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Nowadays, an increase in energy demand, environmental concerns, and the shortage of fossil fuel resources have made energy management researchers explore alternative resources for clean and renewable energy resources. The simultaneous incorporation of a comprehensive set of technical, economic, environmental, and social attributes in decision-making processes is recommended to improve the efficiency and effectiveness of sustainable decisions on energy resource planning. To tackle this challenge, an efficient method is proposed based on the Simultaneous Evaluation of Criteria and Alternatives (SECA) for the optimal selection of renewable energy resources. In the SECA technique, criteria and alternative evaluations are performed simultaneously. The proposed assessment framework is applied in Iran's electricity industry as a real case study, and a two-round fuzzy-based Delphi technique is also adopted to extract the assessment criteria from the experts' opinions. Moreover, the management insights are inferred from sensitivity analysis. According to the study results, solar, wind, biomass, hydroelectric, hydrogen, geothermal, and marine energy resources are sorted in descending order of priority. Finally, the best composite option of sustainable energies encompassing a combination of solar, wind, and biomass energy resources concludes the study.

In this investigation, instrumented mobile platforms are used to spatially map the turbulent flows in Grand Passage, one of the Bay of Fundy's more energetic tidal channels in Nova Scotia, Canada. The aim is to characterize the flow around the PLAT-I floating tidal energy platform developed by Sustainable Marine Energy Canada (SMEC). GPS-tracked surface drifters equipped with fast-sampling acoustic Doppler current profilers (ADCPs) provide turbulence-resolving vertical profiles of velocity and turbulent kinetic energy dissipation rate along drifter trajectories, while vessel-mounted ADCP transects complement the mean flow velocity measurements. These data are used to construct tridimensional quasi-synoptic maps of mean velocities and turbulence parameters for several stages of the tide around PLAT-I's location including peak ebb and flood currents. The data set includes measurements under natural flow conditions, and while the turbines installed on PLAT-I were both not operational and operational. The measurement techniques and resulting maps successfully capture the spatial and temporal structure of the flow for unsteady conditions for various tidal conditions. The combined wake of the four 6.3 m operational PLAT-I turbines was measured for a single tidal stage. Closer to the turbines, the vertical extent of the wake is about 6 m (approximately one turbine diameter), increasing with distance downstream, while the maximum observed velocity deficit is 26% relative to not operating conditions, decreasing with distance downstream.

Most tidal energy site studies concentrate on resource size; few examine other factors that may be of equal or even greater importance in determining site feasibility for tidal turbine array deployments. These factors include aspects such as electrical grid proximity, water depth, the location of marine protected areas, pre-existing users, environmentally significant regions and other restrictions. Using these factors, a more holistic approach to site selection was conducted for Australian waters using a Multi-Criteria Evaluation (MCE) process. This MCE method uses standardized factors combined with weighted linear combinations to calculate a site suitability index, where each factor is multiplied by a weight of relative importance. A sensitivity analysis on the factor weighting was performed to ensure the suitable selection of weighting factors to reduce conformation bias. The developed MCE model identified three promising locations in Australia, with contiguous areas in regions to the north of Broome Western Australia of 534 km2, the Banks Strait region northeast of Tasmania of 67 km2, and the Clarence Strait located in the Northern Territory of

Offshore wind and wave energy resources are possibly the last significantly untapped renewable energy resource, and could play a significant role in mitigating the impacts of climate change via the generation of renewable electricity. While often considered independently, there are significant technical advantages to co-deployment of wave and offshore wind technologies, and will be future competition for limited marine real estate, so there is a distinct need to development holistic assessments of these offshore resources. Currently, offshore wind and wave energy resource assessments have been conducted as independent parallel processes, with little interaction with regard to best practices, lessons learnt, or opportunities to create compatible methodologies for future utilization by the broader marine energy sector. Based on the latest technical specifications from the International Electrotechnical Commission, and the highest fidelity publicly available datasets, the offshore wind and wave conditions at the PacWave site off Oregon, USA were quantified. At the 70m depth site, the results clearly show a significant untapped energy resource an annual average wave energy flux of ∼35 kW/m and a mean average wind speed of 7.8 m/s; suitable for significant offshore wind (fixed and floating) and wave energy technology deployment The offshore wind and wave energy resources both show significant seasonal variation, with offshore wind also featuring a consistent daily profile during summer. Finally, opportunities and challenges associated with developing a holistic assessment of offshore marine energy resources were discussed and recommendations provided.

Surrogate models maximize information utility by building predictive models in place of computational or experimentally expensive model runs. Marine hydrokinetic current energy converters require large-domain simulations to estimate array efficiencies and environmental impacts. Meso-scale models typically represent turbines as actuator discs that act as momentum sinks and sources of turbulence and its dissipation. An OpenFOAM model was developed where actuator disc k-e turbulence was characterized using an approach developed for flows through vegetative canopies. Turbine-wake data from laboratory flume experiments collected at two influent turbulence intensities were used to calibrate parameters in the turbulence-source terms in the k-e equations. Parameter influences on longitudinal wake profiles were estimated using Gaussian process regression with subsequent optimization minimizing the objective function within 3.1% of those obtained using the full model representation, but for 74% of the computational cost (far fewer model runs). This framework facilitates more efficient parameterization of the turbulence-source equations using turbine-wake data.

This paper provides a feasibility study on a low cost system called Hydrokinetic Wells turbine for surface wave energy conversion without using plenum chambers. The elimination of the plenum chamber and its complicated valve systems can reduce the expenses of wave energy conversion up to 23%.The feasibility process were done for high and low frequency conditions. For the low frequency waves, we offer the 300 rpm angular velocity as an optimum selection for further studies. For the high frequency condition a reliable analytical approach based on validated methods was developed. The analytical results indicate that a wells turbine with 60 cm diameter could produce up to 1600 Watts power in high frequency waves. The efficiency and power coefficient values in high frequency condition are less in compared with low frequency situation, nevertheless the vast usage of the small scale and elimination of the plenum chambers can reduce the total cost of the conversion. The abundant availability of high frequency surface waves is a motivation for developing Hydrokinetic Wells turbine farms to harvest a great source of clean energy with lower cost levels.

