Marine Current Potential Energy for Environmental Friendly Electricity Generation in Bali, Lombok and Makassar Straits

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1 Environmental Technology and Management Conference 2006 September 7-8, 2006 Bandung, West Java, Indonesia Marine Current Potential Energy for Environmental Friendly Electricity Generation in Bali, Lombok and Makassar Straits Rima Rachmayani a* ; Genia Atma Nagara a ; Totok Suprijo a ; and Nining Sari Ningsih a a Oceanography Study Program, Institut Teknologi Bandung, Bandung, Indonesia Corresponding Author * : rhyme@geoph.itb.ac.id ABSTRACT Application of three-dimensional hydrodynamics model of Princeton University, Princeton., (1977), POM, accommodating diagnostic condition, tides and wind as generating forces has been ulitized to simulate marine current in Bali, Lombok, and Makassar Straits. It has typically been to identify appropriate sites for marine energy extraction and quantify the potential energy available for extraction. In this study, potential current energy in the three straits was estimated for environmental friendly electricity generation by applying Fraenkel equation. Two weeks simulation of horizontally and vertically marine current show that marine current in Bali, Makassar, and Lombok Straits are very strong. Current pattern in Makassar, Bali and Lombok straits show current movement as the same of tide pattern which in return movement. From the results, indicate that the tide current represent the dominant current component have kinetic energy potency for the electric generation. It also indicate that Lombok Strait have current kinetic energy potency larger compared to other straits. Keywords: hydrodynamics, straits, tides, marine current, potential, environmental friendly, energy 1.0 INTRODUCTION In fact the ocean represent an energy resource which is theoritically far larger than the entire human race could possibly use, although most of this huge resource is inaccessible in practice [7]. It also could be exploited to contribute in a sustainable manner to meeting the increasing global energy demand. Recently, Indonesia has been experiencing explosive economic growth and increasing demands for energy. Indonesia is well-endowed with all forms of renewable energy. One of potential ocean renewable energy sources is marine current, caused by tidal effects and thermal and salinity differences [9]. Due to the complex characteristics of marine current and their energy extraction hydrodynamics, the development of technologies to harness this resource requires a great deal of research. Many fundamentals of curent energy are now well understood, but there is no consensus yet over the best technology to exploit the resource. The technology has the potential to play a growing role in the coming decades [2]. Marine current as kinetic energy, can be converted into electric energy or other energy. Energy from marine currents offers the promise of regular and predictable electrical generation at higher power densities than other renewables. The key is a site with a forceful flow of ocean waters. Strong flows tend to occur within straits, between islands, and at entrances to large bays and harbors. In Indonesia, promising locations are indicate from observation for marine current extraction are Bali, Makassar, and Lombok Straits. Hence, the three straits have high potential current energy [4]. Though the straits are potential for potential current energy exploitation, estimation of potential current energy in the straits has not been completely done, through this study, potential current energy in the three straits was estimated for environmental friendly electricity generation. Because of scarce current measurement data and with the development of both computer and numerical methods by means of mathematical equations for solutions of time-dependent flows, numerical simulation has become an 1 of 10

2 economic and effective way to obtain the required flow parameters and to provide a gain insight in the estimation of current potential energy compared to the high cost of performing field observations. Mathematical modeling has been extensively applied in ocean hydrodynamics studies. It gives significant contribution for understanding and prediction of ocean problems that allows developing a rational contingency planning in design/ construction of marine current turbines and environmental acceptability. Therefore, in this paper we address to model marine currents in the straits by using a fully integrated threedimensional hydrodynamic, Princeton Ocean Model (POM), developed by Princeton University., (1977), Princeton and describe the rationale for the development of technology for converting the kinetic energy in marine currents for large scale electricity generation by applying Fraenkel equation. 2.0 METHODOLOGY Simulation of horizontally and vertically marine current in Bali, Makassar, and Lombok Straits was carried out by means of the 3D hydrodynamics model to simulate water circulation in the area and to generate current field as the input for potential current energy estimation by applying Fraenkel equation. The potential current energy estimation was then run to simulate predictable electrical generation (power density) in the area, especially in Bali, Makassar, and Lombok Straits. 2.1 Hydrodynamic Model The hydrodynamic model is described by the conservation laws of momentum and water mass which is represented by the following governing equations after conversion to sigma coordinates: The continuity equation is: DU DV ω = 0 (1) x y σ t Where U, and V are velocity components in x, and y direction respectively; t is time; D = H + η where H ( x, y ) is the bottom topography and η ( x, y) is the surface elevation. Thus, σ ranges from σ =0 at z = η to σ =-1 at z = H The momentum equations are: 2 UD U 2 D UVD Uω gd 0 ρ ' σ ' D ρ ' KM U fvd + gd + σ = F x D x D X t x y σ x ρ σ σ + o σ σ (2) 2 2 ω η gd 0 ρ ' σ ' D ρ ' KM V fud gd σ F y D y σ D σ y σ ρo σ σ VD VUD V D V = + t x y y (3) In equations (2) and (3) contain velocity local gradient, advection, Coriolis parameter, pressure gradient, density gradient, bottom and surface tension, and turbulence terms. Where ρ o is the reference density; ρ is the in situ density; g is the gravitational acceleration; K M is the vertical eddy diffusivity of turbulent momentum mixing; f is the Coriolis parameter; F x and F y represent the terms of horizontal mixing processes; Note that ω is the transformed vertical velocity; physically, ω is the velocity component normal to sigma surface. The transformation to the Cartesian vertical velocity is: D D D W = ω + U σ + + V σ + + σ + (4) x x y y t t The equations contain fast moving external gravity waves and slow moving internal gravity waves. This technique is known as mode splitting with little sacrifice in 3D computational time. There is two technique, external mode and internal mode. External mode equations are obtained by integrating the internal mode equations over the depth. 2 of 10

