Operation & Maintenance (O&M)
Overview
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The major goals of operations and maintenance are to maintain the equipment and personnel's safety, increase the wind farm's availability and efficiency, reduce downtime and intervention costs, and adhere to contractual and regulatory obligations. Depending on the nature, size, and location of the wind farm, as well as the accessibility of resources and technology, O&M tactics might change.
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​Vessels are needed for maintenance and repair work on offshore wind farms. In the offshore wind energy sector, there are two basic types of O&M boats: vessels for major maintenance and vessels for minor maintenance.
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A crew transfer vessel (CTV) and a service operation vessel (SOV) are two types of vessels that are used in offshore wind farm operations.
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The UK is a dominant offshore wind energy market, with England being the center of most offshore wind activity. The world's largest offshore wind farm, Hornsea 1, is situated off the coast of Yorkshire. In line with the country's green energy goals, the UK government has set a target of achieving 40 GW of offshore wind capacity by 2030 [6].
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However, offshore wind farms face considerable challenges due to harsh marine environments, including strong winds, waves, corrosion, and marine growth, that can adversely impact their performance and reliability. To address these issues, offshore wind farms' operation and maintenance (O&M) play a critical role in ensuring optimal efficiency and safety [7].
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O&M activities encompass a range of duties, such as logistics, inspection, monitoring, diagnosis, repair, and replacement. These activities aim to minimize breakdowns and accidents that could endanger the environment and the safety of the workforce while reducing the levelized cost of energy (LCOE) of offshore wind power. O&M plans should be designed considering the trade-offs between performance, risk, and cost, as well as the UK offshore wind industry's long-term objectives and vision, including achieving net-zero emissions by 2050 [2].
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O&M costs for offshore wind farms in the UK are estimated at around £9 billion per year, with expenses being higher than for onshore wind farms due to the challenges of reaching offshore wind farms. The life cycle costs of offshore wind farms are significantly impacted by O&M costs, with an estimated impact of €2-4 cents/kWh [5].
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The primary objectives of O&M activities are to maintain the effectiveness of the wind farm, reduce downtime and intervention costs, and adhere to contractual and regulatory obligations. O&M methods can vary depending on wind farm size, location, and accessibility of resources and technologies. Vessels for maintenance and repair activities are essential components of offshore wind farms, with two main categories of O&M vessels in the offshore wind energy market: vessels for minor maintenance and vessels for major maintenance. Crew transfer vessels (CTVs) and service operation vessels (SOVs) are commonly used for O&M activities.
Crew Transfer Vessels: CTVs
Crew Transfer Vessels (CTVs) are a popular vessel used in the UK offshore wind farm industry to transfer personnel and equipment to and from offshore wind turbines. CTV’s are responsible for minor & medium repairs and annual services.​They can reach and transfer people and equipment safely and effectively, even in adverse weather and sea conditions, because of their swift, agile, and manoeuvrable design. CTVs are made of lightweight materials like aluminium or composite to maximise fuel efficiency and reduce their environmental impact. They usually have a length of 20 to 40 metres. They can move up to 30 knots thanks to their strong propulsion and engine systems. 12 people, including crew and technicians, can normally fit on CTV vessels in offshore wind farms. It has a range of up to 60 nautical miles and a maximum operating time of 12 hours at sea. Compared to an SOV, it has a lower initial cost but a higher operating cost. Compared to an SOV, it uses more gasoline and needs more maintenance [4].
CTVs have become increasingly common in the UK offshore wind industry, with a growing number of vessels being commissioned to support the country's expanding offshore wind farm portfolio.
Service Operation Vessels: SOVs
Service Operation Vessels (SOVs) are specialised vessels with advanced features and equipment allowing safe and efficient maintenance and operation in harsh marine environments. SOV’s are responsible for major maintenance and major repair. Even in difficult offshore circumstances, technicians can operate on sturdy platforms due to their design. An SOV may sail for up to 30 days and operate 150 nautical miles from land. It is more suited for long-term and far-reaching operations. Compared to a CTV, it uses less fuel and needs less upkeep. As it is less impacted by weather and sea states than a CTV, it also offers superior availability and dependability. They can be deployed in combination with CTVs employing the mothership concept [4].
The fundamental benefit of deploying an SOV over other vessel types, such CTVs or conventional O&M Vessels, is that they can stay offshore for prolonged periods , allowing maintenance workers to operate on the wind turbines for longer periods without the need for regular staff exchanges. This may lead to considerable cost reductions and improved productivity.
CO2 EMISSION IN O&M BY VESSELS
CO2 emission is a primary environmental concern for the offshore wind industry, especially during the wind farm lifecycle's operations and maintenance (O&M) phase. There is 20.4% of total CO2 emission for the O&M section, according to Figure 1 [3].
