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Feasibility study of wave energy harvesting along the southern coast and islands of Iran
Renewable Energy 135 (2019) 502e514
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Feasibility study of wave energy harvesting along the southern coast and islands of Iran Sina Pasha Zanous a, Rouzbeh Shafaghat a, *, Rezvan Alamian a, Mostafa Safdari Shadloo b, Mohammad Khosravi a a b
Sea-Based Energy Research Group, Babol Noshirvani University of Technology, Iran CORIA Lab., CNRS, University and INSA of Rouen, 76000, Rouen, France
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 January 2018 Received in revised form 28 October 2018 Accepted 6 December 2018 Available online 10 December 2018
Due to the distance of remote coastal areas and multiple islands in the south of Iran from the national grid, establishing wave power plants is highly beneficial. Therefore, in this study, the wave energy potential at these regions is investigated. For this purpose, wave characteristics are provided using European Centre for Medium-Range Weather Forecasts (ECMWF) for ten years, and validated against buoy measurements in two different intervals. The annual, seasonal and monthly variations of wave characteristics and seasonal wave energy flux roses along with the annual occurrence probability of different sea states are also assessed. According to the results, the wave energy in the Oman Sea reaches to its maximum, 17 kW/m at Chabahar port, in summer, and the maximum wave energy in Persian Gulf and Strait of Hormuz, which reaches to 10 kW/m in Kish Island, occurs in winter. In fact, wave parameters in the central regions of Persian Gulf have the higher values than Oman Sea in this season. Finally, Chabahar port in Oman Sea, Kangan port, Kish Island and Kharg Island in the Persian Gulf are considered as the wave energy hotspots, and the most suitable wave energy converter (WEC) systems are suggested for the selected hotspots. © 2018 Elsevier Ltd. All rights reserved.
Keywords: Wave energy harvesting Sea states Iranian southern islands Wave energy converter
1. Introduction Since the industrial revolution, the demand for energy started to increase drastically. Up to date, the fossil fuels were and still are the primary source of the energy that in return causes air and environmental pollution. Recently, in the Paris agreement, most of the industrial and developing countries decided to reduce their consumptions to control the global warming phenomenon ultimately. Accordingly, the use of renewable energy resources such as those in wave, wind, solar and, hydrothermal energies are gained considerable attention. In addition to becoming a competitive source of energy in terms of production cost, they are environmentally friendly, i.e., greenhouse gas emissions as the most critical factors on global warming are negligible, and are accessible in remote regions. Additionally, harvesting of renewable energies leads to sustainable development in the economic, social and environmental sectors in any country.
* Corresponding author. E-mail address: [email protected] (R. Shafaghat). https://doi.org/10.1016/j.renene.2018.12.027 0960-1481/© 2018 Elsevier Ltd. All rights reserved.
Seas and oceans are massive sources of motion energies such as those in waves, tides and currents as well as thermal and Salinity energies [1]. Wave energy has long been adopted among sources of renewable energies so that the first WEC model was designed in 1855 [2]. By emerging of the oil crisis in 1970, WECs have gained considerable attention because the density of wave energy is highest among all other solar-based energies [3]. It is interesting to point out that the total wave energy in the coastal region of seas and oceans around the world is about 10Eþ06 MW which is equal to the total energy consumption of the world [1]. In the past years, numerous researches have been performed to investigate the feasibility of wave energy harvesting around the world [4e8]. Among others, Zubaidah et al. [9] studied the feasibility of renewable energies in Malaysia, the South China Sea, and found that wave energy is considerable. In another study, Yaakob et al. [10] investigated the wave energy potential in the exclusive economic zone of Malaysia, where the wave characteristics provided using Radar Altimeter Database System (RADS) and the accuracy of wave data were validated with buoy measurements for ten years. Zheng et al. [11] simulated the long-term series and highresolution wave energy in the China Sea for 1988 to 2009, and the
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northern South China Sea was shown as the wealthiest area. Liang et al. [12] assessed wave energy in China East Adjacent Seas by the Weather Research & Forecasting Model. They found that the largest nearshore wave energy density exists in southern of Korea Peninsula. Sudheesh et al. [13] compared wave modeling results with buoy and satellite altimeter at the Indian Ocean and represented that the satellite data are in good agreement with buoy measurements. However, Sabique et al. [14] demonstrated that satellite data have poor response during cyclones at the Indian Ocean. Neil and Hashemi [15] assessed the wave potential of the northwest European shelf seas by applying the third-generation wave model named Simulating Waves Near shore (SWAN). Defne et al. [7] studied wave energy harvesting for the southeast Atlantic coast of the United States of America (USA), including the North Carolina, South Carolina, Georgia, and northern Florida. They analyzed wave power calculated using wave data from National Data Buoy Center wave stations and spectral wave density. They also found that the farther offshore, the higher power. Other studies on wave energy harvesting at various region around the world include, but not limited to, the works of Iglesias and Carballo along the Death Coast € mürcü near the south-east coast of the of Spain [16], Akpinar and Ko Black Sea [17], Mota and Pinto the coast of Portugal [18], Lavidas and Venugopal at Libyan coast [19], Bernhoff et al. at Baltic Sea [20], Hagerman at Southern New England [21], Ebuchi and Kawamura around Japan [22], Park et al. around Korea [23] and Hwang et al. at the Gulf of Mexico region [24]. For Iranian waters, following their extent and diversity, extensive studies have been conducted in order to assess the harvesting energy from them. Zabihian and Fung [1] studied Marine renewable energy generation methods in Iran and found that all kind of motion energies from seas and oceans except ocean current have potentials to be considered as energy resources. Alamian et al. [25] evaluated the wave characteristics and harvesting energy technologies used in the Caspian Sea, which is located in the northern part of Iran. According to their results, point absorber WEC was selected as the most appropriate device for harvesting wave energy. They also investigated wave energy potential in all part of Caspian Sea, and consequently, Noshahr and Babolsar were selected as proper locations for installation of wave energy conversion systems
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[26]. In another study, conducted by Kamranzad et al. [27], wave energy potential was investigated in Caspian Sea for 11 years. The central region was reported as the most appropriate place for wave energy harvesting in both of these works. Wind and wave energy resources along the Caspian Sea were also assessed by Rusu and Onea [28] using both remotely sensed data and numerical models. They characterized northern part as an adequate environment for wind energy harvesting. Due to the importance of economic activities in Strait of Hormuz, Persian Gulf, and Oman Sea, which are located at the southern part of Iran, these regions have received much attention. On the other hand, due to its connection to the Indian Ocean, by comparing wave energy potential at the southerly waters in Iran with those in the Caspian Sea, it was shown that the wave energy potential is considerable at these regions [3,29,30]. Among those studies concerning southerly waters of Iran, almost all of them reported that the north-eastern parts of the Gulf of Oman can be considered as the most appropriate area for wave energy extraction [31,32]. Soleimani et al. randomly investigated Amirabad port in the Caspian Sea, Asaluyeh port and Faroor Island in Persian Gulf for energy extraction [33]. The Significant wave height and wave period was acquired from time domain analysis during the 2002 in their study. They announced that bottom-fixed heave-buoy array (B-HBA) is most suitable one for wave energy harvesting at these sites due to their shoreline type and wave conditions. However, at the Faroor site, because of its rocky coastline, the U-type Oscillating Water Column (U-OWC) was suggested, which has the best performance and economic efficiency at water depths of 15e25 m. Another point worth mentioning is that there are 17 residential islands in the Persian Gulf and Strait of Hormuz. Due to the pristine nature, museums, ancient places, and many arts and entertainment options, these islands attract many tourists each year which make them very important for the country economically. In addition, since access to these islands is only possible through water, connecting these islands to the national grid is not possible, so their electricity is provided by diesel generators. Due to the high expenses of storage and transmission of fossil fuels, renewable wave energy power plants would play an essential role in these regions [34]. It is also noted that harvesting wave energy in islands has been
Table 1 The information of selected stations. Site ID
