Oscillating-water-column wave energy converters and air turbines: A review

"Comprehensive Renewable Energy" is the only multi-volume reference work of its type at a time when renewable energy sources are seen increasingly as realistic alternatives to fossil fuels. As the majority of information published for the target audience is currently available via a wide range of journals, seeking relevant information (be that experimental, theoretical, and computational aspects of either a fundamental or applied nature) can be a time-consuming and complicated process. "Comprehensive Renewable Energy" is arranged according to the most important themes in the field (photovoltaic technology; wind energy technology; fuel cells and hydrogen technology; biomass and biofuels production; hydropower applications; solar thermal systems: components and applications; geothermal energy; ocean energy), and as such users can feel confident that they will find all the relevant information in one place, with helpful cross-referencing between and within all the subject areas, to broaden their understanding and deepen their knowledge. It is an invaluable resource for teaching as well as in research. Available online via SciVerse ScienceDirect and in print. Editor-in Chief, Professor Ali Sayigh (Director General of WREN (World Renewable Energy Network) and Congress Chairman of WREC (World Renewable Energy Congress, UK) has assembled an impressive, world-class team of Volume Editors and Contributing Authors. Each chapter has been painstakingly reviewed and checked for consistent high quality. The result is an authoritative overview which ties the literature together and provides the user with a reliable background information and citation resource. The field of renewable energy counts several journals that are directly and indirectly concerned with the field. There is no reference work that encompasses the entire field and unites the different areas of research through deep foundational reviews. "Comprehensive Renewable Energy" fills this vacuum, and can be considered the definitive work for this subject area. It will help users apply context to the diverse journal literature offering and aid them in identifying areas for further research. Research into renewable energy is spread across a number of different disciplines and subject areas. These areas do not always share a unique identifying factor or subject themselves to clear and concise definitions. This work unites the different areas of research and allows users, regardless of their background, to navigate through the most essential concepts with ease, saving them time and vastly improving their understanding. There are more than 1000 references from books, journals and the internet within the eight volumes. It is full of color charts, illustrations and photographs of real projects and research results from around the world. The only reference work available that encompasses the entire field of renewable energy and unites the different areas of research through deep foundational reviews. Allows readers, regardless of their background, to navigate through the most essential concepts with ease, saving them time and vastly improving their understanding.

Comprehensive Renewable Energy

Air turbines are used to equip oscillating water column wave energy converters. In almost every case, self-rectifying turbines have been adopted which do not require non-return valves to rectify the reciprocating air flow induced by the water column oscillations. The most frequently used or proposed self-rectifying air turbines are the Wells turbine and the impulse turbine, both of axial-flow type. The fundamentals of the aerodynamic theory of axial-flow turbines are presented and then applied to the Wells turbine and the impulse turbine, including their variants. Information is given on methods of, and results from, air turbine model testing, as well as on self-rectifying air turbines that equipped or equip prototypes tested in the sea. The final part of the chapter is devoted to the analysis of turbine integration into OWC wave energy converter.

8.05 – Air Turbines

A 30 kW fixed-guide-vanes biradial turbine-generator set was designed by Instituto Superior Tecnico (IST) and manufactured by Kymaner, within the framework of the H2020 European project OPERA, for open sea testing at the Mutriku breakwater oscillating water column (OWC) power plant and at the IDOM MARMOK-A-5 OWC spar-buoy, deployed at BiMEP, Basque Country, Spain. The paper reports the design and construction of the prototype, and its dry testing at IST, in a variable-flow test rig, simulating the oscillating flow induced by irregular waves. Results show that the turbine exhibits a peak efficiency of 70% under steady-state conditions and an average efficiency of 56% for the control laws tested.

Test results of a 30 kW self-rectifying biradial air turbine-generator prototype

This paper proposes an optimization based maximum power point tracking (MPPT) algorithm for selection of appropriate external rotor resistances of wound rotor induction generator (WRIG). The generator coupled with a Wells turbine is used in oscillating water column (OWC) wave power plants. The Wells turbine suffers with stalling behaviour that reduces the average output power significantly. Hence, the objective is to prevent aerodynamic stalling of the Wells turbine and hence maximizing the output power simultaneously. But inappropriate selection of rotor resistance leads to excessive power loss. Therefore, two approaches have been applied: (i) the rotor resistance values are selected manually by trial and error method or non-optimized approach (ii) a performance index has been derived and minimized using particle swarm optimization technique to obtain the optimized values of rotor resistance. Simulation results have been performed for turbine efficiency, output power and power loss in external rotor resistance. Finally, the proposed control approach is illustrated for two particular cases of regular and irregular waves.

https://www.mdpi.com/2227-7080/6/1/15/pdf

Maximizing Output Power in Oscillating Water Column Wave Power Plants: An Optimization Based MPPT Algorithm

The near shore Oscillating Water Column (OWC) based Indian wave energy plant was operated with several conceptually different power modules. These include a tapered chord Wells' turbine, a linked guide vane (LGV) impulse turbine and a fixed guide vane (FGV) impulse turbine, while using the same grid connected induction generator. The turbine efficiency is calculated for a wide range of pneumatic power on a cycle to cycle basis. The behaviour of the turbines at various flow coefficients is compared with reported steady state measurements under laboratory conditions. The cycle by cycle analysis of the turbines clearly shows the behaviour under real conditions. The overall comparison shows that among the turbines tested, the FGV is the better choice.

G. Kailash

Papers

Analysis of Power Modules in the Indian Wave Energy Plant