Offshore and inshore wave energy assessment: Asturias (N Spain)

The offshore and inshore wave energy resource in Asturias (N Spain) is studied using wave buoy data and a hindcast dataset spanning 44 years (1958–2001). Offshore average wave power and annual wave energy values are found to exceed 30 kW/m and 250 MWh/m, respectively, at 7 of the 11 study sites. This substantial resource is characterised in terms of the sea states involved. Most of the energy is provided by IV quadrant waves with significant wave heights between 2 m and 5 m and energy periods between 11 s and 13 s. After analysing the offshore resource, numerical modelling is used to investigate the inshore wave patterns. A coastal wave model is validated with wave buoy data and applied to three case studies representative of storm, winter and summer conditions. Inshore wave energy concentration areas, of interest as prospective wave farm sites, are found to occur west of Cape Vidio and on the western side of the Cape Peñas peninsula. The methodology used in this investigation may serve as a model for wave energy assessments in other regions, especially where both the offshore and inshore resources are of consequence.     

Characterizing the wave energy resource of the US Pacific Northwest

The substantial wave energy resource of the US Pacific Northwest (i.e. off the coasts of Washington, Oregon and N. California) is assessed and characterized. Archived spectral records from ten wave measurement buoys operated and maintained by the National Data Buoy Center and the Coastal Data Information Program form the basis of this investigation. Because an ocean wave energy converter must reliably convert the energetic resource and survive operational risks, a comprehensive characterization of the expected range of sea states is essential. Six quantities were calculated to characterize each hourly sea state: omnidirectional wave power, significant wave height, energy period, spectral width, direction of the maximum directionally resolved wave power and directionality coefficient. The temporal variability of these characteristic quantities is depicted at different scales and is seen to be considerable. The mean wave power during the winter months was found to be up to 7 times that of the summer mean. Winter energy flux also tends to have a longer energy period, a narrower spectral width, and a reduced directional spread, when compared to summer months. Locations closer to shore, where the mean water depth is less than 50 m, tended to exhibit lower omnidirectional wave power, but were more uniform directionally. Cumulative distributions of both occurrence and contribution to total energy are presented, over each of the six quantities characterizing the resource. It is clear that the sea states occurring most often are not necessarily those that contribute most to the total incident wave energy. The sea states with the greatest contribution to energy have significant wave heights between 2 and 5 m and energy periods between 8 and 12 s. Sea states with the greatest significant wave heights (e.g.>7 m) contribute little to the annual energy, but are critically important when considering reliability and survivability of ocean wave energy converters.     

Wave energy potential along the northern coasts of the Gulf of Oman, Iran

This study aims to investigate wave power along the northern coasts of the Gulf of Oman. To simulate wave parameters the third generation spectral SWAN model was utilized, and the results were validated with buoy and ADCP data. First, annual energy was calculated in the study region with the hindcast data set covering 23 years (1985-2007). The areas with the highest wave resource were determined and the area proximity to the port of Chabahar is suggested as the best site for the installation of a wave farm. Second, the average monthly wave energy in this area was investigated. The most energetic waves are provided by the southeast Indian Ocean monsoon from June to August. Finally, the wave energy resource was characterized in terms of sea state parameters. It was found that the bulk of annual wave energy occurs for significant wave heights between 1 and 3 m and energy periods between 4 and 8 s in the direction of SSE.     

Wave energy potential along the Death Coast (Spain)

The newly available SIMAR-44 data set, covering a 44-year period, is used together with wave buoy data to assess the wave energy resource along the Death Coast, the craggy stretch from Cape Finisterre to the Sisarga Isles. Its location at the north-western corner of the Iberian Peninsula and its coastline configuration result in exposure to a wide range of wave directions over the long Atlantic fetch. A total of 18 study sites are analysed—16 SIMAR-44 points and two wave buoys. Annual wave power in the Death Coast area is of the order of 50 kWm⁻¹, and annual wave energy exceeds 400 MWhm⁻¹. This vast resource is characterised thoroughly in terms of wave directions, heights and periods. A coastal wave propagation model (SWAN) is then implemented, validated based on wave buoy measurements, and used to investigate the nearshore energetic patterns. The irregular bathymetry of the Death Coast is shown to lead to local concentrations of wave energy off Capes Veo, Tosto and Finisterre and north of the Sisargas Isles, which are more conspicuous in winter and, especially, in storm situations.     