Site, Position
Depth (m)
Coordinate (deg)
Distance from coastline (km)
Characteristics
P1
Imam Port, Persian Gulf
<70
49.148 29.74
44
<70 <70 <70 <70 <70 <70 <70 <70 <70 <70 <70 <70
49.764 50.391 50.312 50.458 51.85 52.87 53.914 54.884 54.521 55.022 55.297 55.506
9 13 6 38 56 29 16 19 3 5 3 14
With 34 docks is the largest active port of the country (shipping), Sandy beach Sandy beach, Oil extraction, Tourism Rocky and sandy beach, Tourism Oil extraction, Sandy beach with coral rock, Deep waters Sandy beach, Commercial (shipping) Oil extraction, Sandy beach Oil extraction, Rocky and sandy beach Coral and sandy beach, Commercial, Free economic zone, Tourism Sandy beach Oil extraction, Rocky and sandy beach Oil extraction, Rocky and sandy beach, Tourism, Shipping and exporting oil Oil extraction, Rocky and sandy beach, Tourism, Shipping Iranian largest island, Rocky, muddy and, Sandy beach, Tourism
P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13
Hendijan Port, Persian Gulf Gonave Port, Persian Gulf Kharg Island, Persian Gulf Booshehr Port, Persian Gulf kangan Port, Persian Gulf Lavan Island, Persian Gulf Kish Island, Persian Gulf Lenge Port, Persian Gulf Siri Island, Persian Gulf Abu Musa Island, Persian Gulf Great Tunb Island, Persian Gulf Gheshm Island, Strait of Hormuz Hengan Island, Strait of Hormuz larak Island, Strait of Hormuz Jask Port, Oman sea Chabahar Port, Oman sea
<70
55.822 26.218 43
Coral and sandy beach, Tourism
<70 <70 <70
56.730 26.428 56 57.777 25.369 30 60.631 25.206 8
Rocky and sandy beach, Tourism Rocky and clay beach Rocky and sandy beach, Important commercial ports
Lat
P14 P15 P16 P17
Long
30.011 29.492 29.146 28.761 27.356 26.803 26.363 26.363 25.868 25.812 26.219 26.460
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extensively recommended around the world. In this regard, Fadaeenejad et al. conducted a review study concerning new approaches in harnessing wave energy for remote islands [35]. In addition to this, Vicinanza et al. [36] provided an extensive study in order to assess wave energy potential in Sardine Island which is one of the largest Islands in the Mediterranean sea where its economy is affected by high power consumptions (Italy). Other examples are the works of Antonio et al. in Pico Island, Azor [37], Stopa et al. in the Hawaiian Islands [38], Zhang et al. in Aashto Island (China) [39] and, Ayat et al., islands in Greece [40]. Based on the cited literature, although the feasibility of harvesting wave energy in southerly waters in Iran has been studied in the past few decades, not much study has been intensively focused on wave energy potential of the islands of this region. Therefore, in this study, a considerable effort is devoted to investigating the wave energy potential of islands aside from the coastal regions of Oman Sea, Strait of Hormuz and the Persian Gulf in order to provide insight into finding the suitable location for selecting and installing the WEC systems.
As mentioned above, 17 sites including both islands and coastal region with different depths and distances from coastline are selected in this study. The information of the selected sites including their coordinates, distances, depths, etc. are given in Table 1. It should be noted that, due to the islands’ concentration with similar climate especially nearby Strait of Hormuz, Only a few of these islands are being assessed. The location of the area of interests and selected sites along with their bathymetry are shown in Fig. 1 [43].
3. Methods In order to investigate the wave energy harvesting in the studied areas, wave data within a certain time interval are required. In this study, wave characteristics such as significant wave height, mean wave period and wave direction were provided using ECMWF explained in wave data section. To evaluate the accuracy of the results, calibrated wave data derived from ECMWF were validated with buoy measurements. It is noted that the buoy datasets belong
2. Area of interest 2.1. Oman sea The Oman Sea has a triangular shape located among Iran, Oman and, Pakistan. Its maximum length is 950 km from northwest to southeast, and its maximum width is about 340 km from northeast to southwest. The deep sea of Oman, which the deepest part of it is over 3400 m, is connected to the Persian Gulf via the Strait of Hormuz. The Oman Sea is directly linked to the Arabian Sea and the Indian Ocean. The maximum water surface temperature occurs in August is 32 Celsius, and the minimum water surface temperature occurs in January and is about 19.8 Celsius [41]. It also has an average salinity of 37 Practical Salinity Unit (PSUs). This region is exposed to the Monsoon blows from the Indian Ocean; therefore, intense storms have been seen in some seasons. Generally, Oman Sea prevailing wind consists of local or Monsoon wind and tropical cyclone such as Super Cyclonic Storm Gonu which occurred in 2007 last time. The direction of prevailing wave in the coast of Oman is from the northeast in winter and southwest in summer [42]. 2.2. Persian Gulf and Strait of Hormuz Persian Gulf with an area of about 237.473 square kilometers is the third largest gulf in the world after the Gulf of Mexico and Hudson Bay. This bay is from the Arvandrood River Delta to the Strait of Hormuz located between Iran and Saudi Arabia with total length of 989 km. Its average depth is about 35 m and its deepest point lies in the Iranian side of Hormuz Strait with a depth of 165 m. The amount of water salinity increases from north to south as a result of increasing water depth and salt domes. The Strait of Hormuz is the narrowest and deepest part of the Persian Gulf connecting this strategic waterway to the Oman Sea [41]. Furthermore, the direction of prevailing wave in the Persian Gulf is from northwest due to the low-pressure zone in the south of Iran [42]. 2.3. Islands There are 17 residential islands in these regions which are divided into two parts. The first part includes residential islands with high population density such as Gheshm, Kish and, Hormuz. The second part consists of residential islands with low population density such as Siri, Lavan, Larak, etc. It is noted that all islands in southerly waters of Iran are of much importance due to their Geographic and strategic positions [34].
Fig. 1. Location map of IRAN: (a) Selected sites (b) Bathymetry map in southerly waters of Iran [42].
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to Iranian meteorological office in Chabahar site. After a quantitative comparison of the two datasets in the validation section, wave characteristics in selected stations were discussed in the result section.
3.1. Wave theory Wave characteristics extensively depend on wind conditions and shape of the seabed. The wave power per unit width of waves in deep water is obtained as [32]:
E¼
rg2 TH2 ðkW=mÞ 64p
(1)
where r is the density of sea water, g is the acceleration of gravity, H is the significant wave height and T is the wave period. The energy is divided between kinetic energy and wave potential. To calculate the wave energy in a specified region, the ranges of wave period and height at which the wave energy is maximum should be considered. It should be noted that these conditions are the basis for WEC design [1].
3.2. wave dataset As mentioned above, the wave data used in this study such as significant wave height, mean wave period and wave direction at 6h intervals for 10 years (from 2006 to 2015) were provided using ECMWF. In this database the local and global meteorological models are simulated by means of satellite data and synoptic stations information at regular interval, and corresponding results are stored [44]. In this study, seasonal classification of area of interest is modulated according to the India Monsoon winds namely, winter (DJF), spring (MAM), summer (JJA) and autumn (SON) [45].
505
3.3. Validation of the wave dataset As in the past investigations [10,32,36,46], the accuracy of wave data acquired from the buoy located in Chabahar station were compared with ECMWF dataset. For this purpose, two different time intervals were considered at 1999 and 2000. The buoy was located at 60.65 E and 25.267 N by Iran Meteorological Organization. In this section, after comparing two set of data, ECMWF dataset were calibrated based on buoy measurements at Chabahar station, and calibrated data were evaluated by means of some quantitative parameters, and finally the results of quantitative parameters were compared with available studies in this field. Figs. 2 and 3 shows the comparison of significant wave height and energy flux, respectively, between two wave datasets (buoy and calibrated ECMWF) at two different time intervals in 1999 and 2000. These figures show that the variations of the two datasets are in agreement. For the quantitative comparison of the results, the statistical parameters such as MAPE, Bias, RMSE, SI, and CC, which are respectively, the mean absolute percentage error, the difference between average values, the root mean square error, the scatter index and, the correlation coefficient are calculated by using [32,46].
MAPE ¼
1 X jyi xi j 100 n xi
Bias ¼ y x;
RMSE ¼
rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1X ðyi xi Þ n
Fig. 2. Comparison of the calibrated significant wave height acquired from ECMWF and buoy measurement at Chabahar station in (a) 1999 (b) 2000.
(2)
(3)
(4)
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Fig. 3. Comparison of the calibrated wave energy flux acquired from ECMWF and buoy measurement at Chabahar station after calibration in (a) 1999 (b) 2000.
SI ¼
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi P 1 ððyi yÞ ðxi xÞÞ2 n
Table 3 MAPE indices for significant wave height [47].
