scholarly journals Effect of tidal stream power generation on the region-wide circulation in a shallow sea

2010 ◽  
Vol 7 (5) ◽  
pp. 1785-1810 ◽  
Author(s):  
G. I. Shapiro
Keyword(s):  
Kinetic Energy ◽  
Ocean Circulation ◽  
Fold Increase ◽  
Tidal Energy ◽  
Energy Extraction ◽  
Shallow Sea ◽  
Residual Currents ◽  
Tidal Stream ◽  
Generation Capacity ◽  
Extracted Power

Abstract. Ocean tides are deemed to become a stable source of renewable energy for the future. Tidal energy has two components, the first is the potential energy due to sea level variations and the second comes from the kinetic energy of the tidal streams. This paper is concerned with the backward effect on the ocean currents by a tidal stream farm located in the open shallow sea. Recent studies in channels with 1-D models have indicated that the power potential is not given purely by the flux of kinetic energy, as has been commonly assumed. In this study, a 3-D ocean circulation model is used to estimate (i) maximum extractable energy at different levels of rated generation capacity of the farm, (ii) changes in the strength of currents due to energy extraction, and (iii) alterations in the pattern of residual currents and pathways of passive tracers. As water flow is influenced both by tidal and non-tidal currents, the model takes into account wind-driven and density-driven currents generated by meteorological forcing. Numerical modelling has been carried out for a hypothetical circular farm located in the Celtic Sea north of Cornwall, an area known for its high level of tidal energy. Modelling results clearly indicate that extracted power does not grow linearly with the increase in the rated capacity of the farm. For the case studies covered in this paper, a 100-fold increase in rated generation capacity of the farm results only in 7-fold increase in extracted power, this loss of efficiency is much greater than was estimated earlier with 1-D models. In case of high rated capacity of the farm, kinetic energy of currents is altered significantly as far as 10–20 km away from the farm. At high levels of extracted energy the currents tend to avoid flowing through the farm, an effect which is not captured with 1-D models. Residual currents are altered as far as a hundred kilometres. The magnitude of changes in the dispersion of tracers is highly sensitive to the location. For the drifters analysed in this study, variations in the end-to-start distance due to energy extraction range from 13% to 238%.

scholarly journals Effect of tidal stream power generation on the region-wide circulation in a shallow sea

Ocean Science ◽  
2011 ◽  
Vol 7 (1) ◽  
pp. 165-174 ◽  
Author(s):  
G. I. Shapiro
Keyword(s):  
Kinetic Energy ◽  
Energy Resource ◽  
Fold Increase ◽  
Ocean Currents ◽  
Energy Extraction ◽  
Shallow Sea ◽  
Residual Currents ◽  
Tidal Stream ◽  
Generation Capacity ◽  
Extracted Power

Abstract. This paper quantifies the backward effect on the ocean currents caused by a tidal stream farm located in the open shallow sea. Recent studies in channels with 1-D models have indicated that the power potential is not given purely by the flux of kinetic energy, as has been commonly assumed. In this study, a 3-D ocean circulation model is used to estimate (i) practically extractable energy resource at different levels of rated generation capacity of the farm, (ii) changes in the strength of currents due to energy extraction, and (iii) alterations in the pattern of residual currents and the pathways of passive tracers. As well as tidal streams, the model also takes into account the wind-driven and density-driven ocean currents. Numerical modelling has been carried out for a hypothetical tidal farm located in the Celtic Sea north of Cornwall, an area known for its high level of tidal energy. Modelling results clearly indicate that the extracted power does not grow linearly with the increase in the rated capacity of the farm. For the case study covered in this paper, a 100-fold increase in the rated generation capacity of the farm results in only 7-fold increase in extracted power. In the case of a high power farm, kinetic energy of currents is altered significantly as far as 10–20 km away from the farm. At high levels of extracted energy the currents tend to avoid flowing through the farm, an effect which is not captured with 1-D models. Residual currents are altered as far as a hundred kilometres away. The magnitude of changes in the dispersion of tracers is highly sensitive to the location. Some of the passive drifters analysed in this study experience significant variations in the end-to-start distance due to energy extraction ranging from 13% to 238% while others are practically unaffected. This study shows that both energy extraction estimates and effects on region wide circulation depend on a complex combination of factors, and the specific figures given in the paper should be generally considered as first estimates.

