Wave Energy

The main method of utilization of wave energy is to generate electricity. Furthermore, wave energy can be utilized for pumping water, heating supply, desalination of seawater and hydrogen production. The utilization plants of wave energy have numerous varieties. The invention patents for utilization device exceed thousands. Therefore, the utilization of wave energy is so called the paradise of inventors.

But all of these plants are mainly originated from the following theory that is to utilize the oscillating and heaving motion of a body under the function of wave; to utilize the changing of wave pressure forces; to utilize the climbing of the wave along the coast to converse wave energy into potential energy of water. The wave-power generation technology has turning close to the practical standard, after experimental research conducted on the varieties of wave plants from 1970s, and the pilot plan and application demonstration research on the working condition since 1980s. The focus research stress on 3 plants which are considered to be of commercial value, including oscillating water column device, pendulum wave power device and wave convergence device.

Wave-power generating device can be considered as a system including 3-stage energy conversion. General speaking, the primary energy conversion institution is directly interact with wave, which can converse wave energy into kinetic energy of the device or potential energy of water or kinetic energy and pressure energy of medium mass i.e. air. The secondary energy conversion institution converse energy obtained from the primary institution into kinetic energy of the rotating mechanics, i.e. hydraulic turbine, air turbine or hydraulic pressure motor. The third energy conversion institution will converse kinetic energy of the rotating mechanics into power energy through the generator. The energy conversion theory and process of three most potential plants are introduced as followings.

a)        Oscillating Water Column Wave Energy Device

The oscillating water column (OWC) device has floating and fixed type. Air is taken as the medium for the built OWC device at present. Its primary energy conversion institution is chamber, while the second is air turbine. The orifice on the bottom of air chamber under the water is connected with seawater, and the orifice on the upper is connected with air. Functioned by the wave force, the column under the air chamber is vibrated strongly to compress air in air chamber reversibly flowing through the orifice, which brings wave energy conversing into pressure energy and kinetic energy of air.

If the orifice is equipped with an air turbine and spin axis of turbine is connected to generator, then it is possible to utilize the compressed airflow to drive the rotating of turbine to power the generator for electricity.

The advantage of OWC device is that the rotating part has no any contact with seawater. As a consequence, it is good at anticorrosion, safe at reliability and convenient at maintenance. But it¡¯s disadvantaged at lower efficient on the secondary energy conversion.

b)        Pendulum Wave Power Device

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The pendulum wave power device also has floating and fixed type. The swing body belongs to the primary energy conversion institution for the pendulum device. Functioned by the wave force, the swing body is swinging back and forth, or up and down, which will converse wave energy into kinetic energy of swing axis. Normally the hydraulic pressure device is connected to the swing axis, which will converse kinetic energy of the pendulum into that of the hydraulic pump to power the generator for electricity.

The motion of swing body is acceptable for the heavy propelling force and the low frequency of the wave. Therefore, the pendulum device has high-efficient conversion efficiency, but it is difficult to repair the mechanics and hydraulic pressure device. Another advantage of the pendulum device is that it can be combined with the phase control technology easily. The phase control technology can make it possible for the wave energy device to absorb the wave energy except the wave contact width of the device, so as to greatly increase the efficiency of the device.

c)        Wave Convergence Reservoir Wave Energy Device

The wave convergence reservoir device takes the bugle-shaped shrink wave channel as its primary energy conversion institution. It has a wide orifice in the side that the wave channel is connected to the sea. And then gradually shrink until to the reservoir. The shrink wave channel can be functioned as the wave convergence equipment and energy transformation equipment. The water head between the reservoir and the open sea can reach 3-8m, which can be utilized for generating the electricity. The advantage of this device is no moving parts for the primary conversion institution, which will be good at reliability and lower at maintenance cost and stable in system. Its disadvantage is that it has requirement on topography for the construction of power stations and it is therefore no good at promotion.

The key technology in utilization of wave energy includes the wave convergence and phase control technology; wave loads of the wave device and the subsistence technology in the marine environment; the marine engineering technology on construction and operation of wave energy device; design and operation optimization of wave energy device for the irregular wave; turbine research for reversible flow.