Tidal Energy Research Articles

Model-Free Control for Doubly Salient Permanent Magnet-Generator-Based Tidal Stream Turbine Considering Flux-Weakening Operation

Renewable energy generation is increasingly important due to serious energy issues. A Doubly Salient Permanent Magnet Generator (DSPMG) can be an interesting candidate for tidal stream renewable energy systems. However, the special structure makes the system nonlinear and strongly coupled even after Park transformation and involves a larger torque ripple. Previous research mainly focused on model-based control for this machine, which is very sensitive to the parameters. Thus, to control the complex systems stably and accurately, two model-free control algorithms, Active Disturbance Rejection-Based Iterative Learning Control (ADRILC) and Active Disturbance Rejection Control–Iterative Learning Control (ADRC–ILC), are proposed for the current and speed control loops of a DSPMG-based Tidal Stream Turbine (TST), respectively. ADRC–ILC uses ADRC to deal with the external non-periodic speed ripple and adopts ILC to reduce the internal periodic speed ripple. ADRILC employs an iterative method to improve the ESO for the enhancement of the convergence rate of ILC. Considering the variable tidal speed, when the speed is above the rated value, Maximum Power Point Tracking (MPPT) must be changed to a power limitation strategy for limiting the generator power to the rated value and extending the system operating range. Thus, Optimal Tip Speed Ratio (OTSR)-based MPPT (for a low tidal current speed) and Leading Angle Flux-Weakening Control (LAFWC) (for a high tidal current speed) strategies are also proposed. According to the simulation results, the proposed ADRC–ILC + ADRILC has the lowest torque ripple, the highest control accuracy, as well as a good current tracking capability and strong robustness. At the rated speed, the proposed method reduces the torque ripple by more than 20% and the speed error by about 80% compared with PI control: the current difference is limited in 2A. The LAFWC proposed for an excessive tidal current speed is effective in conserving the electromagnetic power and increasing the generator speed.

Fluctuation characteristics induced by energetic coherent structures in air-core vortex: The most complex vortex in the tidal power station intake system

The air-core vortex is the most complex vortex in the intake system of tidal power stations. Nearly all power plants prohibit the operation of units with air-core vortices, as these vortices not only contain air but also induce significant inflow fluctuations that can potentially lead to significant damage to the units. The current understanding of the fluctuation characteristics and mechanisms induced by energetic coherent structures in the air-core vortex flow is very limited. To address this, the coupled level-set and volume-of-fluid large-eddy simulations are conducted to investigate the energetic coherent structures that cause power output fluctuations. Two critical frequencies have been identified in the energy spectra of the velocity field: the air-core vortex meandering frequency and the shear vortex shedding frequency. The level and trend of the spectrum density at low frequencies are determined by the large-scale energy structure represented by the air-core vortex. The shear vortices are initially formed from a shear separation layer that eventually evolves into streamwise vortices downstream. When the air-core vortex enters the pipe, it breaks up and merges with the near-wall coherent structures. The enhanced velocity and pressure fluctuations, induced by air-core vortices and coherence structures, are analyzed using the turbulent kinetic energy transport equation, revealing that the production term dominates the development of turbulent kinetic energy. Moreover, the diffusion term is responsible for transferring energy through the evolution of turbulent structures. The energy loss induced by fluctuations is investigated using the entropy production method. We find that the direct dissipation of entropy production is mainly induced by air-core vortices, while the side-wall coherent structures in the pipe contribute to the turbulent dissipation.

Towards a sustainable environment and carbon neutrality: Optimal sizing of standalone, green, reliable, and affordable water-power cogeneration systems

