Research

20 pages, 3259 KiB

Open AccessArticle

Energy Efficiency Analysis of Multi-Type Floating Bodies for a Novel Heaving Point Absorber with Application to Low-Power Unmanned Ocean Device

by Dongsheng Cong, Jianzhong Shang, Zirong Luo, Chongfei Sun and Wei Wu

Energies 2018, 11(12), 3282; https://doi.org/10.3390/en11123282 - 25 Nov 2018

Cited by 10 | Viewed by 3780

Abstract

Long-term energy supplies hinder the application of the low-power unmanned ocean devices to the deep sea. Ocean wave energy is a renewable resource with amount stores of enormous and high density. The wave energy converter (WEC) could be miniaturized so that it can [...] Read more.

Long-term energy supplies hinder the application of the low-power unmanned ocean devices to the deep sea. Ocean wave energy is a renewable resource with amount stores of enormous and high density. The wave energy converter (WEC) could be miniaturized so that it can be integrated into the devices to make up the power module. In this paper, a small novel heaving point absorber of energy supply for low-power unmanned ocean devices is developed based on the counter-rotating self-adaptive mechanism. The floating body as an important part of the heaving point absorber, the geometric parameters is optimized to increase the efficiency of power production. Through constructing the constitutive relation between the geometric parameters, the wave force, the motion displacement, the motion velocity, and the capture width ratio of the floating body, the energy efficiency characteristics of the multi-type floating bodies are calculated, and the optimal shape is selected. On the other hand, in the calculation process of the wave force, the Froude-Krylov method is an effective method to accurately calculate the wave excitation force. Meanwhile, nonlinear static and dynamic Froude-Krylov force effectively overcomes the inaccuracy of the linear models and reduces the time consumed to simulate. Finally, the wave force, heaving velocity, heaving displacement, and capture width ratio of the three floating bodies are compared and analyzed, and the results show that the cylindrical floater that is vertically placed on the wave surface is more suitable for the novel heaving wave energy point absorber. Full article

(This article belongs to the Special Issue Wave and Tidal Energy)

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16 pages, 3949 KiB

Open AccessArticle

Economic Feasibility of Wave Energy Farms in Portugal

by Laura Castro-Santos, Dina Silva, A. Rute Bento, Nadia Salvação and C. Guedes Soares

Energies 2018, 11(11), 3149; https://doi.org/10.3390/en11113149 - 14 Nov 2018

Cited by 46 | Viewed by 4930

Abstract

This paper develops a methodology to determine the economic feasibility of implementing offshore wave energy farms on the Portuguese continental coast. This methodology follows several phases: the geographic phase, the energy phase, the economic phase, and the restrictions phase. First, in the geographic [...] Read more.

This paper develops a methodology to determine the economic feasibility of implementing offshore wave energy farms on the Portuguese continental coast. This methodology follows several phases: the geographic phase, the energy phase, the economic phase, and the restrictions phase. First, in the geographic phase, the height and the period of the waves, the bathymetry, the distance from the farm to the shore, from farm to shipyard, and from farm to port, are calculated. In the energy phase the energy produced by each wave energy converter is determined, and in the economic phase, the parameters calculated in the previous phases are used as input to find the economic parameters. Finally, in the restrictions phase, a limitation by the bathymetry will be added to the economic maps, whose value will be different depending on the floating offshore wave energy converter (WEC). In this study, three wave energy converters have been considered, Pelamis, AquaBuOY, and Wave Dragon, and several scenarios for electric tariffs have been taken into account. The results obtained indicate what the best WEC is for this study in terms of its levelized cost of energy (LCOE), internal rate of return (IRR), and net present value (NPV), and where the best area is to install wave energy farms. Full article

(This article belongs to the Special Issue Wave and Tidal Energy)

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26 pages, 4315 KiB

Open AccessArticle

Modelling Offshore Wave farms for Coastal Process Impact Assessment: Waves, Beach Morphology, and Water Users

by Christopher Stokes and Daniel C. Conley

Energies 2018, 11(10), 2517; https://doi.org/10.3390/en11102517 - 21 Sep 2018

Cited by 9 | Viewed by 3730

Abstract

The emerging global wave energy industry has the potential to contribute to the world’s energy needs, but careful consideration of potential impacts to coastal processes in the form of an impact assessment is required for each new wave energy site. Methods for conducting [...] Read more.

