Electromagnetic wave energy conversion research

Known electromagnetic wave absorbing structures found in nature were first studied for clues of how one might later design large area man-made radiant-electric converters. This led to the study of the electro-optics of insect dielectric antennae. Insights were achieved into how these antennae probably operate in the infrared 7-14um range. EWEC theoretical models and relevant cases were concisely formulated and justified for metal and dielectric absorber materials. Finding the electromagnetic field solutions to these models is a problem not yet solved. A rough estimate of losses in metal, solid dielectric, and hollow dielectric waveguides indicates future radiant-electric EWEC research should aim toward dielectric materials for maximum conversion efficiency. It was also found that the absorber bandwidth is a theoretical limitation on radiant-electric conversion efficiency. Ideally, the absorbers' wavelength would be centered on the irradiating spectrum and have the same bandwith as the irradiating wave. The EWEC concept appears to have a valid scientific basis, but considerable more research is needed before it is thoroughly understood, especially for the complex randomly polarized, wide band, phase incoherent spectrum of the sun. Specific recommended research areas are identified

Fundamental formulae for wave-energy conversion.

The time-average wave power that is absorbed from an incident wave by means of a wave-energy conversion (WEC) unit, or by an array of WEC units-i.e. oscillating immersed bodies and/or oscillating water columns (OWCs)-may be mathematically expressed in terms of the WEC units' complex oscillation amplitudes, or in terms of the generated outgoing (diffracted plus radiated) waves, or alternatively, in terms of the radiated waves alone. Following recent controversy, the corresponding three optional expressions are derived, compared and discussed in this paper. They all provide the correct time-average absorbed power. However, only the first-mentioned expression is applicable to quantify the instantaneous absorbed wave power and the associated reactive power. In this connection, new formulae are derived that relate the 'added-mass' matrix, as well as a couple of additional reactive radiation-parameter matrices, to the difference between kinetic energy and potential energy in the water surrounding the immersed oscillating WEC array. Further, a complex collective oscillation amplitude is introduced, which makes it possible to derive, by a very simple algebraic method, various simple expressions for the maximum time-average wave power that may be absorbed by the WEC array. The real-valued time-average absorbed power is illustrated as an axisymmetric paraboloid defined on the complex collective-amplitude plane. This is a simple illustration of the so-called 'fundamental theorem for wave power'. Finally, the paper also presents a new derivation that extends a recently published result on the direction-average maximum absorbed wave power to cases where the WEC array's radiation damping matrix may be singular and where the WEC array may contain OWCs in addition to oscillating bodies

Slingshot resonance for ocean wave energy conversion

The slingshot effect and its application to converting ocean wave energy are discussed. It is shown that, owing to the large inertia transported by ocean waves and their periodicity, the slingshot effect can result in the transmission of significant kinetic energy to a puck colliding elastically with a pusher plate driven by ocean wave motion. A simplified geometrical model is used to demonstrate that, despite the stochastic nature of the collisions (whereby collisions occur at random times in the wave cycle), head-on collisions occur more frequently, yielding a net average gain of energy. However, the most promising configuration for applying the slingshot effect to ocean wave energy conversion is that which matches, through appropriate design, the travel time of the puck between collisions with the wave period. Then, only head-on collisions occur, resulting in a significant magnification of the puck kinetic energy. Further research will be required before this slingshot effect can be practically implemented for ocean wave energy conversionPostprint (author's final draft

Linear PM generator for wave energy conversion

The main objective of this thesis is to design a selected version of linear PM generator and to determine the electromechanical characteristics at variable operating conditions. To reach this objective, the linear generator with quasi-flat linear machine structure was selected and designed using the magnetic circuit theory. By applying 2-D and 3-D FEM the magnetic circuit was optimized and parameters of equivalent circuit were determined. The performance of generator operation are analyzed in steady-state and in dynamic conditions using MATLAB/SIMULINK. The analysis has been carried out at the secondary variable speed, which is changing sinusoidally according to the motion of the sea waves. The output and the input powers of the generator at rated speed of 2.2 m/s are 34KW and 40KW respectively. The maximun output power is generated when the generator is connected to a resistive load of 7.5Ω. The efficiency obtained for rated average speed of 1.4 m/s and at rated load resistance (of 7.5Ω) is equal to 85%

Improving the Efficiency of an Offshore Wave Energy Converter for Power Generation

Ocean is one of the renewable sources of energy that can supply part of the world’s energy necessities and consequently lessen the percentage of consumption of fossil fuels and additional non-renewable resources. Water waves have a quite high power density with a total global power of approximately 1-10 TW, equivalent to a large segment of the world’s current total energy consumption. The wave to electrical conversion encompasses wave energy converter (WEC), electrical generator, and signal conditioning end. This work is based on the selection and analysis of most suitable electrical generator which makes the overall wave energy conversion system simplest and reliable. The majority of wave energy conversion systems are based on conventional rotational generators which not only require mechanical interface i.e. turbine, hydraulic pump but make complicated system, incur losses and increases maintenance. On the other hand, direct-drive linear generators offer massive advantages in the field of wave energy conversion; they do not require any mechanical part, they form simple configuration and in turn increases the reliability. The literature survey has been carried out on direct-drive linear generators for wave energy conversion, it is analyzed that air-cored linear permanent magnet generator (Li-PMG) is suitable choice as compared to others

Nonlinear Modeling and Verification of a Heaving Point Absorber for Wave Energy Conversion

Although the heaving Point Absorber (PA) concept is well known in wave energy conversion research, few studies focus on appropriate modelling of non-linear fluid viscous and mechanical friction dynamics. Even though these concepts are known to have non-linear effects on the hydrodynamic system, most research studies consider linearity as a starting point and in so doing have a weak approach to modelling the true dynamic behaviour, particularly close to resonance. The sole use of linear modelling leads to limited ability to develop control strategies capable of true power capture optimisation and suitable device operation. Based on a 1/50 scale cylindrical heaving PA, this research focuses on a strategy for hydrodynamic model development and experimental verification. In this study, nonlinear dynamics are considered, including the lumped effect of the fluid viscous and mechanical friction forces. The excellent correspondence between the derived non-linear model and wave tank tested PA behaviours provides a strong background for wave energy tuning and control system design

Wells turbine for wave energy conversion : a review

In the past twenty years, the use of wave energy systems has significantly increased, generally depending on the oscillating water column (OWC) concept. Wells turbine is one of the most efficient OWC technologies. This article provides an updated and a comprehensive account of the state of the art research on Wells turbine. Hence, it draws a roadmap for the contemporary challenges which may hinder future reliance on such systems in the renewable energy sector. In particular, the article is concerned with the research directions and methodologies which aim at enhancing the performance and efficiency of Wells turbine. The article also provides a thorough discussion of the use of computational fluid dynamics (CFD) for performance modeling and design optimization of Wells turbine. It is found that a numerical model using the CFD code can be employed successfully to calculate the performance characteristics of W-T as well as other experimental and analytical methods. The increase of research papers about CFD, especially in the last five years, indicates that there is a trend that considerably depends on the CFD method