3 The continuity equation is: DU DV ω = 0 x y σ t Where U and V are velocity components in x, and y direction integrated over the depth. (5) The momentum equations are: 2 U U UV τsx τbx + + fv = g + + A U H t x y x ρod (6) 2 V V UV τsy τby + + fu = g + + A V H t y y y ρod (7) A H is Where τ, sx τ, bx 2.2 Potential Energy Estimation A are surface stress, bottom stress, and turbulence Prandtl number [6]. H An important feature of marine current is their high energy density, which is the highest among the renewable energy sources. The idea of converting the energy of ocean surface waves into useful energy forms is not new [1]. The power, P, in a marine current has a similar dependence as a wind turbine and is governed by the following Fraenkel equation: 1 3 P = AV (8) 2 Where V is velocity magnitude. However, a marine energy converter or turbine can only harness a fraction of this power due to losses and Eq. (8) is modified as follows: 1 3 P ( ) = ρksknav mean ( peak ) (9) 2 ρ is known as density, A is the cross sectional of the flow, Ks is a velocity shape factor (0.424), Kn is a spring- neap factor (0.57) and V is the maximum spring tide velocity [3]. 3.0 MODEL APPLICATION 3.1 Model Area Figure 1 shows the computational domain and bathymetry of Eastern Indonesia water located at 0 o 15' 00" - 10 o 45' 00" S and 114 o 00' 00" o 50' 00" E. The model area comprises Bali, Makassar and Lombok Straits. It was simulated in the model using horizontally finite difference mesh of 359 x 680 grid squares, equally spaced at 1830 m (1 ) interval, and vertical grid of 10 σ-levels ( σ =0.1). 3.2 Simulation Design The main forcing for the model is tidal elevation, which is imposed at the open sea boundaries and is obtained by carrying out tidal prediction based on 8 tidal constituents (M 2, S 2, N 2, K 2, K 1, O 1, P 1, and Q 1 ) published by the Ocean Research Institute, University of Tokyo. In addition to the tidal elevation data, initial data of climate (surface wind) from satellite data which published by US-NCEP (United States-National Centers for Environmental Prediction) were supplied to the model in order to realistically compute water circulation. Wyrtki (1961) [8] have reported that Indonesia is perfect area in responses to seasonal changes of the monsoon mechanism, which generally plays an important role in the Indonesian coastal ocean circulation as in Java, Flores and Banda Sea. Beside that, strong flows tend to occur within straits, between islands, and at 3 of 10

4 entrances to large bays and harbors as in Bali, Makassar, and Lombok Straits (Figure 2). Hence, the three straits have high potential current energy [4] Verification :Balikpapan Makassar Strait Lombok Strait Bali Strait Figure 1. Computational domain and bathymetry of Eastern Indonesia water Figure 2. Surface currents in August (Wyrtki, 1961) 4.0 RESULTS AND DISCUSSION 4.1 Model Verification Hydrodynamic Model For model verification, the simulated water surface elevation is compared to that of field measurements at Balikpapan (marked in Figure 1), which is carried out by Admiralty Method prediction based on 8 tidal constituents (M 2, S 2, N 2, K 2, K 1, O 1, P 1, and Q 1 ). The verification results of water elevation at that place can be seen in Figure 3. From the figure, it is shown that the model predicts the free surface elevation quite well, mainly for the tidal phases, but the amplitude smaller in the order of less than 0.15 m. 4 of 10