(5)
x
P ððxi xÞðyi yÞÞ CC ¼ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi P P ðxi xÞ2 ðyi yÞ2
(6)
where xi and yi represent the measured and ECMWF values, while x and y are their average values, respectively, and n is the total number of data. The MAPE values between the buoy and calibrated ECMWF are given in Table 2. The small amount of MAPE shows that the agreement between the calibrated ECMWF dataset and buoy measurement is acceptable. Since the ranges of RMSE, SI, Bias and, CC are obtained and reported in the past investigations [46e48], these error indices are also considered for the comparison here. The error indices of wave height acquired in this study and the same parameter ‘s ranges provided by Caires et al. (2002) are compared in Table 3 [47]. It can be seen that all the error values are in the acceptable ranges. 4. Result and discussions In this study, the southerly waters of Iran were investigated in order to assess the wave energy harvesting potential. After
Table 2 MAPE indices for significant wave height and wave energy flux. Variables
Time
MAPE (%)
H(m)
1999 2000 1999 2000
0.7 0.22 0.9 0.3
E (kW/m)
Parameters
Bias (m) RMSE (m) CC SI
Wave heights (m) 1999
2000
0.051 0.2 0.82 0.4
0.055 0.201 0.904 0.19
Caires et al. (H (m))
0.44 ——0.02 0.31e0.71 0.82e0.95 0.13e0.32
verification of ECMWF dataset at the studied area (i.e., for Chabahar station as a sample) in the preceding section, the wave characteristics are studied in the four different sections as follows: 4.1. The annual variations of wave characteristics In this section, the wave characteristics are based on the annual average for ten years. Fig. 4 depicts the mean values of significant wave height, wave period and wave energy flux in the selected stations from 2006 to 2015. It can be seen that Chabahar (P17) located in Oman Sea has the most significant values of significant wave height and wave energy flux, while Larak Island (P15) located in the Strait of Hormuz has the lowest values of wave height and energy. Generally, it can be said that the significant wave height, wave period and wave energy flux in the Oman Sea are larger than those in the Persian Gulf due to the connection of the Oman sea to the Indian ocean. However, the values of significant wave height and wave energy flux in Jask port (P16) are lower than those in the center of the Persian Gulf due to the proximity to the Strait of Hormuz. Furthermore, according to Fig. 4b, after Chabahar (P17), Jask port (P16) and Larak Island (P15) have the highest values of wave periods, respectively. It is worth mentioning that, the existence of Strait of Hormuz, multiple islands and reduction in water depth act as blocks reducing the significant wave height and wave
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507
Fig. 4. Comparison of the mean annual wave characteristics among selected stations for ten years (a) wave period (s) (b) significant wave height (m) (c) wave energy flux (kW/m).
energy flux, and therefore, with regard to Fig. 4a, Larak Island (P15) has the lowest value of wave height in the studied area. In addition, after Larak Island (P15), Hendijan (P2) and Imam Port (P1) located in the westernmost point of the Persian Gulf have the lowest values of significant wave height and wave energy flux, respectively. Regarding the proximity of a large number of stations and the similarity of their results (according to Fig. 4), only three islands
and three ports are considered for the rest of the study. The islands are Gheshm (P13), Kish (P8) and Kharg (P4), which are located respectively, in the Strait of Hormuz, center of Persian Gulf and west of Persian Gulf, while the ports are Chabahar (P17), Lenge (P9) and Kangan ports (P6), which are located respectively, in the Oman Sea, Strait of Hormuz and center of Persian Gulf. It is worth mentioning that, the aforementioned final stations selected such
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Fig. 5. Comparison of the mean monthly wave characteristics among final selected stations for 10 years (a) significant wave height (m) (b) wave energy flux (kW/m).
that an appropriate wave energy potential study can be achieved in all parts of the studied area. 4.2. The seasonal and monthly variations of wave characteristics To evaluate wave energy potential, the mean annual wave characteristic is not enough; seasonal and monthly variations of wave characteristics should be also considered. Therefore, the mean monthly variations of wave characteristics for ten years at final selected stations are given in Fig. 5 in which some monthly fluctuations in the wave height and energy can be seen. As mentioned before, Chabahar has the highest values of significant wave height and energy which these values reach to, respectively, 1.8 m and 15.6 (kW/m) in July because of the southwest monsoon wind. After Chabahar port, Kangan port and Kharg Island have the highest values of wave characteristics, respectively. Other stations including Kish and Gheshm Islands and Lenge port experience small monthly variations of mean significant wave high and wave energy. According to Fig. 5, the studied islands reach the pick value in significant wave high and wave energy flux at three times, in the middle of January, the end of May and, the beginning of December, and also reach the minimum values in those at two times, the end of March and the beginning of August. Among the islands, Kharg has the highest value of significant wave height and wave energy flux which reaches up to 0.74 m and 1.94 kW/m, respectively, and Gheshm has the lowest value of significant wave height and wave energy flux which reaches up to 0.32 m and 0.23 kW/m, respectively. The maximum values of significant wave height, wave period and mean wave energy flux in the final selected stations with the maximum and mean values of wave energy in some other point around the world are given in Table 4 [1]. It is noted that, ()omit according to the distribution of wave energy potential around the world, Western Europe, New Zealand, and Japan are the most energetic locations with very high wave energy potential [49]. It can be seen from Table 4 that the
Table 4 Comparison of the mean and maximum wave energy flux at the final selected stations with some other regions around the world [1]. SITE
Max E (kW/m)
Average E (kW/m)
Khark Kangan Kish Lenge Gheshm Chabahar Japan New Zealand Western Europe
28.8 64.2 45.2 45.9 46 42.7 12.5 100. 70.
1.26 2. 1.44 1.11 0.84 5. 7. 23.6 46.9
maximum wave energy flux values in Iranian sites are comparable with those in the other sites, but the mean annual values which play a vital role in WEC design are very low. Among islands, Kangan and Gheshm have the highest and lowest values of mean energy flux respectively, as already mentioned. Figs. 6 and 7 illustrate the seasonal variations of significant wave height and wave energy flux, respectively, for ten years in the final selected sites. Generally, seasonal variation of the weather and wave climate causes seasonal variation in the wave energy and height distribution. It can be seen from the figures that the significant wave height and wave energy flux have the pick values in the winter of 2007, which is due to the Super Cyclonic Storm Gonu, spring, and autumn of 2010 and spring and winter of 2014. These fluctuations correspond to the tropical storms and cyclones occurred in these years. It is also seen that the significant wave height and wave energy flux at Chabahar in the spring, summer, and autumn are higher than those in other stations, while these parameters reduce intensively in the winter because of the prevailing wind propagation from the northeast of Oman sea. In this season, Kangan port and Kish and Kharg Islands located in the Persian Gulf have the higher values of wave parameters than Chabahar.
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509
Fig. 6. Comparison of the mean annual significant wave height in the different seasons among the final selected stations for ten years.
4.3. The seasonal variations of the wave propagation direction The seasonal variation of wave propagation is also an essential parameter in WEC design. In order to investigate the seasonal variation of wave propagation direction, the wave energy flux rose for each of the final selected stations is shown in Figs. 8 and 9. Fig. 8 illustrates that the prevailing wave direction at Chabahar is from the south in summer, and the wave energy flux reaches the maximum value of 18 kW/m due to the connection to the Indian Ocean. Additionally, the minimum wave energy flux of 4 kW/m occurs in winter. The prevailing wave direction in Kangan port is from west/northwest in all seasons, and the maximum of wave energy flux reaches to 9 kW/m in winter, which stem from the northwest wind at the Persian Gulf, Lenge port, located in Strait of
Hormuz, is influenced by northwest wind and also incoming currents from the Persian Gulf, and the prevailing wave direction is from the west. Finally, the maximum wave energy flux of 6 kW/m also occurs in winter at Lenge port similar to Kangan port. Fig. 9 illustrates the prevailing wave direction in the islands of Persian Gulf and Strait of Hormuz by the wave energy flux roses. As expected, and similar to the ports, as the result of the northwest wind in the Persian Gulf and also incoming currents from the Persian Gulf to the Strait of Hormuz, the prevailing wave direction in Khark Island located in the west of Persian Gulf is from the west/ northwest. Due to the incoming wave from the west point of Persian Gulf to the east, where Kish Island is located, the prevailing wave direction is west/southwest in this region. Finally, the prevailing wave direction in Gheshm Island, located in Strait of
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Fig. 7. Comparison of the mean annual wave energy flux in the different seasons among the final selected stations for ten years.
