Strategies for the Assessment of Tidal Current Energy Resources through Numerical Models
The tidal current energy is highly predictable, and it can provide a stable output to the grid. Especially in the coastal regions, it might enhance the diversity of the energy mix, contribute to the decarbonization of electricity production, increase energy security by exploiting indigenous resources, and fuel economic growth. Due to their advanced technological readiness levels, tidal energy conversion systems are likely to become commercially attractive within a decade, with the potential for a significant market share in future energy systems. Indonesia, with a significant potential of tidal current energy, is one of the many countries aiming to increase the contribution of the tidal currents in their national energy mix. Hence, the country intensifies the research and development efforts to reach this goal. The presented study stresses fundamental research issues regarding the characterization of tidal current energy resources with a focus on Indonesia, leading to a concluding overview of the country’s potentials on tidal current energy. Developed approaches and tools such as high-resolution, three-dimensional numerical models validated by state-of-the-art measurements, are presented. Analyses of the tidal current energy potentials of several promising straits between the Indian Ocean and inner Indonesian Seas are performed. A resource assessment methodology is developed to define energy hotspots within the target domains and to estimate technically extractable powers from each of them. The influence of density-induced flow on tidal stream power generation for the Sunda Strait, located between Java and Sumatra islands, is investigated. Physical impacts of tidal current energy extraction on hydro-environment and performance of tidal turbine arrays are presented in detail for the Strait of Larantuka, which divides East Flores and Adunara islands in eastern Indonesia. Changes in the local flow field due to the operation of turbines as well as the turbine performances for various dissipation levels and array configurations are evaluated. The results underline the potentials of the Indonesian straits of Bali, Larantuka, Boling, Alas, Lombok, Sunda, and Badung for the production of renewable electricity from tidal currents. While the currents with highest power densities are observed in the straits of Bali and Larantuka, Alas Strait was found to have the biggest potential for tidal current energy extraction due to the larger size of its energy hotspot. The technically extractable power potential of all the investigated straits is estimated to exceed a total of 5,000MW. It is found that in the Sunda Strait, the density gradients caused by the water exchange between the Java Sea and the Indian Ocean can seasonally amplify tidal current speeds by up to 100% at the free sea surface. During both northwest and southeast monsoonal seasons, electricity production in Sunda Strait rated for the baroclinic mode resulted in more than twice the electricity production estimated for the barotropic mode. Concerning the impacts of tidal energy extraction, an overall change is observed in the flow fields, which have been simulated due to different dissipation levels and array configurations. Up to 30 – 40% decrease in current speeds is observed downstream the turbine arrays. On the contrary, within the adjacent nearshore shallow waters, up to 80% increase in current speeds was observed mainly due to the blockage effect. Turbines seemed to reach their rated capacities for short periods and to operate with a maximum of 60% efficiency compared to their rated power. The findings emphasize the importance of high-resolution modelling tools for a comprehensive assessment of tidal current energy resources, for optimizing the layout of multi-turbine arrays and for the assessment of potential physical impacts due to tidal current energy extraction.