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Generating electricity from the oceans
Abstract
Ocean energy has many forms, encompassing tides, surface waves, ocean circulation, salinity and thermal gradients. This paper will considers two of these, namely those found in the kinetic energy resource in tidal streams or marine currents, driven by gravitational effects, and the resources in wind-driven waves, derived ultimately from solar energy. There is growing interest around the world in the utilisation of wave energy and marine currents (tidal stream) for the generation of electrical power. Marine currents are predictable and could be utilised without the need for barrages and the impounding of water, whilst wave energy is inherently less predictable, being a consequence of wind energy. The conversion of these resources into sustainable electrical power offers immense opportunities to nations endowed with such resources and this work is partially aimed at addressing such prospects. The research presented conveys the current status of wave and marine current energy conversion technologies addressing issues related to their infancy (only a handful being at the commercial prototype stage) as compared to others such offshore wind. The work establishes a step-by-step approach that could be used in technology and project development, depicting results based on experimental and field observations on device fundamentals, modelling approaches, project development issues. It includes analysis of the various pathways and approaches needed for technology and device or converter deployment issues. As most technology developments are currently UK based, the paper also discusses the UK's financial mechanisms available to support this area of renewable energy, highlighting the needed economic approaches in technology development phases. Examination of future prospects for wave and marine current ocean energy technologies are also discussed
... RES offers numerous advantages, including the utilization of non-fossil fuels, minimal greenhouse gas emissions, low routine maintenance requirements, and cost-effectiveness [4]. In conventional systems, the generated RES output is typically in the form of direct current (DC), while transmission and loads necessitate alternating current (AC) [5,6]. Therefore, an Extended author information available on the last page of the article electronic converter is essential to convert the DC power into AC [7,8]. ...
... Using Eq. (15), the SHE-PWM expressions for the fundamental and the seven lower-order odd harmonics (n = 3,5,7,9,11,13,15) to be eliminated are given below: ...
... In Fig. 18b, the fast Fourier transform (FFT) spectrum of the terminal voltage is presented. It is evident that the MFO-optimized solution successfully minimizes all seven targeted lower odd harmonics (n = 3,5,7,9,11,13,15), while also reducing the 17th order harmonic, which falls outside the elimination range. The dominant harmonic is observed at the 19th order and 950 Hz, beyond the intended frequency range for elimination. ...
The escalating demand for sustainable and environmentally friendly energy sources has driven substantial growth in renewable energy adoption across residential and industrial sectors. To effectively meet this demand, the development of efficient and sustainable renewable energy conversion methods is crucial, with inverters playing a pivotal role in achieving this objective. While researchers strive to enhance inverter power handling capabilities and reduce output harmonic contents, the incorporation of additional power electronic switches and peripheral devices presents challenges such as increased circuit cost, complexity, and size. Additionally, the utilization of high-frequency switching techniques for achieving low output harmonics results in elevated switching losses and electromagnetic interference, adversely affecting sensitive electronic devices. This research introduces a novel approach to address these issues through the introduction of a reduced switch multilevel inverter topology. Unlike existing systems, the proposed topology employs a reduced number of power electronic switches and direct current sources to generate a stable output voltage waveform. Operating in a symmetric mode, the topology achieves a nine-level output voltage with enhanced harmonic elimination capabilities. A multiple-stepped selective harmonic elimination (SHE-PWM) switching control technique, employing a 1/3/3/1 distribution ratio, is utilized to extend the harmonic elimination range from 3 to 7 lower-order harmonics. To optimize the switching angles required for the proposed topology, the moth flame optimization (MFO) algorithm is employed and compared with particle swarm optimization (PSO) and whale optimization algorithms (WOA). The MFO algorithm exhibits faster convergence to the global optima, achieving an optimal fitness value of 3.322e⁻⁰⁸ at 0.78 modulation points. This results in total harmonic distortion values of 0.7%, 0.757%, and 1.069% for MFO, PSO, and WOA, respectively, with corresponding total losses of 71.609W, 71.794W, and 79.792W. The proposed inverter topology is simulated using PSIM software and experimentally verified using a typhoon HIL-402 hardware-in-the-loop testing device. The simulation and experimental results provide compelling evidence for the superior performance of the MFO algorithm compared to PSO and WOA in achieving improved inverter performance. The proposed topology, in conjunction with the MFO algorithm, presents a promising solution for efficient and sustainable renewable energy conversion, thereby contributing to the advancement of renewable energy technologies in both residential and industrial settings.
... Comparado con una central hidroeléctrica que depende del almacenamiento de grandes cantidades de agua, la extracción de energía del océano es más viable y sustentable, debido a que el flujo marino es constante y predecible [5]. Las diferentes formas de generación de energía mediante el océano, son: por corrientes marinas, oleaje, gradiente térmico y salino. ...
... Las diferentes formas de generación de energía mediante el océano, son: por corrientes marinas, oleaje, gradiente térmico y salino. Éstas tecnologías tienen muchísimo potencial de aprovechamiento en el futuro, en especial, la generación por corrientes marinas, ya que se comporta de manera similar al viento en la superficie terrestre, lo que permite extraer grandes can-tidades de energía en regiones con alto flujo marino [5]. La forma de extraer energía de las corrientes marinas, es por medio de los convertidores eléctricos de corrientes (CEC) que se muestran en la Figura 1.2. ...
... m/s por kilómetro mar adentro [10]. Si se considera un rotor para la turbina de 21 metros (ideal por las condiciones de profundidad), se puede aproximar la potencia disponible P en la zona mediante (1): donde: ρ ( kg/m 3 ) es la densidad del flujo, A (m 2 ) es el área de la sección transversal del rotor y V 0 (m/s) es la velocidad del fluido [5]. Sustituyendo los datos recopilados: ...
... Crucially, ocean wave energy possesses high power density and is abundant and widely distributed [2]. It has been considered one of the most promising ocean renewable energy resources [3,4]. Consequentially, various concepts for wave energy conversion have been proposed and tested, including oscillating bodies [5] (i.e., the wave energy is converted to the kinetic energy of floating bodies and then to electricity), overtopping devices [6] (i.e., the wave energy is converted to potential energy and then to electricity) and oscillating water columns (OWCs) [7,8] (i.e., the wave energy is converted to the kinetic energy of an air column and then to electricity). ...
... n and k (3) n are the positive real roots of the following equations: ...
... (12) and (13) respectively. Then the exact particular solutions, ϕ (2) V and ϕ (3) V for the heave mode can be obtained [63,64]: ...
A multi-functional floating foundation integrating an Oscillating Water Column (OWC) Wave Energy Converter (WEC) with a Floating Offshore Wind Turbine (FOWT) is a promising design for achieving cost reduction, adaptability and stability improvements. Yet, such a multi-functional integration is still in a demonstration phase and additional investigations are required to reach industrial maturity. This work assesses the hydrodynamic performance of such a design by carrying out a series of carefully instrumented scaled model tests. Two distinct sets of experimental models were designed accordingly, i.e., a pure FOWT without the OWC device, and the FOWT incorporating the OWC device. The multi-functional foundation is either fixed or allowed to move in heave mode along four vertical sliding rails. The introduction of the OWC device enhances the stability of the FOWT in heave, with a maximum motion reduction rate of 54.1%. The chamber air orifice size and the foundation geometries were optimized. The OWC with an air chamber opening ratio of 3.0% produces the maximum relative capture width. A larger chamber draft and breadth lead to a lower chamber resonance frequency. The main objective of this paper is to guide the design and application of the OWC device integrated into a floating offshore wind turbine.
... An ocean has two types of energy resources. These are waves and wind for producing electricity [1]. The development of offshore wind turbines and wave energy converters (WECs) should not disorganize the ecological balance [2]. ...
... Hence, the equations are expressed versus the amplitude of the motion of each degree of freedom, =1:5 . Therefore equations (13) and (14) are the frequency domain forms of equations (1) and (3), respectively, which have been rearranged. It is noted that radiation, viscose, and hydrostatic forces are defined in a linear form versus the added mass, radiation damping, viscose damping, and hydrostatic stiffness coefficients. ...
... where , , 1 , and 33 are the surface area, draft, horizontal position, and heave acceleration of water particles, respectively. A similar concept can be applied for deriving the scattering force on the water column. ...
A combination of offshore wind turbines and wave energy converters has recently been the focus of the researchers. Many types of converters have been installed on the offshore platform in the design step, and the performance of these hybrid systems has been investigated. The oscillating water column converter is one of the most favorite and commercialized systems due to its efficiency and low maintenance cost. In the present work, a new design including the array of the oscillating water column in a circular arrangement around the spar-type platform is considered. The coupled governing equations are solved based on the simplified analytical approach through the frequency domain analysis. The results obtained show that the increase in the number of energy converters increases the total generated power, and consequently, the converters capture the vibrational energy of the spar platform. Therefore, the dynamic response of the spar decreases in the case with an array of energy converters, which is one of the main objects of this hybrid system.
... This is the reason energy generated from RES needs to be store in energy storage devices (ESD) like battery, fuel cell, super capacitors etc. Energy stored in these storage devices are in direct current (DC) form, whereas mostly appliances works in alternating current (AC) form, A device, that is used to convert DC into AC, called inverter relates to RES or ESD to meet the appliances requirements [4], [5]. Inverters are used for grid-connected, flexible alternating current transmissions systems (FACTS), because of its low cost, flexibility, and effectiveness for Yaqoob) 229 power conversion it is getting an attention for the scholars [6]- [12]. ...
... To get the output of Vdc S1 and S4 are switched on and for -Vdc S2 and S3 are turned on. Since the output voltage of the CHB-MLI is the sum of all the h-bridges as given in (5). The number of levels from this type of inverter can be calculated by n = 2S+1 where S is the number of DC sources [47]. ...