The emerging global wave energy industry has the potential to contribute to the world’s energy needs, but careful consideration of potential impacts to coastal processes in the form of an impact assessment is required for each new wave energy site. Methods for conducting a coastal processes impact assessment for wave energy arrays vary considerably in the scientific literature, particularly with respect to characterising the energy absorption of a wave energy converter (WEC) array in a wave model. In this paper, modelling methods used in the scientific literature to study wave farm impacts on coastal processes are reviewed, with the aim of determining modelling guidance for impact assessments. Effects on wave climate, beach morphology, and the surfing resource for coastal water users are considered. A novel parameterisation for the WEC array transmission coefficient is presented that, for the first time, uses the permitted power rating of the wave farm, which is usually well defined at the impact assessment stage, to estimate the maximum likely absorption of a permitted WEC array. A coastal processes impact assessment case study from a wave farm in south-west Ireland is used to illustrate the application of the reviewed methods, and demonstrates that using the new ‘rated power transmission coefficient’ rather than a WEC-derived transmission coefficient or complete energy absorption scenario can make the difference between significant and non-significant levels of coastal impacts being predicted. Full article

(This article belongs to the Special Issue Wave and Tidal Energy)

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23 pages, 3224 KiB

Open AccessArticle

Historical Evolution of the Wave Resource and Energy Production off the Chilean Coast over the 20th Century

by Alain Ulazia, Markel Penalba, Arkaitz Rabanal, Gabriel Ibarra-Berastegi, John Ringwood and Jon Sáenz

Energies 2018, 11(9), 2289; https://doi.org/10.3390/en11092289 - 30 Aug 2018

Cited by 30 | Viewed by 3457

Abstract

The wave energy resource in the Chilean coast shows particularly profitable characteristics for wave energy production, with relatively high mean wave power and low inter-annual resource variability. This combination is as interesting as unusual, since high energetic locations are usually also highly variable, [...] Read more.

The wave energy resource in the Chilean coast shows particularly profitable characteristics for wave energy production, with relatively high mean wave power and low inter-annual resource variability. This combination is as interesting as unusual, since high energetic locations are usually also highly variable, such as the west coast of Ireland. Long-term wave resource variations are also an important aspect when designing wave energy converters (WECs), which are often neglected in resource assessment. The present paper studies the long-term resource variability of the Chilean coast, dividing the 20th century into five do-decades and analysing the variations between the different do-decades. To that end, the ERA20C reanalysis of the European Centre for Medium-Range Weather Forecasts is calibrated versus the ERA-Interim reanalysis and validated against buoy measurements collected in different points of the Chilean coast. Historical resource variations off the Chilean coast are compared to resource variations off the west coast in Ireland, showing a significantly more consistent wave resource. In addition, the impact of historical wave resource variations on a realistic WEC, similar to the Corpower device, is studied, comparing the results to those obtained off the west coast of Ireland. The annual power production off the Chilean coast is demonstrated to be remarkably more regular over the 20th century, with variations of just 1% between the different do-decades. Full article

(This article belongs to the Special Issue Wave and Tidal Energy)

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14 pages, 6254 KiB

Open AccessArticle

Hydrodynamic Analysis of a Marine Current Energy Converter for Profiling Floats

by Shuang Wu, Yanjun Liu and Qi An

Energies 2018, 11(9), 2218; https://doi.org/10.3390/en11092218 - 24 Aug 2018

Cited by 3 | Viewed by 2907

Abstract

With the continuous improvement of people’s interest in ocean exploration, research on deep-water profiling floats has received more and more attention. Energy supply is the key factor that restricts the working hours of deep-water floats. For this consideration, a marine current energy converter [...] Read more.

