Wave Energy Exploitation Research Articles

Temporal-spatial variation of wave energy and nearshore hotspots in the Gulf of Oman based on locally generated wind waves

This study aims to assess the wave energy at five coastal stations in the Gulf of Oman using the time series of locally generated wind waves obtained by numerical modeling for 11 years. For this purpose, the spatial, seasonal, monthly, directional, inter-annual of wave energy and power were investigated. The spatial distribution shows that the wave power increases towards the Indian Ocean and the highest mean wave power is located at the eastern station in all seasons. In addition, monthly mean wave power is highest during July and August while the monthly maximum wave power is highest during February at all stations. The ratio of monthly maximum to mean wave power is also the lowest during May to August. Moreover, Monthly Variability Index is the highest in west of the domain where there is no significant wave power potential. In addition, annual wave power as well as total and exploitable wave energies increases from west to east, where the dominant waves propagate from the south, and the exploitable wave energy is approximately 20 times greater than of the central stations.

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).

Where is the best site for wave energy exploitation? Case study along the coast of northern Latium (ITALY)

The present work proposes a siting process for the detection of a suitable site for wave energy exploitation. The choice of a suitable site is based on the good agreement between energy availability, environmental sustainability, and equipped facilities to exploit wave energy. The case study in the northern Latium coast is explicative because in this area there are several activities that affect marine ecosystems, and the introduction of renewable energies promote the reduction of anthropic pressures. The nearshore wave power is studied through the numerical wave model (CMS-Wave), and available wave buoys along the coast were used to compare numerical results. In correspondence with Civitavecchia harbour, the largest nearshore wave energy was found; the large depth in front of the breakwater allows to conserve a great part of offshore wave power, with an average dissipation rate of 10 % less than offshore, with mean annual available wave energy of 25.4 MWh/m and seasonal fluctuation of 5.4 MWh/m. This area appears to be an optimal site for nearshore and shoreline wave energy device tests and installations, for energy availability (intermediate level respect Mediterreanean Sea), low potential environmental impact, easier accessibility, and policy oriented towards a larger sustainability of harbour activities.

Exploitable wave energy assessment based on ERA-Interim reanalysis data—A case study in the East China Sea and the South China Sea

Wave energy resources assessment is a very important process before the exploitation and utilization of the wave energy. At present, the existing wave energy assessment is focused on theoretical wave energy conditions for interesting areas. While the evaluation for exploitable wave energy conditions is scarcely ever performed. Generally speaking, the wave energy are non-exploitable under a high sea state and a lower sea state which must be ignored when assessing wave energy. Aiming at this situation, a case study of the East China Sea and the South China Sea is performed. First, a division basis between the theoretical wave energy and the exploitable wave energy is studied. Next, based on recent 20 a ERA-Interim wave field data, some indexes including the spatial and temporal distribution of wave power density, a wave energy exploitable ratio, a wave energy level, a wave energy stability, a total wave energy density, the seasonal variation of the total wave energy and a high sea condition frequency are calculated. And then the theoretical wave energy and the exploitable wave energy are compared each other; the distributions of the exploitable wave energy are assessed and a regional division for exploitable wave energy resources is carried out; the influence of the high sea state is evaluated. The results show that considering collapsing force of the high sea state and the utilization efficiency for wave energy, it is determined that the energy by wave with a significant wave height being not less 1 m or not greater than 4 m is the exploitable wave energy. Compared with the theoretical wave energy, the average wave power density, energy level, total wave energy density and total wave energy of the exploitable wave energy decrease obviously and the stability enhances somewhat. Pronounced differences between the theoretical wave energy and the exploitable wave energy are present. In the East China Sea and the South China Sea, the areas of an abundant and stable exploitable wave energy are primarily located in the north-central part of the South China Sea, the Luzon Strait, east of Taiwan, China and north of Ryukyu Islands; annual average exploitable wave power density values in these areas are approximately 10–15 kW/m; the exploitable coefficient of variation (COV) and seasonal variation (SV) values in these areas are less than 1.2 and 1, respectively. Some coastal areas of the Beibu Gulf, the Changjiang Estuary, the Hangzhou Bay and the Zhujiang Estuary are the poor areas of the wave energy. The areas of the high wave energy exploitable ratio is primarily in nearshore waters. The influence of the high sea state for the wave energy in nearshore waters is less than that in offshore waters. In the areas of the abundant wave energy, the influence of the high sea state for the wave energy is prominent and the utilization of wave energy is relatively difficult. The developed evaluation method may give some references for an exploitable wave energy assessment and is valuable for practical applications.

