Tidal Energy Exploitation Research Articles

Estimation of tidal energy potential in the Vietnam East Sea: A comprehensive analysis using semi-empirical tide models

This study assesses the tidal energy potential in the Vietnam East Sea (VES), a region with complex hydrodynamics and significant interactions with the Western Pacific Ocean. A rigorous validation of six prominent semi-empirical global ocean tide models (FES2014, DTU16, EOT20, GOT4.10c, HAMTIDE12, OSU12.V1) was conducted against an extensive network of 34 tide gauge stations in the VES region. The validation identified FES2014 as the superior model, exhibiting the closest agreement with observations due to its advanced data assimilation techniques, high-resolution grids, and robust hydrodynamic representation influenced by the complex VES bathymetry. Leveraging the FES2014 model, the influential role of the semi-diurnal component (M2) in dictating energy distribution is prominently evident. Evaluation results of tidal amplitudes revealed three emerging hotspots: the Batang Lupar estuary (Malaysia), Anpu Gang (China), and Bac Lieu (Vietnam), with tidal amplitudes up to 326.2 cm. The Anpu Gang exhibited the highest theoretical potential tidal energy of 14.90 Wh/m2, making it the most promising site for localized tidal power development. Although moderate compared to globally renowned sites, the identified VES hotspots merit consideration for small-to-medium scale projects tailored to local conditions. While limited to potential energy assessments, this study provides a crucial baseline for the VES region, highlighting opportunities for sustainable tidal energy exploitation.

Evaluation of Tidal Asymmetry and Its Effect on Tidal Energy Resources in the Great Island Region of the Gulf of California

Hydrokinetic tidal energy is one of the few marine renewable energy resources with sufficiently mature technology for commercial exploitation. However, several parameters affect its exploitability, such as the minimum speed threshold, ambient turbulence levels, or tidal asymmetry, to name but a few. These parameters are particularly important in regions with lower mean speeds than those in first-generation sites, such as the North Sea. The Gulf of California is one of those regions. In this paper, a Delft3D Flexible Mesh Suite (Delft3D FM) model in barotropic configuration is set up over the Gulf of California using a flexible mesh with resolution varying from O (500 m) in the deep regions to O (10 m) in the coastal regions. A simulation is run over the year of 2020, with a tidal forcing of 75 components. The model is validated at four tidal gauge locations and four Acoustic Doppler Current profiler (ADCP) locations. The speed, U, and tidal power density (TPD) indicators used for the validation were the annual means, the annual means for speeds above the 0.5 m s−1 threshold, the annual means of the spring tide maxima, and the annual maxima. The contour maps of the annual means, that is, the annual means for speeds above the 0.5 m s−1 threshold, allow us to identify tidal energy hot spots throughout the Gulf of California, particularly in the Great Island region (GIR). In this region, these hot spots have higher U and TPD values, in agreement with previous studies. The patterns of circulation around Tiburón Island and San Esteban Island on the East, and Ángel de la Guarda Island and San Lorenzo Island on the West, the four islands in the region with the highest tidal energy potential, are also discussed while recognizing that Tiburón Channel, between Tiburón Island and San Esteban Island, has proved to be the best siting location, based on the technical results obtained so far. The hot spots sites are further characterized by computing the tidal asymmetry in these small regions, showing the locations of the sites with smallest asymmetry, which would be the best for tidal energy exploitation. The hot spots around San Esteban Island are particularly important because they have the largest TPD in the GIR, with the model predicting a TPD on the order of 500–1000 W m−2. Here, complementary field measurements obtained with two ADCPs, close to San Esteban Island, one at 15 m depth, SEs (shallow region), and the other at 60 m depth, SEd (deep region), produced TPDs of 1200 W m−2 and 400 W m−2, respectively. The analysis of the vertical profiles and the tidal asymmetry over the vertical shows the importance of developing 3D models in future investigations.

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.