Today, the limited sources of freshwater supply are a significant concern. Exploiting alternative sources, especially seawater, has been the focus, but purifying it is energy-intensive. Integrating desalination with renewable energy is a proposed solution, but it comes with high costs and environmental risks during construction. Hence, this study presents a framework to enhance the modeling, optimization, and evaluation of green water-power cogeneration systems to achieve the sustainability goals of cities and societies. An improved division algorithm (DA) determines the optimal component sizes based on criteria like minimal energy demand, reduced environmental and resource damage, low total life cycle cost (TLCC), and high reliability. Optimization considers varying loss of power supply probability (LPSP) levels (0 %, 2 %, 5 %, and 10 %). The environmental assessment utilizes a life cycle assessment (LCA) approach with IMPACT 2002+ and cumulative energy demand (CED) calculations. The study models the green cogeneration systems based on weather conditions, water demand, and power requirements of Al Lulu Island, Abu Dhabi, UAE. The system comprises photovoltaic panels, wind turbines, tidal generators, and backup systems (fuel cells). Results reveal that TLCC ranges from $186,263 to $486,876 for the highest LPSP. The solar-tidal-based configuration offers the lowest TLCC ($186,263) while substituting solar with wind energy increases TLCC by 160 %. The wind-tidal-based configuration has the lowest specific environmental impact (1020 mPt/yr) and cumulative energy demand (39.06 GJ/yr) for the highest LPSP. In contrast, the solar-tidal-wind-based configuration inflicts the most damage, with 62.63 GJ/yr and 1794 mPt/yr for the highest LPSP. The finding indicates that the DA is faster (100 iterations) than the genetic algorithm (1000 iterations), particle swarm optimization (400 iterations), and artificial bee swarm optimization (300 iterations). The study underscores the solar-tidal-based configuration as the optimal choice across multiple criteria, offering a promising solution for freshwater supply and environmental sustainability on Al Lulu Island.

Blade optimization for hydrodynamic performance improvement of a horizontal axis tidal current turbine

This paper proposes an innovative methodology applied to blade optimization for hydrodynamic performance improvement of a horizontal axial tidal current turbine (HATCT) considering the effect of Reynolds number. Axial induction factor, tangential induction factor and angle of attack are employed for identifying the accuracy and applicability of modified Blade Element Momentum (BEM) theory. Combined with the XFoil software, the hydrofoil shape function is represented by trigonometric functions through Theodorsen method. The hydrodynamic characteristics of the hydrofoil are employed as the optimization targets, and the particle swarm optimization algorithm is used to optimize the original hydrofoil. Based on the modified BEM theory and the optimized hydrofoil, the tidal current turbine power coefficient at different tip speed ratio (TSR) is optimized according to the MATLAB function. The optimized tidal current turbine shows better performance compared with the original tidal current turbine.

ASSESSMENT OF TIDAL ENERGY RESOURCES IN BALI STRAIT

The ocean possesses advantages as a sustainable and predictable source of energy, with tidal energy being one such marine-derived energy source. This study examines the analysis of ocean energy potential in the study location of the Bali Strait. The analysis of tidal energy potential follows the guidelines of the European Marine Energy Center (EMEC) and employs numerical modeling to identify current velocities using Delft3D. This study investigates the influence of water depth columns to determine the optimal depth for the placement of energy conversion technologies. It is found that the highest current velocities occur in the strait's narrowed section. Furthermore, from the analysis of tidal energy potential, it is determined that upper water depth columns (9 m, 19 m, and 26 m) can generate twice as much energy as the lower water depth columns (40 m and 45 m).

Assembling all-wood-derived carbon/carbon dots-assisted phase change materials for high-efficiency thermal-energy harvesters

The collection and storage of renewable, sustainable and clean energy including wind, solar, and tidal energy has attracted considerable attention because of its promising potential to replace fossil energy sources. Advanced energy-storage materials are the core component for energy harvesters, affording the high-efficiency conversion of these new-style energy sources. Herein, originated from nature, a series of all-wood-derived carbon-assisted phase change materials (PCMs) were purposed by incorporating carbon dots-modified polyethylene glycol matrix into carbon skeletons via a vacuum-impregnation strategy. The resultant PCMs possessed desired anti-leakage capability and superior thermophysical behaviors. In particular, the optimum sample posed high latent heat (131.5 J/g) and well thermal stability, where the corresponding enthalpy still reserved 90 % over 100 heating/cooling cycles. More importantly, the as-fabricated thermal-energy harvester presented prominent capability to strorage and release multiple forms of thermal energy, as well as high-efficiency solar-energy utilization, corresponding to a photothermal conversion efficiency of 88 % in simulated sunlight irradiation, far exceeding some reported PCMs. Overall, with the introduction of wood-derived carbon dots and carbon skeletons, the assembled all-wood-derived carbon-assisted PCMs afforded trinity advantages on thermal performance, cycling stability, and energy conversion efficiency, which provide a promising potential for the practical application in thermal-energy harvesters.