Intra-annual wave resource characterization for energy exploitation: A new decision-aid tool

The wave energy resource is usually characterized by a significant variability throughout the year. In estimating the power performance of a Wave Energy Converter (WEC) it is fundamental to take into account this variability; indeed, an estimate based on mean annual values may well result in a wrong decision making. In this work, a novel decision-aid tool, iWEDGE (intra-annual Wave Energy Diagram GEnerator) is developed and implemented to a coastal region of interest, the Death Coast (Spain), one of the regions in Europe with the largest wave resource. Following a comprehensive procedure, and based on deep water wave data and high-resolution numerical modelling, this tool provides the monthly high-resolution characterization matrices (or energy diagrams) for any location of interest. In other words, the information required for the accurate computation of the intra-annual performance of any WEC at any location within the region covered is made available. Finally, an application of iWEDGE to the site of a proposed wave farm is presented. The results obtained highlight the importance of the decision-aid tool herein provided for wave energy exploitation.

The Application of Wave Energy Converter in Hybrid Energy System

As a promising renewable energy resource, wave energy is having more and more interest in both academic research and industry development. In this paper, all subcategories of WECs are presented and discussed with their main feathers. Although there are numerous subcategories of wave energy converter (WEC), wave energy exploitation still haven't reached its commercial stage. Many specific reasons and disadvantages limit its development. To overcome the disadvantages and improve overall performance of WEC, a hybrid concept combining WEC and floating wind turbine is proposed. The specific application of WEC in this hybrid system is also analyzed.

WAVE FARM LAYOUT AND COASTAL IMPACTS

Understanding the impacts of wave energy exploitation is crucial if it is to develop as a fully-fledged renewable. The objective of this work is to investigate whether the impacts of a wave farm on the nearshore wave conditions change significantly depending on its layout, and if so, in which manner. This investigation is carried out through a wave farm project proposed for NW Spain. The impact resulting from one- and two-row layouts of the farm is compared under different wave conditions representative of the area, leading to twelve case studies. We find that the different layouts do produce substantially different wave conditions immediately behind the farm. The differences in the nearshore for the cases studied are, however, not so large, but could increase if the farm is placed closer to the shoreline.

A tool for combined WEC-site selection throughout a coastal region: Rias Baixas, NW Spain

The selection of the appropriate wave energy converter (WEC) and site is the basis for the installation of a wave farm in a region. For this purpose, the estimation of the energy that any WEC would produce at any location of interest is fundamental. Despite all its importance, this information or the elements required for obtaining it are currently available only at specific coastal locations or areas of interest. This work develops a tool for computing the energy that any WEC would generate at any coastal location within the Rias Baixas Region (NW Spain). With this aim, a methodology which allows the consideration of almost all the total energy available is used to characterize the coastal resource with a high spatial resolution. Then, a matlab-based application called WEDGE (Wave Energy Diagram GEnerator) is implemented for easy access to the stored data and automatic reconstruction of the resource at any coastal site in terms of a high-resolution characterization matrix (or energy diagram). As a result, the information required for accurate energy production computation throughout the region is available whereby a combined WEC-site selection can be conducted. Finally, the tool is used to compute the energy production of a total of 23 WEC-site combinations in an area within this region where a wave farm has been recently proposed. The results will underline the importance of a combined WEC-site selection for proper decision-making regarding wave energy exploitation.

Research on the Performance of Point Absorber

Rational exploitation of wave energy makes great contribution to relief the current global energy crisis. Power generation has been taken into the agenda as the main form to utilize wave energy. The point absorber in this paper is simplified to three modules: floater, pontoon and chain. Based on the theory of linear regular wave, the research task of the point absorber is to improve the conversion efficiency and device reliability. This paper researched on the double floater wave energy converter by hydrodynamic numerical calculation, studied the factors that contain the PTO system damping coefficient, wave frequency and the device mass and other factor which can influence the energy conversion efficiency. At last, we found an optimized method for the energy conversion efficiency.