Experimental Optimization Environment for Developing an Intracycle Pitch Control in Cross Flow Turbines

Cross-flow tidal turbines also known as vertical-axis turbines have not reached the efficiency as it is usual found for horizontal-axis turbines. This can be mainly accounted to the intensive development effort dedicated to the latter in the past 30 years in the area of wind energy. Less attention has been given to cross-flow turbines as they present mechanical cyclic loads that detriment their durability. Nevertheless, there is great potential for their employment in tidal energy exploitation as they are intrinsically independent from the flow direction and have a higher power output per area in farm installation. For this reason the research for cross-flow turbines have regain impulse.
 Among various approaches to improve their hydrodynamic characteristics found in the literature, the intracycle pitch control is one of the most promising one. It consists in actively pitching each blade as function of the azimuth angle.
 The present paper will introduce the overall experimental environment and methods for developing an optimal intracycle control for cross-flow turbines in tidal power generation. This is the main component of project OPTIDE at Otto-von-Guericke-University Magdeburg, Germany in cooperation with the LEGI at University Grenoble-Alpes, France and the University of Applied Sciences Magdeburg-Stendal.
 The experimental system consists of a turbine flume model equipped with a speed controlled generator. The three bladed turbine model has independent controlled pitch actuators embedded in each blade and a force sensing system in one of the blade holding arms. Local high-dynamic systems allow to control the speed of the generator and the pitch position as a function of the rotational angle of the runner i.e. pitch trajectory.
 A superimposed governing system which automates the experiment has been implemented. This allows to perform an optimization process with the experiment in the loop. Evolutionary algorithms are employed to solve the two objectives of the optimization: (1) Maximizing the efficiency by (2) minimizing the alternating structural loads on the runner. These kind of problems are usually solved with numerical simulations using finite element method (FEM) and computational fluid dynamics (CFD). However, this commonly comes with very high computational efforts and uncertainty. For this reason in our approach simulations are replaced by an experimental optimization technique.
 The optimization cycle implemented in the superimposed governing system chooses a set of individuals (pitch trajectories) for each generation on base of the genetic algorithm. Each pitch trajectory is performed sequentially while power output and loads are measured. This allows to evaluate each individual in about one minute. The best individuals are then the base for the offspring of the new generation. Cross-over from best performing parents and subsequent mutation ensure both, convergence and a thorough exploration of the entire design space.
 It is expected that this method will fast and reliably find the optimal pitch trajectories under various conditions. Selected cases will be analysed in detail by means of particle-image velocimetry (PIV) with synchronized force and torque measurements to research the underlying hydrodynamic mechanisms and the effects of the flow control performed by the pitching motion.

Methodology to capture the single blade loads on a cross-flow tidal turbine flume model

The OPTIDE project aims to improve the efficiency and durability of Hydro-kinetic cross-flow tidal turbines (CFTT). These turbines are attractive for the exploitation of tidal energy, as the area-based power density of such turbine arrays is higher in comparison to those from horizontal-axis turbines. CFTT also generally feature a simpler design and the ability to operate under varying flow conditions. Nevertheless, the efficiency of single CFTT is lower relative to the most commonly used axial turbine type. Furthermore the life time can be affected by alternating and pulsating stresses, caused by continuous variations of the angle of attack and hydraulic loads during the rotation. These stresses may lead to structural damage and fatigue-induced material failures. A promising approach to overcome these drawbacks is intracycle blade pitching. In this case the angle of attack is continuously adjusted individually for each blade during the rotation. The consequence is smoothed peaks of the load alternations and a higher power coefficient CP . The project aims to explore the influence of active blade pitching on CFTTs and to optimize it with numerical and experimental means. Therefore, a lab-scaled three-bladed experimental turbine with embedded pitch actuators is developed. The model will subsequently be tested in the lab flume of the Institute of Fluid Dynamics and Thermodynamics of the Otto-von-Guericke University Magdeburg. Blade forces in tangential and radial components as well as the machine torque and the rotational speed are measured during the experiments. The turbine is equipped with two full-bridges of strain gauges for the detection of the blade loads, from which the structural stress is calculated subsequently. To ensure the turbine model’s mechanical durability, weakly coupled fluid-solid-interaction (FSI) simulations have been performed and will be presented. To this purpose, a 2D flow analysis, employing the open-source CFD toolkit OpenFOAM (v2206), has been coupled with a 3D structural analysis, using the Mechanical module of the commercial software package Ansys Workbench (2020 R2). The FSI simulations show that the current setup only allows for the measurement of the radial blade load component, because the pitching moment at blade level interferes with the measurements as soon as the profile stalls. The measurements are further distorted by secondary force paths from the loads on the other rotor blades. Possible measures for an improved instrumentation strategy on the flume model will be presented and discussed. It is shown that multiple equipment options allow for a decent investigation of the forces on blade level.

