WAVE ENERGY POTENTIAL IN THE SEA OF MENTAWAI

Thematic Session “Geoscience for energy transition in East and Southeast Asia” 58th CCOP Annual Session, Bandung, Indonesia, 11th October 2022 WAVE ENERGY POTENTIAL IN THE SEA OF MENTAWAI Irwan H. Suherman1 , P. Hadi Wijaya1, Ai Yuningsih1, Dida Kusnida2, Purnomo Raharjo1, Deny Setiady1 1 Marine Geological Institute (MGI) Ministry of Energy and Mineral Resources of Indonesia Jl. Dr. Djunjunan No. 236 Bandung, Indonesia 2 National Research and Innovation Agency of Indonesia JL. Sangkuriang, Kompleks LIPI, 40135, Dago, Bandung, West Java 40135 Corresponding author: [email protected] Abstract The National Electricity Provider Business Plan (RUPTL) 2020–2029 launched a renewable energy generation mix of 23% by 2025 to meet the national electrification ratio target. One location that has ocean renewable energy potency with a low electrification ratio (ER) is Mentawai Islands Regency, West Sumatra, where ER is still 74% (Directorate of Electricity, 2019) and at least 22 villages in the 12 sub-districts that are included in the action plan program (National Electricity Company (PLN), 2018). Western Sumatra waters have a wave energy potential of up to 20 kW/m (Cornett, 2008). Based on annual significant wave height occurance, the significant wave height (Hs) is in the range of 1.5–2.5 meters with an incident frequency of 75% and a wave power potential (occurrence frequency of 35%) is in the range of 16–20 kW/m taking into account monthly and seasonal variability in the interested area at Pasakiat Teileleu, Siberut (PKST). The calculation of wave energy potential assessed uses averaged wave modeling for the ten-year period, taking into account yearly and monsoon variability. From the equation of the calculation of wave energy potency, the average annual wave power is around 8–16 kW/m. The change in monthly average wave power for 10 years (2008–2018) is calculated by referring to AVISO satellite data at coordinates 040-010 S and 980–1010 E within 10x10 spatial resolution with 1 minute resolution GEBCO bathymetry data. From the modeling results, the potential power in the East Monsoon (June-July-August) and the Second Transition Monsoon (September-October-November) reached up to 17 kW/m in the site area. The verification result of the wave model against the altimetry data showed a correlation level of up to 76.23%. The results of the average power generated in the PKST model in the seasons northwest, transition I, southeast, and transition II are 7.48, 10.51, 15.78, and 16.15 (kW/m) respectively, with a maximum power of 16.70, 12.82, 19.06, and 18.52 (kW/m) respectively. From several other locations (Village) in the Mentawai waters in accordance with the low electrification ratio (ER) demand area that produce mean yearly wave potential power where able to be implemented include Madobag & Matotonan (14.06 kW/m), Sagulubbek & Simatalu (19.5 kW/m), Betumonga (18.43 kW/m), Berilou (16.95 kW/m), Silabu (18.25 kW/m), Malakopa (18.67 kW/m), Sigapokna (9.65 kW/), Bosua (11.8 kW/m) and Bulasat (14.81 kW/m). Keywords: Wave Energy, Mentawai, Renewable Energy, Wave Power Potential Model 1 Thematic Session “Geoscience for energy transition in East and Southeast Asia” 58th CCOP Annual Session, Bandung, Indonesia, 11th October 2022 INTRODUCTION To support sustainable national development and energy security, renewable energy resources are one of the most important sources of driving economic growth because they are very much needed by every element of society (Constitution No. 30 Year 2007). Therefore, limited energy resources will be an obstacle that can hinder the pace of economic growth in the future. The steps taken by the government to anticipate energy scarcity/crisis in Indonesia include the National Energy Policy (KEN), Constitution No. 30 Year 2009, and the National Marine Exploitation Policy, which emphasizes energy sustainability through the creation and utilization of renewable energy sources. In PP KEN 2014, the energy mix will be optimized so that in 2025 the composition of energy is expected to be 23% of the new renewable energy sector (Figure 1). One of the renewable energies that is currently developing is marine energy. Several technologies are currently in the development stage to improve the performance of power plants sourced from wave energy (Lopez et al., 2013). The policy of the Ministry of Energy and Mineral Resources (MEMR) in responding to national issues regarding energy with energy diversification is to diversify the supply and use of various new energy sources, one of which is marine energy sources that can be utilized as power plants based on ocean wave energy. From this perspective, in