Enhanced Hybrid Generator with Spring Coupling effect for low-grade water wave energy harvesting

Harvesting continuously water wave energy for on-site power generation offers a promising solution to address the offshore energy shortage. However, challenges arise in ocean wave energy harvesting during low-level sea states. Here, we propose a spring-coupled enhanced hybrid nanogenerator (SC-EHG), wherein the synergistic effects of gravity and elastic force allow it to achieve remarkable power generation capacity under low-level excitation. At a frequency of 0.1 Hz, the SC-EHG becomes operational at a tilted angle of merely 2 °, with sensitivity and energy harvesting direction range improved by sixfold and threefold, respectively, in comparison to configurations lacking a spring coupler. In the real ocean, under wave conditions characterized by a significant frequency (f_s) of 0.31 Hz and a significant wave height (H_s) of 7.87 cm, the output frequency of the SC-EHG reaches up to 0.75 Hz, an effective increase of 2.41 times. At this point, the maximum transferred charge (1.43 μC) and maximum open-circuit voltage (422.6 V) of a TENG module approximate the output values recorded under laboratory wave conditions (f_s = 0.82 Hz, H_s = 6.17 cm). Under ocean wave conditions of f_s = 0.21 Hz and H_s = 4.52 cm, the SC-EHG successfully powered a marine sensing system, enabling 1024 m of long-distance wireless communication by charging a 30 mF capacitor to 8.35 V. The robust performance of the SC-EHG at low level sea states (≤ 1) offers significant support for the establishment of a sustainable marine Internet of Things.