The impact of wave energy farms in the shoreline wave climate: Portuguese pilot zone case study using Pelamis energy wave devices

This paper describes the study of the impact of energy absorption by wave farms on the nearshore wave climate and, in special, the influence of the incident wave conditions and the number and position of the wave farms, on the nearshore wave characteristics is studied and discussed. The study was applied to the maritime zone at the West coast off Portugal, namely in front of São Pedro de Moel, where it is foreseen the deployment of offshore wave energy prototypes and farms between the 30 m and 90 m bathymetric lines, with an area of 320 Km². In this study the REFDIF model was adapted in order to model the energy extraction by wave farms. Three different sinusoidal incident wave conditions were considered. Five different wave farm configurations, varying the position of the wave farm, its number and the width of the navigation channels at each wave farm were analysed. The results for each configuration in terms of the change of the wave characteristics (wave height and wave direction) at the nearshore are presented, compared and discussed for three representative wave conditions.     

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.     

Wave energy and nearshore hot spots: The case of the SE Bay of Biscay

The wave energy resource of the SE Bay of Biscay is investigated using wave buoy data and a hindcast data set covering a 44-year period (1958–2001). Of the total 13 study sites, three correspond to wave buoys (two coastal, one in deep-water) and the rest to hindcast data points. First, the resource is quantified—annual wave energy is found to exceed 200 MWh m^?1 at all the sites (with the exception of the coastal buoys), and average wave power is in the region of 25 kW m^?1. This substantial resource is the result of the Bay of Biscay’s position at the eastern end of the Atlantic Ocean together with the wind regime of the mid-latitudes (prevailing westerlies). Second, the resource is characterised in terms of sea state parameters. The bulk of the annual wave energy is provided by waves with significant wave heights of 1.5–4.0 m, energy periods of 10.5–13.5 s, and mean deep-water direction NW–WNW. Finally, wave interaction with the irregular bathymetry gives rise, in certain nearshore areas, to significant concentrations of wave energy. These hot spots have the highest potential as prospective wave farm sites; their locations are determined using numerical modelling.     

Offshore wave energy resource assessment in the East China Sea

The offshore wave energy resource in the East China Sea (ECS) off the coast of the southern East China is assessed using wave buoy data covering the period of 2011−2013. It is found that the averaged offshore wave power was approximately 13 kW m⁻¹ in the region of interest. Most of the offshore wave energy in the ECS is contributed by the sea states with significant wave heights between 1.5 m and 3.5 m and with wave energy periods between 6 s and 8 s. Seasonal variations are detected in the wave characteristics of significant wave height and wave power. The predominant wave directions are mainly from the II quadrant and the IV quadrant, respectively, in winter and summer, in accordance with the monsoon characteristics in the ECS. Wave heights, periods and power are generally higher in winter and autumn, and weaker in spring and summer; however, extreme values occur in some summer and autumn months due to the extreme conditions caused by typhoons passing over this region. These extreme sea states do not contribute much to the total annual energy, mainly because of their low occurrence, but may bring risks to the wave energy converters.     

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.     

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.     

Wave climate off the Swedish west coast

This paper presents and discusses the wave climate off the Swedish west coast. It is based on 8 years (1997–2004) of wave data from 13 sites, nearshore and offshore, in the Skagerrak and Kattegat. The data is a product of the WAM and SWAN wave models calibrated at one site by a wave measurement buoy. It is found that the average energy flux is approximately 5.2 kW/m in the offshore Skagerrak, 2.8 kW/m in the nearshore Skagerrak, and 2.4 kW/m in the Kattegat. One of the studied sites, i.e. site 9, is the location of a wave energy research site run by the Centre for Renewable Electric Energy Conversion at Uppsala University. This site has had a wave power plant installed since the spring of 2006, and another seven are planned to be installed during 2008. Wave energy as a renewable energy source was the driving interest that led to this study and the results are briefly discussed from this perspective.     

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 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.     

Integration of wave power in Haida Gwaii

Remote communities, such as Haida Gwaii, Canada, often have high energy costs due to their dependence on diesel fuel for generation. Haida Gwaii's lengthy coastline, exposed to the northeast Pacific Ocean, provides opportunities for capturing wave energy to potentially reduce energy costs. A mixed integer optimization model of the Haida Gwaii network is used to develop an operational strategy indicative of realistic operator behaviour. Two offshore locations are analyzed where the annual mean theoretical wave power is 42 kW/m and 16 kW/m, respectively. Results from both models show that the wave energy resource in Haida Gwaii has the potential to reduce the operational cost of energy and carbon dioxide emissions. A maximum allowable capital cost, above which the overall cost of energy would increase, is determined for various levels of installed wave capacity. Offshore transmission cost estimates are included, as well as the effects of the offshore transmission distance.     

Feasibility of large scale offshore wind power for Hong Kong — a preliminary study

This paper investigates the potential and the feasibility of offshore wind energy for Hong Kong. The 1998 wind data taken from an island were analysed. The wind resource yields an annual mean wind speed of 6.6 m/s and mean wind power density of 310 W/m². With commercially available 1.65 MW wind turbines placed on the whole of Hong Kong’s territorial waters, the maximum electricity generating potential from offshore wind is estimated to be 25 TWh which is about 72% of the total 1998 annual electricity consumption. However, potential is significantly reduced if other usages of the sea such as shipping are considered. A hypothetical offshore wind farm of 1038 MW capacity is then sited on the East-side waters. The extreme wind and wave climates, as well as the seasonal variation of wind power and demand are examined. The electricity generation costs are estimated and compared with the local retail tariff. Initial results indicate the wind farm is economically viable and technically feasible.     

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.     

