OWC wave energy devices with air flow control

A review of impulse turbines for wave energy conversion

Renewable energy techniques are now gaining more and more attention as the years pass by, not only because of the threat of climate change but also, e.g. due to serious pollution problems in some countries and because the renewable energy technologies have matured and can be depended upon an increasing degree. The energy from ocean waves bares tremendous potential as a source of renewable energy, and the related technologies have continually been improved during the last decades. In this paper, different types of wave energy converters are classified by their mechanical structure and how they absorb energy from ocean waves. The paper presents a review of strategies for electrical control of wave energy converters as well as energy storage techniques. Strategies of electrical control are used to achieve a higher energy absorption, and they are also of interest because of the large variety among different strategies. Furthermore, the control strategies strongly affect the complexity of both the mechanical and the electrical system, thus not only impacting energy absorption but also robustness, survivability, maintenance requirements and thus in the end the cost of electricity from ocean waves.

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Review on electrical control strategies for wave energy converting systems

Several types of single-plane and multiplane Wells turbines are investigated and compared. The turbines’ aerodynamic losses and overall performances are presented and two successful methods of swirl energy recovery are studied in detail. Guide vanes were fitted to a monoplane turbine whereas the rotors of a biplane turbine were contra-rotated. A double-shaft biplane turbine was also tested. The contra-rotating turbine had an operational range which was similar to that of the monoplane turbine with guide vanes, achieved a similar peak efficiency, but performed better in the post-stall region and also was found to be able to accommodate a much higher pressure-flow ratio.

The energy conversion performance of several types of Wells turbine designs

The control and simulation of the power delivered to the grid are becoming an important topic, particularly when the number of distributed power generation systems increases. In this paper, two different control schemes for an oscillating-water-column Wells-turbine-generator module are simulated, implemented, and compared. In the first method, the control system does appropriately adapt the slip of the induction generator according to the pressure drop entry in order to maximize the generated power, while in the second method, a traditional proportional-integral-derivative-based control is implemented in order to deal with the desired power-reference-tracking problem. It will be shown how the controllers avoid the stalling behavior and that the average power of the generator fed into the grid is significantly higher in the controlled cases than in the uncontrolled one while providing the desired output power.

Modeling and Simulation of Wave Energy Generation Plants: Output Power Control

The paper describes an experimental investigation, and presents the results of the aerodynamic performance of a high-solidity Wells turbine for a wave power plant. A monoplane turbine of 0.6 m rotor diameter with guide vanes was built and tested. The tests were conducted in unidirectional steady airflow. Measurements taken include flow rate, pressure drop, torque, and rotational speed, as well as velocity and pressure distributions. Experimental results show that the presence of guide vanes can provide a remarkable increase in turbine efficiency.

V. Warfield

Papers

Performance of a High-Solidity Wells Turbine for an OWC Wave Power Plant