Yalcin Dalgic

Offshore wind turbine technology is moving forward as a cleaner alternative to the fossil fuelled power production. However, there are a number of challenges in offshore; wind turbines are subject to different loads that are not often experienced onshore and more importantly challenging wind and wave conditions limit the operability of the vessels needed to access offshore wind farms. As the power generation capacity improves constantly, advanced planning of Operation and Maintenance (O&M) activities, which supports the developers in achieving reduced downtime, optimised availability and maximised revenue, has gained vital importance. In this context, the focus of this research is the investigation of the most cost-effective approach to allocate O&M resources which may include helicopter, crew transfer vessels, offshore access vessels, and jack-up vessels. This target is achieved through the implementation of a time domain Monte-Carlo simulation approach which includes analysis of environmental conditions (wind speed, wave height, and wave period), operational analysis of transportation systems, investigation of failures (type and frequency), and simulation of repairs. The developed methodology highlights how the O&M fleets can be operated in a cost-effective manner in order to support associated day-to-day O&M activities and sustain continuous power production.

In far offshore, challenging climate conditions limit the operability and the accessibility of the maintenance vessels significantly.Furthermore, if significant time is spent for the travels between offshore wind farm and O&M port; maintenance tasks cannot be carried out. A mothership can provide the solution for the operators. Due to the fact that the mothership can be moored to a close location to the offshore wind farm, the reaction time to the failures can be minimised; thus the availability of the offshore wind farm can be maximised. In this context, the focus of this research is the cost benefit analysis of the mothership concept and the investigation of the optimum operational practice, which brings financial and operational benefits. This is achieved by performing operational simulations in the offshore wind operational expenditure and logistics optimisation tool StrathOW-OM, which is developed by the University of Strathclyde and commercial partner organisations. Results show that significant time is spent between offshore wind farm and port, which increases the downtime. October-December is identified as the most critical period for chartering a mothership.

Offshore wind projects are moving towards deeper waters and more distinct locations in order to capture stronger winds and eventually increase power productivity. However, challenging climate conditions limit the operability and accessibility of the maintenance vessels significantly; therefore, the turbine downtimes due to vessel inaccessibility become dominant. Moreover, offshore wind farm operators in the UK only perform maintenance activities if there is enough daylight at the offshore wind farm in order to prevent potential accidents. These major difficulties influence the power production undesirably and increase the financial risks of the operating offshore wind farms. In this context, the focus of this research is the investigation of operational and financial benefits that multiple working shifts can bring to the operating offshore farms and the influence of the offshore wind farm location on the operational decisions. The operational simulations are performed by the offshore wind operational expenditure and logistics optimisation tool StrathOW-OM, which is developed by the University of Strathclyde and commercial partner organisations within Technology Innovation Centre (TIC) project. StrathOW-OM examines climate parameters (wind speed, wave height, and wave period) in the offshore wind farm location, size and operational characteristics of the maintenance fleet, failure rates of the turbine components. The operational simulations are performed through multiple scenarios in order to identify the most cost efficient solution. The developed methodology enables offshore wind farm operators to define the O&M fleet composition and highlights how the maintenance fleet is optimally scheduled on a daily basis.

The offshore wind industry, which aims to reduce the operational costs, usually achieved through learning curves and supply chain improvements, has seen drastic cost increase over the last five years. In order to sustain the competitiveness of the offshore wind industry against other renewable energy sources, the cost of offshore wind needs to come down to today's onshore cost. This cost reduction target can be achieved through optimising the offshore related operations which contribute the most to the operating expenditures (OPEX) of the offshore wind farms. In this paper, the investigation of optimum crew transfer vessel fleet, which indicates the influence of fleet size and characteristics of the vessels involved in the operations, is introduced with a focus on power production, total cost of the Operation and Maintenance (O&M) and revenue loss. A time domain Monte-Carlo approach is adopted while taking into consideration the climate parameters, failure characteristics of turbine components, the specification of crew transfer vessels, and the composition of vessel fleet. Through this extensive study, it is concluded the O&M related costs can be reduced significantly while the availability and the productivity of the turbines can be increased by optimising the use of the O&M vessel fleet in terms of fleet size and vessel capabilities.

Operating further from shore increases the logistic challenges of offshore wind Operation and Maintenance (O&M) activities. Therefore, available vessels in the market and the variety of benefits & drawbacks of different vessel chartering strategies have to be considered in the O&M planning. In contrast with the prospects, operating expenditure (OPEX) of the offshore wind farms has been increasing, reflecting greater risk for potential investors and current operators. In this context, significant cost reductions can be achieved through optimising the offshore related operations, considering the fact that vessel associated costs dominate the total OPEX of the projects. In this paper, the investigation of optimum chartering strategy for jack-up vessels, which indicates the influence of the chartering strategy, charter period, and the characteristics of the vessels involved in the operations, is introduced. Climate parameters, failure characteristics of turbine components, and the vessel specifications are synthesised in a time domain Monte–Carlo approach. The results can assist operators in developing long-term O&M plans. Through this extensive study, it is concluded that optimum O&M cost can be achieved by selecting optimum chartering strategy for jack-up vessels. In addition, regional collaborations between different offshore wind developers can be an alternative solution to reduce the O&M costs.

This paper analyses the degree to which lifetime production and availability figures are subject to variation due to inherent inter annual climate variations. This is achieved by performing operational simulations based on different measurement periods chosen from 10 years of historic wind and wave data in the North Sea, establishing the financial implications this has for the industry. The investigation is carried out using a robust Monte Carlo simulation climate and lifetime operational expenditure model. Significant variations are observed with regards to availability, power production and OPEX costs with OPEX costs varying by 15% above and below the average value when a single year is used for the simulation input. It has also been demonstrated that results with similar availability predictions can have divergent power production and OPEX results. This is explained by the correlations between wind speed, wave height, accessibility and power production. The best practice to minimize uncertainty in cost projections from short term measurement campaigns has been identified.

Operation and Maintenance (O&M) contributes a significant share of the expenses during the lifetime of offshore wind farms. When compared to onshore wind, O&M costs are increased, due to the use of specialised vessels, shorter weather windows and challenging environmental conditions. Furthermore, increased frequency of failures, longer downtime and limited accessibility create uncertainties in the planning stage of the O&M tasks. In order to decrease the cost of power generation and increase the competitiveness of offshore wind industry against other alternative energy sectors, it is essential to keep the costs of the vessel fleet used for O&M tasks at minimum level while providing sufficient support to sustain power generation. In order to address these issues, the focus of this paper is to provide decision support for the selection of a Crew Transfer Vessel (CTV) fleet for the offshore wind farm maintenance operations. This is achieved through analyses of environmental conditions, investigation of failures, and assessment of vessel operations. The developed methodology and analysis enable operators to decide the specification of CTVs which will bring the optimum financial benefit, considering both the enhancement of the offshore wind farm power generation as well as the minimisation of the total O&M cost.

Estimating the cost of vessels is an important factor in the Operation & Maintenance (O&M) costs of offshore wind farms. Accurate cost estimation is required during the operation of the wind farm. This paper presents the development of the O&M charter rate modelling for offshore wind turbine jack-up vessels under different operational strategies. The main objectives of this modelling are to explore the differentiation of charter rates associated with the charter periods and with the capabilities of different vessels; as well as to allow offshore wind farm operators to plan their maintenance strategies by considering the share of vessels’ costs in the overall maintenance costs. In this respect, various jack-up vessels in the offshore wind industry are investigated and the most effective charter periods are identified. The seasonal effects on the charter rates are also considered to provide critical insight into the selection of the optimum charter rate scenario.