Hormuz, is from the west/southwest. Another point worth mentioning is that the most energetic waves seen in Kish, Kharg and, Gheshm Islands at winter have the wave energy flux of 10, 5.9 and 5 kW/m, respectively.
4.4. The scattering and occurrence probability of wave energy resources It is worth mentioning that the maximum WEC efficiency can be achieved at the ranges of wave heights and periods where the maximum annual energy occurred. Fig. 10 depicts the occurrence probability of different sea states by investigating the different ranges of wave height, period and corresponding wave energy. The numbers within the contour plot shows the occurrence of sea states, in a number of hours per year, which are the critical factors
in harvesting energy. According to Fig. 10, the horizontal axis consists of five 1-s intervals of wave period and six 1-m intervals of significant wave height. Furthermore, the first and second rows indicate the distribution of annual wave energy sources in the islands and ports, respectively. It can be seen that the waves with heights between 3 and 4 m and energy period less than 1 s have the most substantial probabilities of occurrence (for islands: 42% in Kharg, 37% in kish and, 43% in Gheshm; for ports: 23% in Chabahar, 37% Kangan and, 41% in Lenge), but the bulk of energy is not associated in these intervals which is the crucial role in WEC design, as already mentioned. Consequently, the wave height and period intervals with the maximum annual wave energy and corresponding probabilities of occurrence are given in Table 5.
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511
Fig. 8. Comparison of the mean wave power rose in the different seasons among the Chabahar, Kangan and Lenge port for ten years.
4.5. Identifying terminal hotspots and most suitable WEC systems According to the wave conditions acquired in the previous subsections, the wealthiest sites for wave energy harvesting are determined in this part. Afterward, most appropriate WEC systems are suggested for selected hotspots. In terms of selecting the best site for installation of a wave farm, It can be concluded that Chabahar port with the total amount of wave energy of 88.78 MWh=ðm yearÞ in Oman Sea, Kangan port with the total amount of wave energy of 35.78 MWh=ðm yearÞ in
Fig. 9. Comparison of the mean wave power rose in the different seasons among the Kharg, Kish, and Gheshm ports for ten years.
the Persian Gulf and, Kish and Kharg Islands with the total amount of wave energy of 25 and 22 MWh=ðm yearÞ are determined as the most appropriate regions. As far as selecting WEC systems are concerned, it is worth mentioning that WECs are divided into three groups, shoreline, near shore, and offshore, based on applied location [35]. In the case of offshore locations, WEC systems are more complex due to difficulties associated with mooring point, maintenance, and
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Fig. 10. Scatter contours of annual wave energy flux (MWh=ðm yearÞ) corresponded to the different sea states for ten years.
transmitter electrical cables [35]. In the face of economic crisis in Iran, applying these kinds of WECs is not applicable financially. Nearshore devices extract wave energy in the nearshore and transmit it towards onshore facility for generating electricity, and the cost and difficulties of manufacturing, maintenance and transmission are much less than those of offshore devices. In addition, they are usually attached to the seabed, which offers an appropriate condition for oscillating part to work [35]. Considering wave conditions in the current study and according to the [50], the two nearshore devices, Small bottom-referenced heaving buoy (SBHB) and Bottom-referenced submerged heaving buoy
(BSHB), are suitable for the selected hotspots due to the low wave energy potential of the studied regions in comparison with other energetic locations around the word (Table 4). Finally, Shoreline WECs have the merits of the easies installation and maintenance. Beside, these systems do not need deep-water moorings and long underwater electrical cables [35]. Because SDE and U-OWC are ideal for the part of the shorelines where there is a strong wave energy, such as breakwaters, coastal defenses, harbor walls, and rocky shorelines, these systems could also be suitable at Kharg, Kish and Chabahar sites with rocky shorelines and more extreme wave climate [35].
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Table 5 The wave significant height and period range with the maximum annual energy and annual percentage of occurrence of sea states. Site
Orderreferences
H(m)
Wave Energy (MWh/m)
The probability of Occurrence in Year (%)
5.8
24
4
5
5
8
3
24
2.2
4
17
15
12 8.8
10 9
8.8 6 3
9 11 6
T(s) Khark Island
First Second
Kish Island Gheshm Island
First Second
Chabahar Port
First
Kangan Port
Second First Second
Lenge Port
First
4e5 0e2 5e6 1e2 5e6 1e2 4e5 0e1 5e6 1e2 9.5e10 8e8.5 1e2 5e6 1e2 4e5 1e2 5e6 1e2
5. Conclusions The feasibility of wave energy harvesting along the southern coast and islands of Iran was studied in this paper. The wave characteristics such as significant wave height, mean wave period, and wave directions were provided using ECMWF for ten years. The wave data were validated against buoy measurements in two different periods of times namely, 1999 and 2000. According to the annual variations of wave characteristics, Chabahar located in Oman Sea has the high values of significant wave height and wave energy flux, while larak Island (P15) located in Strait of Hormuz has the lowest values of wave height and energy. It is worth mentioning that, the existence of Strait of Hormuz, multiple islands and reduction in the water depth act as a block reducing the wave energy in the Strait of Hormuz and the Persian Gulf. According to the annual variation of wave characteristics, after Chabahar port, Kangan port and Kharg Island have the highest values of wave characteristics, respectively. Other stations including Kish Island, Gheshm Island and Lenge port experience small variations of mean significant wave height and wave energy during the months of the year. According to the wave energy flux rose, the direction of prevailing wave in the coast of Oman is from south due to the connection to the Indian ocean, and the direction of the prevailing wave in the Persian Gulf is changed from west/ northwest in the middle region to west/southwest in the west region because of the northwest wind in the south of Iran. Finally, the different sea states including wave height and period ranges with a maximum value of annual energy and annual occurrence probability at the studied area were reported. The huge bulk of annual wave energy occurs in these sea states which is the key factor in WEC design. In this regard, Chabahar port with the total amount of wave energy of 88.78 MWh=ðm yearÞ in Oman Sea, Kangan port with the total amount of wave energy of 35.78 MWh=ðm yearÞ in the Persian Gulf and, Kish and Kharg Islands with the total amount of wave energy of 25 and 22 MWh=ðm yearÞ are selected as the most appropriate regions for constituting wave energy power plant. Afterward, regarding the wave and shore conditions, the two nearshore devices, SBHB and BSHB, were chosen for all the selected hotspots. In addition to this, SDE and U-OWC systems, which are ideal for the shorelines with stronger wave energy, were also selected for Kharg, Kish and Chabahar sites with rocky shorelines and more extreme wave
climate. The importance of electricity generation at the remote costal region in south of Iran and multiple islands in Persian Gulf and Strait of Hormuz causes that despite lower values of wave energy potential compared to the other high potential regions around the world, Appling WEC farms, especially in winter, leads to economic development and growth of these regions. References [1] F. Zabihian, A.S. Fung, Review of marine renewable energies: case study of Iran, Renew. Sustain. Energy Rev. 15 (5) (2011) 2461e2474. ment, P. McCullen, A. Falc~ [2] A. Cle ao, A. Fiorentino, F. Gardner, K. Hammarlund, G. Lemonis, T. Lewis, K. Nielsen, S. Petroncini, Wave energy in Europe: current status and perspectives, Renew. Sustain. Energy Rev. 6 (5) (2002) 405e431. [3] M.E. McCormick, Ocean Wave Energy Conversion, Courier Corporation, 2013. [4] B. Liang, F. Fan, Z. Yin, H. Shi, D. Lee, Numerical modelling of the nearshore wave energy resources of Shandong peninsula, China, Renew. Energy 57 (2013) 330e338. [5] G. Kim, W.M. Jeong, K.S. Lee, K. Jun, M.E. Lee, Offshore and nearshore wave energy assessment around the Korean Peninsula, Energy 36 (3) (2011) 1460e1469. [6] M. Gonçalves, P. Martinho, C.G. Soares, Wave energy conditions in the western French coast, Renew. Energy 62 (2014) 155e163. [7] Z. Defne, K.A. Haas, H.M. Fritz, Wave power potential along the Atlantic coast of the southeastern USA, Renew. Energy 34 (10) (2009) 2197e2205. [8] J. Falnes, A review of wave-energy extraction, Mar. Struct. 20 (4) (2007) 185e201. [9] I. Zubaidah, M.D. Siti Zawiah, K. Ramlee, The Fifth Energy Option for Malaysia, 2006. [10] O. Yaakob, F.E. Hashim, K.M. Omar, A.H.M. Din, K.K. Koh, Satellite-based wave data and wave energy resource assessment for South China Sea, Renew. Energy 88 (2016) 359e371. [11] C.-w. Zheng, J. Pan, J.-x. Li, Assessing the China Sea wind energy and wave energy resources from 1988 to 2009, Ocean Eng. 65 (2013) 39e48. [12] B. Liang, F. Fan, F. Liu, S. Gao, H. Zuo, 22-Year wave energy hindcast for the China East Adjacent Seas, Renew. Energy 71 (2014) 200e207. [13] K. Sudheesh, P. Vethamony, M. Babu, S. JayaKumar, Assessment of Wave Modeling Results with Buoy and Altimeter Deep Water Waves for a Summer Monsoon, 2004. [14] L. Sabique, T. Balakrishnan Nair, K. Srinivas, N.S. Nayak, Comparison of grid averaged altimeter and buoy significant wave heights in the northern Indian Ocean, Mar. Geodes. 36 (1) (2013) 72e85. [15] S.P. Neill, M.R. Hashemi, Wave power variability over the northwest European shelf seas, Appl. Energy 106 (2013) 31e46. [16] G. Iglesias, R. Carballo, Wave energy potential along the Death coast (Spain), Energy 34 (11) (2009) 1963e1975. _ Ko €mürcü, Wave energy potential along the south-east coasts [17] A. Akpınar, M.I. of the Black Sea, Energy 42 (1) (2012) 289e302. [18] P. Mota, J. Pinto, Wave energy potential along the western Portuguese coast, Renew. Energy 71 (2014) 8e17. [19] G. Lavidas, V. Venugopal, Wave energy resource evaluation and characterisation for the Libyan Sea, International Journal of Marine Energy 18 (2017) 1e14.
