Cable System Engineering Cost Reductions for Deepwater Floating Offshore Wind

Event:
Global Offshore Wind Conference
Date:
June 2018
Author:
Gilles Gardner, Renan Tapias

Hywind’s installation in 2017 was a watershed moment for floating offshore wind which marked the transition of the technology from pilot projects into an early demonstration of commercialisation. This transition was naturally accompanied by the subject of scale. The advent of large floating wind farms introduces the opportunity to leverage economies of scale in order to achieve cost reductions. One approach to achieving this is through optimisation of the cable configuration.

Along the extensive coastline of several countries in Europe, 80% of potential offshore wind projects are located in water depths greater than 60m. Additionally, one of the largest potential markets for floating offshore wind turbines is located in North America. Approximately 60% of potential US offshore wind projects are located in deeper water (>200m water depth). Each of these areas will require robust subsea solutions. Floating offshore wind turbines present the additional challenge of designing a subsea system that absorbs the vertical motions in the array cable, effectively stopping them from being transmitted in ways that will cause damage over time.

The touchdown point is a critical area for the failure of cables particularly in highly dynamic applications. In order to mitigate fatigue and over bending issues at the array cable touch down point, subsea arches are often considered. These structures isolate the motion of the floating wind turbine unit from the cable touch down point, vastly reducing the loading at the critical bending location. Subsea arches present added cost to a project through materials, additional foundations and extended installation durations, which might not always be the most cost-effective solution. The optimisation of the cable configuration design to minimise the cost impact through serial production and installation campaign
sequencing are discussed.

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