As a way of exploitation and utilization of ocean energy, the waterjet pump is used in a wide range of high-speed marine vessels over 30 knot. This paper aims to investigate the mechanism of the energy loss and pressure fluctuations caused by the non-uniform inflow for a waterjet pump. Unsteady internal flows inside the waterjet pump are simulated using the Reynolds-averaged Navier-Stokes equations with the SST k-ω turbulence model. The predicted pump head and efficiency are in reasonable accordance with the experimental data. The inflow non-uniformity would decrease the hydraulic head, efficiency and increase the axial force fluctuations in the impeller, causing large pulsations in the unsteady energy performance. Based on analyses of the energy loss, the turbulent kinetic energy production and the diffusion of the Reynolds stress are major sources of the energy loss in the waterjet pump. The non-uniform inflow induces a dramatic energy loss in the intake duct and diffuser with an apparent flow separation observed near the trailing edge of the diffuser blade. Due to the inflow non-uniformity, the pressure fluctuates violently at the impeller rotating frequency (fn) in the intake duct, impeller and near the diffuser inlet, but a dominant frequency of 2fn is generated by the unsteady flow separation near the diffuser outlet.

Ocean waves are a huge and largely untapped resource of green energy. In order to extract energy from waves, a novel wave energy converter (WEC) consisting of a floating, hollow cylinder capped by a roof with a variable aperture is presented in this paper. The power take-off (PTO) system is composed of a linear generator attached to the seabed, driven by the heave motion of the floating cylinder through a tether line. The air pressure within the cylinder can be modified by adjusting the roof aperture. The hydrodynamic characteristics of this WEC are investigated through an analytical model based on potential flow theory, in which the wave diffraction/radiation problems are coupled with the air pressure fluctuation and PTO system. Analytical expressions are derived for the maximum power absorbed by the WEC under different optimization principles, revolving around the PTO damping, roof aperture damping and non-negative mooring stiffness. We find that the best power absorption is obtained when the aperture is either completely open or entirely closed, depending on the wave conditions. Intermediate values of the aperture are useful to minimize the heave motion and thus ensure survivability under extreme sea states.

Deep ocean water (DOW) is a renewable alternative to the many sustainability challenges that the Caribbean faces today. DOW can provide seawater air conditioning (SWAC) for buildings and greenhouses, provide electricity through an ocean thermal energy conversion plant (OTEC), and provide nutrients for aquaculture and cosmetic industries. However, today the implementation of DOW technologies in the Caribbean is inexistent, and studies about DOW potential in the Caribbean are limited. We present a methodology for estimating the practical potential of a city while considering constraints in ocean currents, temperature, and salinity. We applied the methodology to five cities in the Caribbean and found that the average potential is about 50 m3/s per city, enough to supply more than 100% of a city’s demand for air conditioning and 60% of its demand for electricity. We also estimated the monthly availability of DOW resource, with maximum extraction potentials between December to March, and minimum values between August to October. These estimations serve as input for future feasibility and design studies on DOW technologies in the Caribbean. Given the assumptions, the found potential may be underestimated; thus, the results of this study can be considered as a minimum reference value, complementary to the maximum theoretical potential found in previous studies.

A near-shore oscillating water column (OWC) device with a surging front-wall, which can be conveniently mounted on various cliff-like shores or coastal structures, is proposed to improve the pneumatic efficiency of wave energy extraction. Based on linear potential theory, the interaction between ocean waves and the OWC device is solved by the matched eigenfunction expansion method (MEEM). Auxiliary functions, expanded in orthogonal polynomials, are introduced to approximate the singular behaviors of fluid field in the vicinity of the salient corner. The effects of the dimensions of lip-wall and the stiffness of the spring on the hydrodynamic performances, such as the response amplitude operator (RAO), average inside free-surface elevation, phase difference between the motions of lip-wall and inside free-surface, and optimum conversion efficiency are taken into consideration. The numerical results show that the existence of a freely surging lip-wall can considerably improve the performance of the device over a wider bandwidth, especially for the intermediate and short wavelength regimes, compared with the fixed one.

As one of the largest energy-consumption nations, the South Korean government has recently invested in the deployment and commercialization of various renewable energy sources to reduce the environmental impacts of fossil fuel-based energy sources. Thus, in order to investigate the likelihood the government will default on the investment of research and development (R&D) in the renewable energy industry, this study utilizes a system-dynamics approach to develop a default-prediction model based on the Black-Scholes-Merton model, while investigating the interactions of uncertainty factors and the impacts of the probability of default (PD) on renewable energy production and carbon emission reduction amounts from 2017 to 2030. The results of this study indicate that R&D investments in marine energy (2.64%) has a high default risk, while the use of waste energy (46.95 B kg CO2) results in the largest reduction in the amount of carbon emissions. In addition, the results show that the PD of the R&D investment decreases when the uncertainty of the unit price, the R&D investment amount, and the renewable energy production amount have increased. Further, the results of a Monte Carlo simulation indicate that the PD of the R&D investment is not greatly affected by the risk-free interest rate.

The effect of an upstream bluff body on energy harvesting performance of a heaving and pitching hydrofoil is investigated numerically using a two-dimensional immersed boundary method at R e = 1000 . The presence of the upstream body changes flow structure around the hydrofoil and enhances efficiency significantly by two mechanisms. Mutual interaction of the vortex shed from the upstream body and the leading-edge vortex of the hydrofoil precipitates the separation of the leading-edge vortex from the hydrofoil and its streamwise transport. The incoming flow deflected by the upstream body changes the effective angle of attack for the hydrofoil. These phenomena significantly increase heaving force and pitching moment during stroke reversal, and major contribution to efficiency enhancement is from the change in pitching moment. 30% increase in efficiency, relative to a hydrofoil without an upstream body, can be achieved for same kinematics. However, the upstream body may be disadvantageous in some configurations. If the hydrofoil is placed closely to the body in transverse direction, the leading-edge vortex formation is suppressed after stroke reversal. When flapping frequency does not match with vortex shedding frequency of the upstream body, non-periodic flow structure formed around the hydrofoil can cause efficiency drop and irregular power generation.