Wave energy and hot spots in Anzali port

Providing energy without unfavorable impacts on the environment is an important issue for many countries. Wave energy is one of the renewable resources with high potential and low impact on the environment, especially in coastal regions. The estimation of the wave characteristics is essential for selection of the appropriate location for wave energy exploitation. In this study, SWAN (Simulating WAves Nearshore) was used for modeling of the wave characteristics and to describe the existence and variability of wave energy in the southern part of the Caspian Sea. The model results were calibrated and verified using in-situ buoy measurements. Wave parameters were simulated and the annual wave energy was estimated in the study area. Then, high-energy spots were determined and the monthly average wave energy and seasonal variations of wave energy in the selected site were investigated. Furthermore, wave energy resource was characterized in terms of sea state parameters i.e. significant wave heights, wave periods and mean directions for selecting the most appropriate wave energy converters in the selected site. It was found that January and February, i.e. winter months, are the most energetic months and the main wave directions with the highest frequencies are northeast and northern-northeast in this site.

Research on the Hydrodynamic Performance of a Wave Energy Converter

Under the pressure of fossil energy shortage, rational exploitation of ocean wave energy is propitious to establish an environmentally friendly society. This paper presents the results of a practical research done in a test tank, on the hydrodynamic performance of a wave energy converter with swing arms and floaters designed purposely. Fixed on a trailer, the converter was composed of two floaters, two swing arms, mechanical transmission devices and generators. The method of this research was to measure the floater’s acceleration and the output voltages of the generator under the movement of waves, analysis the influence of wave height and period on floaters’ movement, then compute the wave energy conversion efficiency. At last, the research findings show that the converter performed well with heaving motion performance and high energy conversion efficiency.

Wave energy potential along the western Portuguese coast

An assessment of nearshore wave energy resource along the Portuguese coast is presented, focusing on identify appropriate locations for testing and developing Wave Energy Converter (WEC) for commercial exploit. The analysis covers the whole west seaside, to which a partition defined by 7 linear sections parallel to the coastline at 50 m depth was considered. Available wave energy at each linear sector was calculated from nearshore wave parameters, using as input the offshore wave conditions provided by a 15-year ocean wind-wave model simulation and considering a simplified but well-established analytical procedure for shoreward wave transformation. Two alternative measures of the nearshore wave energy resource were considered, the standard omni-directional wave power density and the more restricted normally-directed wave energy flux.Offshore wave direction combine to shoreline orientation proved to be determinant on the evaluation of the wave energy resource in each section, since sectors of the shoreline directly facing the offshore annual average wave direction have limited reduction in available wave energy as compare to offshore values. Independently of the wave energy measured criteria used, the analysis suggests that the sector from Peniche to Nazaré is the more suitable location for nearshore wave energy exploitation, with annual wave energy around 200 MWh m−1, closely followed by the adjacent sector from Nazaré to Figueira da Foz.

A high resolution geospatial database for wave energy exploitation

The estimation of energy production of a given WEC (wave energy converter) at a given coastal site is the basis for correct decision-making regarding wave energy exploitation in a coastal region. Nevertheless, the procedure followed by the conventional approach to characterize the wave energy resource does not provide the required information to obtain an accurate estimate. In this work, this information is provided for the region with the greatest resource in the Iberian Peninsula, the Death Coast (NW Spain). For this purpose, a geospatial database is produced by using a methodology which involves the consideration of virtually the totality of the resource together with the implementation of a high resolution spectral numerical model. In addition, a Matlab-based toolbox called WEDGE (Wave Energy Diagram GEnerator) is implemented to access the database and automatically generate high resolution energy diagrams (or characterization matrices) of the wave energy resource at any coastal location within this region. In this way, a precise computation of energy production of any WEC at any site of interest can now be performed. Finally, the functionality of the database is shown through a case study of a recently proposed wave farm.

