International Marine Energy Journal

The advantages and challenges of DC collection grids for offshore floating PV

Oscar Delbeke — 2025-09-16

Offshore floating photovoltaics, tidal turbines and wave converters face similar challenges in terms of grid integration: electrical power must be transferred over long distances through a reliable and efficient grid connection. Whereas AC power collection systems are considered the industry standard for large-scale photovoltaics and (offshore) wind systems, a DC power collection grid may be more suitable for offshore floating photovoltaics. This work provides a qualitative discussion on the advantages and challenges tied to the grid integration of offshore floating PV systems through DC collection grids. The proposed advantages include reduced transmission and power conversion losses, improved power density, reliability, power quality, efficient integration with energy storage and high-voltage DC links, and flexibility in power flow control. Whereas many of these advantages apply onshore as well, this work argues that reduced transmission losses, improved power density and reliability benefits are more significant offshore. To unlock this potential however, challenges such as high capital costs, adequate protection, dynamic grid stability and lack of standards must be addressed.

Review of recent WEC-Sim (v6.1) advanced features

Jeff Grasberger — 2025-09-16

WEC-Sim (Wave Energy Converter SIMulator) is an opensource software for modeling the motions, loads and power generation of wave energy converters. WEC-Sim performs simulations in the time domain using hydrodynamic coefficients calculated by boundary element method (BEM) frequency-domain potential flow solvers such as WAMIT, NEMOH, Capytaine, or Ansys AQWA. WEC-Sim development is ongoing, including various features, applications, and example cases used to demonstrate potential use-cases to meet the needs of the growing marine energy industry. Through input from a broad user base and an extensive team of developers and collaborators, new features of WEC-Sim are developed to expand the software’s use cases and improve overall functionality. Three new WEC-Sim features highlighted in this paper include updating WEC-Sim to be compatible with MoorDyn Version 2, incorporation of second order excitation loads (quadratic transfer functions) and allowing for dynamically changing hydrodynamics.

Frequency array and wave phase realizations for wave energy converter control optimization

Jeff Grasberger — 2025-09-16

Vital to the progression of the wave energy industry is wave energy converter optimization which often relies on frequency-domain evaluations, utilized for efficiency as compared to time-domain. Despite being an integral factor in the resultant solution, the frequency array is rarely described in such studies. This study shows the impacts of the frequency array components and illustrates a general process by which to select a proper frequency array. The main factors to consider are the range and number of frequencies. Furthermore, this study introduces irregular wave phase realizations and suggests the importance of optimizing the system for multiple random sets of wave component phase. Ultimately, the importance of proper selection of both the frequency array and wave phase realizations to the optimization solution is demonstrated for the Pioneer WEC using WecOptTool.

O&M strategies for offshore renewable energy projects in Chile: a comparative analysis

Gonzalo Tampier — 2025-09-16

Operation and maintenance (O&M) are fundamental aspects to study in offshore renewable energy (ORE) projects, due to high economic costs, operational difficulties involved and the immaturity of its development in emerging markets. In this study, a geo-referenced, time-domain discrete event simulation tool is presented, designed to evaluate the life cycle of ORE projects, evaluating different sites, technologies and O&M strategies at an early stage, to support decision-making of project developers and government entities. Using environmental (behind cast) and operational parameters (e.g. port closure criteria), the performance of devices at a site is evaluated, generating information about the energy production and downtime of devices and their effect on total energy production. Considering that maintenance is subject to environmental and operational limits for operations such as cargo handling or crew transfer, the current tool integrates the operational characteristics of both the device and the involved vessels, which are obtained from numerical simulations or model scale experiments. As an application example, a comparison of the effect of selecting monohull- or SWATH-type SOVs (service operations vessels) on a floating wind energy pilot project located in central Chile are presented.

Destructive testing and failure analysis of a full-scale composite tidal turbine blade