Effects on hydrodynamics and ecological costs of climate change and tidal stream energy extraction in a shelf sea

2020 ◽  
Author(s):  
Michela De Dominicis ◽  
Judith Wolf ◽  
Dina Sadykova ◽  
Beth Scott ◽  
Alexander Sadykov ◽  
...  
Keyword(s):  
Climate Change ◽  
Large Scale ◽  
Climate Scenario ◽  
Tidal Energy ◽  
Ocean Model ◽  
Future Climate ◽  
Biogeochemical Model ◽  
Energy Extraction ◽  
Shelf Sea ◽  
Tidal Stream

<p>The aim of this work is to analyse the potential impacts of tidal energy extraction on the marine environment. We wanted to put them in the broader context of the possibly greater and global ecological threat of climate change. Here, we present how very large (hypothetical) tidal stream arrays and a ''business as usual'' future climate scenario can change the hydrodynamics of a seasonally stratified shelf sea, and consequently modify ecosystem habitats and animals’ behaviour.</p><p>The Scottish Shelf Model, an unstructured grid three-dimensional ocean model, has been used to reproduce the present and the future state of the NW European continental shelf. While the marine biogeochemical model ERSEM (European Regional Seas Ecosystem Model) has been used to describe the corresponding biogeochemical conditions. Four scenarios have been modelled: present conditions and projected future climate in 2050, each with and without very large scale tidal stream arrays in Scottish Waters (UK). This allows us to evaluate the potential effect of climate change and large scale energy extraction on the hydrodynamics and biogeochemistry. We found that climate change and tidal energy extraction both act in the same direction, in terms of increasing stratification due to warming and reduced mixing, however, the effect of climate change is ten times larger. Additionally, the ecological costs and benefits of these contrasting pressures on mobile predator and prey marine species are evaluated using ecological statistical models.</p>

Implementation of Tidal Stream Turbines and Tidal Barrage Structures in DG-SWEM

2019 ◽  
Author(s):  
Andrea M. Schnabl ◽  
Tulio Marcondes Moreira ◽  
Dylan Wood ◽  
Ethan J. Kubatko ◽  
Guy T. Houlsby ◽  
...  
Keyword(s):  
Numerical Models ◽  
Shallow Water Equation ◽  
Tidal Energy ◽  
Head Loss ◽  
Equation Model ◽  
Energy Extraction ◽  
Tidal Hydrodynamics ◽  
Low Head ◽  
Tidal Stream ◽  
Two Sides

Abstract There are two approaches to extracting power from tides — either turbines are placed in areas of strong flows or turbines are placed in barrages enabling the two sides of the barrage to be closed off and a head to build up across the barrage. Both of these energy extraction approaches will have a significant back effect on the flow, and it is vital that this is correctly modelled in any numerical simulation of tidal hydrodynamics. This paper presents the inclusion of both tidal stream turbines and tidal barrages in the depth-averaged shallow water equation model DG-SWEM. We represent the head loss due to tidal stream turbines as a line discontinuity — thus we consider the turbines, and the energy lost in local wake-mixing behind the turbines, to be a sub-grid scale processes. Our code allows the inclusion of turbine power and thrust coefficients which are dependent on Froude number, turbine blockage, and velocity, but can be obtained from analytical or numerical models as well as experimental data. The barrage model modifies the existing culvert model within the code, replacing the original cross-barrier pipe equations. At the location of this boundary, velocities through sluice gates are calculated according to the orifice equation. For simulating the turbines, a Hill Chart for low head bulb turbines provided by Andritz Hydro is used. We demonstrate the implementations on both idealised geometries where it is straightforward to compare against other models and numerical simulations of real candidate sites for tidal energy in Malaysia and the Bristol Channel.