A fast hydrodynamic prediction method of horizontal axis tidal turbine with surging motion under wave-current condition

To obtain the hydrodynamic load characteristics of the floating horizontal-axis tidal turbine (HATT) with rotation and surging motion under wave-current conditions, a numerical method based on CFD is established to calculate and analyze the power and axial load characteristics of the HATT under different wave heights, surge periods, surge amplitudes and tip speed ratios. The results demonstrates that the power and axial load coefficients of the HATT fluctuate based on the relative wave and surge frequencies, and the fluctuation amplitude increases gradually with the increase of surge amplitude, surge frequency, and tip speed ratio. In this foundation, a fast prediction model of the power and axial load coefficients is proposed, and the correlation coefficients in the model can be obtained by fitting the CFD calculation results based on the least square method. The results show that the calculation results based on the fast prediction method are basically consistent with the CFD calculation results, verifying that the fast prediction method can effectively predict the hydrodynamic loads of the HATT with rotation and surging motion under wave-current conditions. Research findings can provide a fast calculation method of HATT axial load and power coefficients when the HATT and floating platform are coupled.

Performance evaluation of a bidirectional horizontal axis tidal turbine with S-shaped blades by the sliced section method

Understanding the flow pressure distribution on the blade airfoil of the tidal turbine is of great significance for optimising the energy harvesting performance of the blades. In this paper, a bidirectional type horizontal tidal turbine (BHTT) with special S-shaped blades is proposed, which have a larger pitch diameter ratio provide excellent performance at low oncoming flow velocity by the theoretical, numerical and experimental methods. First, it is verified that the energy harvesting efficiency is basically the same in the case of bidirectional flow, and the S-shaped blade is divided into multiple slice sections, which could quantify the energy harvesting performance of each area of the blade. Then, using the method of mathematical statistics to divide more areas, the probability density shows a skewed distribution. The results show that the energy harvesting performance is less affected by flow velocity fluctuation, and the energy harvesting efficiency could reach 0.25-0.55 when the tip speed ratio is in the range of 0.2-0.5. Furthermore, the slice section method is adopted to make the influence of axial thrust intuitive and clear to study the turbine energy harvesting performance and improve the harvesting efficiency, which could provide a reference for the engineering design of tidal turbines.

Numerical assessment of tidal potential energy in the Brazilian Equatorial Shelf

The Brazilian Equatorial Shelf (BES) is one among the macrotidal regions worldwide. This study used a high-resolution numerical configuration of the ocean model ROMS (Regional Ocean Modeling System) forced with realistic surface and lateral forcing, as well as with tides and river discharges. Tidal heights of more than 2 m were found in three regions in BES due to the large tidal amplification across the estuarine channels inside each region: Amazon, Pará, and Maranhão, and for a considerable time fraction. Heights between 4 and 5 m occurred with a frequency greater than 20%–30% in some regions. All hypothetical barrages proposed in this study were capable of an annual power production, in two-way mode, higher than La Rance (533 GWh year−1, two-way operation, France) and Sihwa (553 GWh year−1, flood-only operation, South Korea), except one with the same production as Sihwa barrage. The installation effort was evaluated using the Gibrat ratio, the ratio between the length of the barrage and its annual energy production. Among the proposed barrages, the most efficient ones have an annual power generation greater than 1500 GWh year−1 and a Gibrat ratios between 1.17 and 3.26, much lower than the Gibrat ratio of Sihwa tidal barrage.