Objective Functions for the Blade Shape Optimisation of a Cross-Flow Tidal Turbine under Constraints

Hydro-kinetic cross-flow tidal turbines (CFTT) are omni-directional and offer higher area-based power density compared to horizontal-axis tidal turbines, making them very attractive for tidal energy exploitation. However, the rotating motion around the vertical axis results in continuously varying angles of attack, causing alternating loads, which may lead to fatigue failure and structural damage. The OPTIDE Project addresses these challenges by implementing intracycle blade pitching to individually control the angle of attack, increasing the power coefficient CP and reducing structural loads. For this purpose a Darrieus turbine is designed with embedded actuators in each blade. Firstly a blade shape optimization will be conducted to fit the actuator at the quarter-chord position while ensuring sufficient thickness. The optimization procedure couples Computational Fluid Dynamics (CFD) with a Genetic Algorithm. The employed optimizer OPAL++ sets ten variables for each individual, which describe the hydrofoil shape, length and tip speed ratio (TSR). A smooth hydrofoil shape is generated from the variables, followed by an automatic mesh generation. Subsequently, numerical simulations of each individual at the desired TSR are conducted, while keeping the blade pitch angle constant. Simulation results provide the CP and stress acting on the turbine blades, which are the two optimization objectives (maximize CP while minimizing stress). This process is repeated during the optimization, aiming to determine the most suitable blade shape, that fits the actuator, and operating point (TSR) in a trade-off between CP and structural loads. This will lead to the increase of efficiency and a longer turbine lifetime.

Sea level rise changes estuarine tidal stream energy

Worldwide, many estuaries have the potential to harness tidal stream energy via the conversion of current velocities into a consumable energy source. However, the effects of future sea level rise on the tidal stream energy resource within different estuary types are largely unknown. To address this knowledge gap, 978 idealised hydrodynamic simulations were carried out to first identify estuary types and the location of hotspots within them that are promising for tidal energy exploitation in present-day conditions, and then provide insights into the altered tidal stream energy of different estuary types under various future sea level rise and river inflow scenarios. The results indicate that, under sea level rise, the tidal stream energy of prismatic estuaries reduces more than that of converging estuaries. This implies that estuaries that are currently worth exploiting for tidal power may cease to be in the future due to accelerating sea level rise. Further, as sea level rise may bring about geomorphic adjustments, the spatial energy patterns within an estuary may shift and optimal energy sites may be eliminated or displaced. These climate change effects pose a serious challenge for the management of tidal energy generation in future. In this context, the findings of this study are of practical significance for decision-makers in designing long-term strategies for the development of tidal energy installations in estuaries under rising mean sea levels.

Passive flow control mechanisms with bioinspired flexible blades in cross-flow tidal turbines

State-of-the-art technologies for wind and tidal energy exploitation focus mostly on axial turbines. However, cross-flow hydrokinetic tidal turbines possess interesting features, such as higher area-based power density in array installations and shallow water, as well as a generally simpler design. Up to now, the highly unsteady flow conditions and cyclic blade stall have hindered deployment at large scales because of the resulting low single-turbine efficiency and fatigue failure challenges. Concepts exist which overcome these drawbacks by actively controlling the flow, at the cost of increased mechatronical complexity. Here, we propose a bioinspired approach with hyperflexible turbine blades. The rotor naturally adapts to the flow through deformation, reducing flow separation and stall in a passive manner. This results in higher efficiency and increased turbine lifetime through decreased structural loads, without compromising on the simplicity of the design.Graphic abstract