5 BALIKPAPAN (01-16 FEBRUARI 2004) 1,5 1 0, ,5-1 -1,5 TIME ( ho urs ) Admiralty Method Prediction Simulation Figure 3a. Tide Verification in Balikpapan 4.2 Simulation Results Surface Water Circulation Pattern Figure 6 shows tide driven circulation at depth of 15 m for spring flood and ebb condition in February, respectively. Tidal elevation at Balikpapan (marked in Figure 1) was chosen as the reference time of the flood and ebb condition. The figure clearly shows the existence of currents that flow back and forth representing flood and ebb conditions. At spring flood condition (Figures 6a and 6b) they flow into Makassar Strait into Java Sea and straight away into Hindia through Lombok Strait. Otherwise, through Bali strait they move from West Hindia to Java Sea. Consequently, one can observe that at spring condition there is an increase of the magnitude of the currents in February compared to that at ebb condition. It showed on Table 1, Table 2 and Table 3 for the three straits. = m/s > m/s > m/s KONDISI PASUT PURNAMA SPRING TIME (a) = m/s > m/s > m/s KONDISI PASUT PURNAMA SPRING TIME (b) Figure 6. Tide driven circulation for spring (a) flood (b) max flood The current coming from Pacific into the Northern Java Sea through Makassar Strait at spring ebb condition (figures 6c and 6d). In Bali Strait the current flow from Java Sea into Hindia, meanwhile it moves from Hindia to Java Sea in Lombok Strait. 5 of 10

6 = m/s > m/s > m/s KONDISI PASUT PURNAMA SPRING TIME (c) = m/s > m/s > m/s KONDISI PASUT PURNAMA SPRING TIME (d) Figure 6. Tide driven circulation for spring (c) ebb (d) min ebb Wind driven circulation at the same depth, tide condition shows that at spring flood the current move into Pacific from Java Sea, in Bali and Lombok Straits current movement directly into Hindia. At spring ebb the current move coming from Pacific into Java Sea, and direct to the Hindia in Bali Strait. The magnitude of the currents is smaller than magnitude of tide driven current. Current pattern in Makassar, Bali and Lombok straits show current movement as the same of tide pattern which in return movement. First scenario with the tide generating force simulation shows tidal current magnitude in Makassar strait m/sec, in Bali strait m/s, in Lombok strait m/sec. Second scenario, with the tide and wind generating forces simulation, shows marine current magnitude in Makassar Strait m/sec, in Bali strait m/s, in Lombok strait m/sec. Tidal Condition Table.1 Tide driven magnitude in Makassar Strait Average Depth 15 M Depth 25 M Depth 35 M Depth 45 M Depth SPS PPS PSS SSS SPN PPN PSN SSN of 10

7 Tidal Condition Average Depth Table.2 Tide driven magnitude in Bali Strait 15 M Depth 25 M Depth 35 M Depth 45 M Depth SPS PPS PSS SSS SPN PPN PSN SSN Tidal Condition Table.3 Tide driven magnitude in Lombok Strait Average Depth 15 M Depth 25 M Depth 35 M Depth 45 M Depth SPS PPS PSS SSS SPN PPN PSN SSN Tidal Condition : SPS = Flood at Spring (135 hour simulation) PPS = Max flood at Spring (138 hour simulation) PSS = Ebb at Spring (141 hour simulation) SSS= Min ebb at Spring (144 hour simulation) SPN = Flood at Neap (294 hour simulation) PPN = Max flood at Neap (299 hour simulation) PSN = Ebb at Neap (308 hour simulation) SSN = Min ebb at Neap (314 hour simulation) Power Density From the Figure 7, indicate that the tide current represent the dominant current component have kinetic energy potency for the electric generation, one can see obviously that the area of high power density (red colour) is more wide in Lombok Strait (zone 3) than the other straits. Two weeks simulation of power density distribution shows that the power density seems to spread farthest in spring time and reach minimum distance of distribution in neap time. The magnitude of the currents during spring tide is stronger than during the neap one and as a consequence it results in the highest power density. Hence, the power density during spring tide is higher than during the neap one. By using Peter Fraenkel converter formula, is calculated energy potency in third straits based on tide dominant current magnitude. Figure 7(a) and (b) presents a potential energy at depth of 15 m for the tide driven for spring and neap tide condition, respectively. Energy which possible extracted in Makassar Strait is kwh/m 2 Bali strait kwh/m 2, in Lombok strait kwh/m 2. Table 4, 5, and 6 shows a complete potential energy which possible extracted in Makassar, Bali, and Lombok Straits. 7 of 10