Renewable energy has a great importance for power generation as it does not use the fossils fuels. Energy generated from alternative energy sources are weather dependent. To generate a continuous power to meet the load requirements, Battery energy storage system are used. Power conversion process must be much efficient as possible to convert the DC stored energy into AC. This conversion process is usually done by the help of inverters. This paper gives the brief overview on three main categories of multilevel inverter like cascaded h-bridge, neutral point clamped and flying capacitor multilevel inverter and highlights their advantages which can also help the scholars to deeply explore the categories of multilevel inverter. Harmonic elimination is usually done by controlling the switching angles of the inverter. Among all the switching angles techniques, selective harmonic elimination pulse width modulation (SHEPWM) technique is widely used, that has also discussed in this paper. Furthermore, to eliminate the harmonics using SHEPWM, it has the set of nonlinear transcendental equations, these set of equations can be effieceintly solved by the optimization methods. The most efficient and reliable optimization method like particle swarm optimization has been discussed with multiple objective functions in this paper. This paper will help the scholars to understand the finest category of multilevel inverter for harmonic elimination in terms of efficiency and output quality.
... Some of the main areas where wave farming is carried out are Portugal, the United Kingdom, Australia, and the United States. Among all Portugal has the very first wave farm, the Agucadoura Wave Farm its about 3 miles offshore, north of Porto [15]. In 2010, United Kingdom also launched a wave farm in Scotland [16]. ...
... In eqn. (11) ρ w is water density (1030 kg/m 3 ), g is gravity constant (9.81 m/s 2 ), T e is wave energy period, H s is the significant wave height and η wav is overall performance of the plant with length L [93]. ...
Renewable energy is not only a viable economic choice in Palestine, but it is also an imperative requirement to end the country's current energy crisis, which is particularly acute in the West Bank and Gaza Strip. The main focus of this study, which makes it the most thorough in its sector, is showcasing Palestine's distinct renewable energy potentials (thermal solar, PV, wind, biomass, and hydropower). The System Advisor Model software (SAM) was used to predict the power potentials for a year. The results indicate that Palestine has a significant potential for PV power generation within 1,700 kWh/kWp. Wind energy can see a considerable difference in capacity, with a mean power density in the high mountains of WB of 600W/m2, a mean power density for all of WB of 300W/m2, and a relatively low power density for GS of less than 100W/m2. Options for investments in the high seas and with the nearby Arabic nations were also offered. About 1,717 GWh of energy equivalent comes from biomass resources. It is determined that the best designed system can produce 82% of the total while only 18% is purchased from the grid using HOMER to retrieve the optimum on-grid hybrid energy system. Furthermore, only 70.7% of the energy produced is consumed, with the remainder being sold back to the grid. Therefore, using renewable energy sources in addition to the grid is advised to cut costs and potentially generate income. Reduce reliance on fossil fuels and combat global warming, as well.
... Spatial mapping of tidal currents is important for a range of sectors and research fields. This work focuses on sites related to tidal stream energy extraction (Bahaj, 2011;Khan et al., 2009) where knowledge of currents is vital at all stages of project development, from initial resource assessment (Carpman et al., 2016;Cossu et al., 2021;Murray et al., 2017;Sentchev et al., 2020) to detailed turbine array planning (González-Gorbeña et al., 2018;Frost et al., 2017;Togneri et al., 2016). However, marine surface current information is also important for aquaculture (Brooks et al., 1999;Mente et al., 2006;Sponaugle et al., 2002;Carral et al., 2021), marine pollution assessment (Bellomo et al., 2015;Keramea et al., 2021;Kim et al., 2010), plankton studies (Geyer et al., 2022), sediment transport (Duvall et al., 2019) and other coastal and environmental projects (Rusdiansyah et al., 2018;McIlvenny et al., 2021;Estournel et al., 2001;Kataoka et al., 2013); the findings presented here are equally applicable to such fields. ...
... Desalination of oceans though remains quite expensive, appears to be one of the promising avenues to furnish potable water to the growing human population of the world (Youssef et al. 2014). The kinetic and thermal energies of the oceans driven by solar insolation can be effectively utilized to extract renewable energy options (Bahaj 2011), though a substantial level of research is still required to enhance the efficacy levels. Thus, the oceans can provide a bundle of provisioning services and most of it can be renewable if the oceanic domain, on the whole, is conserved properly following the guidelines for SDG 14. ...
All the oceans of planet Earth are inter-connected and comprise one huge water body. Due to wind-driven forces and thermohaline circulation, all the water molecules get circulated to every nook and corner of this giant water body. However, based on several physical and chemical properties, as well as geomorphological features, marine water bodies can be classified into several smaller dimensions.
... They are deemed practical and environmentally friendly, with vast potential to alleviate these concerns. Wave energy serves as a notable example of ORE sources [5,6]. Once ORE facilities, like wave power plants, are established, they inherently become significant assets, playing a crucial role as critical infrastructures within a country. ...
Offshore Renewable Energy (ORE) is a promising solution to address the challenges of climate change and the depletion of fossil fuels [1]. Wave power, a form of ORE, is considered one of the purest energy sources with significant growth potential [2]. In addition to investing in these energy sources, nations are also working to enhance the protection of Critical Infrastructure (CI). CI encompasses all services crucial to the functioning of society and the economy, including electric power systems and their various forms of generation, such as renewable energy sources. Hence, in addition to exploring various forms of power generation, the cybersecurity of the networks connecting the devices in these systems is a crucial aspect to consider to prevent attacks and minimize the risk of cyber threats to suppliers and customers [3]. For instance, the European Commission states that reducing CI vulnerability and increasing its resilience is one of the main objectives of the European Union. However, to date, a comprehensive review that synthesizes the various approaches to cybersecurity in ocean energy is yet to be published. The objective of this study is to present a comprehensive survey of the application of cybersecurity measures to renewable energy sources, with a specific focus on ocean energy. A systematic review of the literature was carried out, following the steps outlined by Kitchenham [4]. The methodology steps are illustrated in the flowchart (see Figure 1). Of the 49 articles selected, three main study topics emerged: i) smart ocean, ii) cybersecurity for renewable energy systems, and iii) marine data security. These three topics are interrelated as a smart ocean can be considered as an integrated sensing, communication, and computing ecosystem that connects marine objects in surface and underwater environments [5]. Once the wave energy converters (WECs) are installed, it is also essential to develop safety systems for these devices, as demonstrated in the first report on cybersecurity guidance for MRE (Marine Renewable Energy) systems [6] prepared by the Pacific Northwest National Laboratory (PNNL). In preparation for this report, researchers reviewed the cyber threats and vulnerabilities of information technology (IT) and operational technology (OT) equipment used in various WEC models. Figure 2 presents an example of the possible threats and attacks on WEC devices. In conclusion, this article provides a comprehensive survey of the application of cybersecurity measures in ocean energy, highlighting the importance of reducing vulnerability in the cybersecurity of power plants in this sector. Through a systematic review of the literature, three main study topics were identified and analysed, providing a valuable resource for future research in this area. The findings of this study can inform and guide the development of more secure and resilient systems, contributing to the overall improvement of critical infrastructure in the field of ocean energy. As such, this article offers a significant contribution to the ongoing effort to address the challenges posed by the changing energy landscape and the need to protect critical infrastructure from cyber threats. Please refer to uploaded PDF to see references and figures.
... It is a type of renewable energy (REs) and is described as energy that a natural source can generate, so it is called renewable energy. Examples: solar energy (sunlight) [4]; wind energy (wind movement) [5,6], hydroelectricity (river flow or offshore waves) [7]; geothermal energy (hot springs) [8]. In addition to biofuels such as IOP Publishing doi: 10.1088/1755-1315/1213/1/012097 2 methane extracted from plant or animal waste [9]; or vegetable oil [10] extracted from plant seeds. ...
Energy is an essential component of meeting social needs and economic growth. The international energy agency (IEA) estimates that a 53% increase in global energy consumption is expected by 2030. Pollution of environment, climate change, and the growing of demand energy worldwide require serious attention. Moreover, fossil fuels will significantly contribute to greenhouse gas emissions from combustion and exacerbate climate change. Renewable energies (REs) such as solar, wind, hydropower, geothermal, and biofuels are the right solution to running out of fossil fuels, protecting the environment, and stopping climate degradation. Many countries have jumped into the field of energy production from photovoltaic panels to reduce dependence on fossil fuels and recorded success stories. This paper reviews the great efforts developed countries and the rest of the world made in investing in solar energy. Especially photovoltaic energy, and compares it with the reality of the situation concerning the neighboring countries of Iraq in general and in Iraq in particular, and shows the determinants of developing this industry and the difficulties it faces, especially in the field of providing electricity to cities and farms. Moreover, providing appropriate solutions based on the success stories achieved by other countries.
... Currently, there is an increase in research on potential assessment and technology of marine renewable energy. , With a theoretical production of 2,000 trillion kWh of electricity per year (excluding wind energy), the reserves of renewable energy in the ocean far exceed human energy demand in theory [9], many times the global electricity consumption. By 2050, usable offshore wind energy could reach 16,000 TWha -1 [10,11]. ...
To achieve peak carbon emission and carbon neutrality, marine renewable energy plays an essential role in energy transition in China’s coastal areas. Fujian Province is not only exposed to a shortage of traditional energy resources, but also urgently needs to change its current coal-based energy structure to reduce carbon emissions. In contrast to the scarcity of fossil fuels, Fujian Province has rich marine energy reserves, with an abundant supply of offshore wind, wave, tidal, and ocean current energy. Therefore, the active development of low-carbon and carbon-free marine energy can increase the energy supply and alleviate energy shortages. Furthermore, it can optimize the structure of the energy sector in this region. This study analyzed the energy structure of the Fujian Province, the effort needed to reach the carbon neutrality goal, the reserves of marine energy resources, the background of marine energy development technology, and socio-economic conditions. We believe that the development of the marine energy is a critical action towards solving the current energy resource limitations in Fujian and subsequently propose relevant suggestions for marine energy industry development in Fujian Province in terms of development ideas and pathways.
... Several tidal (Breeze, 2019a) and marine power generation technologies (Breeze, 2019b; Gish, 2020) have been studied over the past decade, and it is estimated that this sector could employ 1 million people worldwide by 2030 (Esteban & Leary, 2012). Despite being variable in intensity, ocean currents are highly predictable, which, along with the high load factors of fluids, make them a reliable resource for electricity generation (Bahaj & Myers, 2003;Bahaj, 2011). ...