With the continuous improvement of people’s interest in ocean exploration, research on deep-water profiling floats has received more and more attention. Energy supply is the key factor that restricts the working hours of deep-water floats. For this consideration, a marine current energy converter for deep-water profiling floats is proposed in this paper. A spiral involute blade is designed so that energy can be captured in two directions. Specifically, in the shallow sea area, the energy of the radial current is captured, and in the deep-sea area, the axial relative flow energy of the floats’ autonomous up and down motions is captured. This captured energy is then converted into electrical energy to charge the battery and extend the working time of the floats. The novel spiral involute blade has unique hydrodynamic characteristics. The turbine’s self-starting performance and its capacity coefficient are the main research topics studied using the computational fluid dynamics technique. Through numerical analysis and simulation, the self-starting response range and energy capture were obtained. This paper verifies the feasibility of this innovative idea using a theory analysis and provides the basis for future prototype testing and further applied research. Full article

(This article belongs to the Special Issue Wave and Tidal Energy)

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19 pages, 10994 KiB

Open AccessArticle

Spatial Environmental Assessment Tool (SEAT): A Modeling Tool to Evaluate Potential Environmental Risks Associated with Wave Energy Converter Deployments

by Craig Jones, Grace Chang, Kaustubha Raghukumar, Samuel McWilliams, Ann Dallman and Jesse Roberts

Energies 2018, 11(8), 2036; https://doi.org/10.3390/en11082036 - 06 Aug 2018

Cited by 10 | Viewed by 4030

Abstract

Wave energy converter (WEC) arrays deployed in coastal regions may create physical disturbances, potentially resulting in environmental stresses. Presently, limited information is available on the nature of these physical disturbance or the resultant effects. A quantitative Spatial Environmental Assessment Tool (SEAT) for evaluating [...] Read more.

Wave energy converter (WEC) arrays deployed in coastal regions may create physical disturbances, potentially resulting in environmental stresses. Presently, limited information is available on the nature of these physical disturbance or the resultant effects. A quantitative Spatial Environmental Assessment Tool (SEAT) for evaluating the potential effects of wave energy converter (WEC) arrays on nearshore hydrodynamics and sediment transport is presented for the central Oregon coast (USA) through coupled numerical model simulations of an array of WECs. Derived climatological wave conditions were used as inputs to the model to allow for the calculation of risk metrics associated with various hydrodynamic and sediment transport variables such as maximum shear stress, bottom velocity, and change in bed elevation. The risk maps provided simple, quantitative, and spatially-resolved means of evaluating physical changes in the vicinity of a hypothetical WEC array in response to varying wave conditions. The near-field risk of sediment mobility was determined to be moderate in the lee of the densely spaced array, where the potential for increased sediment deposition could result in benthic habitat alteration. Modifications to the nearshore sediment deposition and erosion patterns were observed near headlands and topographic features, which could have implications for littoral sediment transport. The results illustrate the benefits of a risk evaluation tool for facilitating coastal resource management at early market marine renewable energy sites. Full article

(This article belongs to the Special Issue Wave and Tidal Energy)

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15 pages, 6749 KiB

Open AccessArticle

Analysis of the Variability of Wave Energy Due to Climate Changes on the Example of the Black Sea

by Yana Saprykina and Sergey Kuznetsov

Energies 2018, 11(8), 2020; https://doi.org/10.3390/en11082020 - 03 Aug 2018

Cited by 12 | Viewed by 2989

Abstract

An analysis of the variability of wave climate and energy within the Black Sea for the period 1960–2011 was made using field data from the Voluntary Observing Ship Program. Methods using wavelet analysis were applied. It was determined that the power flux of [...] Read more.

