDER
2012 and references therein). The components of offshore substations include voltage
transformers, switchgear, back up diesel generator and tank, accommodation facilities, j-tubes, and
medium- and high-voltage cables. Substations are positioned within the windfarm at a location that
minimizes export and IAC distance. Substations are typically 500 tons or more and are placed on
foundations similar to those used for turbines (Figure 2.15). Onshore substations also include
equipment to monitor power quality, such as voltage stability and harmonic disturbances, and
SCADA (Supervisory Control and Data Acquisition) systems allow the behaviour of the entire system
to be monitored and controlled.
Figure 2.15 Substation at Alpha Ventus’ (source: https://www.tennet.eu/our-grid/offshore-projects-
germany/alpha-ventus/).
2.1.6 Associated components
Meteorological Systems
A met mast, to measure the meteorological environment is often among the first structures to be
installed at the potential windfarm sites (Figure 2.16). A mast collects wind data at multiple heights
to characterize the project area’s meteorology. Sensors collect data on vertical profiles of wind
speed and direction, air temperature and barometric pressure, ocean current velocity and direction
profiles, and sea water temperature.
Other moored systems for acquiring data on environmental parameters such as wind speed at
different heights above the water, wave heights and frequency, ocean currents include wind
measurement and oceanographic buoys. These instruments are often equipped with measurement
technology including LiDAR systems.
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LiDAR (Light Detection and Ranging) is a surveying method that measures distance to a target by
illuminating the target with pulsed laser light and measuring the reflected pulses with a sensor.
Differences in laser return times and wavelengths can then be used to make digital 3-D
representations of the target. Lidar can be used to increase the energy output from windfarms by
accurately measuring wind speeds and wind turbulence. Lidar systems can be mounted on the
nacelle of a wind turbine or integrated into the rotating spinner to measure oncoming horizontal
winds, winds in the wake of the wind turbine and proactively adjust blades to protect components
and increase power. Floating LiDAR systems located at points across a windfarm zone is another
alternative. Due to higher accuracy, cost reduction and less safety challenges associated with
offshore mast installations there is a tendency to replace the met masts with LiDAR systems.
Figure 2.16 Met tower in the German EEZ (© BioConsult SH 2011)
A scour protection serves to fix the ground around a structure driven into the seabed. Scour often
occurs where strong currents pass by an object with ground conditions being either sandy or
muddy. Scour protections often have diameter of 20-50m and thus inherit a remarkable footprint
with effect on the benthic community and by providing an alternative