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Tidal Current Energy by Kadir Orhan
Journal of Marine Science and Engineering (ISSN 2077-1312), 2020
The Strait of Larantuka, with highly energetic tidal stream currents reaching speeds of up to 3-4... more The Strait of Larantuka, with highly energetic tidal stream currents reaching speeds of up to 3-4 m/s, is a promising site for renewable electricity production from the ocean. This paper presents the results of an assessment regarding the potential hydrodynamic impacts, wake characteristics, and the performances of large scale turbine arrays in the strait. A high-resolution, three-dimensional baroclinic model is developed using the FLOW module of the Delft3D modeling system to simulate tidal currents. The energy of currents is assumed to be extracted by horizontal-axis tidal turbines, which can harness strong bi-directional flow, positioned on sequential rows and alternating downstream arrangements. Enhanced momentum sinks are used to represent the influence of energy extraction by the tidal turbines. Four different array layouts with rated capacities of up to 35 MW are considered. We find that, in the Strait of Larantuka, array layout significantly affects the flow conditions and the power output, mainly due to the geometric blockage effect of the bounded channel. With respect to undisturbed flow conditions in the strait, decreases in current speeds of up to about 0.6 m/s, alongside increases in the order of 80% near-shore are observed. While operating efficiency rates of turbines reaching around 50%-60% resulted during the spring tide in the arrays with smaller rated capacities, the power output of the devices was negligible during the neap tide.
Energy Procedia, 2017
In this paper, results of a tidal stream resource assessment performed for the Strait of Larantuk... more In this paper, results of a tidal stream resource assessment performed for the Strait of Larantuka, Indonesia are presented. The methodology followed is comprising of the estimates of power yield and evaluation of the effects of power extraction via high-resolution, three-dimensional flow models. Power densities exceeding 10kW/m2 are observed in the main channel. Current velocities, and wake characteristics of the turbines have been resolved reasonably well with low computational cost, considering different levels of energy dissipation. Although the results are promising, investigations using in-situ measurements alongside more advanced modelling techniques are still needed, and currently underway.
E-proceedings of the 38th IAHR World Congress, 2019
In this paper, the results of a numerical model study evaluating the influence of density-induced... more In this paper, the results of a numerical model study evaluating the influence of density-induced flow on tidal stream power generation in the Sunda Strait, Indonesia are summarized. Tidal stream currents with speeds reaching about 2-3m/s and total extractable power of around 300MW turn the Sunda Strait into a promising location for renewable electricity production from the ocean. Furthermore, seasonally varying share of the density currents on the energy flux through the Sunda Strait emphasize the importance of a more comprehensive modelling approach for the selection and evaluation of the deployment sites of tidal turbines. A high-resolution, three-dimensional circulation model providing sufficient spatiotemporal coverage has been developed to simulate tidal currents in barotropic and baroclinic modes. Simulation outputs have been used to reveal the influence of density-induced flow on tidal stream power generation during both northwest and southeast monsoonal seasons. Up to 100% increase in current speeds has been simulated in the strait due to the density gradients, which leads to an enormous increase of the kinetic power. Additionally, energy hotspot shows significant changes due to the variations in density. Energetic section of the strait becomes significantly larger with an overall increase of the kinetic power densities. The findings may help us to understand the importance of including the ocean water density to resolve flow fields with better precision, which can lead to more accurate assessment and more efficient use of the resources of marine renewable energy.
Coastal Engineering Proceedings, 2017
In this paper, an advanced methodology developed for the assessment of tidal stream resources is ... more In this paper, an advanced methodology developed for the assessment of tidal stream resources is applied to several straits between Indian Ocean and inner Indonesian seas. Due to the high current velocities up to 3-4 m/s, the straits are particularly promising for the efficient generation of electric power. Tidal stream power potentials are evaluated on the basis of calibrated and validated high-resolution, three-dimensional numerical models. It was found that the straits under investigation have tremendous potential for the development of renewable energy production. Suitable locations for the installation of the turbines are identified in all the straits, and sites have been ranked based on the level of power density. Maximum power densities are observed in the Bali Strait, exceeding around 10kw/m2. Horizontal axis tidal turbines with a cut-in velocity of 1m/s are considered in the estimations. The highest total extractable power resulted equal to about 1,260MW in the Strait of Alas. Preliminary assessments showed that the power production at the straits under investigation is likely to exceed previous predictions reaching around 5,000MW.
