Committee V.4: Offshore Renewable Energy
Authors: Kolios Atanasios , Kim Kyong-Hwan , Cheng Chen Hsing , Oguz Elif , Morato Pablo , Ralph Freeman , Fang Chuang , Ji Chunyan , Le Boulluec Marc , Choisnet Thomas , Greco Luca , Utsunomiya Tomoaki , Rezanejad Kourosh , Rawson Charles , Rodrigues Jose Miguel 
Published: April 2023

Committee Mandate
Concern for load analysis and structural design of offshore renewable energy devices. Attention shall be given to the interaction between the load and structural response of fixed and floating installations taking due consideration of the stochastic and extreme nature of the ocean environment. Aspects related to design, prototype testing, certification, marine operations, levelized cost of energy and life cycle management shall be considered.

Introduction
This is the sixth time that ISSC has included the Specialist Committee V.4 Offshore Renewable Energy, which started in 2006. Two members of the committee for this term (2018-2022) were involved in the work for the previous term (2016-2018), which formulates a good base for the cooperative work in the last three years.
The mandate of the committee was discussed at the beginning of the work, and it was slightly modified to include extreme environmental conditions and interaction of structures to the seabed, reliability-based design, safety and integrated design, topics which have been central to the discussion for developing offshore renewable energy, and hence should be discussed in the committee report. Another variation of this committee’s report has been the consideration of floating wind developments in a separate chapter as deployments are currently moving further offshore and in deeper waters, as well as the explicit reference to hybrid solutions.
Offshore wind energy still dominates offshore renewable energy technologies with extensive installed capacity and ambitious targets which constitute this technology as a key contributor towards the ambitious 2050 net zero emissions targets. For these targets to be achieved, it is imperative to innovate and further develop not only wind energy but also other offshore, marine and hybrid energy technologies, harvesting as much as possible the energy potential. Challenges related to wind energy include, among others, the upscaling at both a unit as well as a farm level, development of foundations relevant to deep waters, serial production of floating foundations and effective mooring systems, and investigation of support systems to inform end-of-life scenarios including service life extension, repowering or decommissioning. Marine renewables on the other hand, still need to overcome challenges related to structural response in extreme phenomena and reliability of mechanical components which sharply escalate the levelized cost of energy.
Within this report we have considered peer reviewed academic articles, selected conference proceedings and some reference industry reports. Overall, more than 500 sources have been reviewed and 350 have eventually qualified to be included in this state-of-the-art review. The time span of the review includes contributions from August 2017 to August 2021. The term of this committee has been extended due to the COVID-19 pandemic.
The report has been organized into 9 subsections. Following this short introduction, a session on bottom fixed wind turbines is included, following the structure of the previous committee’s report, with the addition of design provisions for extreme phenomena which are particularly relevant in South-East Asia and a subsection on advanced structural analysis. Next, a dedicated section on floating wind turbines is included, following a similar structure, with the addition of moorings and dynamic cables which is relevant to this class of foundations. Next three subsections present developments on wave energy converters, tidal and ocean current turbines, and other offshore renewable energy technologies and hybrid solutions. Following this, a subsection on life-cycle cost and operational management of offshore renewable energy is presented, identifying key cost elements that attract attention for research and development. Section 8 summarizes the efforts of the committee members to investigate a benchmarking study on the comparison of the existing design guidelines with respect to design of mooring systems. Finally, the last section of the report lists some conclusions which stem out of the review and key challenges that research should try to address in the next few years.