Australia has considerable wave and tidal ocean energy resources. Development of the emerging ocean renewable energy (ORE) industry in Australia offers opportunities to build Australia's blue economy, while actively contributing to committed carbon mitigation measures. Many interdisciplinary challenges are currently hampering development of the industry in Australia, and globally, including technology, cost reduction, policy and regulations, potential for environmental effects, awareness and investment, amongst others. In October 2016, ORE technology and project developers, researchers, academics, policy makers and other stakeholders in Australia's emerging ORE industry came together to identify these challenges and develop possible pathways to grow ocean energy in Australia. Four themes were identified: Technology Development; Education and Awareness; Policy and Regulation; and Finance and Investment. This paper documents the outcomes of the meeting identifying challenges and a way forward against each theme. A key element identified across all themes was the need for stronger coordination across the sector, and the need for a representing body to lead necessary initiatives to support growth and management of the ORE industry in Australia, as one element of a burgeoning blue economy.

Ireland offers a complete testing pathway for wave energy devices from small-scale testing in laboratory wave tanks to the Galway Bay Test Site (GBTS), located in a sheltered bay, and the full-scale Atlantic Marine Energy Test Site (AMETS) exposed to the Atlantic Ocean on its west coast. This research investigates the scaling relationships between the GBTS and the AMETS, and also with the Westwave commercial demonstration site. The paper presents (i) detailed wave resource assessments at GBTS and Westwave (ii) a scaling analysis methodology suitable for determining the scale relationships between two sites, and (iii) the appropriate scaling factors for wave energy test sites in Ireland which can be used by developers for prototype testing and commercial deployment. The assessment and scaling analyses were performed using 12-year model outputs from two high resolution wave models from January 2004–December 2015. The models were well-validated using available measured data. The resource assessments determined (1) mean and maximum conditions and (2) operational, high and extreme event conditions for significant wave height, energy period and power. Both annual and seasonal analyses are presented. The 12-year annual mean power was 3 kW/m at GBTS and 50 kW/m at Westwave. Three scaling approaches have been analysed to identify the appropriate scale ratios to be used to upscale GBTS to AMETS for wave height, energy period and power. The distribution fittings method was found to be the most accurate method for resource scalability between GBTS and both AMETS and Westwave sites. The scaling result shows GBTS, although often termed a ¼-scale test site, is not actually ¼-scale proportionate to AMETS or Wavewave. Scaling factors are presented in tabular format, which are based on the Froude scaling method, for seasonal windows that could be used to determine the scale of ocean energy device models for testing in the benign site of GBTS in Ireland to ensure it adequately upscales to the open sea exposed sites of AMETS and Westwave in Ireland.

Previous tidal energy studies in Puget Sound have focused on major deep channels such as Admiralty Inlet that have a larger power potential. This paper focuses on the possibility of extracting tidal energy from minor tidal channels of Puget Sound by using a hydrodynamic model to quantify the power potential and the associated impact on tidal circulation. The study site is a multi-inlet bay system connected by two narrow inlets, Agate Pass and Rich Passage, to the Main Basin of Puget Sound. A three-dimensional hydrodynamic model was applied to the study site and validated for tidal elevations and currents. We examined three energy extraction scenarios in which turbines were deployed in each of the two passages and concurrently in both. Extracted power rates and associated changes in tidal elevation, current, tidal flux, and residence time were examined. Maximum instantaneous power rates reached 250 kW, 1550 kW, and 1800 kW, respectively, for the three energy extraction scenarios. Model results suggest that with the level of energy extraction in the three energy extraction scenarios, the impact on tidal circulation is very small. It is worth investigating the feasibility of harnessing tidal energy from minor tidal channels of Puget Sound.

Accurate assessment of wave energy potential has not been done so far in the offshore and nearshore waters of the Red Sea. In this paper, we present an assessment of wave energy resources in the Red Sea using numerical modelling. The wave conditions are simulated for 1979 to 2010 using a third generation ocean wave model, WAVEWATCH-III by forcing with CFSR winds. The model results are validated against in situ measurements in the Red Sea. The simulated wave parameters are used to estimate the wave power in the Red Sea during the 32 years – a reasonable long-term period for accurate assessment. The estimated wave power has been analyzed on a monthly, seasonal and inter-annual basis. The results indicate robust spatial and seasonal variations in mean wave power. Detailed investigations on wave energy potential have been carried out at a number of coastal locations in the Red Sea that consists of the coasts of Saudi Arabia, Yemen, Egypt, Sudan and Eritrea. Inter-annual variability in the mean wave power is also analyzed and discussed.

As the marine renewable energy industry evolves, in parallel with an increase in the quantity of available data and improvements in validated numerical simulations, it is occasionally appropriate to re-assess the wave and tidal resource of a region. This is particularly true for Scotland - a leading nation that the international community monitors for developments in the marine renewable energy industry, and which has witnessed much progress in the sector over the last decade. With 7 leased wave and 17 leased tidal sites, Scotland is well poised to generate significant levels of electricity from its abundant natural marine resources. In this state-of-the-art review of Scotland's wave and tidal resource, we examine the theoretical and technical resource, and provide an overview of commercial progress. We also discuss issues that affect future development of the marine energy seascape in Scotland, applicable to other regions of the world, including the potential for developing lower energy sites, and grid connectivity.

Marine energy sources are an untapped resource that is able to make a significant contribution to renewable and clean energy generation. In Uruguay, investments in renewable energy have experienced strong growth in recent years, mainly due to the development of wind energy farms. In this research, two marine energy sources are assessed on the Uruguayan shelf seas: wave energy and tidal currents energy. To this end, high-resolution hindcasts of wave and tidal currents were obtained based on state of the art numerical models, forced with reanalysis winds. The results were used to generate maps of energy potential for both resources, and these maps are overlapped on other uses and resources maps to identify potential exploitation zones. The results confirm that since the country is located in a microtidal zone, wave energy is the most promising among the sources analysed. Nevertheless, a zone in the outer Rio de la Plata Estuary is identified as the most promising area for an experimental marine energy farm, where exploitation of both resources could be tested.

