Contents Page

1		Executive Summary
2		Introduction
2.1		Methodology
2.2		Offshore Operation and Maintenance Trends
2.3		Offshore Operation and Maintenance Outlook
3		Component Reliability
3.1		Rotor Blades
3.1.1		Blade Root Connection
3.1.1		Blade Repair
3.2		Tower
3.3.		Foundation
3.4		Drive Train
3.4.1		Gearbox
3.4.2		Generator
3.4.3		Direct Drive
3.5		Electrical Systems
3.5.1		Power Electronics
3.5.2		Transformers
3.6		Balance of Plant
3.6.1		Sub-Marine Conductors
3.6.2.		Electrical Layouts
4		Operation and Maintenance Management
4.1.		Strategic Considerations
4.1.1		Cost Considerations
4.1.2		Marine Conditions
4.1.3		Distance to Shore
4.1.4		Mobilization Resource
4.1.5		Project-Specific Considerations
4.1.6		Planned vs Unplanned
4.2		Preventive Maintenance
4.2.1		Scheduled Maintenance
4.2.2		Predictive Maintenance
4.3		Corrective Maintenance
4.4		Maintenance Optimization
4.4.1		Asset Life Stage Considerations
4.4.2		Remote Monitoring and Event Detection
4.5		Operation & Maintenance Cost
5		Logistics
5.1		Weather Window
5.2		Marine Access
5.2.1		Boat
5.2.2		Helicopter
5.2.3		Accommodation
5.3		Port Facilities
5.4		Ship Availability
5.4.1		Large Component Vessels
5.4.2		Cable-Laying Vessel
5.4.3		Service Vessel
5.4.4		Multi-Purpose Ship
5.4.5		Vessel Building Outlook
5.5		Cost Considerations
6		Health and Safety
6.1		Legislation
6.2		Incidents & Hazards
6.3		Training
6.3.1		Subsea Training
6.4		Nautical Considerations
6.4.1		Safety Zones
6.4.2		Crew Comfort
6.5		Cost
7		Conclusions
8		Other Information
9		Acknowledgements
10		About the Authors
11		References

List of Figures

Figure 1		Offshore Wind Turbine Component-Wise Failure Rates (Faulstich et al. 2011)
Figure 2		Bathtub Curve Reliability Distribution
Figure 3		Offshore Wind Turbine Failure Severity Landscape (WEU Survey 2011)
Figure 4		Offshore Timely Failure Rates (van de Pieterman et al. n.d.)
Figure 5		Wind Park Configuration (van de Pieterman et al. n.d.)
Figure 6		Damage Accumulation (van de Pieterman et al. n.d.)
Figure 7		Structural Failure and Material Damage Modes (McGugan et al. 2008)
Figure 8		LM Wind Power Blade Condition Monitoring System (Korsgaard 2004)
Figure 9		Offshore Wind Turbine Rotor Blade Bathtub Curve (Cavaco C. 2011)
Figure 10		Tower Damage Factors Breakdown (Mühlberg 2010)
Figure 11		Tower Coating Failure (Guy 2010)
Figure 12		Coating Repair Campaign (Guy 2010)
Figure 13		Offshore Wind Turbine Technological Foundation Landscape (Wybren 2011)
Figure 14		Transition Piece Grouting Improvement (DNV 2011b)
Figure 15		Corrosion in Offshore Wind Energy (van der Mijle Meijer 2009)
Figure 16		4MW PMSG Source (The Switch 2011)
Figure 17		Vibratory Sensor (Verbruggen 2010)
Figure 18		RMS Vibratory Response of a Bearing Pre and Post Replacement (Verbruggen 2010)
Figure 19		Middelgrunden Turbine Transformer Impact on Downtime and Production (J. Larsen et al. 2009)
Figure 20		Turbine Transformer Retrofit Campaign Cost Breakdown (J. Larsen et al. 2009)
Figure 21		Middelgrunden Transformer Replacement (J. Larsen et al. 2009)
Figure 22		Power Collection Grid Topology Outage Duration Comparison (Sannino B. K., 2007)
Figure 23		Conductor Cost Breakdown (GMS 2011)
Figure 24		Cable Fault Landscape (from 1959 to 2006)
Figure 25		Lillgrund String Connections and Power Collector System (Vattenfall 2011)
Figure 26		Lillgrund Offshore Substation (Siemens 2011)
Figure 27		Loss of Production Evolution as a Function of Distance to Port (Cavaco C. 2011)
Figure 28		Planned and Unplanned Maintenance Patterns (Cavaco C. 2011)
Figure 29		Annual In-Situ Interventions (WEU Survey 2011)
Figure 30		SCADA and CMS Alarm Resulting in Turbine Shutdown (WEU Survey 2011)
Figure 31		Analytical 5MW Wind Turbine Power Curve (Wind Energy Update 2011)
Figure 32		Condition-Based Monitoring Repair Strategy Example (Verbruggen 2010)
Figure 33		Gearbox Condition Monitoring
Figure 34		Failure Rate of Sensors Compared to other Turbine Components
Figure 35		Maintenance Strategy Allotted Budget Breakdown (WEU Survey 2011)
Figure 36		Corrective Maintenance Data from OPEX Calculations (Trollnes S. 2010)(WEU Survey 2011)
Figure 37		Risk-Based Decision Tree for O&M Planning (Jessen Nielsen & Dalsgaard Sorensen 2010)
Figure 38		Modified Bathtub Curve for Serial Failure (Olme 2009)
Figure 39		OPEX Budget Breakdown (WEU Survey 2011)
Figure 40		Performance-Based Access and Transfer Design Process (DNV 2011a)
Figure 41		Critical Resource to O&M Activity Execution (WEU Survey 2011)
Figure 42		Example Weather Window for a Monohul Crane (Costache 2010)
Figure 43		Cumulative Distribution Function of the Weather Window (Bussel & Bierbooms 2005)
Figure 44		Offshore Wind Supply Vessel (Catamaran Style) (Force 3 Offshore 2011)
Figure 45		Offshore Wind Support Crew (Force 3 Offshore 2011)
Figure 46		SWATH Boat (Maritime Journal 2010)
Figure 47		Fob Lady Access Boat (Offshore Windservice APS 2011)
Figure 48		Ampelmann’s Active Motion Compensation Gangway System (AMPELMANN 2011)
Figure 49		Offshore Access System (Arabian Oil and Gas 2008)
Figure 50		Helicopter Access to the Nacelle Top (Wind Energy The Facts 2011)
Figure 51		BARD 1's BorWin Alpha's Transformer and Accommodation Platform (Finnern 2010)
Figure 52		Maximum Conditions for Current Installation Vessels (Skiba 2010)
Figure 53		Nexans’ Offshore Skagerrak Cable-Laying Vessel (Scottish Enterprise 2011)
Figure 54		Export Cable Carousel
Figure 55		Export Cable Carousel
Figure 56		Dual Sword Cable Trenching ROV (Blue Offshore 2011)
Figure 57		Singe Sword Cable Trenching ROV (Blue Offshore 2011)
Figure 58		Wind farm sizes and distance to shore from 1991 to 2009 (Oliver Heinecke 2010)
Figure 59		Multi-Purpose Maintenance Vessel Rendering (Scandoil 2011)
Figure 60		DNV-OS-J201 Standard (DNV 2011a)
Figure 61		Emergency Flow Chart Example (GL Garrad Hassan 2011a)
Figure 62		Serious HSE Incident Frequency (Statoil 2011)
Figure 63		Total Recordable HSE Injury Frequency (Statoil 2011)
Figure 64		Immediate Incident Cause Breakdown (GL Garrad Hassan 2011a)
Figure 65		Emergency Response Training (Nielsen 2002)
Figure 66		Emergency Rescue Training (Nielsen 2002)