This paper represents the effects of geometry and design of an oscillating water column energy converter air chamber on the airflow response. The primary goal of this research is to use different shapes of air chambers, such as rectangular, cylindrical, and conical air chambers with varying cross sections, to optimize the air velocity entering the turbine, to obtain the maximum power available in a progressive wave with a constant period and wavelength. Modeling and numericalsimulation are performed by using the commercial software ANSYS. Since this paper is concerned with the effect of air flow velocity, a vent is located at the chamber's outlet rather than a turbine. In order to obtain the exit air velocity results, the wave system air characteristics results are applied as an input air flowfor three air chamber cases. The results show that the air velocity flow increasedsignificantly from 7.14 m/s in the rectangular air chamber to 10.4 m/s in cylindrical air chamber and reached a maximum of 14.2 m/s in the conical airchamber.
... Several tidal (Breeze, 2019a) and marine power generation technologies (Breeze, 2019b; Gish, 2020) have been studied over the past decade, and it is estimated that this sector could employ 1 million people worldwide by 2030 (Esteban & Leary, 2012). Despite being variable in intensity, ocean currents are highly predictable, which, along with the high load factors of fluids, make them a reliable resource for electricity generation (Bahaj & Myers, 2003;Bahaj, 2011). ...
An underwater manipulator is one of the most commonly used tools in offshore operations. In the face of the unknown environment of the deep sea and the uncertainty of the operation target, the underwater manipulator needs good control stability and higher control efficiency to prevent accidents, which puts forward higher requirements for the control of the manipulator. Underwater manipulators often need to work under heavy loads and to perform tasks efficiently under light loads, which is crucial for efficient control under load. In this paper, a control algorithm based on proportion and derivative feedback control for an all sea depth load proportional hydraulic manipulator is proposed. The feasibility and progressiveness of this algorithm are verified by building kinematic and dynamic models, building physical platforms for tests, and building sea trial acceptance.
... The research and development of the HOWWE has practically experienced productive and significant progress over the past two decades. The hybrid system has a prodigious potential for improvement and creates a vital part in the EU and global energy policy [4]. The worldwide target capacity of 460 GW offshore-wind and 188 GW wave-energy has been established by 2050 [5]. ...
Renewable energy resources such as offshore wind and wave energy are environment friendly and omnipresent. A hybrid offshore wind-wave energy (HOWWE) system produces a more efficient, economical and sustainable form of energy than exploitation of the individual resources. The objective of this paper is to give a detailed review of co-generation technologies for HOWWE. The proposed areas of this review paper are arranged based on the power conversion techniques, response coupling, control schemes for co-generation and complimentary generation, colocation and the integrated conversion system. This paper aims to offer a systematic review to fully cover recent research and development of the HOWWE system. The current HOWWE structures lack efficiency due to their design and AC-DC-AC power conversion that need to be improved by applying an advanced control strategy. Thus, using different power conversion techniques and control system methodologies, the HOWWE system can be improved and transferrable to the other hybrid models such as hybrid solar and wind energy. The state-of-the-art HOWWE systems are reviewed. Critical analysis of each method is performed to evaluate the best possible combination for development of a HOWWE system.
... There is increasing worldwide interest in using wave energy and sea currents (tidal flow) for electrical power generation. Wave energy is less predictable and is derived from wind energy (Bahaj et al., 2011). Energy production from the sea is achieved in the following ways: Energy production from the sea also has great potential in terms of renewable energy sources. ...
The need for energy resources in the world continues to increase day by day. Energy demand will increase in the coming years in parallel with population growth, industrialization and technological developments, especially in developing countries. The fact that fossil energy sources cause environmental problems, their reserves will be depleted shortly, dependence on source countries causes various political and economic problems, and price instability increases the interest in renewable energy sources. Especially in developed countries, renewable energy sources such as hydraulic, wind, geothermal, solar, biomass, wave, hydrogen etc. Energy sources are used in various ways, especially electricity production. As a developing country, Turkey's need for energy resources increases day by day in parallel with its increasing population and growing economy. Turkey, which is approximately 75% foreign-dependent in terms of its current energy structure, seems to be a necessity rather than a choice to reduce this dependency on renewable energy sources. In this study, Turkey's current renewable energy potential has been revealed, and various suggestions have been made by analyzing the renewable energy potential.
... [82,83], was applied. These authors also suggested a rich energy region would have a minimum of 20 kW/m while [84] stated a 'good' location will have an annual average range of wave energy between 20 and 70 kW/m. The frequency of Pw ! 2 kW/m has been reached in 250 WEC sites out of the 259 site, and only nine WECs disobeyed this rule. ...
Wave energy is foreseen to contribute largely to the renewable energy projected to supply 20% of Egypt's electricity budget to meet burgeoning energy demand. Therefore, this research analyses the Nile Fan wave energy forecasted from numerical modeling for 2020 of the Copernicus Marine Environment Monitoring Service (CMEMS) database, hourly spatially sampled at 0.042° as the finest scale remotely-sensed data available. Wave energy spatial distribution is analyzed using data from 259 points proposed as Wave Energy Converters (WECs). Spectral analyses techniques were appraised for disclosing the frequency and energy return periods of the significant wave height and peak periods and to understand the similarity among selected WECs of varied conditions. Factor analysis is conducted to investigate the magnitude of factors controlling the wave dynamic and energy potential. K-means clustering was used to distinguish energy classes with large inter-class variances. The obtained resources (average wave energy density, around 5.32 KWh/m; maximum recorded value of 112.9 KWh/m; annual wave energy density sum of about 46.96 MWh/m) are among the largest found in the Mediterranean Sea. Spectral analysis clarified a strong periodicity at 21 days, intermittent periods of 2.66 days, and 7.5 days dominate over the year while a 22.6 hourly period dominates in summer. January attained the strongest peak frequency of 8.4 in the west, 6.6 between the NW and SE sites, 5.20 for the near shore sites. Directional analysis indicated a bimodal wave system (325º and 285°-295º) in the west and unimodal (285°295º) in the east, while the central area showed combined distribution; bimodal in the deep water and unimodal near the shore. The 285°-295º wave direction showed largest contribution to the wave energy density. The northwest is the most energetic and most productive area. Monthly and seasonal wave energy clarified maximum of 9.98 MWh/m in January and 22.6 MWh/m in winter that contributes to 21% and 53% of the yearly mean, respectively. The wave energy resource is more than 3.5 times greater in winter than in summer. Exploitable energy density level exceeding 2 KWh/m are recorded for 250 sites out of the 259 site. Factor and detrended correspondence analyses confirmed that more than 98% of the Nile Fan's wave energy variance is controlled, in decreasing order of influence, by the depth, distance to shore, significant wave height, wave peak period, and wave principal direction. Four classes of varied statistics and hence different wave behavior were distinguished affected by the depth, morphology of the shoreline, and the dominating wave direction. Deepest water and near shore classes attained the largest wave energy. Further details on the effect of the environmental factors on the wave shape and corresponding energy are concluded.
... With the rapid development of economy and society, the problems of energy shortage and environmental pollution have become more and more serious, and the exploration of new energy sources has gone to the ocean [1][2][3][4][5]. The climate change in recent years has pushed the development and utilization of clean energy to a new height [6][7][8][9]. ...
Turbine is one of the key components of ocean thermal energy conversion system, and its aerodynamic performance and geometric structure directly affect the performance of the system. At present, the design methods of radial inflow turbines can be roughly divided into three categories: trial method, best velocity ratio method and screening method, which follow no concrete rules and are not comprehensive, and rely mostly on the designers' experience. This study proposes a fully data-based non-parametric model identification and optimization method for ocean thermal energy conversion radial inflow turbines is proposed, and takes the 25 kW R134 working fluid turbine of the ocean thermal energy conversion system as an example for verification and analysis. First, the optimal Latin hypercube sampling method was used to complete the experimental design with seven initial thermodynamic parameters as independent variables. And then according to the test data and the Gaussian process regression identification, the non-parametric turbine thermodynamic model was obtained. At last, on the basis of this model, the NSGA-III multi-objective optimization algorithm was used to optimize the design with the goal to achieve maximum efficiency and minimum diameter, and the optimized results were obtained. The results show that the non-parametric model based on the Gaussian process proposed in this study has higher accuracy, and the optimization results obtained based on this model are more efficient and have a more compact structure. The research work described in this study saves time and cost for completing the aerodynamic performance design of the turbine and further improving the expansion efficiency of the radial inflow turbine. It is of great significance for the practical application of promoting ocean thermal energy conversion.
... The predictable behaviour of most of the tidal currents around the world shows periodic patterns with small fluctuations over the year, e.g. compared to atmospheric wind behaviour ( [19,20]). This characteristic of tidal currents allows the designer to choose the cut-out speed very close to the maximum speed predicted at the deployment site. ...
This work refers to towing-tank experiments and numerical simulations of the hydrokinetic turbines for the GEMSTAR system, designed at the University of Naples. The experimental campaign was aimed to validate the quality of the turbine design procedure, utilising low order methods such as Blade Element Momentum theory (BEMT). Discrepancies were found between BEMT results and experiments. Therefore, higher order CFD numerical models were employed to investigate on the rotor hydrodynamic behaviour, simulating the experiments. Blade section pressure distributions, obtained from 3D simulations, were compared with pressure distributions obtained from 2D calculations to explain discrepancies between BEMT and experiments. It was found that pressure distributions from 2D calculations are significantly different from the ones extracted from CFD, especially at inboard sections. As shown previously in literature for wind turbines, the presence of complex 3D phenomena arising from the combination of rotation and pressure distribution on the blades was demonstrated in water turbines. Finally, a so-called 2.5D approach was developed to improve BEMT results, with the sectional forces extracted from 3D simulations. The 2.5D BEMT was validated against the results of a test series with variable collective pitch, showing an acceptable agreement to the observed data for slight pitch angle variations.
