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Offshore wind projects are major investments and call for specialist expertise to design, plan and realise.

A crucial piece of the puzzle is the planning and design of submarine inter-array cables – vital connections on the seabed linking wind turbines to each other and offshore or onshore substations. Laying these cables is a complex and costly operation, requiring specialised vessels and crews, with cable installation making up a significant share of project budgets. That’s why energy developers are eager to streamline planning, cut costs and reduce complexity from the outset. 

Collaborating with developers in the feasibility phase, we identified a gap – a smarter way to optimise cable routes, lengths and specifications. Seeing the need for a digital tool, we developed a solution to enhance early planning, minimise rework and drive down costs. 

Enter OCTO - a digital tool to improve cable routing  

We set out to create a digital tool that optimises inter-array cable routing, blending our digital expertise with our experience in offshore wind design. 

Bringing together specialists from across our firm – including electrical engineers and software developers – we analysed, developed, and tested a range of potential methodologies to assess and refine our approach. The result of this innovation, collaboration, testing and deployment is our Offshore wind Cable Transmission Optimisation digital tool – OCTO. 

OCTO harnesses technology and industry insights to help developers design cost-effective inter-array cable layouts. It considers key design drivers such as the expected future cost of energy losses, electrical and cost parameters of different types of cable and local site constraints, enabling smarter planning and greater efficiency. We’re already applying OCTO to offshore wind projects across the globe. 

Offshore wind inter array cabling digital image

OCTO in use; an example of an inter-array cable layout for an offshore wind project. OCTO is Arup’s inhouse inter-array cable optimisation tool. 

Optimising the strategy for submarine inter-array cables 

Our goal was to develop a digital tool that optimises the strategy for submarine inter-array cables in offshore wind farms (OWFs). Designing electrical systems for OWFs is a complex, iterative process, requiring multiple rounds of planning across key disciplines to create a feasible and integrated design. We needed a tool that was both flexible – allowing for repeated investigations across projects – and adaptable to specific variables and requirements. 

With countless possible inter-array cable layouts, finding the optimal design depends on factors such as turbine and substation placement, seabed conditions, the wind resources and more. We set out to build a digital tool capable of integrating all these variables, performing mathematical analysis, and generating tailored recommendations. The tool had to balance cost considerations with technical constraints, helping clients make informed decisions on cable topology – whether string, branch, or back-tie structures – by weighing capital expenses against long-term efficiency and reliability. 

Beyond technical optimisation, our broader aim is to lower the cost of developing and operating OWFs, making offshore wind more accessible to a wider range of developers.  

Reducing costs, streamlining decision making 

OCTO helps drive down the cost of offshore wind farm (OWF) infrastructure while simplifying the complex decision-making process via digital technology. By optimising design and operation, it delivers significant efficiency gains, ensuring OWFs are cost effective and high performing. 

So far, we have used the tool to design inter-array cable layouts for eight clients across 14 projects and seven countries – optimising 1065 individual wind turbine generators (WTGs) with a total nominal rated capacity of 17.3 GW. These projects are in Australia, South Korea, Taiwan, Japan, Vietnam, Germany and Hong Kong.  

OCTO has empowered our teams to make decisions on critical project factors, from selecting cable layouts using string, branched, and back-tie structures to configuring networks with one or multiple onshore and offshore substations. It has also helped navigate complex site constraints, including environmentally sensitive areas, ports, maritime traffic corridors, existing subsea cables and defined project boundaries. 

OCTO’s optimisation has played a crucial role in reducing long-term costs by minimising electrical losses and lowering the risk of cable failures, ensuring greater reliability and efficiency for offshore wind projects. 

Scalable for the future

We are continuously enhancing OCTO software and code, allowing it to be integrating with other project-aligned software via application program interfaces (APIs) to give our teams and clients a more comprehensive view of each project.  

Further development will strengthen the connection between OCTO’s optimisation algorithm and downstream detailed electrical analysis, improving technical feasibility and unlocking even greater opportunities for optimisation. In the future, OCTO could transform the sector by enabling fully automated, end-to-end offshore wind farm array design. 

By reducing the costs of OWF development today, OCTO has the potential to scale its impact supporting more efficient infrastructure and contributing to global climate change mitigation. 

Ready to learn more? 

We are committed to supporting developers move confidently through the offshore wind feasibility stage. To learn more about OCTO and how it could benefit your development, reach out to our team.