Study of planning and operational aspects of tidal in-stream power generation

• Main Author: Mahda J. Jahromi
• Other Authors: Ali Iftekhar Maswood
• Format: Theses and Dissertations
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Power electronics; DRNTU::Engineering::Electrical and electronic engineering::Electric power::Auxiliaries, applications and electric industries
• Online Access: https://hdl.handle.net/10356/52042
• Institution: Nanyang Technological University

Even though harnessing marine energy through water wheels can be traced back to the early civilizations, no major step was taken to exploit this vast source of energy until the mid-70s after the first oil crisis. Ever since, many countries have begun to investigate and invest in this vast and predictable source of energy. Nowadays marine energy also referred to as oceanic energy has become a very generic term which spans from the kinetic energy carried by ocean tides and waves to the potential energy of tidal barrages. Out of the aforementioned different types, this study focuses on extracting power from oceanic tidal streams which are generated by the relative motion of the earth and celestial masses interacting via gravitational forces. Based on such generational forces, energy from tidal currents are essentially inexhaustible and as trustworthy as the rising of the sun. The physics of the energy conversion system of tidal currents is very similar, in principle, to the kinetic energy conversion system in the wind industry; resulting in an inevitable, though superficial, resemblance of many of the existing tidal in-stream energy converting devices to those of the wind turbines. Similar to wind power, the power of a tidal current is proportional to the density of the media and cube of its speed. It is the high density of water which makes the tidal power density impressive, in the sense that at similar sizes and flow speeds one tidal turbine can produce as much power as 1000 wind turbines. Apart from the high power density, based on the astronomical underlying forces, tidal stream energy is also very predictable and independent of terrestrial issues such as fog or lack of wind that can impact the performance of other renewables. High power density and robustness to aesthetic issues makes this source of energy very reliable; a factor which is very important when integrating renewable resources into the conventional networks. Consequently my objective in this study has been to look into the electrical challenges of extracting and transferring of tidal stream power to conventional power networks. Although the research trend in this area has been gaining momentum in recent years, when searching for similar literature even on a very generic topic such as marine power systems, one still finds very few papers, and even less when the topic is narrowed down to tidal turbines or in-stream generation. This made this study quite challenging at its very early stages since very little technical information was available to start with. In addition, many of the existing papers such as[1-9] merely focused on the overall trends in the field and were basically generic introductions on the topic of oceanic energies. However eventually specific publications helped shaping the study; out of which site feasibility and technology assessment reports of Siddiqui and EPRI [10-13], the work of Hong-da Liu et. al. on connecting methods of intermittent tidal resources to the grid [14] and the review of transmission alternatives of offshore generation [15] by Alegria, et. al. can be mentioned as a few examples. But probably the most inspiring and influential publications for me were the work of Elghali’s group based in the University of Western Brittany (France) who had studied simulation modeling of potential sites for marine current turbines. Although their papers were mostly dedicated to the development of a mechanical model for the turbine blades, their strategy in looking into different parts of a tidal in stream generation system was very helpful[7, 16]. Currently from their latest publications, it seems that they are moving towards designing specified permanent magnet based marine generators [17, 18]. Another paper which I found very inspiring at the beginning of this work was the paper by Biswarup, et. al. of the Imperial College of London who did a thorough investigation on the performance of an Archimedes Wave Swing (AWS) and its effect on the neighboring networks[19]. Although the paper was centered on a wave converting system and not tidal current generators, the author found it very useful due to the many similarities that exist between the two. In other words since the same astronomical generating forces that form tidal currents, shape tidal waves as well, the resulting captured power profiles are similar and so are many of the other electrical challenges. Despite the limited literature in marine energy systems, when it comes to wind energy and its pertaining technologies, this takes a completely different toll. The wind energy and its affiliated research topics are heading towards maturity and this is very beneficial to marine power systems especially tidal in stream systems which resemble wind turbines both in shape and operational concept. So eventually whenever the required literature in the marine category was missing or was found to be insufficient, the vast literature of the studies in wind energy focusing on similar issues were perceived as inspiring guides and solution to the problem; this is why you will find many of the cited papers in the context to be wind related studies. Out of such, the ones carried out by Reza Iravani of the University of Toronto were most useful particularly his latest book along with A. Yazdani on voltage sourced converters [20].