... [4] Nevertheless, the harvest for such natural energy is intermittent since its collection is generally impacted by complex/random factors (like geographic location, sunshine duration, capricious climate, etc.). [5][6][7] To make effective use of these sustainable energy sources and balance the grid during the peak-power demands, the development of large-scale and low-cost electrochemical energy storage (EES) systems undoubtedly plays a critical "enabler" role. [8] To date, both supercapacitors and batteries have dominated as popular EES devices due to their high charge-storage efficiency, outstanding cyclic durability and design diversity. ...
Abstract The ever‐growing demands for green and sustainable power sources for applications in grid‐scale energy storage and portable/wearable devices have enabled the continual development of advanced aqueous electrochemical energy storage (EES) systems. Aqueous batteries and supercapacitors made of iron‐based anodes are one of the most promising options due to the remarkable electrochemical features and natural abundance, pretty low cost and good environmental friendliness of ferruginous species. Though impressive advances in developing the state‐of‐the‐art ferruginous anodes and designing various full‐cell aqueous devices have been made, there still remain key issues and challenges on the way to practical applications, which urgently need discussing to put forwards possible solutions. In this review, rather than focusing on the detailed methods to optimize the iron anode, electrolyte, and device performance, we first give a comprehensive review on the charge storage mechanisms for ferruginous anodes in different electrolyte systems, as well as the newly developed iron‐based aqueous EES devices. The deep insights, involving the inherent failure mechanisms and corresponding modification/optimization strategies toward iron anodes for the development of high‐performance aqueous EES devices, will then be discussed. The advances in applying iron‐based aqueous EES devices for emerging fields such as flexible/wearable electronics and functionalized building materials will be further outlined. Last, future research trends and perspectives for maximizing the potential of current iron anodes and devices as well as exploiting brand‐new iron‐based aqueous EES systems are put forward.
... The resource forms existing in the immense ocean are diverse and abundant, including offshore wind power, wave energy, tide energy and salinity gradients, etc (Bahaj, 2011). Among them, wave energy is of great potential and stands out owing to its unique advantages, such as high energy density (Drew et al., 2009;Ozkop and Altas, 2017) and low environment impacts (Iglesias and Carballo, 2014). ...
Performance enhancement is always the focus for the exploration in oscillating water column (OWC) wave energy converter devices. In the present study, the hydrodynamic characteristics of a dual-chamber OWC system composed of two 3D circular sub-units is examined under the framework of OpenFOAM. The model-scale simulations are firstly carried out in a wave flume with different widths under the excitation of regular waves. Then, conceived from the side wall effects in narrow flumes, a pair of harbor walls parallel to the wave propagation direction are introduced; by tuning its deployed location and geometric dimension, the enhancement of wave power extraction can be expected. The results indicate that significant estimation errors in the capture width ratio may occur when the incident wave length is nearly equal to the flume width or the resonant frequency of water column is close to the wave frequency in a narrow flume. In addition, the integrated system consisting of OWC and harbor walls shows that the distance between above two structures can be tuned to a threshold value to maximize the capture width ratio by strengthening the fluids and structures interaction. The medium submerged depth of harbor walls may be an alternative when the trade-off between performance enhancement and economic costs has to be considered during practical construction. Moreover, a well agreement between the results from model-scale and prototype-scale prove that the performance enhancement can be scalable to large scales by integrating OWC device with harbor walls.
Buku ini mengajak kita untuk menjelajahi potensi biota laut, mulai dari keanekaragaman hayati seperti ikan, rumput laut, terumbu karang, mangrove, hingga padang lamun yang tak hanya memiliki nilai komersial tinggi tetapi juga memegang peranan krusial dalam konservasi lingkungan laut. Tidak ketinggalan, pembahasan tentang sumber daya kelautan non-hayati seperti minyak dan gas bumi, batubara, pasir besi, garam, dan energi laut turut menjadi fokus utama buku ini, menggambarkan betapa besarnya kontribusi mereka dalam perekonomian global.
Namun, di balik kekayaan yang melimpah, bukanlah tanpa tantangan. Kita akan bersama-sama menjelajahi tantangan-tantangan dalam pengelolaan sumber daya kelautan, mulai dari perubahan iklim hingga masalah polusi yang mengancam keberlangsungan ekosistem laut. Namun, bersama dengan tantangan, buku ini juga membawa harapan. Melalui pembahasan yang mendalam, kita akan menemukan solusi-solusi inovatif untuk mengatasi tantangan tersebut, serta upaya-upaya pengelolaan yang berkelanjutan untuk menjaga kelestarian sumber daya kelautan bagi generasi mendatang.
The oscillating water column (OWC) is an economical and feasible type of wave energy converter with minimal maintenance costs which have been widely investigated. In this study, the effect of lipwalls for a shore-front OWC is investigated using Dual Boundary Equation Method (DBEM) and Computational Fluid Dynamics (CFD) approaches. The boundary value problem is solved using the DBEM method within the framework of linear water wave theory. Whilst in the CFD approach, the volume of fluid (VOF) approach is used for simulating the numerical wave tank, with appropriate boundary conditions and regular wave inlet. The DBEM approach is beneficial to understand the complex phenomena inside the chamber viz. radiation conductance and susceptance. It is inferred that case-B is found to exhibit better performance for a wider range of non-dimensional wave frequencies due to its wave trapping configuration where the position of the lower lipwall is orthogonal. The CFD studies provide interesting insights on the optimal damping ratio concerning wave amplification factor at higher relative water depths, power output, and correlation of phase difference. Besides, the study reveals that the pressure and wave elevation inside the chamber is associated with the inhalation and exhalation process of air is attributed to the lower half of the lipwall.
Today's energy challenges are multifaceted. Over the past 30-40 years, energy issues have been discussed and published on an extensive scale. The green transition involves concrete actions related to increasing energy efficiency, replacing fossil fuels with alternative fuels, producing energy using renewable resources, creating various means of transport that use electric motors, identifying technical solutions that generate an increased energy yield in the case of buildings, and waste reduction, reuse and recycling. In order to attain a climate-neutral environment, it is mandatory to impose regulations, measures and actions to help decarbonize the energy sector. The analysis of published articles on these issues is the subject of this large and information-dense review. Concretely, the transition to climate neutrality will generate obvious advantages at an economic, social and technological level, for example, the opportunity for economic growth, new business models and new markets, and the generation of new jobs or technological development. At the same time, this paper underscores the need for a multifaceted approach, integrating technological innovation, policy intervention and global cooperation for an effective energy transformation. The review suggests future issues and research directions, focusing on viable strategies for energy transition and its socioeconomic environmental impacts.
A developing country's economic interest is to determine when its national income approaches that of developed nations. The availability of energy, natural resources, and geographic location are important factors in this. Renewable energy appears to be the answer of the future, while traditional electricity sources like gas and oil are scarce, costly, and harmful to the environment. Pakistan has the ability to meet its electricity needs, addressing issues like power shortages, pollution, and high production costs. The country is strategically located and has an abundance of renewable resources. If this potential is fully realized, Pakistan might even start exporting electricity. Although the nation has started wind, solar, hydroelectric, and bioenergy projects, tidal energy is still mainly unexplored. Recent research provides evidence for the consideration of tidal energy as a potential renewable source for Pakistan's energy needs. The exploration and utilization of these renewable resources not only address the energy needs of Pakistan but also contribute to global efforts in adopting sustainable energy practices. Efforts towards harnessing tidal energy in Pakistan should be intensified, especially along the coast where natural tidal lagoons are prevalent. In-depth surveys and thorough investigations are crucial, particularly in the creek regions of Sindh province.
This article focuses on the optimization of the layout of a tidal current turbine array (TCTA) using the Quantum Discrete Particle Swarm (QDPS) algorithm. The objective of the optimization is to balance the maximum energy output and minimum levelized cost of energy (LCOE). The optimization model proposed in this paper was constructed by combining a computational tidal model and the QDPS algorithm, which incorporate several advancements, including modeling of underwater terrain, obtaining tidal current field using high-fidelity ocean model, considering turbine properties, formulating partial influence of wakes on turbines, accounting for interactions between multiple wakes, modeling of safe operating distance, developing an LCOE model, and computing the sea space utilization area of a tidal farm. The proposed method was applied to optimize the layout of TCTA in a real waterway, which employed maximum tidal current fields during flooding and ebbing periods of spring tides as input for safety reasons. The results indicate that compared to a regular staggered layout, the total power generation improved by 19% and 16%, and the LCOE reduced by 12% and 15%, respectively, when the concluded optimized layout was utilized. Sea area decreased by 24% when LCOE was minimum. Overall, the proposed method has a better performance and can support the set selection as well as turbines placements of tidal current farms.
Over the last two decades, a large body of academic scholarship has been generated on wave and tidal energy related topics. It is therefore important to assess and analyse the research direction and development through horizon scanning processes. To synthesise such large-scale literature, this review adopts a bibliometric method and scrutinises over 8000 wave/tidal energy related documents published during 2003–2021. Overall, 98 countries contributed to the literature, with the top ten mainly developed countries plus China produced nearly two-thirds of the research. A thorough analysis on documents marked the emergence of four broad research themes (dominated by wave energy subjects): (A) resource assessment, site selection, and environmental impacts/benefits; (B) wave energy converters, hybrid systems, and hydrodynamic performance; (C) vibration energy harvesting and piezoelectric nanogenerators; and (D) flow dynamics, tidal turbines, and turbine design. Further, nineteen research sub-clusters, corresponding to broader themes, were identified, highlighting the trending research topics. An interesting observation was a recent shift in research focus from solely evaluating energy resources and ideal sites to integrating wave/tidal energy schemes into wider coastal/estuarine management plans by developing multicriteria decision-making frameworks and promoting novel designs and cost-sharing practices. The method and results presented may provide insights into the evolution of wave/tidal energy science and its multiple research topics, thus helping to inform future management decisions.