Tidal Energy Potential in the Center Zone of the Colombian Pacific Coast

Introduction: Tidal energy is evidencing interest worldwide because it can be accurately estimated due to the cyclical behavior of the tides. This energy can be extracted from differences in sea level height through the use of gates and turbines of a reservoir (tidal power plant), or extracted from tidal currents through a grid of reversible horizontal axis microturbines as proposed in this study. Thus, the Colombian Pacific region has the opportunity to implement microturbines in strategic areas with the challenge of optimizing them to extract energy with local tidal heights up to 4 m and current velocities up to 1.5 m/s.
 Objective: Calculate the energy potentials from tidal currents in the central zone of the Colombian Pacific coast obtained through hydrodynamic modeling (Delft3D) validated it with in situ information.
 Methodology: The present study starts from level 1 of technological development (Technology Readiness Levels, TRL) till reaching the TRL 2. Then, the research performed a documentary review of national and international experiences related to tidal energy, evidencing the great opportunity that Colombia has to take advantage of this type of energy and join to the growing international interest in the development of clean and renewable energies. In addition, this study characterized the tidal heights and did calculations of energy potentials from tidal currents in the Colombian Pacific derived from hydrodynamic modeling (Delft3D) validated with measured in situ data. The results of this study encourage the application of these technologies in Colombia and represents a contribution to the fulfillment of the UN sustainable development objectives (Affordable and non-polluting energy, SDG 7).
 Results: From the 4 analysis points, the point B (Buenaventura) registered the highest accumulated potential for electricity generation per month (31,546.56 Wh / month). The maximum tidal heights at points A, B, C and D during 2018 were 1.88 m. Furthermore, the mean velocity range at points A, B, C and D was 0.28 m/s to 0.54 m/s, and the maximum velocity for these points were 0.54 m/s, 0.49 m/s, 0.31 m/s and 0.28 m/s respectively. Then, by means of 5 tidal microturbines with a reversible horizontal axis of 1 m sweep area for the point of highest potential (B), it is possible to generate electrical energy to meet the electrical consumption of a house, and with 544 microturbines the consumption of 99 houses. The tidal farm (544 microturbines) would require an area of 2079.36 m2 (e.g. 45.6 m x 45.6 m) and an average depth of 5 m; these requirements are feasible to be met because of the study area characteristics.
 Conclusions: This research determined the tidal energy potential in the central zone of the Colombian Pacific for 4 points of interest, (A, B, C and D) and the highest potentials were found in points A and B located in Bahía Málaga and Buenaventura respectively. In addition, the minimum velocities, the duration of these and the diurnal tidal regime (12 h) were analyzed, and it was found that points A and B showed the lowest times (1 h and 2 h) of minimum velocity, evidencing a capacity of daily electricity generation of 22 h and 20 h respectively. In consideration of the obtained results, this research shows the opportunity to perform studies for promoting the development of reversible horizontal-axis microturbines for the exploitation of tidal energy. The generated energy could be supplied to communities with access difficulties to the electricity distribution network, what would reduce poverty and the emission of Greenhouse Gases (GHG) due to the burning of fossil and plant-based fuels (firewood).
 
 Conclusions: It was determined that the tidal energy potential in the central zone of the Colombian Pacific for 4 points of interest, (A, B, C and D) and the highest potentials were found in points A and B located in Bahía Málaga and Buenaventura respectively. In consideration of the results obtained, this research shows the opportunity performe studies for promoting the development of microturbines for electricity generation from tidal energy. The generated energy would supply to communities with difficulties in accessing the networks of electricity distribution, thus reducing poverty and the emission of Greenhouse Gases (GHG) due to the burning of fossil fuels and of vegetable origin (firewood).

