Technology Progress in Wave Energy

In the past 20 years, the wave energy conversion technology has been developed rapidly. The construction technology has tended to be ripe and the energy conversion efficiency has raised by times, in particular the multi resonance oscillating water column which has played an critical role in the development of symmetrical wing turbine and phase control technology and the applications of following technology of backward duct device and wave convergence reservoir.

The multi resonance oscillating water column device was firstly applied to the 500kW power station in Norway. The method was to increase an incident harbor in the front of air chamber of the wave energy device, thus resulting in the resonance produced by the water column in the front harbor and air chamber and the diverse frequency, which allow the wave energy being amplified in the surroundings of the device so as to raise the width range of absorbing the wave energy and the applied range on the wave frequency variation. Taking advantage of the front harbor make it possible for a narrow wave energy device to absorb the energy outside the contacting wave width in order to increase the efficiency and reduce the cost. The primary energy capture width on a well-developed multi resonance water column device can reach more than 200% than that nearby the resonance frequency.

The phase control technology has been one of the effective channels to raise the wave energy efficiency proposed by scientist of Norway. The method is to control the motion phase of primary energy conversion institution to make the phase of its motion velocity compatible with the phase of incident wave force so as to make the wave being amplified in the surroundings of the device for the purpose of effective absorption of wave energy. Generally speaking, the design of the data can only compatible with some frequency, but the phase control can make the device being adaptable to wide range of frequency. By simply locking out and releasing of the motion of the device, the responding frequency of the device can be minimized, that is to say, it is possible to let a small wave energy device adaptable to large period wave so as to achieve the effect of cost saving and efficiency increasing. However, if to increase the responding frequency of the device, the device should be accelerated its velocity by the energy, which is not applied generally. The results combined with the theory and the practice shows that the phase control technology can mitigate the device dimension and raise the efficiency. But problems still remain unsolved concerning the phase control method in the irregular wave and its application equipment; the technology is not practical for applications until now. But the phase control is one of the futures for the practical use of wave energy.

The symmetrical turbine was invented by professor A.A.Wells in the middle of 1970s, which was also called Wells turbine, and comprises of various hub to tip symmetrical wing vanes with the installed angle of zero. The most advantage of symmetrical turbine lies in its characteristic of being self-rectified, that is to say power can be exerted on in high speed in single-direction rotation on the reversible dual-direction airflow. Due to the periodic variation of the wave motion, if single function turbine is applied to the pneumatic wave energy device, then the rectify valve is requested; but for symmetrical wing turbine, the rectify valve is not requested so that to greatly simplify the structure of the device. At present, most of the pneumatic wave energy device employ symmetrical wing turbine. Of course, disadvantages, such as bad activation and lower efficiency also exist in symmetrical wing turbine. Therefore, high-efficient and dual-functional turbine is still important to the research of wave energy.