Assessment of Tidal Current Energy Resources in the Pearl River Estuary Using a Numerical Method

In this paper, a numerical method is employed to assess tidal current energy resources in the Pearl River Estuary, China. The numerical model for tidal current simulation in the estuary is developed based on the MIKE 21 model, which enables numerical simulations in estuaries, coastal areas, and oceans. The model has a grid resolution that varies from about 2500 m at the open boundary to 500–1000 m inside the estuary. Extensive model validation is performed by comparing the model predictions with field observations of tidal level and velocity at various stations in the Pearl River Estuary. The tidal characteristics are thoroughly analyzed. Energy fluxes and power densities are calculated along selected cross sections to evaluate the feasibility of tidal energy development in the Pearl River Estuary. The results indicate that the distribution of annual average tidal current power density in the Pearl River Estuary generally aligns with the spatial distribution of tidal currents. The annual average power density of tidal energy is typically below 0.10 kW/m2. The theoretical potential of tidal current energy resources in the Pearl River Estuary is assessed to be approximately 11,000 kW.

Design, modeling and experiments of swing L-shape piezoelectric beam applied to tidal and wave energy harvesting

Swing-piezoelectric energy harvesting has the potential to be used for small-scale tidal and wave energy harvesting. A novel method is proposed to capture tidal and wave energy by combining swing motion and piezoelectric elements in this paper. The dynamic equation and electromechanical coupling equation for the Swing L-shaped Beam Piezoelectric Energy Harvester (SLB-PEH) are derived using the Lagrangian equation, and a Simulink-Adams simulation model is constructed. The model's accuracy is confirmed by comparing theoretical, simulated, and experimental outcomes. Furthermore, key parameters' impact on SLB-PEH performance is examined through experiments. The paper introduces an interleaved SLB-PEH to enhance energy capture efficiency within space constraints. It also describes the design of the Integrated Spring Tidal-Wave Piezoelectric Energy Harvester (ISTW-PEH), which is inspired by the interleaved SLB-PEH structure. The experimental results demonstrate that the ISTW-PEH can generate a maximum power output of 13.6 mW at a flow velocity of 0.3 m/s and a maximum power of 57.6 mW under a wave height of 0.08 m and a wave period of 0.08s.

Experimental and numerical investigations on the performance and wake characteristics of a tidal turbine under yaw

This paper presents an extensive examination of the wake characteristics and hydrodynamic performance of a 1:60 scale horizontal axis tidal stream turbine under yawed inflow conditions. Experimental investigations were conducted in a laboratory flume, while numerical simulations utilized the actuator line method and large-eddy simulation technique. The turbine was subjected to an inflow turbulence intensity of 6% and was tested at five different yaw angles (5°, 10°, 15°, 20°, and 30°). The findings demonstrate a substantial reduction in the power coefficient as the yaw angle increases, with a notable drop of 47.1% recorded at a yaw angle of 30°. Furthermore, numerical simulations of wake characteristics, including mean velocity and turbulence intensity, were examined and compared with measurements, yielding satisfactory agreement. The yawed wake flow exhibited asymmetrical distributions of mean velocity and deviations from the centerline. Additionally, distinct deformations of the yawed wake in the y-z cross sections were observed, indicating a discernible curled kidney shape that intensified with larger yaw angles. Moreover, interactions between the turbine wake and support structures affected the width and turbulence intensity of the near wake, introducing additional unsteadiness that accelerated wake recovery.

Investigation of Hydrokinetic Tidal Energy Harvesting Using a Mangrove-Inspired Device

There is a trend towards harvesting tidal energy in shallow water. This study examined how tidal energy can be harvested using a device of oscillating cylinders inspired by the roots of mangroves. A specific focus was placed on optimising the configuration of these devices, informed by the computational fluid dynamics (CFD) analysis of wake interference in the von Kármán vortex street of the cylinders. A maximum efficiency of 13.54% was achieved at a peak voltage of 16 mV, corresponding to an electrical power output of 0.0199 mW (13.5% of the hydrokinetic energy of the water) and a power density of 7.2 mW/m2 for a flow velocity of 0.04 m/s (Re=239). The configuration of upstream cylinders proved to have a significant impact on the power generation capacity, corroborated further in CFD simulations. The effect of wake interference was non-trivial on the magnitude and quality of power, with tandem arrangements showing the largest impact followed by staggered arrangements. Though with comparatively low energy densities, the device’s efficiencies found in this study indicate a great potential to harvest tidal energy in shallow water, which provides a consistent baseload power to supplement intermittent renewables (e.g., solar and wind).