In-Stream Tidal Energy Resources in Macrotidal Non-Cohesive Sediment Environments: Effect of Morphodynamic Changes at Two Bays in the Upper Gulf of California

Because of the need to diversify the renewable energy matrix and because hydrokinetic tidal energy technologies are mature, many in-stream tidal energy resource studies are available globally. Still, there are many questions regarding the effect of seabed changes on tidal energy resources. For coastal regions in particular, where the seabed is generally more mobile than in deep waters, bathymetric evolution could significantly affect tidal energy production. Here, two models are used to analyse the potential effect of natural morphodynamic change on tidal energy resources at two macro-tidal sandy bays, Adaír Bay and San Jorge Bay, in the Upper Gulf of California, Mexico. One of the models is (purely) hydrodynamic, and the other is a morphodynamic model (with hydrodynamic–morphodynamic coupling). The models are validated against tidal current observations obtained with acoustic Doppler current profilers in the region of interest, using three different error statistics, which showed good agreement between models and observations. The results also showed that the most significant bed changes and the largest renewable energy resources are located near the shore. Moreover, there was a good correlation between (a) regions with the most significant depth changes and (b) the areas where the difference in annual energy production with and without depth change was largest. Finally, a two-year simulation with the morphodynamic model permitted to analyse the seabed evolution of a zonal profile off Punta Choya, the headland between the two bays. This profile evolved towards a featureless equilibrium, as expected from the morphological classification for macro-tidal sandy environments under a dominant tidal forcing. However, most importantly, this natural evolution would not be detrimental to tidal energy exploitation at the site.

Feasibility assessment of tidal energy extraction at the Tg Tuan coastal headland: A numerical simulation study

Headland is identified as potential tidal current energy extraction sites. The complex flow circulation at headland initiated a high-resolution Tg Tuan Headland numerical model in this research. Assessment on potential and impact of tidal energy exploitation was conducted through detail assessment for different zones and depths around the headland. The simulated results show that tip of the headland can be a promising site for tidal energy converter deployment fulfilling the depth and flow velocity requirement for marine current energy turbine operation. Further analysis on depth influence to tidal energy converter deployment based on eight different scenarios showed descending relationship between depth effects and velocity changes. The velocity changes due to tidal turbine deployment at deeper area (28.41 m–31.64 m) are much insignificant (<0.001 m/s) than shallower area. The finding from this study indicated the importance of headland zone and depth criterion selection for policy maker and investors.

Wind-Induced Currents in the Gulf of California from Extreme Events and Their Impact on Tidal Energy Devices

Tidal renewable energy is a promising alternative energy resource, and marginal seas are known as excellent sites for tidal energy exploitation. In-stream and tidal energy devices are less exposed to extreme weather events than wind energy. Nevertheless, during tropical storms, the currents may intensify to levels that threaten the integrity of the devices. This paper presents Hurricane Odile and its impact on the currents in the Gulf of California (GC) as a worst case scenario. A methodology to analyze the impact and its potential effects on tidal energy converters installed within the region are presented. The analysis is based on predictions obtained with a 3D shallow water model forced by tides and the meteorological conditions generated by Odile. A tidal model with no wind forcing was used for validation of the tidal model predictions. After validation, the two models were used to analyze the maximum anomaly in surface currents and sea surface height caused by the passage of Odile, and to analyze at which depth the devices could be deemed safe from any impact of the hurricane. Some anomalies extended throughout the water column, even in the deep regions of the GC. This paper highlights the importance of including the meteorological forcing in evaluations of tidal range or in-stream renewable energy resources and introduces new measures of device exposure to the current anomalies.

Wake field study of tidal turbines under realistic flow conditions

Numerical modelling of the flow interactions between tidal turbines in arrays is a prerequisite to assess the energy production potential and to optimise the layout of tidal stream energy farms. It requires (i) a refined representation of the tide propagation and (ii) a reliable estimate of the flow characteristics around the turbines. The Actuator Disk (AD) theory is recognised as a reliable parameterisation to approach the far wake of fixed horizontal-axis turbines and was therefore implemented to provide recommendations as regards to the design of arrays, especially the optimal spacing between devices. However, analysis of the arrangement of tidal stream turbines are typically restricted to schematic test cases with idealised bathymetry and inflow conditions. The present study aims to investigate the flow interactions between turbines in a stream energy site with spatially- and time-varying tidal conditions. The site of application is the Alderney Race (English Channel), an area with strong potential for the exploitation of tidal energy in European shelf seas. The three-dimensional numerical model Telemac3D is used to capture the flow at both the regional and the array scales. Predictions are first assessed against ADCP measurements acquired around the island of Alderney. A series of simulations, representing turbines with the AD theory, are then performed to investigate the influence of the wake interactions on the energy production of individual devices. In those simulations, the turbines are represented with the AD theory. The zone occupied by the turbines is 20D-long and 15D-wide (D is the turbine diameter). Different layouts (isolated, aligned and staggered turbines) and different longitudinal and lateral spacings are considered to investigate the effect of the turbines’ arrangement and density on the array energy production. The results show that, for a given turbines density within the array, the staggered layout produces more than the aligned layout (+16%). When the turbines are staggered, a minimal lateral spacing of 5D is required to avoid wake overlapping. However, when the turbines are aligned, the lateral spacing has a small influence on the turbines production. It is therefore possible to pack the turbines close to each other in the lateral direction. The simulations also outline that the turbulence develops much faster within the array when the turbines are aligned.