The tidal stream energy sector is now at the stage of deploying the world's first pre-commercial arrays of multiple turbines. It is time to study the environmental effects of much larger full-size arrays, to scale and site them appropriately. A theoretical array of tidal stream turbines was designed for the Pentland Firth (UK), a strait between Scotland and the Orkney Islands, which has very fast tidal currents. The practical power resource of a large array spanning the Pentland Firth was estimated to be 1.64 GW on average. The ocean response to this amount of energy extraction was simulated by an unstructured grid three-dimensional FVCOM (Finite Volume Community Ocean Model) and analysed on both short-term and seasonal timescales. Tidal elevation mainly increases upstream of the tidal array, while a decrease is observed downstream, along the UK east coast. Tidal and residual flows are also affected: they can slow down due to the turbines action or speed up due to flow diversion and blockage processes, on both a local and regional scale. The strongest signal in tidal velocities is an overall reduction, which can in turn decrease the energy of tidal mixing and perturb the seasonal stratification on the NW European Shelf.

This paper proposes an analytic dispatch for tidal power plants that centralizes the discharge period in the tides extremes. Since the tide cycles are well predicted by a sinusoidal function, this method provides an accurate power generation as shown in the comparative tests. Furthermore, an optimal generation estimation method is derived considering that all stored water is discharged during the tides extremes, i.e., discharging at maximal water head. This method calculates a more realistic maximal power generation, which is especially simple in double-effect operation mode (power production in ebb and flood tides), since the reservoir geometry is not explicitly considered. The proposed methods are compared with a classical analytic solution and an optimal dispatch formulation.

Marine energy is one of the most promising solutions to attempt the ambitious renewable energy target of 20% by 2020 due to its very substantial energy resource. However, it is often considered uneconomical and difficult, and this may hinder its development. Combined energy systems, such as co-located offshore wind turbines and wave energy converters, have recently emerged as a solution to increase the competitiveness of marine energy by taking advantage of the synergies between renewables; which would lead to reductions in the energy cost and improvements in the power output variability and security. On this basis, finding viable locations for combined offshore renewable energies is fundamental to boosting their development. The objective of this paper is to determine suitable locations for deploying a co-located wind and wave energy farm in the North Sea - an area with several characteristics that make large-scale integration of renewable energy sources attractive. In this assessment we investigate not only the existing resource but also other parameters such as its variability and the correlation between waves and winds by means of the CLF index. In addition, inter- and intra-national user conflicts are considered, while balancing environmental conservation and economic development.

The presence of Tidal Stream Turbines (TST) for tidal power production, leads to changes in the local physical environment that could affect fish. While other work has considered the implications with respect to conventional hydroelectric devices (i.e. hydroelectric dams), including studies such as physical impact with the rotors and pressure variation effects, this research considers the effects of sudden changes in pressure and turbulence on the hypothetical fish with respect to TSTs. Computational fluid dynamics (CFD) is used to investigate changes to the environment, and thus study the implications for fish. Two CFD methods are employed, an embedded Blade Element representation of the rotor in a RANS CFD model, and a blade resolved geometry using a moving reference frame. A new data interpretation approach is proposed as the primary source of environmental impact data; ‘rate of change of pressure’ with time along a streamtrace. This work also presents results for pressure, pressure gradients, shear rates and turbulence to draw conclusions about changes to the local physical environment. The assessment of the local impact is discussed in terms of the implications to individual fish passing a single or array of TST devices.

The present scenario of energy market is highly volatile due to large oscillation in the fossil fuel prices. During these periods, the high energy demand for the industries is being partially met through non-conventional energy sources such as wind and solar power. The large untapped energy potential in the Ocean is yet to be exploited due to many technological constraints. The recent decades have shown positive developments worldwide towards the ocean wave energy converters. In the present study, an improved wave energy potential estimate has been made. Based on various parameters such as physical site characteristics, environmental conditions and socio-economic regional state, the selection criteria have been suggested. This would form the basis for energy device selection for the decision makers.

This paper proposes a novel hybrid approach for feature selection in two different relevant problems for marine energy applications: significant wave height (Hm0) and wave energy flux (P) prediction. Specifically, a hybrid Grouping Genetic Algorithm – Extreme Learning Machine approach (GGA-ELM) is proposed, in such a way that the GGA searches for several subsets of features, and the ELM provides the fitness of the algorithm, by means of its accuracy on Hm0 or P prediction. Since the GGA was specifically created for problems involving a number of groups, the proposed algorithm may be used to evolve different groups of features in parallel, which may improve the performance of the predictions obtained. After the feature selection process with the GGA-ELM, the final results are given by an ELM and also by a Support Vector Machine, both working on the best GGA groups obtained. The performance of the proposed system has been tested in a real problem of Hm0 and P prediction at the Western coast of the USA, obtaining good results.

This paper presents a study of practically implementable active tuning methodsfor a Wave Energy Converter (WEC) power take-off (PTO). It is distinguished from other simulation studies by the level of detail and realism in the inputs and the PTO model. Wave data recorded at the European Marine Energy Centre is used to derive input data for a detailed component level model of a hydraulic PTO. A methodology is presented for obtaining the optimum PTO damping co-efficient for a given sea state, and an open loop active tuning method is used to adjust the PTO parameters to achieve this optimum damping in service. The investigation shows that tuning of a hydraulic PTO to an estimated wave frequency is a difficult task due to sea state estimation errors and the complex dynamics of a realistic PTO. Preview knowledge of the future waves was shown to provide no meaningful improvement in energy capture for the device under investigation. Significantly, power gains observed in similar work using simplified linear PTO models or simplified sea states are not seen here, demonstrating that over-simplification of the PTO during the simulation phase of WEC development could lead to incorrect design decisions and subsequent additional delay and cost.

Electricity generation by tidal current and wave power arrays represents a radical innovation and is confronted by significant technological and financial challenges. Currently, the marine energy sector finds itself in a decisive transition phase having developed full-scale technology demonstrators but still lacking proof of the concept in a commercial project environment. After the decades-long development process with larger than expected setbacks and delays, investors are discouraged because of high capital requirements and the uncertainty of future revenues. In order to de-risk the technology and to accelerate the commercialisation process, we identified stakeholder-wide balanced and realisable strategic targets. The objective is to name the top-level drivers for facilitating technology maturation and thus achieving market acceptance. Our analysis revealed that the two major risks for multi-megawatt projects (funding and device performance) are directly interlinked and that co-ordinated action is required to overcome this circular relationship. As funding is required for improving device performance (and vice-versa), showcasing an “array-scale success” was identified as the interim milestone on the way towards commercial generation. By this game-changing event, both mentioned risk complexes will be simultaneously mitigated. We observed that system dynamics modelling is appropriate for an unbiased analysis of complex multi-level expert interview data. The applied research model was found to be efficient and allows a regular re-assessment of the strategic alignment thus supporting the adaptation to a complex and continuously changing socio-technical environment.