Hydraulic structures can be a promising place for tidal energy extraction due to the high flow velocities, easy
access to the power grid and easy access for maintenance. However, quantification of the impacts of a tidal power
plant in a hydraulic structure is not straight forward. In 2015 a pilot plant consisting of an array of five Tocardo
tidal turbines was installed in the Eastern Scheldt Storm Surge Barrier in the Netherlands. This pilot was
accompanied by monitoring studies to verify that the operation of the plant had no adverse impact on the barrier
and its surroundings. This paper presents the assessment of the hydraulic impact of the tidal power plant in the
storm surge barrier based on an analysis of water level and current measurements, combined with numerical
modeling and followed by an assessment of the environmental impact with emphasis on the effects on the
intertidal areas in the estuary. This validation approach by a pilot plant is imperative to understand the interaction
between tidal turbines and the hydraulic structure on the local scale. This understanding gives extra
credibility to the predictions of the extrapolated large-scale and large array assessments which will always be
fully numerical.
The accuracy of estimated sea conditions, specifically wave height and peak/average wave periods, affects the estimation of electrical energy production from wave energy converters. This study investigates the uncertainty in wave energy harvesting estimated by the SWAN wave model and determines possible improvements by adjusting the model's tunable parameters. Three different wave energy converters (OEBuoy, WaveBob, and Pontoon) and ten different locations along the Atlantic coast of the Iberian Peninsula are used in the study. The SWAN model is calibrated using the ST6 term package based on both wave height and peak period wave parameters. Different wave hindcast data produced by different model settings are used to estimate the wave energy produced by the wave energy converters at ten buoy locations and compared to wave energy produced estimated based on wave observations. The study finds that the physical settings of the SWAN model have a considerable influence on the uncertainty in the estimation of the power output produced by the device. The best-fitting calibrated model improved the mean energy output value of all locations compared to the SWAN default settings. The study concludes that adjusting the SWAN model parameters can improve the accuracy of the estimation of the energy output.
Establishing a renewable marine energy industry demands the development of high-efficiency devices that capture as much energy as possible. The Blow-Jet is a wave energy converter mainly composed of a sloping conical channel in the shape of a brass tube, which concentrates the waves at its widest part and expels a jet of water at its narrow upper end through an orifice that can be turbined. The device has no moving parts and great flexibility in its placement. This research presents an improvement of its geometry, increasing efficiency by minimizing undesired hydrodynamic interactions. The performance of the Blow-Jet was characterized using 3D numerical modeling and laboratory tests in a wave flume. Sixteen geometric configurations of the Blow-Jet were numerically tested, and that showing the best performance was 3D printed and assessed experimentally. The twofold objective was to evaluate the performance of the new Blow-Jet geometry and to validate a numerical tool for further geometrical improvements of the device. The novel geometry is nearly 20% more efficient than the original.
Due to ongoing environmental concerns and increased energy demand, the inclination toward renewable energy sources has increased significantly in the last few decades. The increased share of renewable energy in total energy generation is a sign of sustainable development. Hydropower has been considered better with good predictability and baseload applications. The non-conventional way of harnessing hydropower, viz. hydrokinetic power, is an emerging area of research. The technology to harness hydrokinetic energy plays a vital role in the lives of people living in rural and remote locations for their energy security. To increase the conversion efficiency of hydrokinetic technologies, a lot of investigations are being carried out. In this paper, various technological advancements on hydrokinetic energy technologies have been discussed at different stages of harnessing hydrokinetic energy. Based on the analysis, it has been found that the installations and selection of optimum system parameters are crucial to tap the energy from the hydrokinetic potential site. The investigated results would be useful for the selection of hydrokinetic turbines and to opt for the system parameters corresponding to better performance.KeywordsRenewable energyHydropowerHydrokinetic energyTurbineSystem parameters
China is acknowledged as a leader in establishing new energy generation capacities. The most rapidly growing renewable energy sectors have been hydropower, wind and solar energy, and biofuels. According to the strategic development objectives set by China’s government, renewable sources’ portion in the energy sector will continue increasing. Russia also enjoys a striking potential in renewables’ development, not only natural resources but also technologies and experience. In the 1930s, the Soviet Union first-ever built wind generators. In the 1960s, it installed the world’s first geothermal power plants. However, the abundant availability of hydrocarbons has predetermined Russia’s energy sector growth on the basis of fossil fuels and coal. Today, alternative sources contribute about 1% of Russia’s energy balance. China is particularly interested in expanding energy generation for domestic needs, which makes cooperation with Russia in the Far East and Siberia attractive for Chinese investors. This chapter aims to investigate the opportunities for converging the experience, technical capabilities, resource potential, and economic resources of the two countries to diversify their energy-related industries away from fossils in favor of renewable energy.
China is acknowledged as a leader in establishing new energy generation capacities. The most rapidly growing renewable energy sectors have been hydropower, wind and solar energy, and biofuels. According to the strategic development objectives set by China’s government, renewable sources’ portion in the energy sector will continue increasing. Russia also enjoys a striking potential in renewables’ development, not only natural resources but also technologies and experience. In the 1930s, the Soviet Union first-ever built wind generators. In the 1960s, it installed the world’s first geothermal power plants. However, the abundant availability of hydrocarbons has predetermined Russia’s energy sector growth on the basis of fossil fuels and coal. Today, alternative sources contribute about 1% of Russia’s energy balance. China is particularly interested in expanding energy generation for domestic needs, which makes cooperation with Russia in the Far East and Siberia attractive for Chinese investors. This chapter aims to investigate the opportunities for converging the experience, technical capabilities, resource potential, and economic resources of the two countries to diversify their energy-related industries away from fossils in favor of renewable energy.KeywordsBiofuelsFossil fuelsHydropowerRenewable energy
One of the main challenges for wave energy is to reduce costs and improve reliability and performance of systems. To achieve this in Chile, it is necessary, in addition to an active participation in the development of technologies, to face some additional challenges, particularly those related to supply chain, survival of extreme events sites availability, and coexistence of activities on the marine space. The document presented here, based on recent research and the experiences acquired throughout the execution of the MERIC project, seeks to contribute to some of these aspects and intends to be a useful guide for the selection of adequate wave energy technologies for the particular conditions of the Chilean coast.
The global energy consumption has been on the rise since the last industrial revolution and continues to be. So far the demand could be satisfied by a mixture of conventional and renewable energies. With the global effort to eliminate conventional energies to stop the anthropological climate change, the demand for reliable and predictable renewable energies is growing. Under these circumstances, more attention is drawn towards the development of non-intermittent ocean energy systems. Apart from waves, thermal and salinity gradients, currents are an abundant and reliable ocean energy source. Inspired by state-of-the-art technology, a unique system for current energy, the Current Kite, is presented in the following paper. This tethered undersea kite (TUSK) consist of a wing to which a turbine is attached. The wing drags the turbine through the water in a certain trajectory, sweeping a large area at a relative speed that is several times the actual speed of the underwater current. In the following paper we present the general setup and design of our first and second prototype. The first prototype was build as a prove of concept. It was equipped with active steering and several on board sensors. With the second prototype the aim was to build a more sophisticated system, which would make the active steering redundant and use more efficient, circular flight paths. A wing which would adjust itself in the current and follow the predefined circular path, was designed using numerical simulations. To achieve this circular flight movement without twisting the electrical cable, a swivel and a stress reducer were designed and built to connect the TUSK as well as transfer electrical power to land. In addition the tracking-system was redesigned, communicating by modulation over the power line. This provides a fully autonomous ocean current power plant, which communicates in real time data and has a promising outlook in efficiency, regarding to the state of art. Due to Covid-19 regulations it was not possible to test the prototype. Therefore the paper mainly focuses on the design and construction process, up to the production of the TUSK.
Ocean energy plays essential roles in reducing carbon footprint and transforming towards carbon neutrality, with cleaner power production, whereas the vertical cascade ocean energy systems with spatiotemporal power supply characteristics might lead to fluctuated power frequency, disruptive disturbance and grid shock. Hybrid renewable energy dispatch, coordinated demand-side management, and electrical energy storages for grid ancillary services provision with different response time-durations are effective solutions to integrate ocean energy with stable and grid-friendly operation. This study is to review advanced ocean energy converters with thermodynamic, hydrodynamic, aerodynamic, and mechanical principles. Power supply characteristics from multi-diversified ocean energy resources are analysed, with intermittency, fluctuation, and spatiotemporal uneven distribution. Hybrid ocean energy storages with synergies are reviewed to overcome the intermittency and provide grid ancillary services, including pumped hydroelectric energy storage, ocean compressed air energy storage, and ocean hydrogen-based storage in different response time durations. Applications of diversified ocean energy systems for coastal residential communities are reviewed, with energy management and controls, collaboration on multi-carrier energy networks. Furthermore, application of artificial intelligence is reviewed for sustainable and smart ocean energy systems. Results indicated that, effective strategies for stable and grid-friendly operations mainly include complementary hybrid renewable system integrations, synergies on hybrid thermal/electrical storages, and collaboration on multi-carrier energy networks. Furthermore, depending on the geographical location, flexible on-shore and off-shore installation of transformers can provide large-scale ocean energy system integrations for long-distance transmission, with low transmission losses, low resistive losses, and simple system configuration. Research results can provide a heuristic overview on ocean energy integration in smart energy systems, providing alternatives for solar and wind energy resources and paving path for the carbon-neutrality transition.
The ocean is a huge energy conversion field, and ocean renewable energy (ORE) can provide us with a constant source of energy. Research on ORE collection and utilization has been emerging in recent years, and the number of ORE research results has been increasing. This paper visualizes the trends and current research status of ORE by performing bibliometric analysis using VOSviewer and CiteSpace. The results are analyzed in terms of annual publications, countries, institutions, authors, journals, keywords, topics, and references. The results indicate that current research hotspots include (1) theoretical calculations and simulation modeling, (2) design of ocean renewable energy devices (OREDs), (3) deployment of OREDs and optimization improvements, and (4) evaluation of ORE projects. Wave energy harvesting applications, offshore wind energy harvesting applications, design and improvement of triboelectric nanogenerator, and artificial reefs or islands are the frontiers of research in the field of ORE. With the development of energy conversion technologies, the future of ocean power generation will have a promising and attractive prospect. The results of the study provide a comprehensive overview of the evolution of research hotspots in this field and can help those researchers willing to work in this research area to quickly understand the research frontiers and the general situation.