An integrated energy conversion and storage facility for offshore wind and wave energy exploitation along the west coasts of North America and Europe

An integrated energy conversion and storage facility based on a floating foundation is introduced. It consists of an on-board 10 MW wind turbine and eighteen wave energy capturing buoys along the front of a floating foundation, with pumped hydro-energy storage. The proposed floating foundation is designed for waters off the west coasts of North America and Europe, where strong winds and high waves prevail. To operate the wind turbine safely, the design provides viable performance in waves and possesses the hydrodynamic attribute of being a wave amplifier such that the buoys may capture twice as much wave energy as in open water. The proposed wave energy capture and conversion design provide both protection against breaking wave impacts and good access for repair and maintenance, heretofore two major technical obstacles in the way of offshore wave energy exploitation. As shown by rough assessment of the proposed floating facility, its improved cost effectiveness may allow a major move from onshore to offshore wind turbines. Since the levelized cost of onshore wind farms is about equal to conventional coal plants and roughly 30% lower than an advanced coal plant with carbon dioxide capture and storage, the proposed offshore facility may prove a viable, large scale alternative to coal plants since available land and wind resource are somewhat limited for onshore wind farms.

Wave electricity production in Italian offshore: A preliminary investigation

In this paper the feasibility of wave energy exploitation off the Italian coasts is investigated. At this aim, the energy production and the performance characteristics of three of the most promising and documented wave energy converters (AquaBuOY, Pelamis and Wave Dragon) are estimated for two of the most energetic Italian locations. The sites are Alghero, on the western coast of Sardinia and Mazara del Vallo, on the Sicily Strait and they have respectively an average annual wave power of 10.3 kW/m and 4 kW/m, and an available annual wave energy of 90 MWh/m and 35 MWh/m.The energy production of the hypothetical wave farms is calculated based on the performance matrices of the wave energy converters (WECs) and on 21 years of wave buoy records, covering the period from 1990 to 2011. The estimated capacity factors are low (between 4% and 9%) compared to the ones obtained for the same wave energy converters in other locations and are affected by a strong seasonal variability. This indicates that the considered WECs are oversized with respect to the local wave climate and that a more efficient energy conversion would be obtained if they were downscaled according to the typical wave height and period of the study sites. As a consequence of the optimization of the device scale, at Alghero the deployment of 1:2.5 AquaBuOY, Pelamis or Wave Dragon devices would result in capacity factors around 20% and in a quite constant energy production throughout the year. In fact, the size reduction of the wave energy converters allows to capture the energy of the small waves which would otherwise be lost with the original WECs.The results of the present work suggest that deploying classic wave energy converters in Italian seas would not be cost effective but if the devices could accommodate a proper downscaling, their performance in energy conversion would become economically attractive also for some Italian locations.

Stochastic Rating of Storage Systems in Isolated Networks with Increasing Wave Energy Penetration

The future success of wave energy in the renewable energy mix depends on the technical advancements of the specific components and systems, on the grid access availability and, ultimately, on the economical profitability of the investment. Small and remote islands represent an ideal framework for wave energy exploitation, due both to resource availability and to the current high cost of electricity that mostly relies on diesel generation. Energy storage can be the enabling technology to match the intermittent power generation from waves to the energy needs of the local community. In this paper real data from La Palma, in the Canary Islands, are used as a basis for the considered test case. As a first step the study quantifies the expected power production from Wave Energy Converter (WEC) arrays, based on data from the Lifesaver point absorber developed by Fred. Olsen. Then, a stochastic optimization approach is applied to evaluate the convenience of energy storage introduction for reducing the final cost of energy and to define the corresponding optimal rating of the storage devices.

Ocean Wave Properties of Terengganu for Renewable Energy Potential

The development of renewable energy sources together with the expansion of those currently exploited is crucial in reducing the emissions of greenhouse gases as prescribed by the Kyoto protocol. Among renewable energy sources, ocean waves contain the highest energy density. This allows for substantial energy generation in relatively small areas from a virtually inexhaustible energy source. Wave energy has a number of significant advantages with respect to other renewable energy sources -- predictability, abundance, high load factor and low environmental impact, among others. In spite of these advantages, wave energy exploitation is still in its infancy due to technological challenges still ahead. Although wave energy potential has been reported for a few countries around the world, reliable and year-long wave data is still needed for Malaysia. This study therefore addresses this need. The wave resource characterization is a crucial point towards the exploitation of wave energy. Wave power along the Terengganu coast was analyzed at a time scale of months to examine the seasonal dependencies. These investigations show that the Terengganu coast could provide a source of low wave power. The wave climate in the Terengganu coast is among the harshest in Malaysia. The maximum wave height varies between 1--13 m and 3.13 m. The month of December has the highest probability of occurrence of significant wave heights greater than 2 m (2.15%), the possibility of this occurrence begins in November and lasts through January. Similarly, the month of December has the highest probability of occurrence of maximum wave heights greater than 2 m (44.09%) followed by January (40.86%) and November (32.78%). An identical evolution is seen for the wave heights in the classes 1--2 m, the highest frequency of occurrence is in December and represents 68.01% of the total of the month. The wave mean period varies between 2.76 and 5.28 sec and monthly averaged wave peak period varies between 3.94 and 8.28 sec. The main direction in terms of wave energy is North. Further, its high wave energy potential is available during northeast monsoon season. It may be concluded that the Terengganu coast of Malaysia can consider northeast monsoon period for wave energy exploitation.