8. Kıyı Mühendisliği Sempozyumu, 2014
Bir Almanya-Endonezya ortak projesi olan “Ocean Renewable Energy ORE-12” kapsamında Endonezya’dak... more Bir Almanya-Endonezya ortak projesi olan “Ocean Renewable Energy ORE-12” kapsamında Endonezya’daki okyanus alanları incelenip dalgalar ve gelgit akıntıları üzerinden yüksek verimle enerji üretimi yapılabilecek bölgeler saptanmaya çalışılmaktadır. Proje neticesinde bir karar destek sistemi (DSS), oluşturulması planlanmaktadır. Bu sistem kapsamında yenilenebilir enerji kaynaklarının tespiti için stratejiler; entegre bir coğrafi bilgi sistemi veri tabanı; data işleme ve görüntüleme sistemleri; akıntı, dalga, sediment taşınımı ve morfodinamik özelliklerin değişiminin belirlenmesi için nümerik modeller ve seçilen bölgelerdeki enerji potansiyellerinin hesaplanmasına yönelik araçlar oluşturulması hedeflenmektedir. Bunların yanında bölge kaynaklarının enerji üretiminde kullanılmasının yaratacağı çevresel etkinin de değerlendirilmesine yönelik bir çalışma yapılacaktır. Bu çalışmada ORE-12 projesinin metodolojisi hakkında bilgi verilmiştir. Ayrıca başlangıç aşamasında kurulan nümerik modellerin sonuçları sunulmuştur.
EGU ABSTRACTS by Kadir Orhan
Anthropogenic climate change requires an effective and appropriate response, with a view to accel... more Anthropogenic climate change requires an effective and appropriate response, with a view to accelerating the reduction of global greenhouse gas emissions. The ocean provides a vast source of potential energy resources, which can be utilized without inflicting any considerable damage to the global ecosystem. To this end, the conversion of tidal current power is recently growing up to a crucial sector of the ocean renewable energy. Previously, tidal stream resources of several straits between the Indian Ocean and inner Indonesian seas have been investigated, and results have revealed that tidal current power potential of Indonesia is likely to exceed 5, 000MW (Orhan et al., 2016). In this study, a methodology for evaluation of the hydrodynamic impacts and the performance of a commercial scale tidal farm is described, and results of an application carried out at the Strait of Larantuka, Indonesia are summarized. Current speeds in the Strait of Larantuka reach about 3-4m/s and total extractable power from tidal currents is around 300MW (Orhan & Mayerle, 2017). A high-resolution, three-dimensional flow model providing sufficient spatiotemporal coverage has been developed for predictions. Much attention has been given to the meteorological forcing and conditions at the open sea boundaries to adequately capture density gradients and flow fields in the computational domain. The model has been verified using tidal records. The energy of the tidal currents in the strait is assumed to be removed by 65 horizontal-axis tidal turbines with rotor diameters of ca. 15m, positioned on 10 sequential rows and in an alternating downstream arrangement. An additional drag force dissipating 40% of the pre-existing kinetic power within a flow cross-section is introduced to account for the drag of the devices. A second-order turbulence closure model (k-ε) is selected to involve the effects of the turbulent kinetic energy and turbulent kinetic energy dissipation. Spatial variation of the average kinetic power density within and around the farm area and average extractable electric power by each device are determined. In particular, characteristics, recovery and interactions of the turbine wakes are resolved in detail. Results show temporary energy dissipations in the downstream of the turbines, which seem to recover after each row in a distance equal to approximately ten times the rotor diameter. It is also seen that in a narrow channel such as the Strait of Larantuka, installation of the devices mid-channel can cause increased current velocities over the slopes on both sides, which can result in erosion of the seabed and increasingly turbulent flow conditions affecting the power generation. In light of the findings and considering the physical constraints, a suitability ratio is proposed to optimize the locations for the installation of tidal stream turbines.
