Offshore wind installation costs - A comparative assessment for UK offshore rounds 1, 2 and 3
2, Federico D'Amico2, Philipp Thies1, Rafet Kurt4, Gareth Harrison3
1University of Exeter, Exeter, Devon, UK, 2EDF Energy R&D, Croydon, London, UK, 3University of Edinburgh, Edinburgh, Midlothian, UK, 4University of Strathclyde, Glasgow, Lanarkshire, UK
Marine operations play a pivotal role throughout all phases of a wind farm's life cycle. In particular uncertainties associated with offshore installations can extend construction schedules and increase the capital expenditure (CAPEX) required for a given project. Installation costs typically account for about 1/3 of the overall project cost. Therefore, informed engineering decisions and uncertainty reductions in this area hold the potential for risk and cost reductions. One of the governing factors are uncertainties in weather downtime for installation vessels, which can incur significant cost fluctuations. This has driven the creation of a variety of software tools in the offshore wind sector to predict installation schedules, assess the bids from participating contractors, optimise planning and identify the subsequent financial allowance required to cover these associated costs.
This paper considers the installation modelling for UK offshore Wind Rounds 1, 2 and 3. Through detailed sensitivity studies of key windfarm characteristics such as distance to shore and the number of turbines, an assessment of vessel performance was completed for generic representative sites for each round by comparing the sensitivities of predicted durations. The results provide a quantification of installation vessel performance, approximated costs and the associated deviations. The derived sensitivities can be used as measure of installation risk to support planning, management and efficient use of project resources.
The analysis is based on time-domain predictions for the completion of key installation operations under user specified exceedance probabilities. Installation vessel technology is analysed to reveal if modern vessel designs will reduce observed OWF installation costs. Three representative installation strategies are used including typical vessel spreads and operational limits. These fixed variables are used in conjunction with upper and lower boundary values for specific parameter distributions of the project characteristics for each round. The software tool considers risk as delays to the installation, imposed by adverse weather conditions applied across the vessels' operability characteristics. The Vessel type and day rate used for each installation phase, is then applied to provide an approximation of the installation costs for the key operations across the three installation rounds.
The results indicate that the lowest downtime and costs are associated with Round 1, which is justified by the sheltered near-shore location of these sites, meaning the vessels were protected from severe weather conditions expected at Rounds 2 and 3 sites. This is affirmed with the results for Round 2 which exhibits the largest downtime and resulting costs. The higher cost is caused by the limitations of the vessels employed for these installations and high costs associated with the heavy lift vessels employed for the foundation and transition piece installations. The Round 3 results suggest that the evolution of vessel technology is able to reduce downtimes and installation costs despite the larger distance to shore and the more challenging weather conditions expected for these projects.
The installation phases predicted to have the largest installation risk, highlight areas where precautionary or mitigation steps may be required when chartering vessels with similar capabilities. The paper finds that the selection of the vessels identified in Round 1, would generally result in acceptable costs but there may be significant variation in the Foundation, Transition Piece and Turbine installation phases, highlighting potential risk associated with these operations. The vessels specified for Round 2 exhibit considerably less variation but the generally large downtimes in comparison to Round 1, lead to significantly higher cost estimations. The results for Round 3 demonstrate reduced risk and costs similar to Round 1, demonstrating that modern vessels can contribute to the overall CAPEX reductions for more challenging installation characteristics.
This paper assesses the environmental capabilities of the vessels and aims to identify those aspects of vessel design which may be key in meeting the needs of this industry and to offer guidance on vessel charter. As the study has been compartmentalised by UK offshore wind rounds it is intended that operatives will be able to assess which round of characteristics relate to their project and refer to the vessel cost predictions. It is confirmed that the evolution of installation vessel technology has addressed the needs of offshore wind development as projects extend into deeper and more challenging waters. Beyond this the developed approach will be useful to assess installation risks for current and future offshore wind deployments.