22-Year wave energy hindcast for the China East Adjacent Seas

In order to investigate the wave energy resource, the third-generation wave model SWAN is utilised to simulate wave parameters of the China East Adjacent Seas (CEAS) including Bohai, Yellow and East China Sea for the 22 years period ranging from 1990.1 to 2011.12. The wind parameters used to simulate waves are obtained by the Weather Research & Forecasting Model (WRF). The results are validated by observed wave heights of 7 stations. The spatial distributions of wave energy density in the CEAS are analysed under the 22-year largest envelop, mean annual and season averaged wave conditions. Along China east coastal, the largest nearshore wave energy flux occurs along the nearshore zones between Zhoushan Island and south bound of CEAS area. The wave energy resources at Liaodong Peninsula Headland and East Zhoushan Island where economy develops rapidly are also studied in detail. For the two sites, the monthly averaged wave energy features of every year for the 22 years are investigated. The wave energy resources of the two potential sites are characterised in terms of wave state parameters. The largest monthly averaged density for the two sites occurs at Zhoushan Island adjacent sea and amounts to 29 kW/m.     

Wave power for La Isla Bonita

The island of La Palma (Spain), dubbed La Isla Bonita for its beauty, is a UNESCO Biosphere Reserve in the Atlantic Ocean. The island’s authorities are aiming for energy self-sufficiency based on wave energy and other renewables. In this research its wave resource is investigated using a 44-years hindcast dataset obtained through numerical modelling and validated with wave buoy records. First, its distribution around La Palma is studied. Significant variations are found, with the largest resource occurring off the north and northwest coasts; the northwest presents operational advantages (proximity to a port). Second, the seasonal variations in this area are studied. Wave energy is provided essentially by powerful NNW-NW swells in winter and autumn, by less energetic NNE-N waves in summer and spring. Finally, the resource is characterised in terms of sea states; it is found that the bulk of the energy is provided by waves between 9.5 s and 13.5 s of energy period and 1.5 m and 3.5 m of significant wave height, so the selection of the Wave Energy Converters to be installed should guarantee maximum efficiency in these ranges.     

Offshore and nearshore wave energy assessment around the Korean Peninsula

A wave resource assessment is presented for the region around the Korean peninsula. Offshore wave power was obtained from significant wave heights and peak periods, and wave directions hindcast for the period of 1979-2003. The spatial distributions for the seasonal and annual averaged wave power were obtained on a 1/6° grid covering the longitudes of 117-143°E and latitudes of 20-50°N. The highest monthly averaged wave power (25 kW/m) was observed on the southwestern side of the peninsula in winter. In order to obtain the wave power around Hongdo, numerical simulations were performed with respect to the monthly averaged waves. The correlation between the significant wave height and energy period was considered to adjust the nearshore wave power obtained by the numerical simulation. The correction procedure was validated from comparing the simulated data with wave buoy data.     

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.     

A linearized model for estimating the performance of submerged resonant wave energy converters

A realistic performance analysis of oscillating water column wave energy converters (WECs) addresses to a set of non-linear differential equations that need to be integrated in time, by using a stochastic approach, under the hypothesis of random wind-generated sea waves, for all the sea states which characterize the location of the system. Non-linearities of the differential equations have several origins:

• minor and major losses of the unsteady flow of water and air;

• compressibility of air and heat exchange with the walls of the air chamber;

• non-linear characteristics of the turbine.