An analysis of the variability of wave climate and energy within the Black Sea for the period 1960–2011 was made using field data from the Voluntary Observing Ship Program. Methods using wavelet analysis were applied. It was determined that the power flux of wave energy in the Black Sea fluctuates: the highest value is 4.2 kW/m, the lowest is 1.4 kW/m. Results indicate significant correlations among the fluctuations of the average annual wave heights, periods, the power flux of wave energy, and teleconnection patterns of the North Atlantic Oscillation (NAO), the Atlantic Multi-decadal Oscillation (AMO), the Pacific Decadal Oscillation (PDO) and the East Atlantic/West Russia (EA/WR). It was revealed that, in positive phases of long-term periods of AMO (50–60 years) as well as PDO, NAO, and AO (40 years), a decrease of wave energy was observed; however, an increase in wave energy was observed in the positive phase of a 15-year period of NAO and AO. The positive phase of changes of EA/WR for periods 50–60, 20–25, and 13 years led to an increase of wave energy. The approximation functions of the oscillations of the average annual wave heights, periods, and the power flux of wave energy for the Black Sea are proposed. Full article

(This article belongs to the Special Issue Wave and Tidal Energy)

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19 pages, 2066 KiB

Open AccessArticle

Grid Integration and Power Smoothing of an Oscillating Water Column Wave Energy Converter

by Gimara Rajapakse, Shantha Jayasinghe, Alan Fleming and Michael Negnevitsky

Energies 2018, 11(7), 1871; https://doi.org/10.3390/en11071871 - 18 Jul 2018

Cited by 19 | Viewed by 4045

Abstract

This paper applies model predictive control (MPC) for the power processing of an oscillating water column (OWC) wave energy conversion (WEC) system to achieve smooth power delivery to the grid. The particular air turbine design adopted in this study produces large power pulses [...] Read more.

This paper applies model predictive control (MPC) for the power processing of an oscillating water column (OWC) wave energy conversion (WEC) system to achieve smooth power delivery to the grid. The particular air turbine design adopted in this study produces large power pulses ranging from 0 to 1 MW in magnitude, and thus, direct connection to the grid is practically impossible, especially in weak grid conditions. Therefore, energy storage is an essential element that should be integrated into this particular WEC system in order to absorb power pulses and thereby ensure smooth delivery of power to the grid. Taking into account the repetitive nature, duration, and magnitude of the power pulses, this study has chosen “supercapacitor” as the suitable energy storage technology. The supercapacitor energy storage (SCES) is integrated into the dc-link of the back-to-back power converter of the WEC system through a bidirectional dc-dc converter. In order to achieve the desired operation of this complex power converter arrangement, a finite control set MPC strategy is proposed in this paper. Performance of the proposed energy storage system (ESS) and control strategy are evaluated through computer simulations. Simulation results show that the proposed SCES system and the control strategy are able to achieve smooth power delivery to the grid amidst power pulses coming from the generator. Full article

(This article belongs to the Special Issue Wave and Tidal Energy)

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16 pages, 3797 KiB

Open AccessArticle

The Effect of Control Strategy on Tidal Stream Turbine Performance in Laboratory and Field Experiments

by Carwyn Frost, Ian Benson, Penny Jeffcoate, Björn Elsäßer and Trevor Whittaker

Energies 2018, 11(6), 1533; https://doi.org/10.3390/en11061533 - 12 Jun 2018

Cited by 14 | Viewed by 3517

Abstract

The first aim of the research presented here is to examine the effect of turbine control by comparing a passive open-loop control strategy with a constant rotational speed proportional–integral–derivative (PID) feedback loop control applied to the same experimental turbine. The second aim is [...] Read more.

The first aim of the research presented here is to examine the effect of turbine control by comparing a passive open-loop control strategy with a constant rotational speed proportional–integral–derivative (PID) feedback loop control applied to the same experimental turbine. The second aim is to evaluate the effect of unsteady inflow on turbine performance by comparing results from a towing-tank, in the absence of turbulence, with results from the identical machine in a tidal test site. The results will also inform the reader of: (i) the challenges of testing tidal turbines in unsteady tidal flow conditions in comparison to the controlled laboratory environment; (ii) calibration of acoustic Doppler flow measurement instruments; (iii) characterising the inflow to a turbine and identifying the uncertainties from unsteady inflow conditions by adaptation of the International Electrotechnical Commission technical specification (IEC TS): 62600-200. The research shows that maintaining a constant rotational speed with a control strategy yields a 13.7% higher peak power performance curve in the unsteady flow environment, in comparison to an open-loop control strategy. The research also shows an 8.0% higher peak power performance in the lab compared to the field, demonstrating the effect of unsteady flow conditions on power performance. The research highlights the importance of a tidal turbines control strategy when designing experiments. Full article