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 resources along the Hawaiian Island chain

Hawaii's access to the ocean and remoteness from fuel supplies has sparked an interest in ocean waves as a potential resource to meet the increasing demand for sustainable energy. The wave resources include swells from distant storms and year-round seas generated by trade winds passing through the islands. This study produces 10 years of hindcast data from a system of mesoscale atmospheric and spectral wave models to quantify the wind and wave climate as well as nearshore wave energy resources in Hawaii. A global WAVEWATCH III (WW3) model forced by surface winds from the Final Global Tropospheric Analysis (FNL) reproduces the swell and seas from the far field and a nested Hawaii WW3 model with high-resolution winds from the Weather Research Forecast (WRF) model capture the local wave processes. The Simulating Waves Nearshore (SWAN) model nested inside Hawaii WW3 provides data in coastal waters, where wave energy converters are being considered for deployment. The computed wave heights show good agreement with data from satellites and buoys. Bi-monthly median and percentile plots show persistent trade winds throughout the year with strong seasonal variation of the wave climate. The nearshore data shows modulation of the wave energy along the coastline due to the undulating volcanic island bathymetry and demonstrates its importance in selecting suitable sites for wave energy converters.     

Wave energy assessment in Sicily (Italy)

This research presents an estimation of wave energy potential in Sicily (Italy) carried out using both buoy wave measurements from Rete Ondametrica Nazionale (RON), the Italian Government wave buoy network, and wave parameter data by ERA-INTERIM, a recent meteorological reanalysis project of the European Centre for Medium-Range Weather Forecasts (ECMWF). Starting from these offshore data, we first identified the western part of Sicily as the area with a higher availability of offshore wave energy; subsequently, we selected a study area in the western part of the south coast and assessed the nearshore potential energy by performing propagation using a spectral model (SWAN). The nearshore analysis highlights the presence of a “hot spot” relatively close to the coast where energy concentration produces even higher energy availability than offshore. Based on this result, the site may be a possible location for a wave energy farm, provisional on a technical–economic feasibility analysis.     

Wave resource in El Hierro—an island towards energy self-sufficiency

The island of El Hierro (Spain), a UNESCO Biosphere Reserve in the Atlantic Ocean, aims to become the first 100% renewable energy island in the world. With a €54 million wind project already under way, the present research looks at the island’s wave resource using a 44-year hindcast dataset obtained through numerical modelling. The geographical distribution of wave energy is examined on the basis of eight study sites around the island. A substantial resource is found west and north of El Hierro, with average wave power in the order of 25 kW m^?1 and total annual energy in excess 200 MW h m^?1; the resource is less abundant east and south of the island. In addition to these geographical variations, wave energy in El Hierro presents seasonal variations, with energetic winters and mild summers. After analysing the total resource and its spatial and seasonal variations, its composition in terms of sea states (significant wave heights and energy periods) is examined, and how this composition affects the selection of the Wave Energy Converters to be installed is discussed.     

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.     

Choosing the site for the first wave farm in a region: A case study in the Galician Southwest (Spain)

Where should the first wave farm in a region be installed? The nearshore area with the largest resource is the prime candidate. But how should this area be determined? Wave resource analyses typically consider a small number of wave patterns. Does the number of wave patterns influence the outcome? And, more generally, what is the best procedure for selecting the area? This work proposes an approach based on a large number of nearshore wave patterns and applies it to the Galician Southwest, where the first administrative concession for a wave farm (at a site to be determined) is expected to be issued shortly. The sensitivity of the results to the number of wave patterns, hence to the percentages of the total annual energy and time covered in the analysis, is investigated. It is found that the area that emerges as having the largest resource does depend on these percentages. For this reason, conventional analyses based on a small number of wave patterns are not sufficient to reliably determine the area with the largest resource. It is necessary to ensure that a sufficiently large percentage of the total energy is considered, using a procedure like the one proposed in this work.     

Wind energy potential assessment for the offshore areas of Taiwan west coast and Penghu Archipelago

The average wind speed and wind power density of Taiwan had been evaluated at 10 m, 30 m and 50 m by simulation of mesoscale numerical weather prediction model (MM5). The results showed that wind energy potential of this area is excellent. Taiwan has offered funds to encourage the founding of offshore wind farms in this area. The purpose of this study is to make a high resolution wind energy assessment for the offshore area of Taiwan west coast and Penghu archipelago by using WAsP. The result of this study has been used to the relative financial planning of offshore wind farm projects in Taiwan. The basic inputs of WAsP include wind weather data and terrain data. The wind weather data was from a monitoring station located on a remote island, Tongi, because that all of weather stations in the area of Taiwan west coast are affected by urbanization. SRTM was selected to be used as terrain data and downloaded from CGIAR-CSI for voids problem. The coverage of considered terrain area in this assessment work is about 300 km × 400 km that made some difficulties to run wind energy assessment of the whole area with a high resolution of 100 m. So the interested area of this study is divided into 19 areas for the wind energy assessment and mapping. The assessment results show the Changhua area has best wind energy potential in the area of Taiwan west coast which power density is above 1000 W/m² height and the areas of Penghu archipelago are above 1300 W. These results are higher than the expected from NWP. 180 of 3 MW wind turbines were used in the study of micro sitting in the Changhua area.The type and number of the wind turbines and the layout of the wind farm is similar to the prior study of Taipower Company for demonstrating the reliability of this study. The assessment result of average net annual energy production (AEP) of the wind farm is about 11.3 GWh that is very close to the prior study. The terrain effect is also studied. The average net annual energy production will decrease about 0.7 GWh if the wind turbines were moved eastward 3600 m closer to the coast because of terrain effect. As the same reason, the average net annual energy production would be increased to 11.392 GWh if the wind farm is moved westward 3600 m away from the coast.