the next few decades, ocean wave energy is expected to generate at least 10% of global energy demand (Silva et al., 2016). Figure 1. Energy mix achievement targets in 2025. The Mentawai Islands are one of the regencies in West Sumatra Province, which is located opposite the Indian Ocean with a recorded area of 6,011.35 km2 and a coastline of 1,402.66 km. Its existence as a leading island in the territory of the Republic of Indonesia makes it a strategic area for national security defense. Geographically, the Mentawai Islands are located in West Sumatra Province, which is located at the coordinates of 98°35'00"– 100°32'00" East Longitude and 0°55'00"– 3°21'00" South Latitude. The Mentawai Islands Regency consists of four large islands plus small islands. These four major islands are Siberut Island, Sipora Island, North Pagai Island, and South Pagai Island. The Mentawai Islands, West Sumatra, still do not have electricity. Of the 43 villages in the Mentawai Islands Regency, 23 villages are not yet connected to the PLN grid. The Mentawai electrification ratio is the lowest among all regions in West Sumatra, at only around 66.0% (Bisnis.com, 2019). According to data from the Directorate General of Electricity, MEMR, it is stated that the potential demand for electricity in West Sumatra Province, one of which is the Mentawai Islands, has unfulfilled electricity 2 Thematic Session “Geoscience for energy transition in East and Southeast Asia” 58th CCOP Annual Session, Bandung, Indonesia, 11th October 2022 needs in seven sub-districts, including South Pagai, North Pagai, South Sipora, Sipora, North, Southwest Siberut, Central Siberut, and North Siberut. Meanwhile, there are seven villages that have low electrification, including Bulasat, Sinaka, Malakopa, Mara, Pasakiat Teileleu, Saibi Samukop, and Sirilogui (Figure 2). According to National Electricity Company (PLN) data, on Siberut Island, 8 villages are electrified, while 12 other villages are not yet connected to electricity. On other islands, such as Pagai (Sikakap) and seven other villages, there is no PLN electricity network. Figure 2. The location of the Mentawai Islands Regency, West Sumatra Province, which is not yet fully electrified (Directorate General of Electricity ESDM, 2017). MATERIALS AND METHOD The study site was selected as one of the areas that has wave energy potential along the west coast of Sumatra, with an average wave energy flux estimated to reach 20–30 kW/m (Cornett et al., 2008). The waters between Asia and Australia and the Pacific and Indian Oceans are positions of waters with a geographically specific structure (Wrytki, 1961). This approach is based on a comparison between numerical predictions and the measurement results of significant heights and peak periods. The Mentawai Islands' western waters are used for the Domain area. Secondary bathymetric data were obtained from GEBCO (Global Bathymetric Chart of Oceans) with 1 minute resolution (Figure 3). Figure 3. Bathymetry of the Mentawai waters of West Sumatra. The secondary wave data is obtained from AVISO satellite data. The period of satellite data used as verification starts from September 14, 2009 to May 19, 2018 (9 years) with a spatial resolution of 10x10 (Figure 4). Wind data was obtained from the NCDC satellite at the Tabing Padang location, West Sumatra, which was compiled with reference to the J-OCE Undip (Dewi et al., 2017), which processed wind data for 10 years (2006–2015) from the BMKG Tabing Padang, which was converted into wave data which was then modeled using these assumptions. A. Study Description From the measurement data at coordinates 01° 33' 20.0" South Latitude and 99° 12' 32.8" East Longitude at a depth of 10 meters, which was carried out from August 9 to September 3, 2015 in the waters of Siberut Island, and which was compiled with secondary wave data from the AVISO 3 Thematic Session “Geoscience for energy transition in East and Southeast Asia” 58th CCOP Annual Session, Bandung, Indonesia, 11th October 2022 altimetry satellite, which was taken from September 14, 2009 until May 19, 2018 (9 years) in Mentawai waters at coordinates 04°-01° South Latitude and 98°-101° East Longitude, significant wave height and period data were obtained for each season. The wave height and period data are then sorted to obtain representative wave data as presented in Table 1. Figure 4. Secondary wave data in Mentawai waters (Source: AVISO Altimetry Sattelite). Table 1. Representative Waves of Predicted Seasonal Waves (Dewi et al., 2017) and wave acquisition data (MGI, 2020) 24.38 km from shore to offshore (Figure 5). In the open boundary, the processed wave data is used as input, including