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Contents lists available at ScienceDirect
Renewable Energy journal homepage: www.elsevier.com/locate/renene
Feasibility study of wave energy harvesting along the southern coast and islands of Iran Sina Pasha Zanous a, Rouzbeh Shafaghat a, *, Rezvan Alamian a, Mostafa Safdari Shadloo b, Mohammad Khosravi a a b
Sea-Based Energy Research Group, Babol Noshirvani University of Technology, Iran CORIA Lab., CNRS, University and INSA of Rouen, 76000, Rouen, France
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 January 2018 Received in revised form 28 October 2018 Accepted 6 December 2018 Available online 10 December 2018
Due to the distance of remote coastal areas and multiple islands in the south of Iran from the national grid, establishing wave power plants is highly beneficial. Therefore, in this study, the wave energy potential at these regions is investigated. For this purpose, wave characteristics are provided using European Centre for Medium-Range Weather Forecasts (ECMWF) for ten years, and validated against buoy measurements in two different intervals. The annual, seasonal and monthly variations of wave characteristics and seasonal wave energy flux roses along with the annual occurrence probability of different sea states are also assessed. According to the results, the wave energy in the Oman Sea reaches to its maximum, 17 kW/m at Chabahar port, in summer, and the maximum wave energy in Persian Gulf and Strait of Hormuz, which reaches to 10 kW/m in Kish Island, occurs in winter. In fact, wave parameters in the central regions of Persian Gulf have the higher values than Oman Sea in this season. Finally, Chabahar port in Oman Sea, Kangan port, Kish Island and Kharg Island in the Persian Gulf are considered as the wave energy hotspots, and the most suitable wave energy converter (WEC) systems are suggested for the selected hotspots. © 2018 Elsevier Ltd. All rights reserved.
Keywords: Wave energy harvesting Sea states Iranian southern islands Wave energy converter
1. Introduction Since the industrial revolution, the demand for energy started to increase drastically. Up to date, the fossil fuels were and still are the primary source of the energy that in return causes air and environmental pollution. Recently, in the Paris agreement, most of the industrial and developing countries decided to reduce their consumptions to control the global warming phenomenon ultimately. Accordingly, the use of renewable energy resources such as those in wave, wind, solar and, hydrothermal energies are gained considerable attention. In addition to becoming a competitive source of energy in terms of production cost, they are environmentally friendly, i.e., greenhouse gas emissions as the most critical factors on global warming are negligible, and are accessible in remote regions. Additionally, harvesting of renewable energies leads to sustainable development in the economic, social and environmental sectors in any country.
* Corresponding author. E-mail address: [email protected] (R. Shafaghat). https://doi.org/10.1016/j.renene.2018.12.027 0960-1481/© 2018 Elsevier Ltd. All rights reserved.
Seas and oceans are massive sources of motion energies such as those in waves, tides and currents as well as thermal and Salinity energies [1]. Wave energy has long been adopted among sources of renewable energies so that the first WEC model was designed in 1855 [2]. By emerging of the oil crisis in 1970, WECs have gained considerable attention because the density of wave energy is highest among all other solar-based energies [3]. It is interesting to point out that the total wave energy in the coastal region of seas and oceans around the world is about 10Eþ06 MW which is equal to the total energy consumption of the world [1]. In the past years, numerous researches have been performed to investigate the feasibility of wave energy harvesting around the world [4e8]. Among others, Zubaidah et al. [9] studied the feasibility of renewable energies in Malaysia, the South China Sea, and found that wave energy is considerable. In another study, Yaakob et al. [10] investigated the wave energy potential in the exclusive economic zone of Malaysia, where the wave characteristics provided using Radar Altimeter Database System (RADS) and the accuracy of wave data were validated with buoy measurements for ten years. Zheng et al. [11] simulated the long-term series and highresolution wave energy in the China Sea for 1988 to 2009, and the
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northern South China Sea was shown as the wealthiest area. Liang et al. [12] assessed wave energy in China East Adjacent Seas by the Weather Research & Forecasting Model. They found that the largest nearshore wave energy density exists in southern of Korea Peninsula. Sudheesh et al. [13] compared wave modeling results with buoy and satellite altimeter at the Indian Ocean and represented that the satellite data are in good agreement with buoy measurements. However, Sabique et al. [14] demonstrated that satellite data have poor response during cyclones at the Indian Ocean. Neil and Hashemi [15] assessed the wave potential of the northwest European shelf seas by applying the third-generation wave model named Simulating Waves Near shore (SWAN). Defne et al. [7] studied wave energy harvesting for the southeast Atlantic coast of the United States of America (USA), including the North Carolina, South Carolina, Georgia, and northern Florida. They analyzed wave power calculated using wave data from National Data Buoy Center wave stations and spectral wave density. They also found that the farther offshore, the higher power. Other studies on wave energy harvesting at various region around the world include, but not limited to, the works of Iglesias and Carballo along the Death Coast € mürcü near the south-east coast of the of Spain [16], Akpinar and Ko Black Sea [17], Mota and Pinto the coast of Portugal [18], Lavidas and Venugopal at Libyan coast [19], Bernhoff et al. at Baltic Sea [20], Hagerman at Southern New England [21], Ebuchi and Kawamura around Japan [22], Park et al. around Korea [23] and Hwang et al. at the Gulf of Mexico region [24]. For Iranian waters, following their extent and diversity, extensive studies have been conducted in order to assess the harvesting energy from them. Zabihian and Fung [1] studied Marine renewable energy generation methods in Iran and found that all kind of motion energies from seas and oceans except ocean current have potentials to be considered as energy resources. Alamian et al. [25] evaluated the wave characteristics and harvesting energy technologies used in the Caspian Sea, which is located in the northern part of Iran. According to their results, point absorber WEC was selected as the most appropriate device for harvesting wave energy. They also investigated wave energy potential in all part of Caspian Sea, and consequently, Noshahr and Babolsar were selected as proper locations for installation of wave energy conversion systems
503
[26]. In another study, conducted by Kamranzad et al. [27], wave energy potential was investigated in Caspian Sea for 11 years. The central region was reported as the most appropriate place for wave energy harvesting in both of these works. Wind and wave energy resources along the Caspian Sea were also assessed by Rusu and Onea [28] using both remotely sensed data and numerical models. They characterized northern part as an adequate environment for wind energy harvesting. Due to the importance of economic activities in Strait of Hormuz, Persian Gulf, and Oman Sea, which are located at the southern part of Iran, these regions have received much attention. On the other hand, due to its connection to the Indian Ocean, by comparing wave energy potential at the southerly waters in Iran with those in the Caspian Sea, it was shown that the wave energy potential is considerable at these regions [3,29,30]. Among those studies concerning southerly waters of Iran, almost all of them reported that the north-eastern parts of the Gulf of Oman can be considered as the most appropriate area for wave energy extraction [31,32]. Soleimani et al. randomly investigated Amirabad port in the Caspian Sea, Asaluyeh port and Faroor Island in Persian Gulf for energy extraction [33]. The Significant wave height and wave period was acquired from time domain analysis during the 2002 in their study. They announced that bottom-fixed heave-buoy array (B-HBA) is most suitable one for wave energy harvesting at these sites due to their shoreline type and wave conditions. However, at the Faroor site, because of its rocky coastline, the U-type Oscillating Water Column (U-OWC) was suggested, which has the best performance and economic efficiency at water depths of 15e25 m. Another point worth mentioning is that there are 17 residential islands in the Persian Gulf and Strait of Hormuz. Due to the pristine nature, museums, ancient places, and many arts and entertainment options, these islands attract many tourists each year which make them very important for the country economically. In addition, since access to these islands is only possible through water, connecting these islands to the national grid is not possible, so their electricity is provided by diesel generators. Due to the high expenses of storage and transmission of fossil fuels, renewable wave energy power plants would play an essential role in these regions [34]. It is also noted that harvesting wave energy in islands has been