Resource quantification is vital in developing a tidal stream energy site but challenging in high energy areas. Drone-based large-scale particle image velocimetry (LSPIV) may provide a novel, low cost, low risk approach that improves spatial coverage compared to ADCP methods. For the first time, this study quantifies performance of the technique for tidal stream resource assessment, using three sites. Videos of the sea surface were captured while concurrent validation data were obtained (ADCP and surface drifters). Currents were estimated from the videos using LSPIV software. Variation in accuracy was attributed to wind, site geometry and current velocity. Root mean square errors (RMSEs) against drifters were 0.44 m s⁻¹ for high winds (31 kmh) compared to 0.22 m s⁻¹ for low winds (10 kmh). Better correlation was found for the more constrained site (r² increased by 4%); differences between flood and ebb indicate the importance of upstream bathymetry in generating trackable surface features. Accuracy is better for higher velocities. A power law current profile approximation enables translation of surface current to currents at depth with satisfactory performance (RMSE = 0.32 m s⁻¹ under low winds). Overall, drone video derived surface velocities are suitably accurate for “first-order” tidal resource assessments under favourable environmental conditions.
Our team of Cal Poly Mechanical Engineers ideated, designed, built, and tested a system to help combat the growing problem of widespread drought in coastal and island communities. We developed a proof-of-concept model of a wave powered, mechanical system to desalinate ocean water using a reverse osmosis process. From topical research, it was found that there are many ways to harness a portion of the huge amount of energy that the ocean provides. While large scale ocean water desalination plants are already in operation, smaller scale desalination units powered by ocean waves are largely underdeveloped. Our relatively small and inexpensive system proved to be effective in many aspects of our testing process, confirming the feasibility of our design concept as we exceeded a flowrate of 1 gallon per hour of desalinated water during ocean testing. In an era where global access to clean drinking water is a huge issue that has been unresolved for decades, this system may be able to make an impact in small coastal communities everywhere around the world.
The inherently advantageous geographical location of East and Southeast Asia provides a great potential for the development of diverse ocean energy technologies along its densely populated coastlines. This review paper focuses on the flexibility and feasibility of emerging ocean energy technologies in this region, including wave, tidal and ocean-current energy converters, floating photovoltaics, and offshore wind-turbines. Recent research on wave energy in the region has achieved advancements such as modifying oscillating water columns to exchange higher pneumatic energy, reshaping oscillating devices to capture more kinetic energy, and improving overtopping converters to absorb more incident waves. Regarding tidal energy, the paper reviews barrage-based and stream-based turbines and investigates the efficiency improvement, flexibility enhancement and adaptation to the unique regional features. Regarding ocean current energy, research on low-velocity turbines and optimized energy storage systems has made their application in the region more competitive. In addition, offshore deployments of floating photovoltaics have recently drawn the sector's attention and are beginning to emerge in the region, although their robustness against extreme weather and wave conditions should be addressed. Furthermore, compared to other ocean technologies, offshore wind technologies have attracted the most investment in the region. Due to the fluctuation of wind-energy generation, enhancing the energy flexibility to increase its grid penetration has become a recent focus in both the academic and industrial communities. However, despite the good research and demonstrations, most of the abovementioned ocean technologies still encounter considerable techno-economic and techno-environmental challenges that limit their competitiveness in the East and Southeast Asian markets.
Worldwide viable energy requisite keeps on developing with tidal energy giving a noteworthy wellspring of sustainable energy. The ability to produce power from tidal waves is gigantic. Tidal energy is an illimitable source that has an extra incentive in the future as to other sustainable power sources owing to its greater uniformity. Like other renewable power sources, tidal energy has its difficulties at various levels. More sacrifices are to be seen in local communities dealing with tidal energy and when the project is too big. Despite the undertaking benefits that could be decreasing carbon dioxide release and green innovation, likewise has more ecological effects that can forestall the execution of tidal energy. The major challenges are its effect on marine animals, cost, availability and efficiency. The market for tidal energy is smaller and more local, in places where the grid is weak or non-existent. The World Energy Council and Bloomberg New Energy Finance (BNEF) assessed that power created from sea developments costs eightfold to ninefold the amount of the most noteworthy normal cost for wind energy. The market for flowing vitality appears to be restricted, and it relied upon to remain that route soon. The United States’ Department of Energy (US-DOE) expenditure of $20 million in financing for wave and tidal energy extends this year. Tidal energy is advantageous for locales that are close to drift and have the situations to make this novel type of energy less expensive. The chapter covers an overview of all the challenges faced by this ideal energy and resolve them to have a clean and renewable form of energy.
The operation of tidal stream energy farms may interfere with other uses of the marine space, especially in depth-limited areas (estuaries, rivers, etc.) which are typically subject to multiple demands of use. The Marine Spatial Planning Directive (MSP) was passed by the European Commission in 2014 to ensure a harmonic coexistence between different maritime activities and to protect the marine environment. In this context, the objective of this work is to present a methodology based on MSP tools for tidal-farm siting in depth-limited areas. The methodology is illustrated through a case study: Ria de Ribadeo, a shallow-water estuary in NW Spain. Having considered a number of uses (archaeological, biodiversity, fishing, aquaculture, recreational and navigation), two exploitable tidal farm sites (Areas A and C) with annual energy densities of 1 GWhm−2 were found. The estuary is periodically dredged to maintain navigation. Dredging-related risks were analysed using a novel indicator, the Dredging Associated Risk (DAR), based on which Area C was discarded and Area A had its exploitable surface area reduced by 25%. In sum, the methodology proposed was proven to be effective for tidal stream farm planning.
With growing energy crisis in this era, developing and utilizing sustainable energy sources are required because the conventional energy sources cannot be restored. Among the various sustainable energy sources, the ocean wave energy is considered as one of the best sustainable energy sources. However, the conventional technologies to harvest the ocean energy show some limitations such as corrosion. Hence, guaranteeing the high resistance to corrosion of the harvesting devices has become a critical challenge for ocean-energy harvesting. Herein, a mat-shaped solid-liquid triboelectric nanogenerator is fabricated to harvest the blue energy while overcoming the shortcomings of the conventional technologies. The fabricated device is composed of the polydimethylsiloxane embedded in a conductive carbon black utilized as the electrode of the proposed device and it can directly harvest the blue energy. Moreover, through acquired energy from the simulated waves, the fabricated device can operate an anemometer and can split the seawater to produce the hydrogen. Also, the human motions can be distinguished through the k-mean clustering method with the high classification of 96.67%. Considering these results, the fabricated device is expected to be utilized as the promising blue energy harvester as well as the self-powered human motion sensor in near future.
There has been a growing interest in the utilisation of marine current turbines for electrical power production. The ability to predict the hydrodynamic performance of a marine current turbine is essential for the design and analysis of such systems. Marine current turbines are subject to a non-uniform inflow due to variations on the tidal direction and to the site velocity profile. Due to these spatial variations of the inflow, the turbine blades are subject to time-dependent inflow conditions causing an unsteady flow field around the blades. This flow field is responsible for unsteady loads on the blades which are important for the analysis of fatigue loadings, and, possibly, for the occurrence of unsteady cavitation phenomena. A fully three-dimensional potential flow Boundary Element Method for the analysis of the unsteady flow around marine current turbines is presented. The method is based on a low order potential Morino formulation. The application of the method to the analysis of a controllable pitch horizontal axis marine current turbine is illustrated for straight and yawed inflow conditions at two different pitch settings in a wide range of tip-speed-ratios. Comparison of the numerical calculations with experimental measurements available in the literature is presented. The effect of a tidal velocity profile on the unsteady turbine blade loadings is included.
The use of altimeter measurements of significant wave height and energy period for quantifying wave energy resource is investigated. A new algorithm for calculating wave period from altimeter data, developed by the authors in previous work, is used to estimate the power generated by the Pelamis wave energy converter and compared to estimates from collocated buoy data. In offshore locations accurate estimates of monthly and annual mean power can be achieved by combining measurements from six altimeter missions. Furthermore, by averaging along sections of the altimeter ground track, we demonstrate that it is possible to gauge the spatial variability in nearshore areas, with a resolution of the order of 10 km. Although measurements along individual tracks are temporally sparse, with TOPEX/Poseidon and Jason on a 10 day repeat orbit, GFO 17 days, and ERS-2 and ENVISAT 35 days, the long record of altimeter measurements means that multi-year mean power from single tracks are of a useful accuracy.
Marine current energy conversion technology is presently at the prototype stage where single devices are deployed, or planned for installation, at isolated testing sites. There is little detailed knowledge of the flow field properties at highly energetic tidal energy sites. Often peak flow speeds are measured but the nature of wave and bed-generate turbulence and the potential effects upon tidal energy devices are uncertain. This may lead to prototype devices being installed at sheltered or benign sites where the effects of waves are minimised and bed conditions induce low levels of turbulence. Another solution is for devices to avoid operation in these turbulent regions of flow but both solutions may result in reduced energy capture as rotor swept areas are constrained and potentially higher energy flows are not intercepted.
With little detailed knowledge of flow conditions at tidal energy sites it is difficult to model at smaller scale. However, there are methods of accurately reproducing scale seabed conditions and new lab-based high frequencies velocity measurements equipment can aid in the characterisation of the flow field. This work describes the modelling of sea bed roughness in the 21m tilting flume at the Chilworth hydraulics laboratory, University of Southampton. Mean flow velocity and higher order flow effects have been evaluated at locations upstream and downstream of porous mesh disks in order to quantify the effects of seabed roughness compared to smooth bed conditions upon both the general flow field and the downstream wake region.
Results show that the greater tractive forces close to the roughened bed induce a much more pronounced vertical velocity profile and increased turbulence in the lower region of the water column. However, this does not lead to increased wake mixing downstream of the rotor disk and indeed ensures that rotor disk proximity to the bed is a far more important issue than for smooth bed conditions.
