Apollo, in collaboration with DOF for ORE Catapult, developed a comprehensive study addressing the challenges and solutions for installing a Gigawatt-scale floating offshore wind farm, focusing on cost, schedule, and innovative methodologies to overcome critical installation bottlenecks.
The problem
The installation of a single, state-of-the-art floating offshore wind turbine (FOWT) with its mooring lines and infield cables is a significant offshore marine operation. To develop a Gigawatt-scale floating wind farm, sixty FOWTs will be required.
This is an order of magnitude greater than current 10MW to 100MW demonstrator projects, and installation presents a major challenge of scale.
The background
The work was performed by Apollo and DOF on behalf of the ORE Catapult’s Floating Offshore Wind Centre of Excellence.
Apollo has developed detailed reports to understand exactly how a Gigawatt-scale floating wind array will be installed, how much it will cost, and how long it will take. The focus of this work is on installation step changes, which have the potential to address critical installation bottlenecks.
The process
Focusing on the requirements of the UK sector, the study explores methodologies, schedule, and cost implications for a representative 100m water depth, 900 MW ScotWind site. Typical vessels and port facilities are assumed in an investigation of how to pre-install the mooring components, tow-out the commissioned FOWTs, connect the moorings and install the dynamic cables.
A ‘base case’ installation method was developed, by scaling up current practice for demonstrator floating wind arrays, which itself is built on oil and gas and fixed wind experience. Looking to emerging solutions, ‘future case’ installation scenarios were detailed to explore their potential impact.
The details
The headline gigawatt-scale installation costs are equivalent to the mooring and cable system purchase costs; therefore, design for installation is a critical consideration. The costs exclude weather downtime; a major installation bottleneck is scheduled running into the winter season, which drives project risk and installation costs.
A serious bottleneck was identified as the availability of AHTS capable of handling 175mm chain. Unless the global fleet of highly capable AHTS vessels grows substantially in the next decade, it may prove impossible to source vessels to handle the required construction and tow to port demand at acceptable cost.
The solution
Approaches to accelerate the schedule and protect against emergent delays have been identified:
- Use of taut nylon moorings, which enable a more efficient mooring pre-installation process by avoiding long lengths of heavy catenary chain.
- If drag anchors are used, there are clear opportunities to follow a smarter risk-based approach to anchor tensioning requirements.
- A novel installation method – modelled on O&G umbilical installation – allows cable pull-in time to be halved, with installation completed earlier in the year and at significantly lower cost.
- Using quick connect systems could reduce cable pull-in costs even further and represent an opportunity to optimise a system for both installation and maintenance.
The outcome
Understanding the challenges of the installation process early helps developers to make better decisions.
The findings of this study will help developers and the supply chain to inform their project front end engineering design (FEED) scoping and technology development activities.
Feedback
Sean Snee, Team Leader for Floating Offshore Wind at ORE Catapult, said: “This project is extremely valuable to the industry as it highlights an important topic of floating offshore wind installation at gigawatt scale. The insights and outcomes delivered in this report, demonstrate some of the methodologies proposed to be utilised for floating offshore wind, as well as highlighting some of the challenges to be overcome.”
“The £145k investment in this study underscores the importance of understanding the challenges of gigawatt-scale floating wind installation early on,” commented Apollo’s Offshore Renewable Director, Nigel Robinson. “By examining different mooring and cable system designs and their influence on the overall installation scope, we can make informed decisions that drive progress in the offshore renewable energy sector.”
DOF shared their enthusiasm for the study, with Karl Daly, VP Renewable, stating, “This study marks a pivotal advancement in deploying gigawatt-scale floating offshore wind projects. By focusing on practical vessel-specific case studies, we gain valuable installation insights that enable us to enhance scalability and efficiency. This collaborative effort underscores our commitment to refining the complexities of floating offshore wind.”
Full Report
For more information and to access the full report, visit: https://fowcoe.co.uk/industry-insights/reports/gigawatt-scale-cable-and-mooring-installation/
Get in touch: renewables@apollo.engineer