The effects of oblique waves and currents on the loadings and performance of tidal turbines

Tidal energy exploitation is at an early deployment stage and costs need to be reduced to improve the long term economic viability of the sector. High costs of tidal turbines are, in part, the result of load uncertainties, which lead to the use of high factors of safety in the design to ensure survival. One of the most important causes of uncertainty is hydrodynamic loadings. To date, most of the scaled model experiments with horizontal axis turbines investigating this issue have been carried out with collinear wave and current directions. To the authors' knowledge, the work presented herein is the first experimental investigation of a horizontal axis turbine model subjected to combined oblique waves and current. Turbine performance and loading are measured for a 1:15 scale model tested in the FloWave circular, combined wave and current basin at the University of Edinburgh (UK). Three different flow directions were tested and each of them were also combined with regular waves in three different directions non-collinear with the flow. Fifteen physical quantities were measured including flow velocity, rotor and foundation loads and turbine speed. Characterisation of loads and turbine performance in those oblique current and wave conditions are presented. Waves affect means and standard deviation of rotor power and thrust, but off-axis waves are associated with lower thrust loads than head-on waves. Compared to current only, rotor torque and thrust standard deviations are higher in the presence of waves and almost twice as high when the wave crest is parallel to the rotor plan. The experimental data associated with this article can be downloaded from http://dx.doi.org/10.7488/ds/2360.

Experimental evaluation of the wake characteristics of cross flow turbine arrays

One key factor in the exploitation of tidal energy is the study of interactions of turbines when working in tidal turbine farms. The Momentum Reversal and Lift (MRL) turbine is a novel cross flow turbine. The three blades rotate around a common central horizontal axis which is parallel to their own axis and perpendicular to the flow. The novelty of the MRL turbine is that it relies on the combination of both lift and momentum reversal (drag) for energy extraction. Scaled MRL turbine models of 0.164m in diameter were used to characterise the flow in three different tidal array settings. Detailed maps of axial velocity profiles and velocity deficits downstream of the turbine are presented, enabling the visualisation of characteristic flow patterns. The results show that the MRL generates lower velocity deficits and turbulence intensities in the near wake than those associated with horizontal axis turbines. The downstream wake was not completely symmetrical which was related to the geometry of the device but also due to the flow developed in the flume. Amongst the three array configurations studied, a fence of turbines with the lowest separation provided the highest power output.

Preface to Special Topic: Marine Renewable Energy

Marine renewable energy (MRE) is generates from waves, currents, tides, and thermal resources in the ocean. MRE has been identified as a potential commercial-scale source of renewable energy. This special topic presents a compilation of works selected from the 3rd IAHR Europe Congress, held in Porto, Portugal, in 2014. It covers different subjects relevant to MRE, including resource assessment, marine energy sector policies, energy source comparisons based on levelized cost, proof-of-concept and new-technology development for wave and tidal energy exploitation, and assessment of possible inference between wave energy converters (WEC).

Estimation of the Energy Potential of the Euripus' Gulf Tidal Stream Using Channel Sea-surface Slope

Potential energy extraction from tidal currents is investigated in this work. Recordings on the streams' velocity and the sea level in the Euripus' strait in Evia, Greece are used to calculate the energy yield. Data on sea level measurements were used to extract information for the current velocity profile through harmonic analysis method. Requirements, limitations and possible new designs that will improve the energy extraction from the low velocity tidal current of the area are discussed. Also, exploitation of tidal energy in cooperation with RES microgrid is proposed for areas where the abundance of sun, wind, island communities and coast areas such as the Mediterranean.