Wave energy resource in the Estaca de Bares area (Spain)

The area around Cape Estaca de Bares (the northernmost point of Iberia) presents a great potential for wave energy exploitation owing to its prominent position, with average deepwater wave power values exceeding 40 kW/m. The newly available SIMAR-44 dataset, composed of hindcast data spanning 44 years (1958–2001), is used alongside wave buoy data and numerical modelling to assess this substantial energy resource in detail. Most of the energy is provided by waves from the IV quadrant, generated by the prevailing westerlies blowing over the long Atlantic fetch. Combined scatter and energy diagrams are used to characterise the wave energy available in an average year in terms of the sea states involved. The lion's share is shown to correspond to significant wave heights between 2 and 5 m and energy periods between 11 and 14 s. The nearshore energy patterns are then examined using a coastal wave model (SWAN) with reference to four situations: average wave energy, growing wave energy (at the approach of a storm), extreme wave energy (at the peak of the storm) and decaying wave energy (as the storm recedes). The irregular bathymetry is found to produce local concentrations of wave energy in the nearshore between Cape Prior and Cape Ortegal and in front of Cape Estaca de Bares, with similar patterns (but varying wave power) in the four cases. These nearshore areas of enhanced wave energy are of the highest interest as prospective sites for a wave energy operation. The largest of them is directly in the lee of a large underwater mount west of Cape Ortegal. In sum, the Estaca de Bares area emerges as one of the most promising for wave energy exploitation in Europe.

Wave energy potential in Galicia (NW Spain)

Wave power presents significant advantages with regard to other CO 2-free energy sources, among which the predictability, high load factor and low visual and environmental impact stand out. Galicia, facing the Atlantic on the north-western corner of the Iberian Peninsula, is subjected to a very harsh wave climate; in this work its potential for energy production is assessed based on three-hourly data from a third generation ocean wave model (WAM) covering the period 1996–2005. Taking into account the results of this assessment along with other relevant considerations such as the location of ports, navigation routes, and fishing and aquaculture zones, an area is selected for wave energy exploitation. The transformation of the offshore wave field as it propagates into this area is computed by means of a nearshore wave model (SWAN) in order to select the optimum locations for a wave farm. Two zones emerge as those with the highest potential for wave energy exploitation. The large modifications in the available wave power resulting from relatively small changes of position are made apparent in the process.

Analysis of the nearshore wave energy resource

Earlier studies have indicated that the gross nearshore wave energy resource is significantly smaller than the gross offshore wave energy resource implying that the deployment of wave energy converters in the nearshore is unlikely to be economic. However, it is argued that the gross wave energy resource is not an appropriate measure for determining the productivity of a wave farm and an alternative measure, the exploitable wave energy resource, is proposed. Calculation of a site's potential using the exploitable wave energy resource is considered superior because it accounts for the directional distribution of the incident waves and the wave energy plant rating that limits the power capture in highly energetic sea-states. A third-generation spectral wave model is used to model the wave transformation from deep water to a nearshore site in a water depth of 10 m. It is shown that energy losses result in a reduction of less than 10% of the net incident wave power. Annual wave data for the North Atlantic coast of Scotland is analysed and indicates that whilst the gross wave energy resource has reduced significantly by the 10 m depth contour, the exploitable wave energy resource is reduced by 7 and 22% for the two sites analysed. This limited reduction in exploitable wave energy resource means that for many exposed coasts, nearshore sites offer similar potential for exploitation of the wave energy resource as offshore sites.