Figure 1: %Total CO2 emission for offshore wind farm
O&M activities require extensive marine logistics between the shore and the wind farm, involving different types of vessels. These vessels typically use marine fuel, which emits greenhouse gases such as CO2 when burned. According to a recent report by the Department for Transport and the Foreign, Commonwealth and Development Office, the O&M vessels in the North Sea offshore wind sector are responsible for an estimated 284 kt CO2e/year [8] .
To reduce the CO2 emission from O&M vessels, the offshore wind industry needs to adopt clean maritime innovations that can improve marine logistics' efficiency, performance and sustainability [8].
Turbine Failures
Offshore wind turbines are a promising source of renewable energy, but they also face various challenges and risks. One of the major issues is the failure of components or systems, which can lead to downtime, reduced performance, increased costs, and safety hazards. Offshore wind turbine failures can be classified into three categories: major, minor, and major replacement.
Major failures are those that require significant repairs or replacements of components or systems, such as blades, gearboxes, generators, or transformers. These failures can cause long periods of outage and high costs. Some of the causes of major failures are temperature problems, hydraulic system problems, malfunctioning anemometers, cooling system problems, misaligned wind directional tracking system, poor pitch alignment or calibration, badly balanced rotor, poor control parameters, mechanical breakdowns due to larger turbines, serial defects due to faster development, and material failures due to fatigue or corrosion [1].
Minor failures are those that require minor repairs or adjustments of components or systems, such as sensors, cables, switches, or valves. These failures can cause short periods of outage and low costs. Some of the causes of minor failures are electrical faults, software glitches, human errors, or environmental factors [1].
Major replacement failures are those that require complete replacement of the offshore wind turbine or its foundation. These failures can cause permanent loss of the turbine and very high costs. Some of the causes of major replacement failures are structural damage due to extreme weather events, collisions with ships or icebergs, fires or explosions, or foundation failure due to scouring or erosion [1].
Offshore wind turbine failures can be prevented or mitigated by improving the design, quality, reliability, and maintenance of the components and systems. It is also important to monitor the performance and condition of the offshore wind turbines and conduct regular inspections and tests by O&M.
Reference
[1] Castellà, X. (2020). OPERATIONS AND MAINTENANCE COSTS FOR OFFSHORE WIND FARM ANALYSIS AND STRATEGIES TO REDUCE O&M COSTS. Available at: https://upcommons.upc.edu/bitstream/handle/2117/329731/master-thesis-xavier-turc-castell-.pdf.
[2] Department for Business, Energy & Industrial Strategy (2020). The Ten Point Plan for a Green Industrial Revolution (HTML version). [online] GOV.UK. Available at: https://www.gov.uk/government/publications/the-ten-point-plan-for-a-green-industrial-revolution/title.
[3] HaskoningDHV, R. (2020). Norfolk Boreas Offshore Wind Farm Carbon Footprint Assessment. [online] Available at: https://infrastructure.planninginspectorate.gov.uk/wp-content/ipc/uploads/projects/EN010087/EN010087-002432-Carbon%20Footprint%20Assessment.pdf.
[4] Lazakis, Iraklis, and Shahroz Khan. “An Optimization Framework for Daily Route Planning and Scheduling of Maintenance Vessel Activities in Offshore Wind Farms.” Ocean Engineering, vol. 225, 1 Apr. 2021, p. 108752, www.sciencedirect.com/science/article/pii/S0029801821001876, https://doi.org/10.1016/j.oceaneng.2021.108752. Accessed 31 Mar. 2021.
[5] Rene van de Pieterman. “Cost Modeling for Offshore Wind Operations and Maintenance.” Renewable Energy World, 10 Apr. 2013, www.renewableenergyworld.com/om/cost-modeling-for-offshore-o-m/#gref. Accessed 7 May 2023.
[6] Simon Brett (2021). Can the UK meet its 40GW by 2030 offshore wind target? [online] RenewableUK Blog. Available at: https://www.blog.renewableuk.com/post/can-the-uk-meet-its-40gw-by-2030-offshore-wind-target.
[7] Tomaselli, P.D., Dixen, M., Bolaños Sanchez, R. and Sørensen, J.T. (2021). A Decision-Making Tool for Planning O&M Activities of Offshore Wind Farms Using Simulated Actual Decision Drivers. Frontiers in Marine Science, 7. doi:https://doi.org/10.3389/fmars.2020.588624.
[8] “UK Launches Operation Zero to Decarbonise Offshore Wind O&M Vessels.” Www.nautilusint.org, 11 Nov. 2021, www.nautilusint.org/en/news-insight/news/uk-launches-operation-zero-to-decarbonise-offshore-wind-om-vessels/. Accessed 7 May 2023.
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