© 2015 Elsevier Ltd. This study explores typical characteristics of the mean and turbulent profiles at a mixed low tidal energy site (40 m mean water depth) where the waves have limited effects on the currents. The turbulence profiles were derived from secondary current data using a 5-beam ADCP which was optimised for wave measurements. The tidal currents have peak flows of ~1 m/s during spring tide. The turbulence intensity is no less than 10% at peak flows and compares well with values at other tidal channels (at ~5 m from seabed). The Reynolds stresses show symmetry at the neap tide but less so for the spring tide. Although the qualitative profiles of TKE are similar between the neap and spring tides, the values of TKE for flood flow are the largest throughout the deployment. The integral length scales are in good agreement with theory, and with estimates based on the mixing length concept. The measured turbulence parameters are sensitive to flow inhomogeneity, Doppler noise, and ADCP tilt. The findings demonstrate the practical benefits of exploiting secondary current data at a mixed low tidal energy site for estimating typical turbulence characteristics; such information can be used to define design standards and protocols for marine energy devices.

In addition to technical and economic constraints, tidal energy leasing is generally governed by demand for sites which contain the highest tidal streams, and does not take into account the phase relationship (i.e. the time lag) between sites. Here, the outputs of a three-dimensional tidal model are analysed to demonstrate that there is minimal phase diversity among the high tidal stream regions of the NW European shelf seas. It is therefore possible, under the current leasing system, that the electricity produced by the first generation of tidal stream arrays will similarly be in phase. Extending the analysis to lower tidal stream regions, we demonstrate that these lower energy sites offer more potential for phase diversity, with a mean phase difference of 1.25 h, compared to the phase of high energy sites, and hence more scope for supplying firm power to the electricity grid. We therefore suggest that a state-led leasing strategy, favouring the development of sites which are complementary in phase, and not simply sites which experience the highest current speeds, would encourage a sustainable tidal energy industry.

Previous research has shown that helical vertical axis turbines exhibit lower torque fluctuation levels than straight-bladed turbines; however little is known of the impact of blade helicity on turbine performance characteristics. To investigate these relationships the hydrodynamic characteristics of straight and helical-bladed vertical axis turbines were investigated using Three-Dimensional (3D) Computational Fluid Dynamics (CFD) models using a commercial Unsteady Reynolds Averaged Navier-Stokes (URANS) solver. Simulations of power output, torque oscillations, and mounting forces were performed for turbines with overlap angles from 0° to 120° and section inclination angles from −15° to 45°. Results indicated that straight-bladed turbines with 0° blade overlap generated the highest power output. Helical turbines were found to generate decreasing power outputs as blade overlap angle increased due to the resultant blade inclination to the inflow. Blade section inclination to the inflow was also found to influence power output. Some benefits of helical-bladed turbines over their straight-bladed counterparts were established; helical turbine torque oscillation levels and mounting forces were reduced when compared to straight-bladed turbines. For both straight and helical-bladed turbines maximum mounting force levels were found to exceed the average force levels by more than 40%, with large cyclical loading forces identified.

National efforts to reduce energy dependency on fossil fuels have prompted examination of macrotidal nearshore sites around the United Kingdom (UK) for potential tidal stream resource development. A number of prospective tidal energy sites have been identified, but the local hydrodynamics of these sites are often poorly understood. Tidal energy developers rely on detailed characterisation of tidal energy sites prior to device installation and field trials. Although first-order appraisals may make macrotidal tidal straits appear attractive for development, detailed, site-specific hydrodynamic and bathymetric surveys are important for determining site suitability for tidal stream turbine (TST) installation. Understanding the ways in which coastal features affect tidal velocities at potential TST development sites will improve identification and analysis of physical constraints on tidal energy development. This paper presents and examines tidal velocity data measured in Ramsey Sound (Pembrokeshire, Wales, UK), an energetic macrotidal strait, which will soon host Wales' first TST demonstration project. While maximum tidal velocities in the strait during peak spring flood exceed 3 m s−1, the northern portion of Ramsey Sound exhibits a marked flood-dominated tidal asymmetry. Furthermore, local bathymetric features affect flow fields that are spatially heterogeneous in three dimensions, patterns that depth-averaged velocity data (measured and modelled) tend to mask. Depth-averaging can therefore have a significant effect on power estimations. Analysis of physical and hydrodynamic characteristics in Ramsey Sound, including tidal velocities across the swept area of the pilot TST, variations in the stream flow with depth, estimated power output, water depth and bed slope, suggests that the spatial and temporal variability in the flow field may render much of Ramsey Sound unsuitable for tidal power extraction. Although the resource potential depends on velocity and bathymetric conditions that are fundamentally local, many prospective tidal energy sites are subject to similar physical and hydrodynamic constraints. Results of this study can help inform site selection in these complicated, highly dynamic macrotidal environments. In order to fully characterise the structure of the tidal currents, these data should be supplemented with 3-D modelling, particularly in areas subject to a highly irregular bathymetry and complicated tidal regime.

Among the various ocean energy resources in Korea, the tidal currents in the South western sea have a large potential for development tidal current power generation. The biggest advantage of tidal power is that it is not dependent on seasons or weather and is always constant. This makes power generation predictable and makes tidal power a more reliable energy source than other renewable energy sources. Marine current turbines convert the kinetic energy in tidal currents for power production. Single rotor turbines can obtain a theoretical maximum power coefficient of 59.3%, whereas dual rotor can obtain a maximum of 64%. Therefore by optimizing the counter rotating turbines, more power can be obtained than the single rotor turbines. In this study, we investigated the effect of varying the distance between the dual rotors on the performance and efficiency of a counter-rotating current turbine by using computational fluid dynamics (CFD) and experimental methods. It was found that the dual rotor produced more power than the single rotor. In addition, the blade gap distance affects the flow on the rear rotor blades as well as power output and performance of the turbine. The distance can be used a parameter for counter rotating turbine design. Finally, the numerical setup used for this study can be further used to evaluate the design of larger counter rotating blade designs.

