A sunflower-inspired nonwoven fabric evaporator for autonomous phototropic tracking and continuous efficient evaporation under sunlight

Solar evaporators are widely used for their high energy efficiency, environmental sustainability, fast evaporation rates, and low maintenance costs. However, they often fail to optimally and intelligently harness solar energy. Inspired by the phototropic behavior of sunflowers, we developed a novel solar vapor generation (SVG) device that integrates a flexible deflection structure with a conventional evaporator. In our study, the benchmark evaporation performance under vertical light at a zenith angle of 0° achieved a rate of 3.43 kg·m⁻² and an efficiency of 120.90%. However, finite element simulations showed that the highest temperature point dynamically shifts with the sun's position in real conditions, leading to a significant reduction in efficiency for fixed-angle evaporators. To address this, we fabricated a soft, self-adjusting phototropic deflection structure using high-precision direct ink writing, enabling rapid actuation across all azimuth angles (0°to 360°) and zenith angles (−60°to 60°). In practical evaporation scenarios, when the zenith angle reached 60°, the evaporation rate increased by 64.828% compared to fixed-angle evaporators, restoring the rate to 3.087 kg·m⁻². This study provides new insights for designing efficient, multifunctional SVG devices, demonstrating the potential of biomimetic phototropic structures to maximize solar energy capture and utilization, particularly in solar-driven water evaporation applications.