Wave tank experiments on the power capture of a float-type wave energy device with a breakwater

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The objective of this study is to discuss the configuration and hydrodynamic performance of a float-type shoreline wave energy converter coupled with a breakwater. The energy converter is designed to extract wave power by making use of the wave-induced pitch motion of the float which is hinged on a breakwater. Meanwhile, the float is connected with hydraulic pistons, generating the high pressure water stream to drive alternators for electricity generation. A scale model was built in the laboratory at Hohai University, and the friction force was employed as the power take-off damping source. During the experiments, variations in several key parameters, including the wave elevation, wave energy converter (WEC) response (decay motion, free response, or damped motion of the WEC with varying damping levels), and wave-induced tensile forces on the steel wires were instantaneously measured. With these data, the wave reflection coefficient, instantaneous output power, and wave energy conversion efficiency of the model were estimated. The experimental results show that the developed WEC is effective in dissipating the incident wave energy, especially for longer waves, and is able to extract wave energy at a meaningful rate from regular waves. The average output power and wave energy conversion efficiency of the model under the resonance state can be up to 0.13 W and 32.6%, respectively. Although the WEC model harnesses more energy under longer waves, further examination reveals that the device is more efficient when installed in less energetic seas. Meanwhile, the water depth and the spacing between the breakwater and the float are significant factors for the posture and motion characteristics of the float during the process of interaction with water waves.