Tidal energy dissipation is estimated for eight semi-diurnal and diurnal constituents using a global inverse solution constrained by TOPEX/Poseidon altimeter data. Very similar spatial patterns are obtained for all semi-diurnal constituents, with about one third of the total dissipation occurring in the deep ocean over rough topography. Maps for diurnal constituents are also similar amongst themselves, but quite different from the semi-diurnal results. For diurnals a smaller fraction of dissipation, roughly 10%, occurs in the deep ocean. Much of the difference can be explained by the very different spatial pattern of diurnal and semi-diurnal tidal currents. The lack of free internal waves at frequencies poleward of 30° at diurnal frequencies also probably plays a role, limiting the effectiveness of baroclinic conversion as an energy sink for barotropic diurnal tides.
Actuator discs may be used as a simple method for simulating horizontal axis tidal turbines, both in experiments and
CFD models. They produce a similar far wake to a real turbine, but eliminate some of the scaling issues which occur
in experiments, and reduce the mesh density required in CFD simulations. This paper examines methods for applying
a simple actuator disc in a commercial CFD code, Ansys CFX, and compares the wake produced with experimental
results for similar values of disk thrust coefficient (CT ). The results show that the CFD model gives reasonable
agreement with the experimental results. The main factors affecting the wake structure are the initial CT value, the
ambient turbulence levels, and potentially the disc induced turbulence. The main differences between the models and
experiments were in terms of the turbulence levels throughout the model. With further development, it is considered
that the CFD actuator disc could be an accurate and validated method for numerically modelling tidal turbines
The potential of electric power generation from marine tidal currents is enormous. Tidal currents are being recognised as a resource to be exploited for the sustainable generation of electrical power. The high load factors resulting from the fluid properties and the predictable resource characteristics make marine currents particularly attractive for power generation and advantageous when compared to other renewables. There is a paucity of information regarding various key aspects of system design encountered in this new area of research. Virtually no work has been done to determine the characteristics of turbines running in water for kinetic energy conversion even though relevant work has been carried out on ship’s propellers, wind turbines and on hydro turbines. None of these three well established areas of technology completely overlap with this new field so that gaps remain in the state of knowledge. This paper reviews the fundamental issues that are likely to play a major role in implementation of MCT systems. It also highlights research areas to be encountered in this new area. The paper reports issues such as the harsh marine environment, the phenomenon of cavitation, and the high stresses encountered by such structures are likely to play a major role on the work currently being undertaken in this field.
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.
Laboratory measurements of the performance of the Anaconda are presented, a wave energy converter comprising a submerged water-filled distensible tube aligned with the incident waves. Experiments were carried out at a scale of around 1:25 with a 250 mm diameter and 7 m long tube, constructed of rubber and fabric, terminating in a linear power take-off of adjustable impedance. The paper presents some basic theory that leads to predictions of distensibility and bulge wave speed in a pressurized compound rubber and fabric tube, including the effects of inelastic sectors in the circumference, longitudinal tension and the surrounding fluid. Results are shown to agree closely with measurements in still water. The theory is developed further to provide a model for the propagation of bulges and power conversion in the Anaconda. In the presence of external water waves, the theory identifies three distinct internal wave components and provides theoretical estimates of power capture. For the first time, these and other predictions of the behaviour of the Anaconda, a device unlike almost all other marine systems, are shown to be in remarkably close agreement with measurements.
Tidal stream power generation offers the prospect of predictable, low-CO2
power at a number of locations around the UK and the world. Previous
assessments of tidal energy resources have taken the form of desk studies
based on simplified navigational data. Where numerical model data has been
used it has been at too low a resolution to capture high velocity tidal flows
constrained by coastal topography. Analytical solutions for maximum energy
extraction in simple tidal channels have been produced, but they have not
been extended to more complex open-boundary cases such as flow around
headlands and islands. There is therefore a role for site-specific numerical
modelling, which when validated, offers the twin advantages of a
high-resolution picture of the resource and allowing simulation of momentum
extraction within the model to take place.
In order to parameterize the sub-grid-scale momentum extraction in such
models, a new analytical model of the velocity reduction in a large array of
tidal turbines has been derived. The model extends previous models of large
wind turbine arrays and uses analogies with flow through submerged
vegetation. It provides an equivalent added drag coefficient suitable for use in
a 2-D coastal numerical model.
A numerical model of the flows in the region of the Portland Bill headland
has been produced, forced by tidal elevations at the free boundary. A site
selection exercise was carried out for the Portland Bill location and an area of
around 12 km2 was identified as having a high potential for development
using mean cubed speed found through tidal analysis of model results
without energy extraction.
A large tidal stream generator array has also been simulated within the
Portland Bill model—linked to the new model for momentum extraction—and
was found to have a significant effect on the tidal parameters in the locality.
This was the first time that a large tidal array has been simulated in a realistic
coastal domain of large extent, with a parameterization that takes into account
the interaction of the turbines with the rough-wall flow in the natural state.
Results predict that there is a region downstream of the array extending
approximately 5–10 km around the simulated tidal stream turbine array in
which the tidal stream ellipse major axis is reduced by at least 5%. In the area
of momentum extraction the principal semi-diurnal tidal stream ellipse major
axis length was reduced by 10–15%.
Inter-device spacing within wave and tidal arrays will affect many aspects of array performance including power production, installation, maintenance and the effect upon the wider flow field. It follows that inter-device spacing within an array will vary based upon a number of factor including (but not limited to) characteristics of the incoming resource, water depth, device type and installation/maintenance methods. Therefore it is clear that the issues surrounding interaction effects within arrays are complex with a high degree of linkage between certain aspects of design. Despite the low level of understanding of many issues surrounding wave and tidal energy arrays there are a number of areas where guidance can be given to developers in order to assist in array design. One such area is the classification of arrays by size and complexity. Other more generic advice can be given to advise upon potential interaction effects whilst guiding early array design to encompass knowledge gathering to inform subsequent arrays that are greater in size and complexity
At many locations with high tidal stream velocities – and potential for tidal stream energy generation – the flow is approximately rectilinear, that is to say the flow direction is always 0 degrees or 180 degrees with respect to a particular orientation. At some sites, however, there is an appreciable change in flow direction (‘swing’) away from 180 degrees between the two maxima of flow speed. In order to assess the performance of horizontal axis marine current turbines in non rectilinear currents, measurements of a model rotor have been made in a towing tank. Curve fits have been calculated as a function of the cosine of the yaw angle squared and the thrust as cosine of the yaw angle. The curve fits have been used in a case study to investigate the impact of fixed-orientation or yawing rotor designs on average annual energy output, at three locations in the English Channel. All three sites are of the type where flow is accelerated around a headland or cape, but their tidal streams vary in deviation from rectilinearity. For two of the sites - Portland Bill (Dorset, UK) and Race of Alderney (Alderney, Channel Islands/Normandy, France) - available data consisted of tidal stream diamonds printed on Admiralty navigational charts. These rely on local tidal elevations for interpolation of tidal streams. At the other site – St. Catherine’s Point, Isle of Wight, Hampshire – current meter measurements of duration one month were available from the British Oceanographic Data Centre (BODC), allowing a direct tidal analysis. …
The flow field in the near wake region of a tidal current turbine is strongly driven by the combined wake of the device support structure and the rotor. Accurate characterisation of this region of flow is important but it is characterised by highly turbulent, slow-moving fluid. Wake flow field characteristics of a 1:20th-scale horizontal axis turbine has been have been measured in a large water channel facility. A downstream map of both the channel base flow and downstream wake was made using both laser and acoustic doppler velocimeters. Wake mapping was conducted with the rotor in both operational an inactive states to quantify the effect of the turbine support structure upon the near wake flow properties. Results indicate that the wake created by the turbine support structure has a significant effect upon the near wake flow field with strong synergistic effects of both rotor and supporting structure close to the downstream centre plane of the rotor which diminish with increasing lateral (cross channel) distance. Determination of higher order flow properties was difficult close behind the turbine (<4 rotor diameters) due to extremely high levels of turbulence. Furthermore, it is clear that the form of the rotor support structure has a strong influence upon near wake properties and this will change for the various forms of tidal energy devices either deployed or at the design stage
At the present time there are no approved standards or recognised best practices being implemented for the performance appraisal and benchmarking of wave and tidal energy converters. As such, this develops considerable misunderstanding between device developers, testing centres, investors/ financiers etc when attempting to quantify the performance of a device since it makes it very difficult to reference and benchmark the performance of a marine energy converter. The EC Framework Programme VII EquiMar project has set out to develop a suite of Best Practices to be adopted when undertaking the performance evaluation of such systems in order to address this deficiency. This paper reports the development of a set of ‘Best Practices’ within the ECFPVII EquiMar project to be adopted for the performance quantification of wave and tidal energy converters as they evolve from an engineering concept to commercial scale deployment
Marine current energy converters or tidal turbines represent an emerging renewable energy technology that can provide a predictable supply of electricity. Single devices are in operation around the world with aspirations to deploy farms or arrays of multiple devices. We present an experimental study that has characterised the downstream wake flow around a 1/15th-scale turbine in a large circulating water channel and a series of experiments involving static actuator disks at 1/120th-scale allowing simulation of multiple-device layouts. Our analysis demonstrates that the near wake is highly turbulent with structures generated by the rotor and support structure. This region of flow may prove difficult to numerically simulate with a high degree of accuracy. In the far wake the performance of static actuator disks can be matched to mechanical rotors reducing scale and cost facilitating replication of complex array geometries. Here the ambient turbulence and geometric properties of the device/channel drive the wake recovery towards free stream conditions. Devices operating downstream of others will be subject to a non-steady flow field making comparative performance difficult. We discuss the possibility of unequal device specification and rated power within an array (unlike wind farms) providing a more representative measure of array performance.
An investigation has been carried out into the lift, drag and cavitation characteristics of two-dimensional foil sections, which may typically be used as a starting point in the design of blade sections for marine current turbines. Cavitation tunnel experiments and numerical predictions using a panel code were carried out on four representative sections derived from the NACA series 4415, 6615, 63-215 and 63-815. The experimental lift and drag results show reasonable correlation with published wind tunnel data. The sections were modelled numerically using the two-dimensional panel code XFoil. The numerical cavitation predictions in most cases showed satisfactory agreement with the experiments and it is considered that such predictions could be used with reasonable confidence for predicting cavitation at the preliminary design stage. Overall, the results of the investigation provide detailed information that should assist in the design and operation of marine current turbines.