Climate change is an urgent and potentially irreversible threat to human societies and the planet... more Climate change is an urgent and potentially irreversible threat to human societies and the planet and thus requires an effective and appropriate response, with a view to accelerating the reduction of global greenhouse gas emissions. At this point, a worldwide shift to renewable energy is crucial. In this study, a methodology comprising of the estimates of power yield, evaluation of the effects of power extraction on flow conditions, and near-field investigations to deliver wake characteristics, recovery and interactions is described and applied to several straits in Indonesia. Site selection is done with high-resolution, three-dimensional flow models providing sufficient spatiotemporal coverage. Much attention has been given to the meteorological forcing, and conditions at the open sea boundaries to adequately capture the density gradients and flow fields. Model verifications using tidal records show excellent agreement. Sites with adequate depth for the energy conversion using horizontal axis tidal turbines, average kinetic power density greater than 0.5 kW/m 2 , and surface area larger than 0.5km 2 are defined as energy hotspots. Spatial variation of the average extractable electric power is determined, and annual tidal energy resource is estimated for the straits in question. The results showed that the potential for tidal power generation in Indonesia is likely to exceed previous predictions reaching around 4,800MW. Models with higher resolutions have been developed to assess the impacts of devices on flow conditions and to resolve near-field turbine wakes in greater detail. The energy is assumed to be removed uniformly by sub-grid scale arrays of turbines. An additional drag force resulting in dissipation of the pre-existing kinetic power from 10% to 60% within a flow cross-section is introduced to capture the impacts. k-ε model, which is a second order turbulence closure model is selected to involve the effects of the turbulent kinetic energy and turbulent kinetic energy dissipation. Preliminary results show the effectiveness of the method to capture the effects of power extraction, and wake characteristics and recovery reasonably well with low computational cost. It was found that although there is no significant change regarding water levels, an impact has been observed on current velocities as a result of velocity profile adjusting to the increased momentum transfer. It was also seen that, depending on the level of energy dissipation, currently recommended tidal farm configurations can be conservative regarding the spacing of the tidal turbines.
Indonesia is one of the priority countries in Southeast Asia for the development of ocean renewab... more Indonesia is one of the priority countries in Southeast Asia for the development of ocean renewable energy facilities and The National Energy Council intends to increase the role of ocean energy significantly in the energy mix for 2010-2050. To this end, the joint German-Indonesian project "Ocean Renewable Energy ORE-12" aims at the identification of marine environments in the Indonesian Archipelago, which are suitable for the efficient generation of electric power by converter facilities. This study, within the ORE-12 project, is focused on the tidal stream currents on the straits between the Indian Ocean and Flores Sea to estimate the energy potentials and to develop strategies for producing renewable energy. FLOW module of Delft3D has been used to run hydrodynamic models for site assessment and design development. In site assessment phase, 2D models have been operated for a-month long periods and with a resolution of 500 m. Later on, in design development phase, detailed 3D models have been developed and operated for three-month long periods and with a resolution of 50 m. Bathymetric data for models have been obtained from the GEBCO_08 Grid and wind data from the Global Forecast System of NOAA's National Climatic Data Center. To set the boundary conditions of models, tidal forcing with 11 harmonic constituents was supplied from TPXO Indian Ocean Atlas (1/12 • regional model) and data from HYCOM+NCODA Global 1/12 • Analysis have been used to determine salinity and temperature on open boundaries. After the field survey is complete, water level time-series supplied from a tidal gauge located in the domain of interest (8 • 20´9.7" S, 122 • 54´51.9" E) have been used to verify the models and then energy potentials of the straits have been estimated. As a next step, correspondence between model outputs and measurements taken by the radar system of TerraSAR-X satellite (DLR) will be analysed. Also for the assessment of environmental impacts caused by tidal stream current power plants, studies are being conducted in a cooperation with CRM (Coastal Research & Management) company.