significant height (Hs), average period (Te), wave direction ( 0 ) and wave distribution direction (  ). The model domain boundary consists of 3 sides (southeast, southwest and northwest). Simulations are carried out with the assumption of 1 year, namely the simulation of the northwest monsoon (DJF), transitional season 1 (MAM), southeast season (JJA), and transitional season 2 (SON). The basic Manning friction coefficient is 32 m1/3/s and the Smagorinsky horizontal diffusivity is 0.28, and the quadraplet wave coefficient is 0.25. C. Calculation of Wave Energy Potential Calculation of wave energy potential is the basis for planning the use of wave converter technology design (Falcao, 2009). Figure 5. Location area domain Pasakiat Teileleu, Mentawai waters, West Sumatra. B. Model Setup The model area is discretized with the largest grid of 5000 m2 consisting of 93 nodes and 147 elements with a distance of Calculation of wave electric power using the equation as a variable function of the wave parameters. Estimation of electrical power resulting from the conversion of ocean wave energy is carried out using the following equation (Holthuijsen et al., 2007): 4 Thematic Session “Geoscience for energy transition in East and Southeast Asia” 58th CCOP Annual Session, Bandung, Indonesia, 11th October 2022 g2 2 kW   H m 0Te   0.5 3  H m2 0Te , 64 m .s   where: P = Electrical power per unit wavelength (W/m)  = Water density (1025 kg/m3) g = Gravitational acceleration (m/s2) H m 0 = Significant wave height (meter) P Te = Wave periode (second) In the wave model, the calculation is used at each node of the grid domain area model so as to produce a lateral distribution of wave power (P). RESULT AND DISCUSSION A. Comparison with Point Data Wave Model Verification is obtained in the form of seasonal patterns in Mentawai waters. In the northwest monsoon, the maximum significant height (Hs) obtained is 2.08 meters, while the wave peak period (Tp) is 8.22 seconds, while the average wave height (Hmean) is 1.17 meters, a standard deviation of wave direction (DirStDev) of 17.82, and an average wave power (P) of 7.48 kW/m. The wave modeling was verified against the basic statistics calculated based on the significant Hs height at the selected location points based on altimetry satellite data (99°East, 2°South). From the results of statistical calculations at the measurement point, an overall correlation of 76.23% is obtained (Figure 6). From the results of the modeling of the distribution of significant height, it can be seen that areas that have large significant wave heights are in the seasons northwest, southwest, and 2nd transition with values reaching more than 2 meters in the western region of Siberut Island, Mentawai waters. The validation results show that the significant high value of the modeling results is greater than the altimetry data. This is because the significant field height (Hs) which is simulated using SMB data is 1,959 from the altimetry data obtained (Muliati, Y., et al., 2016). Therefore, the analysis for modeling results is focused on that location. Figure 6. Comparison graph of Hs simulation model against altimetry satellites based on seasonality throughout the year. B. Regional Wave Power Assessment The wave energy pattern in the western Sumatera waters, including Mentawai and Enggano Island, is shown in the annual average wave power for 4 seasons with 147 grid cells distribution of wave parameters, Hs in the waters along the coast of Sumatera, especially in Mentawai and wave power around the location of the model area which changes with space and time (Figure 7). C. Local Wave Power Analysis The greatest wave power occurs in the waters of Pasakiat Teileleu, which is 15 5 Thematic Session “Geoscience for energy transition in East and Southeast Asia” 58th CCOP Annual Session, Bandung, Indonesia, 11th October 2022 Figure 7 Predicted average of wave power (P) for 10 years (2008-2018) 6 Thematic Session “Geoscience for energy transition in East and Southeast Asia” 58th CCOP Annual Session, Bandung, Indonesia, 11th October 2022 kW/m. The average wave power decreased from 36 kW/m in deep water and when entering the shallow waters of Pasakiat Teileleu to 4 kW/m. The spatial variability dissipation results in 8-15 kW/m in shallow water, with a decrease below 10 kW/m in the area behind Siberut Island. The results of the comparison of modeling to altimetry have a correlation of 67.78%. In the first transition season the Hs value is 1.85 meters, Tp is 7.64 seconds. Meanwhile, the average wave height (Hmean) is 1.66 meters, with P 10.51 kW/m. The results of the comparison of model simulation to altimetry have a correlation of 76.33%. In the