List of Tables

Table 1		Severity Rating of Failure Mode and Effect Analysis (Durham University, 2011)
Table 2		Failure Mobilization Requirement (Kotsonis 2010)
Table 3		Damage Classification of Offshore Rotor Blades (CP.MAX 2011)
Table 4		Rotor Blade Failure Rates (Cavaco C. 2011)
Table 5		Offshore Wind Turbine Blade Reliability (Sørensen 2007)
Table 6		Blade Aging Timeline (Cavaco C. 2011)
Table 7		Offshore Wind Tower Coating Protection Cost (Guy 2010)
Table 8		Offshore Wind Tower Coating Protection and Offshore Repair Cost Estimation
Table 9		Gearbox Failure Rates (Cavaco C. 2011)
Table 10		Generator Failure Rates (Cavaco C. 2011)
Table 11		Electrical System Failure Rates (Cavaco C. 2011)
Table 12		Control System Failure Rates (Cavaco C. 2011)
Table 13		Offshore Wind Turbine Gearbox and Generator Details
Table 14		Turbine Transformer Failure Rate and MTTR (Holmstrom & Negra 2007)
Table 15		Conductor Failure Rate (Sannino B. K., 2007)
Table 16		Seasonal Mean Time to Repair (Sannino B. K., 2007)
Table 17		Switchgear Failure Rate (Sannino & Breder, 2006)
Table 18		O&M Element Cost Estimate (Cavaco C. 2011)
Table 19		Availability Category (GL Garrad Hassan 2011b)
Table 20		Component-Based Monitoring Examples
Table 21		UK Offshore Round I Economics (10% Discount Rate)
Table 22		Access System Wave Height and Wind Speed Acceptance (Bussel & Bierbooms 2005)(Kotsonis 2010)
Table 23		Maintenance Actions for an Offshore Wind Farm and Their Occurrence (Tveiten 2011)
Table 24		Jack-Up Vessel Market Potential (Nerland 2010)
Table 25		Vessels Used in Offshore Wind Farm Construction in Europe (Kaiser & Snyder 2010)
Table 26		Specification for Newly Built Vessels (Kaiser & Snyder 2010)
Table 27		OPEX Generic Project Cost Breakdown (Scottish Enterprise 2011)
Table 28		Hazards for O&M Work in Offshore Wind Farms (Tveiten 2011)
Table 29		Training Requirements at Lillgrund Offshore Wind Farm (Vattenfall 2011)

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