Journal of Marine Science and Engineering (ISSN 2077-1312), 2020
The Strait of Larantuka, with highly energetic tidal stream currents reaching speeds of up to 3-4... more The Strait of Larantuka, with highly energetic tidal stream currents reaching speeds of up to 3-4 m/s, is a promising site for renewable electricity production from the ocean. This paper presents the results of an assessment regarding the potential hydrodynamic impacts, wake characteristics, and the performances of large scale turbine arrays in the strait. A high-resolution, three-dimensional baroclinic model is developed using the FLOW module of the Delft3D modeling system to simulate tidal currents. The energy of currents is assumed to be extracted by horizontal-axis tidal turbines, which can harness strong bi-directional flow, positioned on sequential rows and alternating downstream arrangements. Enhanced momentum sinks are used to represent the influence of energy extraction by the tidal turbines. Four different array layouts with rated capacities of up to 35 MW are considered. We find that, in the Strait of Larantuka, array layout significantly affects the flow conditions and the power output, mainly due to the geometric blockage effect of the bounded channel. With respect to undisturbed flow conditions in the strait, decreases in current speeds of up to about 0.6 m/s, alongside increases in the order of 80% near-shore are observed. While operating efficiency rates of turbines reaching around 50%-60% resulted during the spring tide in the arrays with smaller rated capacities, the power output of the devices was negligible during the neap tide.
Energy Procedia, 2017
In this paper, results of a tidal stream resource assessment performed for the Strait of Larantuk... more In this paper, results of a tidal stream resource assessment performed for the Strait of Larantuka, Indonesia are presented. The methodology followed is comprising of the estimates of power yield and evaluation of the effects of power extraction via high-resolution, three-dimensional flow models. Power densities exceeding 10kW/m2 are observed in the main channel. Current velocities, and wake characteristics of the turbines have been resolved reasonably well with low computational cost, considering different levels of energy dissipation. Although the results are promising, investigations using in-situ measurements alongside more advanced modelling techniques are still needed, and currently underway.
E-proceedings of the 38th IAHR World Congress, 2019
In this paper, the results of a numerical model study evaluating the influence of density-induced... more In this paper, the results of a numerical model study evaluating the influence of density-induced flow on tidal stream power generation in the Sunda Strait, Indonesia are summarized. Tidal stream currents with speeds reaching about 2-3m/s and total extractable power of around 300MW turn the Sunda Strait into a promising location for renewable electricity production from the ocean. Furthermore, seasonally varying share of the density currents on the energy flux through the Sunda Strait emphasize the importance of a more comprehensive modelling approach for the selection and evaluation of the deployment sites of tidal turbines. A high-resolution, three-dimensional circulation model providing sufficient spatiotemporal coverage has been developed to simulate tidal currents in barotropic and baroclinic modes. Simulation outputs have been used to reveal the influence of density-induced flow on tidal stream power generation during both northwest and southeast monsoonal seasons. Up to 100% increase in current speeds has been simulated in the strait due to the density gradients, which leads to an enormous increase of the kinetic power. Additionally, energy hotspot shows significant changes due to the variations in density. Energetic section of the strait becomes significantly larger with an overall increase of the kinetic power densities. The findings may help us to understand the importance of including the ocean water density to resolve flow fields with better precision, which can lead to more accurate assessment and more efficient use of the resources of marine renewable energy.
Coastal Engineering Proceedings, 2017
In this paper, an advanced methodology developed for the assessment of tidal stream resources is ... more In this paper, an advanced methodology developed for the assessment of tidal stream resources is applied to several straits between Indian Ocean and inner Indonesian seas. Due to the high current velocities up to 3-4 m/s, the straits are particularly promising for the efficient generation of electric power. Tidal stream power potentials are evaluated on the basis of calibrated and validated high-resolution, three-dimensional numerical models. It was found that the straits under investigation have tremendous potential for the development of renewable energy production. Suitable locations for the installation of the turbines are identified in all the straits, and sites have been ranked based on the level of power density. Maximum power densities are observed in the Bali Strait, exceeding around 10kw/m2. Horizontal axis tidal turbines with a cut-in velocity of 1m/s are considered in the estimations. The highest total extractable power resulted equal to about 1,260MW in the Strait of Alas. Preliminary assessments showed that the power production at the straits under investigation is likely to exceed previous predictions reaching around 5,000MW.