Table 1 The information of selected stations. Site ID
Site, Position
Depth (m)
Coordinate (deg)
Distance from coastline (km)
Characteristics
P1
Imam Port, Persian Gulf
<70
49.148 29.74
44
<70 <70 <70 <70 <70 <70 <70 <70 <70 <70 <70 <70
49.764 50.391 50.312 50.458 51.85 52.87 53.914 54.884 54.521 55.022 55.297 55.506
9 13 6 38 56 29 16 19 3 5 3 14
With 34 docks is the largest active port of the country (shipping), Sandy beach Sandy beach, Oil extraction, Tourism Rocky and sandy beach, Tourism Oil extraction, Sandy beach with coral rock, Deep waters Sandy beach, Commercial (shipping) Oil extraction, Sandy beach Oil extraction, Rocky and sandy beach Coral and sandy beach, Commercial, Free economic zone, Tourism Sandy beach Oil extraction, Rocky and sandy beach Oil extraction, Rocky and sandy beach, Tourism, Shipping and exporting oil Oil extraction, Rocky and sandy beach, Tourism, Shipping Iranian largest island, Rocky, muddy and, Sandy beach, Tourism
P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13
Hendijan Port, Persian Gulf Gonave Port, Persian Gulf Kharg Island, Persian Gulf Booshehr Port, Persian Gulf kangan Port, Persian Gulf Lavan Island, Persian Gulf Kish Island, Persian Gulf Lenge Port, Persian Gulf Siri Island, Persian Gulf Abu Musa Island, Persian Gulf Great Tunb Island, Persian Gulf Gheshm Island, Strait of Hormuz Hengan Island, Strait of Hormuz larak Island, Strait of Hormuz Jask Port, Oman sea Chabahar Port, Oman sea
<70
55.822 26.218 43
Coral and sandy beach, Tourism
<70 <70 <70
56.730 26.428 56 57.777 25.369 30 60.631 25.206 8
Rocky and sandy beach, Tourism Rocky and clay beach Rocky and sandy beach, Important commercial ports
Lat
P14 P15 P16 P17
Long
30.011 29.492 29.146 28.761 27.356 26.803 26.363 26.363 25.868 25.812 26.219 26.460
504
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extensively recommended around the world. In this regard, Fadaeenejad et al. conducted a review study concerning new approaches in harnessing wave energy for remote islands [35]. In addition to this, Vicinanza et al. [36] provided an extensive study in order to assess wave energy potential in Sardine Island which is one of the largest Islands in the Mediterranean sea where its economy is affected by high power consumptions (Italy). Other examples are the works of Antonio et al. in Pico Island, Azor [37], Stopa et al. in the Hawaiian Islands [38], Zhang et al. in Aashto Island (China) [39] and, Ayat et al., islands in Greece [40]. Based on the cited literature, although the feasibility of harvesting wave energy in southerly waters in Iran has been studied in the past few decades, not much study has been intensively focused on wave energy potential of the islands of this region. Therefore, in this study, a considerable effort is devoted to investigating the wave energy potential of islands aside from the coastal regions of Oman Sea, Strait of Hormuz and the Persian Gulf in order to provide insight into finding the suitable location for selecting and installing the WEC systems.
As mentioned above, 17 sites including both islands and coastal region with different depths and distances from coastline are selected in this study. The information of the selected sites including their coordinates, distances, depths, etc. are given in Table 1. It should be noted that, due to the islands’ concentration with similar climate especially nearby Strait of Hormuz, Only a few of these islands are being assessed. The location of the area of interests and selected sites along with their bathymetry are shown in Fig. 1 [43].
3. Methods In order to investigate the wave energy harvesting in the studied areas, wave data within a certain time interval are required. In this study, wave characteristics such as significant wave height, mean wave period and wave direction were provided using ECMWF explained in wave data section. To evaluate the accuracy of the results, calibrated wave data derived from ECMWF were validated with buoy measurements. It is noted that the buoy datasets belong
2. Area of interest 2.1. Oman sea The Oman Sea has a triangular shape located among Iran, Oman and, Pakistan. Its maximum length is 950 km from northwest to southeast, and its maximum width is about 340 km from northeast to southwest. The deep sea of Oman, which the deepest part of it is over 3400 m, is connected to the Persian Gulf via the Strait of Hormuz. The Oman Sea is directly linked to the Arabian Sea and the Indian Ocean. The maximum water surface temperature occurs in August is 32 Celsius, and the minimum water surface temperature occurs in January and is about 19.8 Celsius [41]. It also has an average salinity of 37 Practical Salinity Unit (PSUs). This region is exposed to the Monsoon blows from the Indian Ocean; therefore, intense storms have been seen in some seasons. Generally, Oman Sea prevailing wind consists of local or Monsoon wind and tropical cyclone such as Super Cyclonic Storm Gonu which occurred in 2007 last time. The direction of prevailing wave in the coast of Oman is from the northeast in winter and southwest in summer [42]. 2.2. Persian Gulf and Strait of Hormuz Persian Gulf with an area of about 237.473 square kilometers is the third largest gulf in the world after the Gulf of Mexico and Hudson Bay. This bay is from the Arvandrood River Delta to the Strait of Hormuz located between Iran and Saudi Arabia with total length of 989 km. Its average depth is about 35 m and its deepest point lies in the Iranian side of Hormuz Strait with a depth of 165 m. The amount of water salinity increases from north to south as a result of increasing water depth and salt domes. The Strait of Hormuz is the narrowest and deepest part of the Persian Gulf connecting this strategic waterway to the Oman Sea [41]. Furthermore, the direction of prevailing wave in the Persian Gulf is from northwest due to the low-pressure zone in the south of Iran [42]. 2.3. Islands There are 17 residential islands in these regions which are divided into two parts. The first part includes residential islands with high population density such as Gheshm, Kish and, Hormuz. The second part consists of residential islands with low population density such as Siri, Lavan, Larak, etc. It is noted that all islands in southerly waters of Iran are of much importance due to their Geographic and strategic positions [34].
Fig. 1. Location map of IRAN: (a) Selected sites (b) Bathymetry map in southerly waters of Iran [42].
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to Iranian meteorological office in Chabahar site. After a quantitative comparison of the two datasets in the validation section, wave characteristics in selected stations were discussed in the result section.
3.1. Wave theory Wave characteristics extensively depend on wind conditions and shape of the seabed. The wave power per unit width of waves in deep water is obtained as [32]:
E¼
rg2 TH2 ðkW=mÞ 64p
(1)
where r is the density of sea water, g is the acceleration of gravity, H is the significant wave height and T is the wave period. The energy is divided between kinetic energy and wave potential. To calculate the wave energy in a specified region, the ranges of wave period and height at which the wave energy is maximum should be considered. It should be noted that these conditions are the basis for WEC design [1].
3.2. wave dataset As mentioned above, the wave data used in this study such as significant wave height, mean wave period and wave direction at 6h intervals for 10 years (from 2006 to 2015) were provided using ECMWF. In this database the local and global meteorological models are simulated by means of satellite data and synoptic stations information at regular interval, and corresponding results are stored [44]. In this study, seasonal classification of area of interest is modulated according to the India Monsoon winds namely, winter (DJF), spring (MAM), summer (JJA) and autumn (SON) [45].
