Fish farming is the fastest growing food production sector worldwide and now accounts for most human fish consumption. Expansion of finfish aquaculture to exposed offshore marine environments is appealing where additional sheltered areas are unavailable. While more energetic environments may reduce waste accumulation and parasite exposure, effects on fish health and wellbeing are largely speculative. The multiple stressors faced by fish on offshore farms may interact synergistically and increase their cumulative impact. We used 20 months of health and welfare data from eight Atlantic salmon (Salmo salar) sea pen farms in Scotland along a wave exposure gradient to assess the effects of, and interactions between, environmental variables and management treatments on fish mortality and parasite loads. While farms showed high variability in mortality rate and sea lice infections, multi-level Bayesian modelling indicated that wave exposure primarily modulated effects of other variables. Higher exposure farms showed steeper increases in mortality with time and with extreme temperatures. Similarly, sea lice infections tended to increase with time, with higher exposure farms seeing steeper increases at higher Amoebic Gill Disease (AGD) scores and at high temperatures. The effect of AGD was greater at slow water speeds. Treatments against parasites were more frequent at low exposure farms, leading to uncertainty in their impact on welfare across farms. The support for interactive effects of wave exposure with other variables rather than strong direct effects suggests an accumulation of chronic and acute stressors. Expansion of aquaculture to more energetic offshore environments may have negative impacts on fish health in some circumstances, requiring adaptation of practices. In particular, the stronger increase in mortality over time may have implications for cycle length in different environments, and the more dramatic impacts of the warmest temperatures at high exposure farms call for consideration of the change in water temperature both inshore and offshore.

Tidal energy projects require numerical modelling for the assessment of tidal site conditions and turbine/array performance. The Interreg TIGER project has offered a unique opportunity to implement a wide range of numerical models. This paper provides an overview and comparison of the different numerical models developed by academic partners in the TIGER project. The models cover a variety of spatial and temporal scales. The largest scale models provide long-term climatic studies covering the entire English Channel region, at relatively low resolution, whilst the highest-resolution models provide detailed information about short-term and small-scale turbulent flow and its interaction with tidal turbines. The models are used for various purposes. At one end of the scale, the models have been used to inform the large-scale techno-economic assessment of tidal energy and its impact on the energy mix in the UK and France. At the other end of the scale, the numerical models provide information that feeds into detailed engineering design of tidal turbines at particular sites, and assessment of the energy yield. The models showcase the range of computational tools available to aid the development of the tidal energy industry. This paper will be useful for investors, technology developers and project stakeholders to help identify suitable numerical models to support and develop ongoing and future tidal stream projects.

The next stage of development of the tidal stream industry will see a focus on the deployment of tidal turbines in arrays of increasing device numbers and rated power. Successful array development requires a thorough understanding of the resource within potential deployment sites. This is predictable in terms of flow speeds, based upon tidal constituents. However, the operating environment for the turbine is more complex than the turbine experiencing a uniform flow, with turbulence, shear and wave conditions all affecting the loading on the turbine components. This study establishes the accuracy with which several alternative modelling tools predict the resource characteristics which define unsteady loading—velocity shear, turbulence and waves—and assesses the impact of the model choice on predicted damage equivalent loads. In addition, the predictions of turbulence are compared to a higher fidelity model and the occurrence of flow speeds to a Delft3D model for currents and waves. These models have been run for a specific tidal site, the Raz Blanchard, one of the major tidal stream sites in European waters. The measured resource and predicted loading are established using data collected in a recent deployment of acoustic Doppler current profilers (ADCPs) as part of the Interreg TIGER project. The conditions are measured at three locations across the site, with transverse spacing of 145.7 m and 59.3 m between each device. Turbine fatigue loading is assessed using measurements and model predictions based on an unsteady blade element momentum model applied to near-surface and near-bed deployment positions. As well as across-site spatial variation of loading, the through life loading over a 5-year period results in an 8% difference to measured loads for a near-surface turbine, using conditions purely defined from a resource model and to within 3% when using a combination of modelled shear with measured turbulence characteristics.