southeast monsoon the Hs value is 2.16 meters, while the Tp is 8.32 seconds, and the average wave height (Hmean) is 1.94 meters with P 15.78 kW/m. The results of model validation on altimetry have a correlation of 84.20%. In the second transition season, Hs is 2.13 meters, while Tp is 8.31 seconds, with an average wave height (Hmean) of 1.98 meters, P value is 16.15 kW/m. The results of model validation on altimetry have a correlation of 76.60%. The west coast of Sumatra has an average wave energy flux ranging from 20-30 kW/m based on a global scale model with a period of 10 years, namely from 1997-2006 (Mark, et. al., 2010). The same thing was stated by Magagna and Andreas, 2008, that the western waters of Sumatra have the potential for wave energy ranging from 20-30 kW/m. This becomes a reference in calculating the time and space variability, and wave climate. Further research is related to the spatial and temporal variability of wave power in Mentawai waters. Monthly changes in wave power in the western waters of Siberut Island for 10 years indicate a difference between energy during the west and east monsoons (Figure 8). Figure 8. Prediction of mean wave power (P) in annual kW/m (top left) northwest monsoon, (top right) transitional season I, (bottom left) southeast monsoon, and (bottom right) transitional season II in Pasakiat Teileleu in the period 2009-2018. The change in seasonal power in the west of Siberut is the difference in energy during the west and east monsoons which results in conditions with different energies in these months (Figure 9). From November to March, the resulting wave power is 10 kW/m with the largest value reaching 18 kW/m in August to September. In the quiet month period, values below 10 kW/m occur in February and May. The time series of the mean monthly wave power in the Siberut west area domain accurately identifies the annual variability of the wave energy flux in the waters west of Siberut Island (Figure 10). The wave flux energy experiences a dominant annual variation throughout the month for 10 years. The period that 7 Thematic Session “Geoscience for energy transition in East and Southeast Asia” 58th CCOP Annual Session, Bandung, Indonesia, 11th October 2022 produced the most energy was in July 2014 with an average wave power of 38 kW/m. waters of the Indian Ocean. However, the seconds. Thus, the resulting wave power is estimated to be only 1-2 kW/m because the Figure 10. Annual time series of predictions of overall wave power in the western waters of the Mentawai (Siberut). Figure 9. Monthly average wave power in the western waters of the Mentawai (Siberut) in June, July, and August 2014 and 2017. D. Inter-Annual and Inter-Seasonal Variabilities The propagation of waves towards the coast affects changes in the value of the energy potential caused by local mechanism factors such as energy dissipation (Vannucchi et. al, 2016). Referring to the morphology of Pasakiat Teileleu, it is not recommended for four locations (Sirilogui, Saibi Samukop, Mara, and Sinaka). Geographically, the area does not have significant wave energy potential. The wave energy potential in the western region of Siberut Island (Sirilogui and Saibi Samukop) is relatively small, with a height of significant wave height (SWH) less than 0.8 meters and a period of 4.56 area is not in direct contact with the open area is close to the Muara Siberut PLN grid with a distance of about 1.2 km. This area is the same as the previous location, with the minimum number of local residents living far from the coast and a considerable distance to the PLN Sikakap grid. There are 4 seasons that represent the distribution of wave power. The wave height between 1.5 – 2.5 meters is more than 75% of the number of events with a fairly constant period between 7.79 – 8.30 seconds during the year so that it affects the maximum value of the wave flux power (Figure 11). From the simulation results in table 2 below, the exact coordinates for installing a wave power plant are in the second simulation (Site-2) at the Pasakiat Teileleu location, with an average wave power of around 10.7 kW/m to 15 kW/m. In comparison, waves with a height of between (0.5 – 1.5 m) can produce 25% of occurrences during one year with a rated power of between 0.1 – 9 kW/m. The 8 Thematic Session “Geoscience for energy transition in East and Southeast Asia” 58th CCOP Annual Session, Bandung, Indonesia, 11th October 2022 Table 2. Location, depth, distance to shoreline and average wave energy flux calculated for 2006-2015 in four seasons. distribution of the direction of the wave arrival represents the variability associated with the shoaling process in shallow waters such as depth, refractive