Under the hypothesis of random sea waves with Gaussian distribution, the authors propose an original methodology for linearizing the differential equations that describe the flow motion inside a wholly submerged WEC. Under such hypothesis, the linearized model can be used for predicting the power output by means of the calculations in the frequency domain and for control design. The developed methodology has been applied to the estimation of the performance of the new “resonant sea wave energy converters”, called REWEC, patented by Boccotti in 1998, and consisting of several caissons, characterized by a structure similar to the caissons of the traditional breakwaters and placed on the seabed, close one to each other, to form a submerged breakwater. Each caisson is connected to a vertical duct wholly beneath the sea level, where a hydraulic Wells turbine is placed.The matching between turbine and resonance characteristic of the system is carefully analysed in order to maximize the energy conversion efficiency.Some results, given for a small installation in the Mediterranean sea, confirm that the REWEC system is able to absorb a large share of the incident wave energy due to a very simple regulation system which permits the tuning on sea states with different significant heights.     

An experimental study on the efficiency of the submerged plate wave energy converter

Several studies have been made using submerged plates for wave-damping purpose. A pulsating flow occurs opposite to the direction of wave propagation below these wave breakers. This water flow can be used for energy production purposes. In this study, the energy efficiency of the plate wave energy converter is determined experimentally. The length of the plate L=1 m, the water depth d=60 cm, the width of the plate b=60 cm and the thickness t=2 cm were held constant through all the experiments. Each experiment set has a total number of 20 different wave properties composed of T=1.16, 1.50, 1.87 and 2.05 s wave periods and H=2, 4, 6, 8 and 10 cm wave height values. The velocity and the wave length of the water flow occuring below the plate were measured for several conditions such as: 1. the plate only, 2. the plate and a triangular structure below it, with five different heights, 3. The plate and a vertical wall below it, with two different heights. In this manner, the submerged plate wave energy converter efficiency values were determined for 20 different conditions. It is understood that the efficiency of the submerged plate wave energy converters can reach up to 60% and the existence of a vertical wall below the plate rather than a triangular form is more efficient.     

Developments in the design of the PS Frog Mk 5 wave energy converter

This paper describes one of the innovative wave energy converters under development by the Lancaster University Renewable Energy Group. An offshore point-absorber wave energy converter, PS Frog Mk 5 consists of a large buoyant paddle with an integral ballasted ‘handle’ hanging below it. The waves act on the blade of the paddle and the ballast beneath provides the necessary reaction. When the WEC is pitching, power is extracted by partially resisting the sliding of a power-take-off mass, which moves in guides above sea level. Totally enclosed in a steel hull, with no external moving parts, PS Frog Mk. 5 is at least as robust as a ship and the survivability of the device is currently under investigation, though such work is beyond the scope of this paper. Such a device could be very economic in terms of power output per unit of capital cost. New inventive steps with experimental results and computer studies have led to promising improvements to the hull shape. The WEC is maintained in a resonant state by the use of special means to maintain a high dynamic magnifier in irregular seas. A robust feedback control system has been developed to ensure stability and maintain efficient power take-off. Some of these developments are described and illustrated with the results of computer simulations that show power outputs and device motion over a range of conditions. It is shown that useful advances have been made, with the power capture bordering on 2 MW in an increasing proportion of sea states.     