8. Kıyı Mühendisliği Sempozyumu, 2014
Bir Almanya-Endonezya ortak projesi olan “Ocean Renewable Energy ORE-12” kapsamında Endonezya’dak... more Bir Almanya-Endonezya ortak projesi olan “Ocean Renewable Energy ORE-12” kapsamında Endonezya’daki okyanus alanları incelenip dalgalar ve gelgit akıntıları üzerinden yüksek verimle enerji üretimi yapılabilecek bölgeler saptanmaya çalışılmaktadır. Proje neticesinde bir karar destek sistemi (DSS), oluşturulması planlanmaktadır. Bu sistem kapsamında yenilenebilir enerji kaynaklarının tespiti için stratejiler; entegre bir coğrafi bilgi sistemi veri tabanı; data işleme ve görüntüleme sistemleri; akıntı, dalga, sediment taşınımı ve morfodinamik özelliklerin değişiminin belirlenmesi için nümerik modeller ve seçilen bölgelerdeki enerji potansiyellerinin hesaplanmasına yönelik araçlar oluşturulması hedeflenmektedir. Bunların yanında bölge kaynaklarının enerji üretiminde kullanılmasının yaratacağı çevresel etkinin de değerlendirilmesine yönelik bir çalışma yapılacaktır. Bu çalışmada ORE-12 projesinin metodolojisi hakkında bilgi verilmiştir. Ayrıca başlangıç aşamasında kurulan nümerik modellerin sonuçları sunulmuştur.
Anthropogenic climate change requires an effective and appropriate response, with a view to accel... more Anthropogenic climate change requires an effective and appropriate response, with a view to accelerating the reduction of global greenhouse gas emissions. The ocean provides a vast source of potential energy resources, which can be utilized without inflicting any considerable damage to the global ecosystem. To this end, the conversion of tidal current power is recently growing up to a crucial sector of the ocean renewable energy. Previously, tidal stream resources of several straits between the Indian Ocean and inner Indonesian seas have been investigated, and results have revealed that tidal current power potential of Indonesia is likely to exceed 5, 000MW (Orhan et al., 2016). In this study, a methodology for evaluation of the hydrodynamic impacts and the performance of a commercial scale tidal farm is described, and results of an application carried out at the Strait of Larantuka, Indonesia are summarized. Current speeds in the Strait of Larantuka reach about 3-4m/s and total extractable power from tidal currents is around 300MW (Orhan & Mayerle, 2017). A high-resolution, three-dimensional flow model providing sufficient spatiotemporal coverage has been developed for predictions. Much attention has been given to the meteorological forcing and conditions at the open sea boundaries to adequately capture density gradients and flow fields in the computational domain. The model has been verified using tidal records. The energy of the tidal currents in the strait is assumed to be removed by 65 horizontal-axis tidal turbines with rotor diameters of ca. 15m, positioned on 10 sequential rows and in an alternating downstream arrangement. An additional drag force dissipating 40% of the pre-existing kinetic power within a flow cross-section is introduced to account for the drag of the devices. A second-order turbulence closure model (k-ε) is selected to involve the effects of the turbulent kinetic energy and turbulent kinetic energy dissipation. Spatial variation of the average kinetic power density within and around the farm area and average extractable electric power by each device are determined. In particular, characteristics, recovery and interactions of the turbine wakes are resolved in detail. Results show temporary energy dissipations in the downstream of the turbines, which seem to recover after each row in a distance equal to approximately ten times the rotor diameter. It is also seen that in a narrow channel such as the Strait of Larantuka, installation of the devices mid-channel can cause increased current velocities over the slopes on both sides, which can result in erosion of the seabed and increasingly turbulent flow conditions affecting the power generation. In light of the findings and considering the physical constraints, a suitability ratio is proposed to optimize the locations for the installation of tidal stream turbines.