Offshore aquaculture has gained momentum in recent years, and the production of an increasing number of marine fish species is being relocated offshore. Initially, predictions of the advantages that offshore aquaculture would present over nearshore farming were made without enough science-based evidence. Now, with more scientific knowledge, this review revisits past predictions and expectations of offshore aquaculture. We analysed and explained the oceanographic features that define off-shore and nearshore sites. Using Atlantic salmon ( Salmo salar ) as a case study, we focussed on sea lice, amoebic gill disease, and the risk of harmful algal blooms, as well as the direct effects of the oceanography on the health and physiology of fish. The operational and licencing challenges and advantages of offshore aquaculture are also considered. The lack of space in increasingly saturated sheltered areas will push new farms out to offshore locations and, if appropriate steps are followed, offshore aqua-culture can be successful. Firstly, the physical capabilities of the farmed fish species and infrastructure must be fully understood. Secondly, the oceanography of potential sites must be carefully studied to confirm that they are compatible with the species-specific capabilities. And, thirdly, an economic plan considering the operational costs and licencing limitations of the site must be developed. This review will serve as a guide and a compilation of information for researchers and stakeholders.

Efficient and resilient design of tidal turbines requires knowledge of the environmental conditions which they will be exposed to over the course of their design life. Several sites in the English Channel have been identified by technology developers for potential deployments of tidal farms. These sites are exposed to strong tidal currents and large wave conditions. At sites of interest for tidal energy extraction, the largest currents are primarily driven by astronomical forcing and can be predicted from harmonic analysis of relatively short datasets. In contrast, wave conditions are stochastic in nature and require long hindcasts to accurately estimate extreme conditions. Moreover, at sites relevant to tidal energy, currents have a significant influence on the wave conditions. This necessitates that extremes of waves and currents are assessed using joint probabilistic models, in order to specify combinations of waves and currents to be used in the structural design of tidal turbines. In this work we use a coupled wave-current model of the English Channel to create a 31-year hindcast of conditions. We examine the joint distribution of wave and current conditions for tidal energy sites near the Isle of Wight (UK) and in the Alderney Race, off the coast of France. We construct 3D environmental contours of current speed, significant wave height and relative direction between the waves and currents. It is shown that the largest waves occur when waves and currents are in opposing directions. The directional misalignment between waves and currents is examined and the potential impact that this may have on the design of tidal turbines is discussed.

Numerical modeling of currents and waves is used throughout the marine energy industry for resource assessment. This study compared the output of numerical flow simulations run both as a standalone model and as a two-way coupled wave–current simulation. A regional coupled flow-wave model was established covering the English Channel using the Delft D-Flow 2D model coupled with a SWAN spectral wave model. Outputs were analyzed at three tidal energy sites: Alderney Race, Big Roussel (Guernsey), and PTEC (Isle of Wight). The difference in the power in the tidal flow between coupled and standalone model runs was strongly correlated to the relative direction of the waves and currents. The net difference between the coupled and standalone runs was less than 2.5%. However, when wave and current directions were aligned, the mean flow power was increased by up to 7%, whereas, when the directions were opposed, the mean flow power was reduced by as much as 9.6%. The D-Flow Flexible Mesh model incorporates the effects of waves into the flow calculations in three areas: Stokes drift, forcing by radiation stress gradients, and enhancement of the bed shear stress. Each of these mechanisms is discussed. Forcing from radiation stress gradients is shown to be the dominant mechanism affecting the flow conditions at the sites considered, primarily caused by dissipation of wave energy due to white-capping. Wave action is an important consideration at tidal energy sites. Although the net impact on the flow power was found to be small for the present sites, the effect is site specific and may be significant at sites with large wave exposure or strong asymmetry in the flow conditions and should thus be considered for detailed resource and engineering assessments.

This paper presents a methodology for the reliability and power flow analysis of islands or off-grid power networks for situations of scarce data and information. It offers a new and pragmatic approach to derive the required power network information, including the power cable parameters and the load at each power node. The paper aims to present the developed methodology, and to illustrate its application, using Ushant Island as a case study. The assessment of the current power network status and the reliability analysis are presented. Grid performance parameters are further compared for conventional diesel generator operation and renewable energy generation scenarios, demonstrating the advantages of replacing the existing diesel units with renewable energy sources in terms of system reliability. The analysis shows that by introducing renewable energy systems to the island’s grid, the reliability of the grid increases by up to 50% and cable capacity usage reduces by up to 30%. Furthermore, this work suggests that it would not be necessary to modify the grid cables when substituting the diesel generator. The paper will be of interest to network planners, community stakeholders, project developers and decision-makers concerned with renewable energy investment on islands and in remote rural areas.