(This article belongs to the Special Issue Wave and Tidal Energy)

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15 pages, 7603 KiB

Open AccessArticle

Wave Resource Characterization Using an Unstructured Grid Modeling Approach

by Wei-Cheng Wu, Zhaoqing Yang and Taiping Wang

Energies 2018, 11(3), 605; https://doi.org/10.3390/en11030605 - 09 Mar 2018

Cited by 15 | Viewed by 4662

Abstract

This paper presents a modeling study conducted on the central Oregon coast for wave resource characterization, using the unstructured grid Simulating WAve Nearshore (SWAN) model coupled with a nested grid WAVEWATCH III^® (WWIII) model. The flexibility of models with various spatial resolutions [...] Read more.

This paper presents a modeling study conducted on the central Oregon coast for wave resource characterization, using the unstructured grid Simulating WAve Nearshore (SWAN) model coupled with a nested grid WAVEWATCH III^® (WWIII) model. The flexibility of models with various spatial resolutions and the effects of open boundary conditions simulated by a nested grid WWIII model with different physics packages were evaluated. The model results demonstrate the advantage of the unstructured grid-modeling approach for flexible model resolution and good model skills in simulating the six wave resource parameters recommended by the International Electrotechnical Commission in comparison to the observed data in Year 2009 at National Data Buoy Center Buoy 46050. Notably, spectral analysis indicates that the ST4 physics package improves upon the ST2 physics package’s ability to predict wave power density for large waves, which is important for wave resource assessment, load calculation of devices, and risk management. In addition, bivariate distributions show that the simulated sea state of maximum occurrence with the ST4 physics package matched the observed data better than with the ST2 physics package. This study demonstrated that the unstructured grid wave modeling approach, driven by regional nested grid WWIII outputs along with the ST4 physics package, can efficiently provide accurate wave hindcasts to support wave resource characterization. Our study also suggests that wind effects need to be considered if the dimension of the model domain is greater than approximately 100 km, or O (10² km). Full article

(This article belongs to the Special Issue Wave and Tidal Energy)

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21 pages, 19772 KiB

Open AccessArticle

Identifying the Optimal Offshore Areas for Wave Energy Converter Deployments in Taiwanese Waters Based on 12-Year Model Hindcasts

by Hung-Ju Shih, Chih-Hsin Chang, Wei-Bo Chen and Lee-Yaw Lin

Energies 2018, 11(3), 499; https://doi.org/10.3390/en11030499 - 27 Feb 2018

Cited by 14 | Viewed by 4091

Abstract

A 12-year sea-state hindcast for Taiwanese waters, covering the period from 2005 to 2016, was conducted using a fully coupled tide-surge-wave model. The hindcasts of significant wave height and peak period were employed to estimate the wave power resources in the waters surrounding [...] Read more.

A 12-year sea-state hindcast for Taiwanese waters, covering the period from 2005 to 2016, was conducted using a fully coupled tide-surge-wave model. The hindcasts of significant wave height and peak period were employed to estimate the wave power resources in the waters surrounding Taiwan. Numerical simulations based on unstructured grids were converted to structured grids with a resolution of 25 × 25 km. The spatial distribution maps of offshore annual mean wave power were created for each year and for the 12-year period. Waters with higher wave power density were observed off the northern, northeastern, southeastern (south of Green Island and southeast of Lanyu) and southern coasts of Taiwan. Five energetic sea areas with spatial average annual total wave energy density of 60–90 MWh/m were selected for further analysis. The 25 × 25 km square grids were then downscaled to resolutions of 5 × 5 km, and five 5 × 5 km optimal areas were identified for wave energy converter deployments. The spatial average annual total wave energy yields at the five optimal areas (S1)–(S5) were estimated to be 64.3, 84.1, 84.5, 111.0 and 99.3 MWh/m, respectively. The prevailing wave directions for these five areas lie between east and northeast. Full article

(This article belongs to the Special Issue Wave and Tidal Energy)

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