A Probabilistic Methodology for Determining Collision Risk of Marine Animals with Tidal Energy Turbines

Commercial development of tidal stream energy is hampered by technical and financial challenges, and impeded by uncertainty about potential environmental effects that drive environmental risk assessments and permitting (consenting) processes. The effect of greatest concern for operational tidal stream energy devices is the potential for marine animals to collide with turbine blades, resulting in injury or death. Due to the turbulent and often turbid waters that frequently characterize tidal turbine sites, there is an absence of empirical evidence about collisions with marine animals. This paucity of observations often leads to risk-averse permitting decisions that further restrict the deployment of tidal energy devices that are needed to collect this evidence. This paper relies on the framework of stressors and receptors that is widely used in marine energy studies and outlines a stepwise probabilistic methodology that applies existing knowledge to further elucidate the risk to marine animals from operational tidal turbines. A case study using striped bass from the Bay of Fundy, Canada, accompanies the methodology, to partially demonstrate its application.

Assessment of tidal current potential in the Pará River Estuary (Amazon Region – Brazil)

World energy consumption will grow by almost 50 % between 2018 and 2050, resulting in a 79 % increase in electricity generation over this period. In general, renewable energy has been an important source of electricity generation for several years due to its ability to produce unlimited energy. Among the renewable energies are the oceanic ones, which depend on the resources of the tidal waters and the oceans. Tides are a promising energy source, given their periodicity and predictability, using techniques of harmonic analysis or ocean modeling. The Amazon is a region with multiple sparsely distributed populations, with difficult access to energy. Renewable sources are an alternative to bring energy and development to these communities. This paper focuses on the assessment of the power of tidal currents in the Pará River Estuary (PRE, Brazilian Amazon) as an alternative source of electricity generation in the region. This estuary is characterized by particularities such as not having its own source, it has an extension of 300 km and a depth between 0 and 70 m. The methodology was based on the two-dimensional hydrodynamic model (2DH) of SisBahia. The results show the occurrence of five areas with potential for tidal energy exploitation. Power densities for these areas are in the range of 0.4–0.7 MWh/m2 in a spring and neap tidal cycle. This article demonstrates the relevance of choosing parameterized quantities that do not depend on specific equipment, as well as the importance of an adequate characterization of the hydrodynamic patterns in the PRE, necessary to optimize the use of hydrokinetic energy.

The Integration of Tools for the Techno-Economic Evaluation of Fixed and Floating Tidal Energy Deployment in the Irish Sea

Marine renewable energy (MRE) development will be crucial to achieve worldwide energy decarbonization. In Europe, 1 GW and 40 GW of ocean energy are set to be developed by 2030 and 2050, respectively. Support is essential if wave and tidal stream arrays are to become more economically viable than they currently are. Four recently developed open-access software tools are used in this study to investigate the critical and expensive elements of potential demonstration and commercial scale tidal projects. The tools have been designed and built to assist users with array configurations, foundation and mooring (F&M) design, operation and maintenance (O&M) strategies, and techno-economic analysis. Demonstration of their use is performed in this study to model scenarios for 2 MW, 10 MW, 40 MW, and 100 MW tidal energy projects employing typical 500 kW fixed and 2 MW floating turbines at the West Anglesey Tidal Demonstration Zone in the Irish Sea. The following metrics are examined: the power output and wake losses of staggered and line configurations; the design and costs of simple gravity-based foundations, gravity-based anchors and the four-chain catenary mooring system of a single turbine; the mean O&M costs and farm availability over the project life; and the breakdown of levelized cost of energy (LCoE) for all eight scenarios to ultimately reveal minimum values of 173 EUR/MWh and 147 EUR/MWh for fixed and floating tidal energy technologies, respectively. The thorough analysis facilitated within these four tools to forecast realistic situations in a specific location can help users design a tidal energy project for an area with considerable potential for commercial scale projects, and thus assist the ocean energy community in promoting and nurturing the sector in the years and decades ahead.