Climate change is an urgent and potentially irreversible threat to human societies and the planet... more Climate change is an urgent and potentially irreversible threat to human societies and the planet and thus requires an effective and appropriate response, with a view to accelerating the reduction of global greenhouse gas emissions. At this point, a worldwide shift to renewable energy is crucial. In this study, a methodology comprising of the estimates of power yield, evaluation of the effects of power extraction on flow conditions, and near-field investigations to deliver wake characteristics, recovery and interactions is described and applied to several straits in Indonesia. Site selection is done with high-resolution, three-dimensional flow models providing sufficient spatiotemporal coverage. Much attention has been given to the meteorological forcing, and conditions at the open sea boundaries to adequately capture the density gradients and flow fields. Model verifications using tidal records show excellent agreement. Sites with adequate depth for the energy conversion using horizontal axis tidal turbines, average kinetic power density greater than 0.5 kW/m 2 , and surface area larger than 0.5km 2 are defined as energy hotspots. Spatial variation of the average extractable electric power is determined, and annual tidal energy resource is estimated for the straits in question. The results showed that the potential for tidal power generation in Indonesia is likely to exceed previous predictions reaching around 4,800MW. Models with higher resolutions have been developed to assess the impacts of devices on flow conditions and to resolve near-field turbine wakes in greater detail. The energy is assumed to be removed uniformly by sub-grid scale arrays of turbines. An additional drag force resulting in dissipation of the pre-existing kinetic power from 10% to 60% within a flow cross-section is introduced to capture the impacts. k-ε model, which is a second order turbulence closure model is selected to involve the effects of the turbulent kinetic energy and turbulent kinetic energy dissipation. Preliminary results show the effectiveness of the method to capture the effects of power extraction, and wake characteristics and recovery reasonably well with low computational cost. It was found that although there is no significant change regarding water levels, an impact has been observed on current velocities as a result of velocity profile adjusting to the increased momentum transfer. It was also seen that, depending on the level of energy dissipation, currently recommended tidal farm configurations can be conservative regarding the spacing of the tidal turbines.
Indonesia is one of the priority countries in Southeast Asia for the development of ocean renewab... more Indonesia is one of the priority countries in Southeast Asia for the development of ocean renewable energy facilities and The National Energy Council intends to increase the role of ocean energy significantly in the energy mix for 2010-2050. To this end, the joint German-Indonesian project "Ocean Renewable Energy ORE-12" aims at the identification of marine environments in the Indonesian Archipelago, which are suitable for the efficient generation of electric power by converter facilities. This study, within the ORE-12 project, is focused on the tidal stream currents on the straits between the Indian Ocean and Flores Sea to estimate the energy potentials and to develop strategies for producing renewable energy. FLOW module of Delft3D has been used to run hydrodynamic models for site assessment and design development. In site assessment phase, 2D models have been operated for a-month long periods and with a resolution of 500 m. Later on, in design development phase, detailed 3D models have been developed and operated for three-month long periods and with a resolution of 50 m. Bathymetric data for models have been obtained from the GEBCO_08 Grid and wind data from the Global Forecast System of NOAA's National Climatic Data Center. To set the boundary conditions of models, tidal forcing with 11 harmonic constituents was supplied from TPXO Indian Ocean Atlas (1/12 • regional model) and data from HYCOM+NCODA Global 1/12 • Analysis have been used to determine salinity and temperature on open boundaries. After the field survey is complete, water level time-series supplied from a tidal gauge located in the domain of interest (8 • 20´9.7" S, 122 • 54´51.9" E) have been used to verify the models and then energy potentials of the straits have been estimated. As a next step, correspondence between model outputs and measurements taken by the radar system of TerraSAR-X satellite (DLR) will be analysed. Also for the assessment of environmental impacts caused by tidal stream current power plants, studies are being conducted in a cooperation with CRM (Coastal Research & Management) company.