Combining wave energy with wind and solar: Short-term forecasting

While wind and solar have been the leading sources of renewable energy up to now, waves are increasingly being recognized as a viable source of power for coastal regions. This study analyzes integrating wave energy into the grid, in conjunction with wind and solar. The Pacific Northwest in the United States has a favorable mix of all three sources. Load and wind power series are obtained from government databases. Solar power is calculated from 12 sites over five states. Wave energy is calculated using buoy data, simulations of the ECMWF model, and power matrices for three types of wave energy converters. At the short horizons required for planning, the properties of the load and renewable energy are dissimilar. The load exhibits cycles at 24 h and seven days, seasonality and long-term trending. Solar power is dominated by the diurnal cycle and by seasonality, but also exhibits nonlinear variability due to cloud cover, atmospheric turbidity and precipitation. Wind power is dominated by large ramp events–irregular transitions between states of high and low power. Wave energy exhibits seasonal cycles and is generally smoother, although there are still some large transitions, particularly during winter months. Forecasting experiments are run over horizons of 1–4 h for the load and all three types of renewable energy. Waves are found to be more predictable than wind and solar. The forecast error at 1 h for the simulated wave farms is in the range of 5–7 percent, while the forecast errors for solar and wind are 17 and 22 percent. Geographic dispersal increases forecast accuracy. At the 1 h horizon, the forecast error for large-scale wave farms is 39–49 percent lower than at individual buoys. Grid integration costs are quantified by calculating balancing reserves. Waves show the lowest reserve costs, less than half wind and solar.     

Prototype testing of the wave energy converter wave dragon

The Wave Dragon is an offshore wave energy converter of the overtopping type. It consists of two wave reflectors focusing the incoming waves towards a ramp, a reservoir for collecting the overtopping water and a number of hydro turbines for converting the pressure head into power.In the period from 1998 to 2001 extensive wave tank testing on a scale model was carried at Aalborg University. Then, a 57×27 m wide and 237 tonnes heavy (incl. ballast) prototype of the Wave Dragon, placed in Nissum Bredning, Denmark, was grid connected in May 2003 as the world's first offshore wave energy converter.The prototype is fully equipped with hydro turbines and automatic control systems, and is instrumented in order to monitor power production, wave climate, forces in mooring lines, stresses in the structure and movements of the Wave Dragon.In the period May 2003 to January 2005 an extensive measuring program has been carried out, establishing the background for optimal design of the structure and regulation of the power take off system. Planning for deployment of a 4 MW power production unit in the Atlantic by 2007 is in progress.     

Further analysis of change in nearshore wave climate due to an offshore wave farm: An enhanced case study for the Wave Hub site

This paper addresses the use of numerical wave models for assessing the impact of offshore wave farms on the nearshore wave climate. Previous studies have investigated the effect of energy extraction by wave energy devices through the use of spectral models such as SWAN, representing a wave farm as one or more barriers within the model domain and applying a constant wave energy transmission percentage across the whole wave spectrum incident at the barrier. However, this is an unrealistic representation of the behaviour of real wave energy converters. These will exhibit frequency-dependent energy absorption characteristics that will correspond to the spectral response of the device, and may reflect its ability to be tuned to extract energy at particular frequencies. This study describes a modification of the SWAN source code to enable frequency-dependent wave energy transmission through a barrier. A detailed analysis of the wave climate at the Wave Hub wave farm site is also presented, with a particular focus on the occurrence of bimodal sea states. The modified SWAN code is used to assess how impact predictions for typically occurring sea states may differ when using frequency-dependent rather than constant wave energy transmission, with reference to a previous study using the unmodified code (Millar, Smith and Reeve, 2007 [1]). The results illustrate the dependence of the magnitude of the impact on both the response function of the devices and the spectral sea state in which they are operating.     

Wave climate analysis for the design of wave energy harvesters in the Mediterranean Sea

The objective of this paper is to provide a synthetic tool for determining expeditiously the wave climate conditions in several areas of the Mediterranean Sea. In the open literature, several authors have already conducted this specific analysis also for the area under examination in this paper. However, the need of discussing aspects strictly related to the design of wave energy harvesters is still relevant. Therefore, considering the variety of devices and the amount of information needed for conducting both an energy-wise optimization and a structural reliability assessment, a holistic view on the topic is provided. Specifically, the paper elucidates the theoretical aspects involved in the estimation of wave energy statistics and in the calculation of relevant return values. Next, it provides synthetic data representing the mean wave power and the return value of extreme events in several coastal areas of the Mediterranean Sea. In this regard, the paper complements information available in the open literature by discussing the influence of the directional pattern of the sea states in the determination of sea state statistics as well as in the design of a wave energy harvester.     