As a renewable energy, the assessment of wave power potential around a country is crucial. Knowledge of the temporal and spatial variations of wave energy is required for locating a wave power plant. This study investigates the variations in wave power at 19 locations covering the Indian shelf seas using the ERA-Interim dataset produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). The ERA-Interim data is compared with the measured wave parameters in the Arabian Sea and the Bay of Bengal. Along the western shelf seas of India, the seasonal oscillations lead to variation of the wave power from the lowest seasonal mean value (2.6 kW/m) in the post-monsoon period (October–January) to the highest value (25.9 kW/m) in the south-west monsoon (June–September) period. Significant (10–20%) inter-annual variations are detected at few locations. The mean annual wave power along the eastern Indian shelf seas (2.6–9.9 kW/m) is lower than the mean annual wave power along the western part (7.9–11.3 kW/m). The total annual mean wave power available along the western shelf seas of India is around 19.5 GW. Along the eastern shelf seas, it is around 8.7 GW. In the Indian Shelf seas, the annual mean wave power is highest (11.3 kW/m) at the southern location (location 11), and the seasonal variation in wave power is also less. Hence, location 11 is a better location for a wave power plant in the Indian shelf seas.

Ocean wave energy is one of the world's most powerful forms of energy and the energy density in ocean waves is the highest among renewable energy sources. Wave energy converters are employed to harness this energy and convert it into usable electrical energy. However, in order to efficiently extract the energy, the wave energy converter must be optimised in the design stage. Therefore, in this paper, a methodology is presented which aims to optimise the structural geometric configuration of the device to maximise the average power extraction from its intended deployment site. Furthermore, a case study of the Atlantic marine energy test site, off the west coast of Ireland, is undertaken in order to demonstrate the methodology. Using the average annual wave energy spectrum at this site as the input, the optimum structural geometric configuration was established, along with an analysis of the optimum configuration for different radius devices. In addition, the optimum damping coefficient of the PTO mechanism is determined and the total mean absorbed power for the structure at the site over the entire scatter diagram of data is calculated.

Many regions throughout the world that are suitable for exploitation of the wave energy resource also experience large tidal ranges and associated strong tidal flows. However, tidal effects are not included in the majority of modelling studies which quantify the wave energy resource. This research attempts to quantify the impact of tides on the wave energy resource of the northwest European shelf seas, a region with a significant wave energy resource, and where many wave energy projects are under development. Results of analysis based on linear wave theory, and the application of a non-linear coupled wave-tide model (SWAN–ROMS), suggest that the impact of tides is significant, and can exceed 10% in some regions of strong tidal currents (e.g. headlands). Results also show that the effect of tidal currents on the wave resource is much greater than the contribution of variations in tidal water depth, and that regions which experience lower wave energy (and hence shorter wave periods) are more affected by tides than high wave energy regions. While this research provides general guidelines on the scale of the impact in regions of strong tidal flow, high resolution site-specific coupled wave-tide models are necessary for more detailed analysis.

The objective of this work is to investigate how the impact of a wave farm on the nearshore wave conditions depends on its location and, more specifically, its distance to the coast. For this purpose eight case studies in an area with a very substantial wave resource are considered; they encompass three values of the farm-to-coast distance (2 km, 4 km and 6 km) plus a baseline situation (with no farm), in combination with two wave conditions representative of winter and summer scenarios. A coastal wave model is implemented on a high-resolution nested grid. The interaction between the individual Wave Energy Converters (WECs) of the array and the waves is simulated by the model on the basis of experimental data, i.e., the wave transmission coefficients are obtained from laboratory tests. To characterise the nearshore impact of the wave farm we define a series of impact indicators, including the Nearshore Impact (NI), the Maximum absolute Nearshore Impact (NImax) and the Relative Nearshore Impact (RNI). We find that increasing the farm-to-coast distance does not guarantee a reduction of the Maximum absolute Nearshore Impact, and that the distance influences the location of the point of occurrence of the maximum impact along the coast.

Colombia's exclusive location surrounded by the warm tropical waters of the Caribbean Sea and the eastern equatorial Pacific Ocean make it a suitable region for ocean thermal energy conversion (OTEC). These are systems that can produce significant amounts of renewable electricity. From the assessment of the temperature gradient and the bathymetric, environmental and socio-economical characteristics, the maritime area around the island of San Andres (in the northwestern Caribbean Sea) was found to be ideal for an OTEC facility since sea surface temperature varies only slightly during annual and interannual timescales. The thermal difference encountered from the surface to a depth of 1000 m is always around 22°–24 °C and cold waters are available for intake at around 450–750 m, within a short horizontal distance from the coast (less than 2.5 km). At these depths, the 20 °C thermal gradient required for OTEC operations is achieved. Furthermore, winds, waves and surface currents around the island are of relatively weak intensity. Presently, energy sources based entirely on Diesel generators are inducing negative impacts on the sustainable development of the region and on the fragile marine ecosystem. An environmentally friendly 10 MW OTEC facility could be part of future energy and water management solutions for the island. It would cover nearly 50% of total electricity demands and provide important additional advantages such as chilled soil agriculture, aquaculture, freshwater, mariculture and seawater air conditioning.

The vision of large-scale commercial arrays of floating marine energy converters (MECs) necessitates the robust, yet cost-effective engineering of devices. Given the continuous environmental loading, fatigue has been identified as one of the key engineering challenges. In particular the mooring system which warrants the station-keeping of such devices is subject to highly cyclic, non-linear load conditions, mainly induced by the incident waves. To ensure the integrity of the mooring system the lifecycle fatigue spectrum must be predicted in order to compare the expected fatigue damage against the design limits. The fatigue design of components is commonly assessed through numerical modelling of representative load cases. However, for new applications such as floating marine energy converters numerical models are often scantily validated. This paper describes an approach where load measurements from large-scale field trials at the South West Mooring Testing Facility (SWMTF) are used to calculate and predict the fatigue damage. The described procedure employs a Rainflow cycle analysis in conjunction with the Palmgren–Miner rule to estimate the accumulated damage for the deployment periods and individual sea states. This approach allows an accurate fatigue assessment and prediction of mooring lines at a design stage, where field trial load measurements and wave climate information of potential installation sites are available. The mooring design can thus be optimised regarding its fatigue life and costly safety factors can be reduced. The proposed method also assists in monitoring and assessing the fatigue life during deployment periods.