505
3.3. Validation of the wave dataset As in the past investigations [10,32,36,46], the accuracy of wave data acquired from the buoy located in Chabahar station were compared with ECMWF dataset. For this purpose, two different time intervals were considered at 1999 and 2000. The buoy was located at 60.65 E and 25.267 N by Iran Meteorological Organization. In this section, after comparing two set of data, ECMWF dataset were calibrated based on buoy measurements at Chabahar station, and calibrated data were evaluated by means of some quantitative parameters, and finally the results of quantitative parameters were compared with available studies in this field. Figs. 2 and 3 shows the comparison of significant wave height and energy flux, respectively, between two wave datasets (buoy and calibrated ECMWF) at two different time intervals in 1999 and 2000. These figures show that the variations of the two datasets are in agreement. For the quantitative comparison of the results, the statistical parameters such as MAPE, Bias, RMSE, SI, and CC, which are respectively, the mean absolute percentage error, the difference between average values, the root mean square error, the scatter index and, the correlation coefficient are calculated by using [32,46].
MAPE ¼
1 X jyi xi j 100 n xi
Bias ¼ y x;
RMSE ¼
rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1X ðyi xi Þ n
Fig. 2. Comparison of the calibrated significant wave height acquired from ECMWF and buoy measurement at Chabahar station in (a) 1999 (b) 2000.
(2)
(3)
(4)
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Fig. 3. Comparison of the calibrated wave energy flux acquired from ECMWF and buoy measurement at Chabahar station after calibration in (a) 1999 (b) 2000.
SI ¼
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi P 1 ððyi yÞ ðxi xÞÞ2 n
Table 3 MAPE indices for significant wave height [47].
(5)
x
P ððxi xÞðyi yÞÞ CC ¼ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi P P ðxi xÞ2 ðyi yÞ2
(6)
where xi and yi represent the measured and ECMWF values, while x and y are their average values, respectively, and n is the total number of data. The MAPE values between the buoy and calibrated ECMWF are given in Table 2. The small amount of MAPE shows that the agreement between the calibrated ECMWF dataset and buoy measurement is acceptable. Since the ranges of RMSE, SI, Bias and, CC are obtained and reported in the past investigations [46e48], these error indices are also considered for the comparison here. The error indices of wave height acquired in this study and the same parameter ‘s ranges provided by Caires et al. (2002) are compared in Table 3 [47]. It can be seen that all the error values are in the acceptable ranges. 4. Result and discussions In this study, the southerly waters of Iran were investigated in order to assess the wave energy harvesting potential. After
Table 2 MAPE indices for significant wave height and wave energy flux. Variables
Time
MAPE (%)
H(m)
1999 2000 1999 2000
0.7 0.22 0.9 0.3
E (kW/m)
Parameters
Bias (m) RMSE (m) CC SI
Wave heights (m) 1999
2000
0.051 0.2 0.82 0.4
0.055 0.201 0.904 0.19
Caires et al. (H (m))
0.44 ——0.02 0.31e0.71 0.82e0.95 0.13e0.32
verification of ECMWF dataset at the studied area (i.e., for Chabahar station as a sample) in the preceding section, the wave characteristics are studied in the four different sections as follows: 4.1. The annual variations of wave characteristics In this section, the wave characteristics are based on the annual average for ten years. Fig. 4 depicts the mean values of significant wave height, wave period and wave energy flux in the selected stations from 2006 to 2015. It can be seen that Chabahar (P17) located in Oman Sea has the most significant values of significant wave height and wave energy flux, while Larak Island (P15) located in the Strait of Hormuz has the lowest values of wave height and energy. Generally, it can be said that the significant wave height, wave period and wave energy flux in the Oman Sea are larger than those in the Persian Gulf due to the connection of the Oman sea to the Indian ocean. However, the values of significant wave height and wave energy flux in Jask port (P16) are lower than those in the center of the Persian Gulf due to the proximity to the Strait of Hormuz. Furthermore, according to Fig. 4b, after Chabahar (P17), Jask port (P16) and Larak Island (P15) have the highest values of wave periods, respectively. It is worth mentioning that, the existence of Strait of Hormuz, multiple islands and reduction in water depth act as blocks reducing the significant wave height and wave
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Fig. 4. Comparison of the mean annual wave characteristics among selected stations for ten years (a) wave period (s) (b) significant wave height (m) (c) wave energy flux (kW/m).
energy flux, and therefore, with regard to Fig. 4a, Larak Island (P15) has the lowest value of wave height in the studied area. In addition, after Larak Island (P15), Hendijan (P2) and Imam Port (P1) located in the westernmost point of the Persian Gulf have the lowest values of significant wave height and wave energy flux, respectively. Regarding the proximity of a large number of stations and the similarity of their results (according to Fig. 4), only three islands
and three ports are considered for the rest of the study. The islands are Gheshm (P13), Kish (P8) and Kharg (P4), which are located respectively, in the Strait of Hormuz, center of Persian Gulf and west of Persian Gulf, while the ports are Chabahar (P17), Lenge (P9) and Kangan ports (P6), which are located respectively, in the Oman Sea, Strait of Hormuz and center of Persian Gulf. It is worth mentioning that, the aforementioned final stations selected such
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Fig. 5. Comparison of the mean monthly wave characteristics among final selected stations for 10 years (a) significant wave height (m) (b) wave energy flux (kW/m).
that an appropriate wave energy potential study can be achieved in all parts of the studied area. 4.2. The seasonal and monthly variations of wave characteristics To evaluate wave energy potential, the mean annual wave characteristic is not enough; seasonal and monthly variations of wave characteristics should be also considered. Therefore, the mean monthly variations of wave characteristics for ten years at final selected stations are given in Fig. 5 in which some monthly fluctuations in the wave height and energy can be seen. As mentioned before, Chabahar has the highest values of significant wave height and energy which these values reach to, respectively, 1.8 m and 15.6 (kW/m) in July because of the southwest monsoon wind. After Chabahar port, Kangan port and Kharg Island have the highest values of wave characteristics, respectively. Other stations including Kish and Gheshm Islands and Lenge port experience small monthly variations of mean significant wave high and wave energy. According to Fig. 5, the studied islands reach the pick value in significant wave high and wave energy flux at three times, in the middle of January, the end of May and, the beginning of December, and also reach the minimum values in those at two times, the end of March and the beginning of August. Among the islands, Kharg has the highest value of significant wave height and wave energy flux which reaches up to 0.74 m and 1.94 kW/m, respectively, and Gheshm has the lowest value of significant wave height and wave energy flux which reaches up to 0.32 m and 0.23 kW/m, respectively. The maximum values of significant wave height, wave period and mean wave energy flux in the final selected stations with the maximum and mean values of wave energy in some other point around the world are given in Table 4 [1]. It is noted that, ()omit according to the distribution of wave energy potential around the world, Western Europe, New Zealand, and Japan are the most energetic locations with very high wave energy potential [49]. It can be seen from Table 4 that the
Table 4 Comparison of the mean and maximum wave energy flux at the final selected stations with some other regions around the world [1]. SITE
Max E (kW/m)
Average E (kW/m)
Khark Kangan Kish Lenge Gheshm Chabahar Japan New Zealand Western Europe
28.8 64.2 45.2 45.9 46 42.7 12.5 100. 70.
1.26 2. 1.44 1.11 0.84 5. 7. 23.6 46.9
maximum wave energy flux values in Iranian sites are comparable with those in the other sites, but the mean annual values which play a vital role in WEC design are very low. Among islands, Kangan and Gheshm have the highest and lowest values of mean energy flux respectively, as already mentioned. Figs. 6 and 7 illustrate the seasonal variations of significant wave height and wave energy flux, respectively, for ten years in the final selected sites. Generally, seasonal variation of the weather and wave climate causes seasonal variation in the wave energy and height distribution. It can be seen from the figures that the significant wave height and wave energy flux have the pick values in the winter of 2007, which is due to the Super Cyclonic Storm Gonu, spring, and autumn of 2010 and spring and winter of 2014. These fluctuations correspond to the tropical storms and cyclones occurred in these years. It is also seen that the significant wave height and wave energy flux at Chabahar in the spring, summer, and autumn are higher than those in other stations, while these parameters reduce intensively in the winter because of the prevailing wind propagation from the northeast of Oman sea. In this season, Kangan port and Kish and Kharg Islands located in the Persian Gulf have the higher values of wave parameters than Chabahar.