Marine renewable energy devices require mooring and foundation systems that suitable in terms of device operation and are also robust and cost effective. In the initial stages of mooring and foundation development a large number of possible configuration permutations exist. Filtering of unsuitable designs is possible using information specific to the deployment site (i.e. bathymetry, environmental conditions) and device (i.e. mooring and/or foundation system role and cable connection requirements). The identification of a final solution requires detailed analysis, which includes load cases based on extreme environmental statistics following certification guidance processes. Static and/or quasi-static modelling of the mooring and/or foundation system serves as an intermediate design filtering stage enabling dynamic time-domain analysis to be focused on a small number of potential configurations. Mooring and foundation design is therefore reliant on logical decision making throughout this stage-gate process. The open-source DTOcean (Optimal Design Tools for Ocean Energy Arrays) Tool includes a mooring and foundation module, which automates the configuration selection process for fixed and floating wave and tidal energy devices. As far as the authors are aware, this is one of the first tools to be developed for the purpose of identifying potential solutions during the initial stages of marine renewable energy design. While the mooring and foundation module does not replace a full design assessment, it provides in addition to suitable configuration solutions, assessments in terms of reliability, economics and environmental impact. This article provides insight into the solution identification approach used by the module and features the verification of both the mooring system calculations and the foundation design using commercial software. Several case studies are investigated: a floating wave energy converter and several anchoring systems. It is demonstrated that the mooring and foundation module is able to provide device and/or site developers with rapid mooring and foundation design solutions to appropriate design criteria.

For Marine Renewable Energy (MRE) to become a viable alternative energy source, it must encompass large arrays of devices. Arrays may include 1000s of devices. The associated foundations or anchors may encounter a range of seafloor sediment types and geotechnical properties. Wave and tidal energy convertors induce unique loads on foundations and anchors that are different from other seafloor engineering applications. Thus, there is a need for a combination of advanced site analysis and performance assessment. Geotechnical engineering plays the vital role of ensuring that foundation and anchor systems perform successfully for MRE devices. Our paper reviews the unique frequency and magnitude of loading regimes experienced by MRE arrays. We examine potential loading conditions on the foundation-anchor systems. Loading regimes include environmental and system loads from single devices or arrays of devices. We present specific load examples from field data. We explore the applicable geotechnical approaches to address these conditions, including constitutive models that may or may not adequately capture the response of the seafloor sediments to the MRE loads. Partially to fully dynamic constitutive model formulations may be necessary to properly model sediment-fluid hydromechanical response to MRE loading. Spacing of full MRE arrays and spatial variability in sediment properties may require multiple foundation types.

This paper characterises wave and current fields at two different marine energy site with investigation of WCIs (wave current interactions) and turbulence. The features of a 5-beam ADCP are utilised whereby it is found to accurately measure wave spectra up to high frequencies as well as providing directional wave data. Deployments were conducted in 2010 and 2011 using a Teledyne RDI 5-beam ADCP (Acoustic Doppler Current Profiler) recording waves and currents at 2Hz at the North Cornwall Wave Hub site in the UK. While the one conventional four beam 600 kHz unit ADCP was deployment at The Pentland Firth off the North coast of Scotland in March 2013. Current velocity off the North Cornwall coast is influenced principally by the semi-diurnal variation in tidal flow and by the regular cycle of spring and neap tides, with a maximum of 1 m/s Current Magnitude. The interaction between waves and currents has been studied and the important of the direction angle between wave of current has been under light in order to find appreciate interaction in the site. In the second site up of Scotland there are completely different sea state with the current magnitude up of 5 m/s where it is shows clearly the Doppler Shift effect and the wave direction influenced by the current. Most places in the world we can safely assume that the water velocity we measure is predominantly a superposition of waves and currents, but in the Penland Firth, The new assumption is that the measured velocity is really a superposition of waves, currents and turbulence, it is fundamental to investigate for the design of Marine Energy Converters (MECs).