The conversion of the kinetic energy presented by ocean or marine currents offers an exciting proposition as it can provide regular and predictable energy resource. The majority of the proposed designs for converting this type of kinetic energy are based on the concept of the horizontal axis turbines, which has common characteristics to those being used in wind energy. Although a lot can be learnt and transferred from wind turbine technology, there are significant differences. These include the effects of the free surface and the occurrence of cavitation. Consequently, any developed numerical methods need to be verified. This study reports on the development and verification of simulation tools based on blade element momentum theory—a commercial code (GH-Tidal Bladed) and an academic in-house code (SERG-Tidal). Validation is derived from experimental measurements conducted on a model 800mm diameter turbine in a cavitation tunnel and a towing tank. The experimental data includes measurements of shaft power and thrust generated by the turbine for a series of blade pitch settings and speeds. The results derived from the two codes are compared. These indicate that the two developed codes demonstrate similar trends in the results and provide a satisfactory representation of the experimental turbine performance. Such results give the necessary confidence in the developed codes resulting in appropriate tools that can to be utilised by developers of marine current turbines.
This volume examines the interaction between ocean waves and oscillating
systems. With a focus on linear analysis of low-amplitude waves, the
text is designed to convey a thorough understanding of wave
interactions. Topics include the background mathematics of oscillations,
gravity waves on water, the dynamics of wave-body interactions, and the
absorption of wave energy by oscillating bodies. While the focus is on
linear theory, the practical application of energy storage and transport
is interwoven throughout. Each chapter ends with problems. A solutions
manual is available for instructors.
There is an upper bound to the amount of power that can be generated by turbines in tidal channels as too many turbines merely block the flow. One condition for achievement of the upper bound is that the turbines are deployed uniformly across the channel, with all the flow through them, but this may interfere with other uses of the channel. An isolated turbine is more effective in a channel than in an unbounded flow, but the current downstream is non-uniform between the wake of the turbines and the free stream. Hence some energy is lost when these streams merge, as may occur in a long channel. We show here, for ideal turbine models, that the fractional power loss increases from 1/3 to 2/3 as the fraction of the channel cross-section spanned by the turbines increases from 0 to close to 1. In another scenario, possibly appropriate for a short channel, the speed of the free stream outside the turbine wake is controlled by separation at the channel exit. In this case, the maximum power obtainable is slightly less than proportional to the fraction of the channel cross-section occupied by turbines.
Project development. Initial site selection, project feasibility assessment including the measure-correlate-predict technique for estimating energy yields from wind farm sites, micro-siting of turbines, the importance of public consultation and an overview of the preparation of environmental impact assessments.Visual and landscape assessment. Wind farm design and mitigation measures, assessment of visual impact and the use of Zones of Visual Impact (ZVI), wire-frame representations and photomontages.Noise. Terminology and basic concepts, sources of noise from a wind turbine, measurement and prediction of wind farm noise.Electro-magnetic interference. Impact of wind farms on various types of communication signals, modelling and prediction of electro-magnetic interference from wind turbines.Ecological assessment. Impact on birds.Financing wind farm developments. Project appraisal using discounted cash flow techniques, project finance and support mechanisms for wind energy development.
At present a small number of full-scale marine current energy converters are undergoing sea trials to demonstrate commercial viability of the technology. In order to provide meaningful quantities of electrical power to the grid, the next phase in the development of the technology will be the installation and operation of farms or arrays composed of multiple devices. As most tidal current sites are bi-directional and with bathymetry constraints, array layouts will necessarily take the form of highly optimized geometric configurations with reduced lateral inter-device spacing. This work discusses the concept of array layouts and proposes an appropriate and clear classification that can aid developers in understanding how arrays operate. This classification is supported by experimental studies conducted using several arrangements of multiple actuator disks to simulate early generation marine current energy converter arrays. The work presents quantification of the flow field around a 2-row array, device/device interaction as well as a study of the structure of the far wake region where subsequent devices could be installed. The results highlight an optimal lateral spacing between devices where, under certain conditions flow can be accelerated between a pair of rotor disks. For the work presented here this accelerated region of flow possessed 22% more kinetic energy than the flow far upstream with no measurable negative effect upon the 2 actuator disks. This enhanced flow speed gives rise to the counterintuitive notion of a downstream row of devices producing more power than the upstream row. This will lead to a synergistic effect whereby an array of devices can generate more power than an equivalent number of isolated machines.
At a commercial scale tidal stream turbines are likely to be installed in multi-device arrays to maximise power output from a tidal site. This paper demonstrates a computationally efficient method for predicting the performance of an array. The approach parameterises the turbine by deriving momentum source terms using blade element (BE) theory. The source terms are added to Reynolds-averaged Navier-Stokes (RANS) momentum equations. The RANS+BE method is similar to blade element momentum (BEM) theory but can predict the flow field as well as the performance of the rotor. This investigation first verifies the RANS+BE method against BEM theory and shows good agreement, although tip-losses still need to be included. Secondly, it compares the RANS+BE approach to a parameterisation based on a uniform resistance coefficient, over a range of ambient turbulence values and thrust coefficients. The RANS+BE method generates increased azimuthal velocities in the near wake compared to the uniform approach. Finally the investigation compares results of a model of an infinitely wide array of turbines with five rows. The RANS+BE model can predict the performance of each turbine. and shows more rapid wake velocity recovery within the array. The investigation provides a detailed insight into the applicability of wake modelling techniques for the configuration of tidal stream turbine arrays.
Understanding the flow field around horizontal axis marine current turbines is important if this new energy generation technology is to advance. The aim of this work is to identify and provide an understanding of the principal parameters that govern the downstream wake structure and its recovery to the free-stream velocity profile. This will allow large farms or arrays of devices to be installed whilst maximising device and array efficiency. Wake characteristics of small-scale mesh disk rotor simulators have been measured in a 21 m tilting flume at the University of Southampton. The results indicate that wake velocities are reduced in the near wake region (close behind the rotor disk) for increasing levels of disk thrust. Further downstream all normalised wake velocity values converge, enforcing that, as for wind turbines, far wake recovery is a function of the ambient flow turbulence. Varying the disk proximity to the water surface/bed introduces differential mass flow rates above and below the rotor disk that can cause the wake to persist much further downstream. Finally, the introduction of increased sea bed roughness whilst increasing the depth-averaged ambient turbulence actually decreases downstream wake velocities. Results presented demonstrate that there are a number of interdependent variables that affect the rate of wake recovery and will have a significant impact on the spacing of marine current turbines within an array.
The development of a blade element momentum (BEM) model for the hydrodynamic design of marine current turbines is presented. The model includes routines for interpolation of 2D section data and extrapolation for stall delay. The numerical model is compared with experimental data obtained from tests of an 800 mm diameter model rotor carried out in a cavitation tunnel. The theoretical predictions are in good agreement with the experiments. Using this validated model, a typical 3D rotor is used to demonstrate parametric variations of the design parameters. The effect of tip immersion on possible cavitation is assessed for this rotor. The model is then used to solve the dynamic effects of a tidal profile. The effect of an increase in blade roughness is presented, indicating a relatively small reduction in power. This work demonstrates that the numerical model developed can provide a useful tool for the investigation of the hydrodynamic design and operation of marine current turbines.
The uncertainty in estimates of the energy yield from a wave energy converter (WEC) is considered. The study is presented in two articles. This first article deals with the accuracy of the historic data and the second article considers the uncertainty which arises from variability in the wave climate. Estimates of the historic resource for a specific site are usually calculated from wave model data calibrated against in-situ measurements. Both the calibration of model data and estimation of confidence bounds are made difficult by the complex structure of errors in model data. Errors in parameters from wave models exhibit non-linear dependence on multiple factors, seasonal and interannual changes in bias and short-term temporal correlation. An example is given using two hindcasts for the European Marine Energy Centre in Orkney. Before calibration, estimates of the long-term mean WEC power from the two hindcasts differ by around 20%. The difference is reduced to 5% after calibration. The short-term temporal evolution of errors in WEC power is represented using ARMA models. It is shown that this is sufficient to model the long-term uncertainty in estimated WEC yield from one hindcast. However, seasonal and interannual changes in model biases in the other hindcast cause the uncertainty in estimated long-term WEC yield to exceed that predicted by the ARMA model.
The results of cavitation tunnel and tank tests on an 800 mm diameter model of a marine current turbine (MCT) are presented. The tests were carried out in a 2.4 m×1.2 m cavitation tunnel and the 60 m towing tank. Results for power and thrust coefficients are presented for a range of tip speed ratio and pitch settings for various conditions. The results of this investigation provided an insight into the operation of a singe turbine in straight or yawed flow, the effect on performance of changes in the tip immersion of the rotor, the interference between twin rotors and the likely areas of cavitation inception. In addition, the analysed results presented provide useful information for the hydrodynamic design of MCTs and detailed data for the validation of numerical models.
3401 3.1. Energy extraction from marine currents conversion
- Marine Current Energy Conversion
Marine current energy conversion................................................................................................................... 3401
3.1.
Energy extraction from marine currents conversion........................................................................................ 3401
3407 5.1. Deploy-and-plug ocean zones
- Farms..................................................................................................................................................................................................................................................................................................................................... Array
Array and farms...................................................................................................................................... 3407
5.1.
Deploy-and-plug ocean zones................................................................................................................ 3407
5.2.
Plugging the knowledge gap................................................................................................................. 3407
3409 7. UK approach for technology development
- ............................................................................................................................. Economic
Economic assessment................................................................................................................................ 3409
7.
UK approach for technology development and support............................................................................................ 3409
7.1.
Support instruments and incentives......................................................................................................... 3409
7.2.
Impact on marine energy technology development......................................................................................... 3410
Results from the work of the European Thematic Network on Wave Energy. T. Pontes et al. European Community
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An expression for the limiting velocity deficit in a large array of tidal turbines
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Development of the Anaconda all-rubber WEC
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Experimentally validated Q2 numerical method for the hydrodynamic design of horizontal axis tidal turbines
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