Enhancing Islanded Power Systems: Microgrid Modeling and Evaluating System Benefits of Ocean Renewable Energy Integration

The energy transition hinges on the effective integration of renewable energy sources into the power grid. Islands can provide invaluable insights into the challenges and opportunities of integrating variable renewable energy into the grid due to their relatively small power systems, isolated grids, and diverse availability of renewable energy resources. This paper presents a study on the system benefits and challenges of marine energy integration in insular power systems, focusing on the Orkney Islands as a case study. A microgrid modeling approach that optimizes the mix of renewable sources and energy storage systems for future scenarios considering strategic time horizons (2030, 2040, and 2050) was employed. Results suggest that integrating ocean energies, namely, wave and tidal energy, yields notable benefits compared to traditional renewable energy sources exclusively. These benefits encompass reduced installed capacity, minimized energy storage requirements, lower excess generation, and overall cost-saving.

Quantifying conditional probabilities of fish-turbine encounters and impacts

Tidal turbines are one source of marine renewable energy but development of tidal power is hampered by uncertainties in fish-turbine interaction impacts. Current knowledge gaps exist in efforts to quantify risks, as empirical data and modeling studies have characterized components of fish approach and interaction with turbines, but a comprehensive model that quantifies conditional occurrence probabilities of fish approaching and then interacting with a turbine in sequential steps is lacking. We combined empirical acoustic density measurements of Pacific herring (Clupea pallasii) and when data limited, published probabilities in an impact probability model that includes approach, entrainment, interactions, and avoidance of fish with axial or cross-flow tidal turbines. Interaction impacts include fish collisions with stationary turbine components, blade strikes by rotating blades, and/or a collision followed by a blade strike. Impact probabilities for collision followed by a blade strike were lowest with estimates ranging from 0.0000242 to 0.0678, and highest for blade strike ranging from 0.000261 to 0.40. Maximum probabilities occurred for a cross-flow turbine at night with no active or passive avoidance. Estimates were lowest when probabilities were conditional on sequential events, and when active and passive avoidance was included for an axial-flow turbine during the day. As expected, conditional probabilities were typically lower than analogous independent events and literature values. Estimating impact probabilities for Pacific herring in Admiralty Inlet, Washington, United States for two device types illustrates utilization of existing data and simultaneously identifies data gaps needed to fully calculate empirical-based probabilities for any site-species combination.

Design of Micro Hydrokinetic Energy Harvester of Marine Animal Movement for Underwater Monitoring

The underwater mobile monitoring platform that utilizes marine animals as carriers provides a new solution to address the issues of short endurance, high costs, and bulky size associated with traditional underwater mobile monitoring platforms. Based on most marine animals that have the behavioral habit of long‐duration swimming, a micro hydrokinetic energy harvesting system is proposed. This system applies a miniature vertical‐axis water turbine as its energy conversion component. The hydrokinetic energy is derived from the relative movement between marine animals and the surrounding seawater. A conceptual design of a novel underwater mobile monitoring platform is presented. A finite element model of the external‐rotor permanent magnet synchronous generator is established to comprehensively evaluate the performance of the generator. Numerical simulation is utilized to conduct a comparative analysis of different diversion channel designs. Preliminary water tank experiments show that the designed micro energy harvester can effectively capture the hydrokinetic energy generated by water flow movement. The startup flow rate of the harvester is around 0.16 m s−1. The output power increases with the increase in water flow velocity, reaching a maximum value of ≈57 mW within the range of water flow rate of about 0.2–0.5 m s−1.

Automated Detection and Tracking of Marine Mammals in the Vicinity of Tidal Turbines Using Multibeam Sonar

Understanding how marine animals behave around tidal turbines is essential if we are to quantify how individuals and populations may be affected by the installation of these devices in the coming decades. Our particular interest is in collision risk, and how this may be affected by the fine-scale behaviour of seals and small cetacean species around devices. We report on a study in which multibeam sonar data were collected close to an operational tidal turbine in Scotland continuously over a twelve-month period. The sonars provide high-resolution (a few cm) data over a 120° angle out to a range of 55 m at a rate of 10 frames per second. We describe a system which uses automatic computer algorithms to detect potential targets of interest, verified by human analysts using a sophisticated computer user interface to confirm detections and assign target species. To date, we have identified 359 tracks of marine mammals in the data, as well as several thousand tracks from fish and diving birds. These are currently being parameterised to study how these species react to the moving turbine rotors, and the data are now being used to explore the development of improved automated detection and classification algorithms.