8 Zone 1 Zone 1 Zone 2 Zone 3 Zone 2 Zone Figure 7. Power Density Makassar, Bali, and Lombok Straits at (a) Spring (b) Neap (c) (d) Figure 7. Power Density in Lombok Straits (Zone 3) at (c) Spring (d) Neap 8 of 10

9 Table 4. Potential Power Density in Zone 1 (Makassar Strait) Power Density Tide Driven Wind Driven Simulation (kwh/m 2 Neap Neap ) Spring Tide Spring Tide Tide Tide Average Depth M Depth M Depth M Depth M Depth Table5. Potential Power Density in Zone 2 (Bali Strait) Power Density Tide Driven Wind Driven Simulation (kwh/m 2 ) Neap Neap Spring Tide Spring Tide Tide Tide Average Depth M Depth M Depth M Depth M Depth Table 6. Potential Power Density in Zone 3 (Lombok Strait) Power Density Simulation Tide Driven Wind Driven (kwh/m 2 ) Spring Tide Neap Tide Spring Tide Neap Tide Average Depth M Depth M Depth M Depth M Depth From figure 7(c) and 7(d), the largest possible extracted energy in Lombok Strait, is kwh/m 2 in 15 m depth and smaller potency obtained in Makassar Strait and Bali Strait at the surface, with the possible energy extracted for each strait equal to ± 9.74 and kwh/m ENVIRONMENTAL CONSIDERATION Environmental considerations play an important part in the siting, design, construction, operation and public acceptability of all major energy developments. At the present time, since this is still new technology and no comparable facilities are in place anywhere, there is no directly applicable, practical experience upon which to base an assessment of the environmental and socioeconomic impacts [5]. Excerpt of Triton Consultants Ltd., 2002 [5]: Tidal current power plant of electricity generation does not result in any discharges or emissions and would therefore make no contribution to the problems of air pollution or global climate change. Such a demonstration unit would provide a much-needed opportunity to assess this technology and its environmental effects especially those related to fish and marine mammal impacts, marine traffic, and marine pollution as the direct effects. 6.0 CONCLUSIONS The 3D hydrodynamics called POM and Fraenkel equation has been applied to estimate potential current energy in Makassar, Bali and Lombok Straits. 9 of 10

10 The application of the model to the three straits show that tides and wind are the main causes of variations of power density in this area. At spring tide, the power density is higher that that during the neap one due to the stronger current. Two weeks simulation of power density distribution shows that the power density seems to spread farthest in spring time and reach minimum distance of distribution in neap time. It also indicates that Lombok Strait is the largest possible extracted energy and one of promising location in Indonesia which have high potential current energy. ACKNOWLEDGEMENTS We gratefully acknowledge the support from the LPPM for funding this research under grants of ITB Research. REFERENCES [1] Bahaj AS, Myers LE. Analytical Estimates of the Energy Yield Potential from the Alderney Race (Channel Island) Using Marine Current Energy Converter. Renewable Energy 2004 ; [2] Boud, R., Status and Research And Development Priorities, Wave And Marine Current Energy, Future Energy Solutions, Part Of Aea Technology Plc, [3] Fraenkel, P., Power from Marine Currents, Marine Currents Turbines Ltd., 1999 [4] Hadi.et.al, Research of Mapping ofnon-conventional Resource, LAPI-ITB, Bandung, 2001 [5] Hydro, B.C., Green Energy Study for British Columbia, Vancouver, 2002 [6] Mellor, G.L., Users Guide for a Three Dimensional, Primitive Equation, Numerical Ocean Model, Princeton Univrsity, Princeton, [7] Melville, G.T., Rados,K., Bryden, I.G., Model to Optimise the Electrical and Economic Perfomance of Tidal Current Energy Conversion Systems published in the proceedings of Marine Renewable Energy Conference (MAREC) 2001, University of Newcastle. (2001) [8] Wyrtki, K., Physical Oceanography of the Southest Asian Waters, California, 1961 [9] 1992 Ambassadors Tour : Energy Conservation & Renewable Energy, U.S-ASEAN Council for Business and Technology, Inc., of 10