Reserve Assessment and Potential Exploitation of Tidal Energy in Shanghai’s Sea Area of China

Rapid economic development induces energy shortage and environmental pollution, and the utilization of renewable energy becomes a hot topic. Taking the tidal energy in Shanghai as a research object, this article analyzes the reserves, potential developing mode, and potential capacity on the basis of observation data for 18 years. The results show that the tidal energy resources are abundant in Shanghai’s sea area of China. Through tidal range analysis and tidal energy reserves calculation, the tidal barrage can be built to explore the tidal energy from the water head difference between the flood tide and the ebb in the north branch of Yangtze River Estuary, while the tidal turbines can be built to generate electricity in the Northern Hangzhou Bay. The tidal energy reserve is 3.65 million kW per year in Shanghai’s sea area of China. The annual electricity generating capacity is 10.07 billion kWh, which is equivalent to 3.63 million tons of standard coal, accounting for 3.72% of Shanghai energy consumption in 2007. It can also reduce 9.50 million tons of carbon dioxide emissions each year, 30.8 thousand tons of sulfur dioxide emissions, and 26.8 thousand tons of nitrogen oxides emissions. The utilization of tidal energy is an effective method to solve environmental problems and energy issues.

IMPACT OF TIDAL STREAM ENERGY EXPLOITATION ON ESTUARINE HYDRODYNAMICS

During the last years there has been an increasing interest towards the exploitation of marine energies and, in particular, of tidal stream energy. Although the impact of tidal stream farms is expected to be much lesser than that the conventional barrages, there are numerous environmental variables likely to be altered. This is of particular interest in the case of the Galician Rias that present complex 3D flow patterns, which is one of the main causes of their large oceanic productivity. Therefore, its modification as a result of tidal energy exploitation should be analysed by means of 3D modelling. The present study investigates the environmental impacts of tidal energy extraction in the Ria de Ortigueira located in the NW of Spain. For this purpose, a numerical model was implemented in Ria de Ortigueira (NW Spain), a promising region for tidal stream energy exploitation. First, the model was successfully validated on the basis of field measurements of water levels and magnitude and direction of the tidal currents, then, it was used to describe the potential effects resulting from the operation of a previously proposed tidal stream farm during typical winter and summer conditions. For this purpose, the momentum sink approach was used. Overall, it was found that the resulting transient flow modifications were concentrated in the vicinity of the farm, with nearly negligible effects outside the inner ria. Furthermore, important asymmetry effects were also observed; although the inner part of the estuary is flood dominated, the complex geometry of this area causes that the most important effects occur during the ebb with modifications of up to 15 % of the unaltered flow, which represent an impact almost twice as strong as that during the flood. Finally, the effects on the residual flow are of the same order, in terms of percentage of velocity variation, as in the case of the transient flow; however, they extend over a wider region, affecting the middle ria, where a complex 3D circulation pattern (a positive estuarine circulation) develops.

Prospects for Fundy tidal power

The Bay of Fundy in Canada probably possesses the most favourable conditions in the world for the exploitation of tidal energy. The results of the comprehensive investigations carried out during the past quarter-century are reviewed together with operating and environmental aspects of the modest (20 MW) Annapolis Tidal Power Station, commissioned in 1984, the primary purpose of which was to evaluate the operation of a large (7.6 m) diameter Straflo turbine unit under low heads. The results of the operating and maintenance experience for the Annapolis Station are reviewed as well as the results of the environmental/ecological studies that have been on-going in the Annapolis Basin. The tidal power investigations have shown that a 1400 MW development at the mouth of the Cumberland Basin, at the head of the bay of Fundy, is technically and economically feasible and that its output would probably be competitive with fossil-fired plants, particularly if a green accounting technique were applied to such energy sources. The importance of timing, if the exploitation of this non-polluting, renewable and completely predictable source is to be used to meet the future electrical energy needs of the maritime provinces, is discussed.