currents and dissipation caused by bottom friction and breaking waves. Maximum wave energy is generated from the southeast and south directions, with wave power exceeding 1620 kW/m. At this location, more than 20% of the wave energy is produced at less than 10 kW/m. This area is formed by the intermediate density of wave energy with the direction of the wave incident producing values in excess of 16 kW/m for more than 30% of occurrences. The PKST power model is calculated based on the relationship between the significant height variable function ( H m 0 ) and the wave period ( Te ) (Figure 12). Figure 11 Predicted percentage of significant wave height (Hs) and mean Power Density (P) at PKST model locations. The power flux graph varies according to the period pattern and the wave height is significant because the relationship is linear. The average power generated in the PKST model in the northwest, transition I, southeast, and transition II seasons is 7.48, 10.51, 15.78, and 16.15 (kW/m) respectively, with a maximum power of 16.7, 12.82, respectively. , 19.06, and 18.52 (kW/m). Figure 12 The relationship between the PKST wave power potential equation in the northwest monsoon; 1st transitional; southeast monsoon; and 2nd transitional. CONCLUSIONS The waters of the western Mentawai produce energy with an average wave power of about 20 kW/m for a certain period. Wave prediction produces annual and seasonal variability of wave power in a particular season which is analyzed in four seasons with the largest average resulting from significant variability in height and wave direction. Meanwhile, on the west coast, Pasakiat Teileleu represents maximum energy (>16 kW/m). The wave model gives good results for wave fluxes with a potential of up to 20 kW/m. In addition, a Feasibility Study is needed to analyze the technical carrying capacity factor to the calculation of the economic value of each appropriate Wave Energy Conversion (WEC) Technology in the site of Mentawai. 9 ACKNOWLEDGMENT The authors are particularly grateful to the Head of Marine Geological Survey and Mapping (BBSPGL), Geology Agency, Ministry of Energy and Mineral Resources for his permission to conduct a study of the potential for wave energy in the Mentawai, West Sumatra. As a result, we are extremely grateful to all renewable energy business partners for providing any support for the promising future energy. And as well, we are very proud of PLN, Directorate General of Electricity, Directorate General of New and Renewable Energy & Energy Conservation, and all the technical data providers to support this research. This study was carried out in collaboration between the World Bank-MEMR in 2018, as well as BBSPGL colleagues and all parties who have assisted in writing this paper. REFERENCES Cornett, A.M., 2008. A Global Wave Energi Resource Assesement. Proceeding of the 18th International Offshore and Polar Engineering Conference. Vancouver. Dewi, A., Purwanto, Sugianto, D.N., 2017. Analisis Deformasi Gelombang di Pulau Siberut Kabupaten Kepulauan Mentawai Sumatera Barat, vol 6, No. 2, hal 330 – 340. Departemen Oseanografi, Universitas Diponegoro. Falcao, A.F.O., 2009. Wave energi utilisation: a review of the technologies, Renewable and Sustainable Energi Reviews, vol. 14, pp. 901. Holthuijsen, L.H., 2007. Waves in Oceanic and Coatal Waters, Cambridge, Cambridge University Press. ISBN 978-0-521-86028-4. Lopez, I., Andreu, J., Ceballos, S., Alegria, I. M., and Kortabaria, I., 2013. Review of Wave Energy Technologies and The Necessary Power Equipment, Renewable and Sustainable Energy Reviews, vol. 27, pp. 413-433. Magagna and Andreas, 2014. JRC Ocean Energi Status Report - Technology, market and economic aspects of ocean energy in Europe, Report EUR 26983 EN, European Commission. Mark, G., Bartsow, S., Kabuth, A., Pontes, T., 2010. Assessing the Global Wave Energi Potential. Paper presented at the 29th International Conference on Ocean, Offshore mechanics and Artics Engineering, Shanghai. Muliati, Y., Wurjanto, A., Pranowo, W., S., 2016. Validation of Altimeter Significant Wave Height Using Wave Gauge Measurement in Pacitan Coastal Waters East Java Indonesia, IJAER vol. 12, p. 23, India. Silva, D., Rusu, E., and Soares, C., G., 2016. High Resolution Wave Energy Assessment in Shallow Water Accounting for Tides, Energies MDPI Journal, p.1. Vannucchi, V., Cappietti, L., 2016. Wave Energy Assessment and Performance Estimation of State of the Art Wave Energy Converters in Italian Hotspots, Sustainability, p.5, University of Florence, Italy. Wyrtki, K., 1961. The flow of water into the deep sea of the western south Pasific Ocean, Aust. J. Mar. Freshw. Res., 12 (1), 1 - 16. 10