Fergus Cuthill — 2025-09-16

Tidal stream turbines play a pivotal role in harnessing marine energy, yet their reliability remains a critical challenge, impeding the cost-effectiveness of tidal energy. Deviations in blade performance can significantly impact turbine efficiency, potentially leading to unbalanced loads and consequential damage to the turbine and ad- jacent blades. Experience of blade failure, attributed to factors including material fatigue, manufacturing defects, environmental conditions, and operational stresses, under- scores the urgency for comprehensive investigation and development of mitigation strategies. This study addresses these challenges by subjecting a composite tidal blade to a series of incremental static and fatigue tests, culminating in controlled failure experiments conducted at the FastBlade structural fatigue testing facility. The facility’s advanced capabilities include a regenerative digital displacement hy- draulic pump system yielding substantial energy savings; an advanced multi-camera digital image correlation system; and an acoustic emission crack detection system. Using these we systematically explore the factors contributing to blade failure. The failure modes examined in this study include: metal-composite bond failure; crack propagation in thick-section composites; and adhesive failure of the hydrodynamic outer skin. Our findings have significant implications for the structural engineering, composite ma- terial, and tidal energy development communities. Notably, our study offers valuable insights into the mechanisms underlying both blade failure under extreme loads and the accumulation of damage in large, thick composite struc- tures. This research represents an important step towards enhancing the reliability and efficiency of tidal turbine blades, thus advancing the viability of tidal stream energy as a sustainable power source.

Predictive Modelling and Optimisation of Power Generation for the M4 Wave Energy Converter: A Deep Learning Approach

Samantha Hoekstra — 2025-09-16

This paper investigates the use of a nonlinear autoregression neural network for wave field predictions, and its implementation into a power-take off passive loading control system which tunes the damping coefficient for a wave energy converter. The wave energy converter considered in this study is a part of a multi-institutional demonstrator project which has seen the deployment of a moored multimodal multibody (M4) attenuator wave energy converter in King George Sound in Albany, Western Australia. The device consists of a 1-2-1 float configuration and is approximately 20 meters in length. The developed neural network was used to predict wave elevations and energy spectrums for 10-second and 20-second ahead of time intervals. Findings of this study show that the neural network was able to accurately predict up to 10 s intervals (where RMSE = 1.32E-02), however the accuracy of predictions fell for 20 s predictions (where RMSE = 5.20E-02). A linear numerical model of the prototype M4 device was used to find the optimal PTO damping coefficient for the observed wave fields at King George Sound. This allowed for optimisation of mean absorbed power for a generated 3-hour JONSWAP unidirectional timeseries using variable damping coefficients. Here, the power output was able to be increased by 106% for a significant wave height of 0.63 m and peak period of 3 s and resulted in an overall increase in capture width ratio across the 3-hour wave dataset.

CRIMSON Project: Full-scale Turbine Demonstration By Tank Tests

Massimo Falchi — 2025-09-16

The results of demonstration tests of a full-scale hydrokinetic turbine for river and tidal sites, are presented at the conclusion of
the EU-funded CRIMSON project.
The turbine features a 3-bladed crossflow, 9.0 m2 capture area rotor, representing one module of the ORPC RivGen(c) technology. A comprehensive matrix of operational trials was performed to characterize the turbine hydrodynamic performance and the efficiency of the power conversion system. An advanced blade structural monitoring equipment based on fiber-optics strain sensors was implemented and validated.
The full-scale turbine tests were carried out at the hydrodynamics testing infrastructure at the Institute of Marine Engineering
of the Italian National Research Council (CNR-INM). This facility, among the largest of its kind globally, provided fully
controlled and repeatable conditions that allowed to deliver a high-quality dataset on system performance and realiability, contributing to develop new knowledge for the enhancement of hydrokinetic turbine technology.

Review and Evaluation of Offshore Wind Energy: Resources, Markets and Technologies

Qiang Gao — 2025-09-16

Offshore wind energy is rapidly emerging in the global shift towards sustainable energy, offering vast potential to meet increasing energy demands with minimal environmental impact compared to other onshore renewables. Australia has demonstrated world-class offshore wind potential; however, its industry remains relatively immature compared to major offshore wind regions in the EU and Asia, particularly in terms of resource assessment, technology readiness, market development, and regulatory framework. This paper aims to provide a comprehensive review and evaluation of offshore wind, encompassing resource assessment, market development, and technological advancements, offering valuable insights for major stakeholders in Australia. This study first reviews global offshore wind development, highlighting regions with significant wind resources, and then examines the offshore wind resources and potential markets in Australia. The key technologies in offshore wind, including wind turbine generators, foundations (both bottom-fixed and floating), power electronics, control topologies, and transmission technologies, are comprehensively evaluated and discussed with a focus on development in Australia.

