An omnidirectional hybrid wind-wave energy harvester based on a coaxial contra-rotation mechanism for unmanned surface vessels

•An ocean energy harvester for unmanned surface vessels is proposed.•The proposed harvester recovers hybrid wind and wave energy omnidirectionally.•The effect of tilt angle and azimuth on wind energy harvesting is investigated.•The maximum power of the harvester is 56.25 mW based on coaxial contra-rotation. In recent years, unmanned surface vessel (USV) has become a vital platform for marine environment investigation. Various monitoring devices are installed on these vessels to ensure reliability, and the power supply is a critical problem for the operation of these devices. The current study proposes a wind-wave hybrid energy harvester (WWHEH) for self-powered application in USV. The proposed WWHEH comprises three modules: energy input module, electromagnetic generation module and power management module. The energy input module can continuously harvest wind and wave energy and convert them into kinetic energy. The electromagnetic generation module works efficiently base on an enhancement mechanism. The power management module can achieve functions of current rectification, energy storage, and sensor power supply. Experimental investigations were carried out to identify the optimal configuration of the wind cups and the interaction of the two energy harvesting sections simultaneously. The results yielded the harvesting performance of wind cups at different pitch and azimuth angles. Additionally, a mixing experiment was conducted, and the superior performance of the hybrid energy harvesting system was verified (13.5% and 709.5% higher than a single wind energy capture part and wave energy capture part, respectively) Moreover, the experimental investigations conclude that the proposed wind-wave hybrid energy harvester can produce a maximum output power of 56.25 mW at a wind speed of 8 m/s. These findings indicate that the proposed WWHEH can effectively power the monitoring devices of USV.