Many candidate sites for tidal stream power extraction are tidal channels, and the power that can be generated from these sites will be directly related to the amplitude and phase of the principal tidal constituents driving flow through the channel. This paper investigates this interaction between energy extraction and tidal constituents, and also the effect that power extraction may have on harmonics of the principal constituents (i.e. compound tides and overtides). Firstly, the variation in power extraction and available power (defined as the fraction of extracted power removed by idealised tidal turbines) are investigated over a spring/neap tidal cycle using a simple theoretical model. Results from the model are used to derive analytical bounds to the variation in power at spring and neap tide. These bounds are shown to depend on the channels natural dynamic balance and are of practical importance to tidal stream device developers looking to supply power to the electricity grid. Secondly, changes in the higher harmonics in channel flow rate are investigated for deployments of tidal farm in channels of various length and geometry. Specifically, it is shown that in general if the turbines provide a uniform drag resistance to the flow through the channel, even harmonics in the flow rate will decay with power extraction (leading to a more symmetric tide), whilst odd harmonics in the flow rate may decay or increase depending on the natural tidal dynamics. These variations can have significant effect on residual flows and the local environment. Throughout the paper results from the theoretical model are compared with a complex numerical model of energy extraction from the Pentland Firth. Good agreement is shown in all cases.

Since the Fukushima nuclear disaster of 2011, Japan has relied on imported fossil fuels for electricity generation, but is quickly increasing its share of renewable energy sources. Recent development has been in biomass, geothermal, wind, and solar PV, though little attention has been given to the potential of marine energy resources. The present paper carries out an analysis of the economic viability of this resource using real wave and tidal current data. The results show that marine energy technologies could be cost-effective at several locations in Japan, and can pragmatically add reliable and predictable power to the energy generation mix. Deployed in straits with strong tidal flows near large population centers in western Japan, SeaGen and Verdant-type tidal turbines are shown to operate at costs far below the current price of electricity in the country. In northern Japan, the Aquabuoy, Pelamis, WaveDragon, and Guarda-type Oscillating Water Column Wave Energy Converters show costs near the current price of electricity. Even though Aquabuoy and Pelamis are now defunct, it is likely that in the future new generation wave energy converters would be able to produce electricity at even lower costs and further enhance the practicality of developing wave power in northern Japan. Keywords Japan; Tidal current; Wave; Cost; Electricity price; Capacity factor Highlights •Tidal current data and wave buoy measurements throughout Japan are utilized. •Energy generated by tidal stream turbines and wave energy converters is calculated. •In heavily populated western Japan, tidal stream turbines are very economical. •In northern Japan, wave energy farms can break even without subsidies. •Developing ocean energy resources reduces emissions and promotes energy independence.

There is a growing interest in utilizing tidal currents for power generation which has led to extensive research on this source of renewable energy. The amount of energy that can be extracted from tidal currents has been a topic of considerable interest to researchers for many years; still, there is no consensus on the extent to which this resource can be exploited. A turbine generates no power if it presents no resistance to the flow or if it presents so much resistance that there is no flow through it. At the same time, the estimation of exploitable resource should take into consideration the environmental, economic and social constraints. In view of these, the design of efficient turbines driven by bi-directional tidal currents has been a challenge to researchers for some time. There appears to be a general agreement among researchers that a number of turbines spread over the width of the channel can extract more energy compared to an isolated turbine. The present work is aimed at quantifying the improvement in the performance of a given type of turbine by utilizing a larger area of the channel. Numerical experiments were performed using the commercial CFD code ANSYS-CFX to study the performance of a bi-directional cross-flow turbine by simulating two cases of i) a single turbine and ii) a number of equally spaced turbines. It was found that the Coefficient of Power can be increased significantly by employing a larger area of the channel.

A variety of tidal current turbines (TCT) are emerging, the majority focussing on large-scale extraction of renewable energy at global tidal hot-spots. Concurrently, some turbines are small and may be suitable also for micro-scale applications (micro-TCT) in remote areas, such as decentralized electrification in countries where fuel-independent energy systems with high power predictability are particularly important. In shallow waters the force of tidal currents varies considerably over short distances and very site-specific measurements are important for assessment of localization, but are also expensive. For micro-TCT to be of interest site-screening and evaluation must be inexpensive, and low-cost methods are thus required. This study proposes a simplified tidal model that is calibrated to site-specific conditions by short-term observations using lightweight equipment. By measurements comprising down to 8% of the monthly tidal period the potential power output can be estimated, with uncertainty intervals up to ±20%, for currents applicable for micro-TCT. This site-screening method was tested at five sites in Mozambique where near-shore tidal currents were measured with lightweight current meters. At three of the sites, currents were estimated to exceed 1 m s−1 and power output was calculated based on technical assumptions for a micro-TCT device. Results are discussed from the perspective of micro-TCT development and decentralized remote area electrification.

This study investigates the wear characteristics of polymeric journal bearings while immersed in seawater, and their applicability towards wave energy conversion. A block on ring wear machine was used to test four commercially available bearing materials under unidirectional and oscillatory sliding conditions at low pressure. It was observed that wear generally increases with counterface roughness; however, major deviations to this trend exist, depending on the bearing’s composition. Stable wear rates were shown to vary widely depending on velocity profile, though a general trend could not be established for the sample group as a whole. It was shown that polymer wear rates cannot be attributed to any one parameter, and that detailed testing at several characteristic pressures and velocities is needed to determine a material’s applicability towards wave energy converters operating in real seas.