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

2015 ◽  
Vol 3 (4) ◽  
pp. 23-42 ◽  
Author(s):  
Aphrodite Ktena ◽  
Christos Manasis ◽  
Dimitrios Bargiotas ◽  
Vasilis Katsifas ◽  
Takvor Soukissian ◽  
...  
Keyword(s):  
Sea Level ◽  
Tidal Energy ◽  
Energy Yield ◽  
Energy Extraction ◽  
Low Velocity ◽  
Energy Potential ◽  
Yield Data ◽  
Island Communities ◽  
Tidal Stream ◽  
Harmonic Analysis Method

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.

scholarly journals Comparative Effects of Climate Change and Tidal Stream Energy Extraction in a Shelf Sea

2018 ◽  
Vol 123 (7) ◽  
pp. 5041-5067 ◽  
Author(s):  
Michela De Dominicis ◽  
Judith Wolf ◽  
Rory O'Hara Murray
Keyword(s):  
Climate Change ◽  
Energy Extraction ◽  
Shelf Sea ◽  
Tidal Stream ◽  
Tidal Stream Energy

scholarly journals Is the Ocean Speeding Up? Ocean Surface Energy Trends

2020 ◽  
Vol 50 (11) ◽  
pp. 3205-3217
Author(s):  
Carl Wunsch
Keyword(s):  
Kinetic Energy ◽  
Potential Energy ◽  
Ocean Circulation ◽  
State Estimate ◽  
Monotonic Trend ◽  
Energy Inputs ◽  
Oceanic Surface ◽  
Data Density ◽  
Power Inputs ◽  
Noisy Background

AbstractA recent paper by Hu et al. (https://doi.org/10.1126/sciadv.aax7727) has raised the interesting question of whether the ocean circulation has been “speeding up” in the last decades. Their result contrasts with some estimates of the lack of major trends in oceanic surface gravity waves and wind stress. In general, both the increased energy and implied power inputs of the calculated circulation correspond to a small fraction of the very noisy background values. An example is the implied power increase of about 3 × 108 W, as compared to wind energy inputs of order 1012 W. Here the problem is reexamined using a state estimate that has the virtue of being energy, mass, etc. conserving. Because it is an estimate over an entire recent 26-yr interval, it is less sensitive to the strong changes in observational data density and distribution, and it does not rely upon nonconservative “reanalyses.” The focus is on the energy lying in the surface layers of the ocean. A potential energy increase is found, but it is almost completely unavailable—arising from the increase in mean sea level. A weak increase in kinetic energy in the top layer (10 m) is confirmed, corresponding to an increase of order 1 cm s−1 yr−1 over 26 years. An estimate of kinetic energy in the full water column shows no monotonic trend, but the changes in the corresponding available potential energy are not calculated here.

scholarly journals A Formulation of the Thrust Coefficient for Representing Finite-Sized Farms of Tidal Energy Converters

Energies ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3861
Author(s):  
Karina Soto-Rivas ◽  
David Richter ◽  
Cristian Escauriaza
Keyword(s):  
Ocean Circulation ◽  
Spatial Organization ◽  
Local Environment ◽  
Tidal Energy ◽  
Tidal Channels ◽  
Complex Flow ◽  
Thrust Coefficient ◽  
Spatial And Temporal Scales ◽  
Flow Phenomena ◽  
Streamwise Distance

Tidal energy converter (TEC) arrays in tidal channels generate complex flow phenomena due to interactions with the local environment and among devices. Models with different resolutions are thus employed to study flows past TEC farms, which consider multiple spatial and temporal scales. Simulations over tidal cycles use mesoscale ocean circulation models, incorporating a thrust coefficient to model the momentum sink that represents the effects of the array. In this work, we propose an expression for a thrust coefficient to represent finite-sized farms of TEC turbines at larger scales, C t F a r m , which depends on the spatial organization of the devices. We use a coherent-structure resolving turbulence model coupled with the actuator disk approach to simulate staggered turbine configurations in more detail, varying the separation among devices and the ratios between the channel depths and hub heights. Based on these simulations, we calculate the resultant force for various subsets of devices within the farm, and their corresponding effective thrust coefficient, C t F a r m . We conclude that the thrust coefficient depends solely on the lateral separation of the devices, S y , for farms with only two rows. For farms with more than two rows, the streamwise distance, S x , must be considered as well. With the proposed expression, it is possible to calculate efficiently the effects of finite-sized TEC farms and incorporate a momentum sink into ocean circulation models, without assuming a constant coefficient derived from an infinite farm approximation.

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