An Evaluation of Blade Repair Techniques and Applicability for Tidal Turbines

Ben Thomas — 2025-09-16

The number of tidal stream energy installations is set to rise rapidly as countries deploy increased renewable energy capacity to meet net zero targets. The year 2023 was a pivotal year for the tidal stream industry in the UK, with 11 Contracts for Difference being awarded to tidal stream projects in Allocation Round 5. This will grow UK deployed capacity to nearly 100MW by 2028. In wind energy, an estimated 3800 incidents of blade damage occurred for 700,000 installed turbines in 2020. This has resulted in significant attention on optimisation of repair procedures to minimise operational downtime. As a result, this is now supported by a skilled and experienced repair industry with developed practices. Wind and tidal blades share significant similarities in composite material construction and design, and as tidal energy scales, similar attention to blade repair will likely be required to ensure that tidal turbine blades can be kept in service with minimal downtime. This study reviews and contrasts the observed and expected damage experienced by in-service composite wind and tidal turbine blades to establish a baseline for transfer of existing techniques between the industries. The tidal-specific repair requirements and impacts of blade design and operating conditions are assessed, enabling assessment of the applicability and suitability of developed wind industry procedures, techniques, and tools for tidal blade repair. The challenges surrounding the unique design features of tidal blades such as thick sections, ply tapering, and large curvature are assessed to identify areas requiring novel repair approaches. The study acts as a primer to allow tidal stream project developers and operators to anticipate blade maintenance requirements and better understand the transferability of existing wind repair practices to bolster future growth in the tidal stream industry.

Cable solutions for Ocean Energy: Latest design configurations, failure modes, and monitoring methods

Hayden Marcollo — 2025-09-16

Subsea cables are critical system components that enable operation of ocean energy technology devices. For technology demonstration of ocean-based energy systems through to commercial arrays of devices, due consideration must be given to the cable architecture to reduce single points of failure. This paper discusses potential cable architecture options applicable to i) three wave energy converter types; ii) two tidal energy types; and iii) ocean thermal energy converters. Risks, lessons learnt, historical failure data, and analogous experience from the offshore wind and oil and gas sectors are presented and interpreted for the aforementioned ocean energy converter systems. Finally, monitoring solutions and integrity management of subsea power cables systems are discussed in the context of pre-commercial projects.

This paper is intended to provide a summary of the subsea cable technologies available and guidance for researchers and developers who are contemplating the first or subsequent deployment of a marine energy concept that includes power export to shore.

Comparison of floating offshore wind and tidal range for green hydrogen production and storage for industrial decarbonization

David Pegler — 2025-09-16

UK Government targets 5 GW of electrolysers by 2030, however the role of green hydrogen for decarbonisation is not explicit. The government identifies the need to research the “archetypes” of production, transport, storage, and use. This paper presents a techno-economic model, comparing Floating Offshore Wind (FLOW) to tidal range, supplying uninterrupted power and hydrogen for industrial decarbonisation. The model employs Levelised Cost of Electricity (LCoE) and Hydrogen (LCoH), with sensitivities for Discount Rate (DR) and electrolyser efficiency. Storage is essential; FLOW must overcome seasonal patterns and changeability between years, and tidal must bridge both the springs‑neaps, and equinox cycles. The Royal Society identifies salt caverns as optimal for GWh storage, and the British Geological Society (BGS) report halite beneath the Celtic Sea. The model includes an onshore electrolyser, desalination, compression, subsea pipeline, storage platform, Underground Hydrogen Storage (UHS), and Hydrogen Gas Turbine Generator (HGTG). Components are scaled to meet demands over 25 years. When renewable generation falls below demand, hydrogen is withdrawn from storage to top-up electrolyser production to meet the continuous gas demand, and as fuel for the HGTG. The study shows how marine renewables can provide continual power and hydrogen for decarbonisation, and hydrogen’s ability as an energy store and flexible fuel. FLOW was found to require a smaller generating and electrolyser capacity, with lower LCoE and LCoH. Tidal’s predictability results in a smaller storage. Costs are most sensitive to DR. Tidal merits further investigation due to its long asset life and compatibility with alternative storage technologies.

Preface to the special issues of the International Conference on Ocean Energy 2024

Irene Penesis — 2025-09-16

The International Conference on Ocean Energy (ICOE) 2024 marked a significant milestone in the event’s history, taking place in Melbourne, Australia, from September 16–18, 2024. This was particularly notable as it was the first time the conference has been hosted in the Southern Hemisphere. The conference programme covered all aspects of the ocean energy sector, from markets and technology developments to socio-economic and environmental aspects and future investment opportunities, and ICOE continues to be highly relevant for professionals, researchers, and policymakers from around the world who are dedicated to advancing ocean energy technologies, policy, and collaboration. This biennial conference, renowned for its focus on the development of ocean energy - wave energy, tidal and ocean currents, ocean thermal energy and salinity gradient – continued its tradition of fostering innovation, collaboration, and dialogue in these sectors.