Interest in the marine renewable energy devices, and particularly tidal stream turbines, has increased significantly over the past decade and several devices such as vertical and horizontal axis turbines and reciprocating hydrofoils are now being designed around the world to harness tidal stream energy. While tidal stream turbines are being developed at a high rate and getting closer to commercialisation, it is important to acquire the right tools to assist planners and environmentalists, not only in finding a right location for the turbines, but also in identifying their potential impacts on the surrounding marine and coastal environment. In this study, a widely used open source depth integrated 2D hydro-environmental model, namely DIVAST, was modified to simulate the hydro-environmental impacts of the turbines in the coastal environment. The model predictions showed very good agreement with previously published 1D model results. Then, for demonstration purposes, the model was applied to an arbitrary array of tidal stream turbines in the Severn Estuary and Bristol Channel which has the third highest tidal range in the world. The model has shown promising potential in investigating the impacts of the array on water levels, tidal currents and sediment and faecal bacteria levels as well as the generated tidal power, which facilitates investigating the relative far-field impacts of the arrays under various climate change scenarios or different formations of the array.

The tidal stream power potential along the coast of the state of Georgia is evaluated based on numerical modeling and validated with the available data. The Georgia coast consists of a complex network of tidal rivers and inlets between barrier islands that funnel and locally amplify the strength of the ambient tidal currents in the region. The number of existing tidal current prediction locations is not sufficient to resolve the temporal and spatial changes in the current speeds and patterns. Therefore, the currents are modeled with the Regional Ocean Modeling System (ROMS) to determine the locations with high tidal stream power potential and the results are validated against measurements. The wetlands and the topographical features are integrated in the computational model with wetting and drying of computational cells. The locations with the largest mean tidal stream power density are identified and their characteristics are provided. The effect of power extraction on estuarine hydrodynamics is simulated by implementing an additional retarding force in the governing momentum equations in ROMS. Two different power extraction schemes are simulated at the Canoochee River. The first scheme involves extracting 20% of the original kinetic power across the entire cross-section of the river, and is found to have substantially lower impact on the original flow than the second scheme with 45% extraction. The summation of removed and residual kinetic powers is found to be larger than the original kinetic power in the cross-section, which is attributed to the recovery in the flow momentum through reorganization of stream flow energy. In both of the cases the major impact on the currents is limited to a partial reach of the river. The change in the maximum and minimum water levels is observed to be on the order of centimeters.

Traditionally, wells turbines have been widely used in OWC plants. However, an alternative has been studied over recent years: a self-rectifying turbine known as an impulse turbine. We are interested in the radial version of the impulse turbine, which was initially proposed by M. McCormick. Previous research was carried out using CFD (FLUENT®), which aimed to improve knowledge of the local flow behavior and the prediction of the performance for this kind of turbine. This previous work was developed with a geometry taken from the literature, but now our goal is to develop a new geometry design with a better performance. To achieve this, we have redesigned the blade and vane profiles and improved the interaction between them by means of a new relation between their setting angles. Under sinusoidal flow conditions the new design improves the turbine efficiency by up to 5% more than the geometry proposed by Professor Setoguchi, in 2002. In this paper, the design criteria we have used is described, and the flow behavior and the performance of this new design are compared with the previous one.

Power levels available from the kinetic energy of tidal flows can be significant in coastal or estuarine regions with relatively modest tidal ranges. For example, the central Maine coast, where the mean semi-diurnal tidal range is about 3 m, includes several river estuaries with narrow interconnecting passages where tidal currents exceed 2 m s−1. A numerical circulation model applied to this region shows that the vigorous tidal flows lead to available power peaks exceeding 3 kW per square meter of turbine aperture in several sites during a spring tide. At one promising location, the peak power density is 6.5 kW/m2 near the surface and the energy capacity in a 500 m2 section under mean tidal conditions is about 2700 MWh per year, sufficient to meet the average consumption needs of about 150 homes connected to an electrical grid capable of accepting the tidal power pulses and blending them with traditional sources.

This paper details the design, deployment and operation of a power take off system for a 1:4 scale offshore Oscillating Water Column (OWC) Wave Energy Converter (WEC). Ocean energy device prototypes at this scale present a unique set of challenges in that the integration of prime movers and generators typically begins to take place at this particular development stage, which may also represent first deployment at sea.The presence of electrical equipment and rotating machinery in the offshore environment brings its own engineering and operational difficulties. Moreover, such devices are typically not grid connected, necessitating the development of custom power conversion and control equipment. The paper describes the design considerations, details of design, deployment experiences, operational experiences of such a system and concludes with recommendations for future projects in the area.

The uncertainty in estimates of the energy yield from a wave energy converter (WEC) is considered. The study is presented in two articles. The first article considered the accuracy of the historic data and the second article, presented here, considers the uncertainty which arises from variability in the wave climate. Mean wave conditions exhibit high levels of interannual variability. Moreover, many previous studies have demonstrated longer-term decadal changes in wave climate. The effect of interannual and climatic changes in wave climate on the predictability of long-term mean WEC power is examined for an area off the north coast of Scotland. In this location anomalies in mean WEC power are strongly correlated with the North Atlantic Oscillation (NAO) index. This link enables the results of many previous studies on the variability of the NAO and its sensitivity to climate change to be applied to WEC power levels. It is shown that the variability in 5, 10 and 20 year mean power levels is greater than if annual power anomalies were uncorrelated noise. It is also shown that the change in wave climate from anthropogenic climate change over the life time of a wave farm is likely to be small in comparison to the natural level of variability. Finally, it is shown that despite the uncertainty related to variability in the wave climate, improvements in the accuracy of historic data will improve the accuracy of predictions of future WEC yield.

A nationally consistent wave resource assessment is presented for Australian shelf ( −1 (90th percentile of 60–78 kW m −1 ), delivering 800–1100 GJ m −1 of energy in an average year. New South Wales and southern Queensland shelves, with moderate levels of wave power (time-average: 10–20 kW m −1 ; 90th percentile: 20–30 kW m −1 ), are also potential sites for electricity generation due to them having a similar reliability in resource delivery to the southern margin. Time-average wave power for most of the northern Australian shelf is −1 . Seasonal variations in wave power are consistent with regional weather patterns, which are characterised by winter SE trade winds/summer monsoon in the north and winter temperate storms/summer sea breezes in the south. The nationally consistent wave resource assessment for Australian shelf waters can be used to inform policy development and site-selection decisions by industry.