计及恶劣天气约束的海上风能波浪能资源分布研究

基于ERA5和全球海洋波浪再分析资料,统计分析2005—2019年间110°E~130°E、15°N~35°N海域的恶劣天气事件时空分布特征,在剔除恶劣天气时段下,对风能密度、波浪能密度、风能变异系数和波浪能变异系数进行分析。结果表明：2005—2019年间恶劣天气事件整体呈递增趋势,季节性差异大;总体上深远海海域恶劣天气出现时段比近海多,南海北部恶劣天气事件出现时段最多;在剔除恶劣天气时段后,东海深远海存在风能丰富且波浪能较密集的海域,台湾海峡以南近海风能丰富且稳定,但波浪能不密集且不稳定,南海北部近海海域波浪能比深远海更密集且更稳定,这与不剔除恶劣天气时段情况下波浪能分布特征存在较大差异。     

An integrated system of the floating wave energy converter and electrolytic hydrogen producer

The amount of energy produced now by the world community and that of energy flows caused by natural phenomena demonstrates commensurability of both power sources. Power production based on the conventional technologies is accompanied by environmental pollution, greenhouse and overheating effects resulting in biosphere degradation. It is apparent that the most intelligent solution of the problem of power production growth is the development of environmentally compatible power system using the regional renewable power resources. A system consisting of sea wave energy converter and electrolytic installation for hydrogen production is under consideration in this article.A potential candidate for wave energy conversion is an offshore Float Wave Electric Power Station (FWEPS), which is in the development stage. The second component of the system is the hydrogen producing facilities based on sea water electrolysis. Hydrogen as an ecologically safe fuel can be used in different branches of economy. The tentative studies showed that direct sea water electrolysis is technically feasible and is a perspective procedure for an environmentally-clean commercial production of hydrogen and associate products.Real performance of the system components allow to treat it as realizable.     

Modelling and simulation of a heaving wave energy converter based PEM hydrogen generation and storage system

The research on wave energy systems has been ongoing for decades. However, there are not many operational wave energy converters in use. The hydrogen energy systems also have a great potential. The proposed solution is to combine wave energy system with hydrogen energy system. The study provides details of simulation models and related simulation results. It is environmentally friendly, safe, feasible and effective. The results indicate that the proposed system model has a very high potential. With the use of low to medium energy density sea states, it is appears to be possible to generate (for DS1, DS2 and DS3, m_H2 = 350.8 kg, 623.9 kg and 2124 kg, respectively) a considerable amount of hydrogen in 20-min. The presented results include WEC motion properties, instantaneous and moving average value of other system parameters. The future promising simulations results indicate that next generation wave energy converter systems could be accompanied by hydrogen generation and storage systems.     

Numerical modeling of the effects of wave energy converter characteristics on nearshore wave conditions

Modeled nearshore wave propagation was investigated downstream of simulated wave energy converters (WECs) to evaluate overall near- and far-field effects of WEC arrays. Model sensitivity to WEC characteristics and WEC array deployment scenarios was evaluated using a modified version of an industry standard wave model, Simulating WAves Nearshore (SWAN), which allows the incorporation of device-specific WEC characteristics to specify obstacle transmission. The sensitivity study illustrated that WEC device type and subsequently its size directly resulted in wave height variations in the lee of the WEC array. Wave heights decreased up to 30% between modeled scenarios with and without WECs for large arrays (100 devices) of relatively sizable devices (26 m in diameter) with peak power generation near to the modeled incident wave height. Other WEC types resulted in less than 15% differences in modeled wave height with and without WECs, with lesser influence for WECs less than 10 m in diameter. Wave directions and periods were largely insensitive to changes in parameters. However, additional model parameterization and analysis are required to fully explore the model sensitivity of peak wave period and mean wave direction to the varying of the parameters.