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Fig. 6. Comparison of the mean annual significant wave height in the different seasons among the final selected stations for ten years.
4.3. The seasonal variations of the wave propagation direction The seasonal variation of wave propagation is also an essential parameter in WEC design. In order to investigate the seasonal variation of wave propagation direction, the wave energy flux rose for each of the final selected stations is shown in Figs. 8 and 9. Fig. 8 illustrates that the prevailing wave direction at Chabahar is from the south in summer, and the wave energy flux reaches the maximum value of 18 kW/m due to the connection to the Indian Ocean. Additionally, the minimum wave energy flux of 4 kW/m occurs in winter. The prevailing wave direction in Kangan port is from west/northwest in all seasons, and the maximum of wave energy flux reaches to 9 kW/m in winter, which stem from the northwest wind at the Persian Gulf, Lenge port, located in Strait of
Hormuz, is influenced by northwest wind and also incoming currents from the Persian Gulf, and the prevailing wave direction is from the west. Finally, the maximum wave energy flux of 6 kW/m also occurs in winter at Lenge port similar to Kangan port. Fig. 9 illustrates the prevailing wave direction in the islands of Persian Gulf and Strait of Hormuz by the wave energy flux roses. As expected, and similar to the ports, as the result of the northwest wind in the Persian Gulf and also incoming currents from the Persian Gulf to the Strait of Hormuz, the prevailing wave direction in Khark Island located in the west of Persian Gulf is from the west/ northwest. Due to the incoming wave from the west point of Persian Gulf to the east, where Kish Island is located, the prevailing wave direction is west/southwest in this region. Finally, the prevailing wave direction in Gheshm Island, located in Strait of
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Fig. 7. Comparison of the mean annual wave energy flux in the different seasons among the final selected stations for ten years.
Hormuz, is from the west/southwest. Another point worth mentioning is that the most energetic waves seen in Kish, Kharg and, Gheshm Islands at winter have the wave energy flux of 10, 5.9 and 5 kW/m, respectively.
4.4. The scattering and occurrence probability of wave energy resources It is worth mentioning that the maximum WEC efficiency can be achieved at the ranges of wave heights and periods where the maximum annual energy occurred. Fig. 10 depicts the occurrence probability of different sea states by investigating the different ranges of wave height, period and corresponding wave energy. The numbers within the contour plot shows the occurrence of sea states, in a number of hours per year, which are the critical factors
in harvesting energy. According to Fig. 10, the horizontal axis consists of five 1-s intervals of wave period and six 1-m intervals of significant wave height. Furthermore, the first and second rows indicate the distribution of annual wave energy sources in the islands and ports, respectively. It can be seen that the waves with heights between 3 and 4 m and energy period less than 1 s have the most substantial probabilities of occurrence (for islands: 42% in Kharg, 37% in kish and, 43% in Gheshm; for ports: 23% in Chabahar, 37% Kangan and, 41% in Lenge), but the bulk of energy is not associated in these intervals which is the crucial role in WEC design, as already mentioned. Consequently, the wave height and period intervals with the maximum annual wave energy and corresponding probabilities of occurrence are given in Table 5.
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Fig. 8. Comparison of the mean wave power rose in the different seasons among the Chabahar, Kangan and Lenge port for ten years.
4.5. Identifying terminal hotspots and most suitable WEC systems According to the wave conditions acquired in the previous subsections, the wealthiest sites for wave energy harvesting are determined in this part. Afterward, most appropriate WEC systems are suggested for selected hotspots. In terms of selecting the best site for installation of a wave farm, It can be concluded that Chabahar port with the total amount of wave energy of 88.78 MWh=ðm yearÞ in Oman Sea, Kangan port with the total amount of wave energy of 35.78 MWh=ðm yearÞ in
Fig. 9. Comparison of the mean wave power rose in the different seasons among the Kharg, Kish, and Gheshm ports for ten years.
the Persian Gulf and, Kish and Kharg Islands with the total amount of wave energy of 25 and 22 MWh=ðm yearÞ are determined as the most appropriate regions. As far as selecting WEC systems are concerned, it is worth mentioning that WECs are divided into three groups, shoreline, near shore, and offshore, based on applied location [35]. In the case of offshore locations, WEC systems are more complex due to difficulties associated with mooring point, maintenance, and
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Fig. 10. Scatter contours of annual wave energy flux (MWh=ðm yearÞ) corresponded to the different sea states for ten years.
transmitter electrical cables [35]. In the face of economic crisis in Iran, applying these kinds of WECs is not applicable financially. Nearshore devices extract wave energy in the nearshore and transmit it towards onshore facility for generating electricity, and the cost and difficulties of manufacturing, maintenance and transmission are much less than those of offshore devices. In addition, they are usually attached to the seabed, which offers an appropriate condition for oscillating part to work [35]. Considering wave conditions in the current study and according to the [50], the two nearshore devices, Small bottom-referenced heaving buoy (SBHB) and Bottom-referenced submerged heaving buoy
(BSHB), are suitable for the selected hotspots due to the low wave energy potential of the studied regions in comparison with other energetic locations around the word (Table 4). Finally, Shoreline WECs have the merits of the easies installation and maintenance. Beside, these systems do not need deep-water moorings and long underwater electrical cables [35]. Because SDE and U-OWC are ideal for the part of the shorelines where there is a strong wave energy, such as breakwaters, coastal defenses, harbor walls, and rocky shorelines, these systems could also be suitable at Kharg, Kish and Chabahar sites with rocky shorelines and more extreme wave climate [35].
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Table 5 The wave significant height and period range with the maximum annual energy and annual percentage of occurrence of sea states. Site
Orderreferences
H(m)
Wave Energy (MWh/m)
The probability of Occurrence in Year (%)
5.8
24
4
5
5
8
3
24
2.2
4
17
15
12 8.8
10 9
8.8 6 3
9 11 6
T(s) Khark Island
First Second
Kish Island Gheshm Island
First Second
Chabahar Port
First
Kangan Port
Second First Second
Lenge Port
First
4e5 0e2 5e6 1e2 5e6 1e2 4e5 0e1 5e6 1e2 9.5e10 8e8.5 1e2 5e6 1e2 4e5 1e2 5e6 1e2
5. Conclusions The feasibility of wave energy harvesting along the southern coast and islands of Iran was studied in this paper. The wave characteristics such as significant wave height, mean wave period, and wave directions were provided using ECMWF for ten years. The wave data were validated against buoy measurements in two different periods of times namely, 1999 and 2000. According to the annual variations of wave characteristics, Chabahar located in Oman Sea has the high values of significant wave height and wave energy flux, while larak Island (P15) located in Strait of Hormuz has the lowest values of wave height and energy. It is worth mentioning that, the existence of Strait of Hormuz, multiple islands and reduction in the water depth act as a block reducing the wave energy in the Strait of Hormuz and the Persian Gulf. According to the annual variation of wave characteristics, after Chabahar port, Kangan port and Kharg Island have the highest values of wave characteristics, respectively. Other stations including Kish Island, Gheshm Island and Lenge port experience small variations of mean significant wave height and wave energy during the months of the year. According to the wave energy flux rose, the direction of prevailing wave in the coast of Oman is from south due to the connection to the Indian ocean, and the direction of the prevailing wave in the Persian Gulf is changed from west/ northwest in the middle region to west/southwest in the west region because of the northwest wind in the south of Iran. Finally, the different sea states including wave height and period ranges with a maximum value of annual energy and annual occurrence probability at the studied area were reported. The huge bulk of annual wave energy occurs in these sea states which is the key factor in WEC design. In this regard, Chabahar port with the total amount of wave energy of 88.78 MWh=ðm yearÞ in Oman Sea, Kangan port with the total amount of wave energy of 35.78 MWh=ðm yearÞ in the Persian Gulf and, Kish and Kharg Islands with the total amount of wave energy of 25 and 22 MWh=ðm yearÞ are selected as the most appropriate regions for constituting wave energy power plant. Afterward, regarding the wave and shore conditions, the two nearshore devices, SBHB and BSHB, were chosen for all the selected hotspots. In addition to this, SDE and U-OWC systems, which are ideal for the shorelines with stronger wave energy, were also selected for Kharg, Kish and Chabahar sites with rocky shorelines and more extreme wave
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