An energy harvester for all seasons

© C w he harvesting of sunlight, wind, heat nd even raindrops to produce electrial energy has attracted significant attenion to address the global energy crisis, reuce environmental pollution from fosil fuels, and limit the use of batteries 1 –3 ]. One challenge to harvesting reewable energy sources is their inhernt variability, where changes in weather an occur on a daily basis or as a result f diurnal cycles and seasonal changes Fig. 1 a). The recent research by Zhou et al. [ 4 ] . as aimed to address this issue by creating n all-weather energy harvester based n a non-planar dielectric architecture o induce controlled changes in thermal nd electrostatic fields (Fig. 1 b, upper mage). First, the high transmittance of he non-planar structure is able to focus unlight to induce rapid in-plane temperture fluctuations within a pyroelectric lement. The change in polarization of he pyroelectric leads to the generation f a charge, where the current is proporional to the rate of temperature change d T/ d t ) (Fig. 1 b, lower left). Second, the urved and textured nature of the nonlanar dielectric leads to the spreading nd separation of raindrops to produce apid changes in droplet-solid contact rea (d S/ d t ); see lower right Fig. 1 b. The apid change in droplet area acts to enance the triboelectric output as a result f liquid-solid contact electrification. By aking this hybrid approach, this harester was able to produce an enhanced lectrical output due to a combination f a solar-induced pyroelectric response nd raindrop-induced triboelectric ffects. As observed in Fig. 1 c [ 4 ], their exerimental results showed that the nonFigure 1. All-weather non-planar energy harvester. (a) Potential weather scenarios, where heat and wind induce pyroelectric effects, while rain droplets induce triboelectric effects. (b) Mechanism for a non-planar dielectric to produce rapid non-uniform temperature fluctuations ( dT/dt , left) and rapid changes in droplet-solid contact area ( dS/dt , right). (c) Comparison of output power for both planar and non-planar approaches. (d) Deployment of scaleable harvester, and corresponding (e) image of non-planar energy harvester; Scale bar: 2 cm [ 4 ].


An energy harvester for all seasons
Qingping Wang 1 , 2 and Chris Bowen 2 , * The harvesting of sunlight, wind, heat and even raindrops to produce electrical energy has attracted significant attention to address the global energy crisis, reduce environmental pollution from fossil fuels, and limit the use of batteries [ 1 -3 ].One challenge to harvesting renewable energy sources is their inherent variability, where changes in weather can occur on a daily basis or as a result of diurnal cycles and seasonal changes (Fig. 1 a).
The recent research by Zhou et al. [ 4 ] .has aimed to address this issue by creating an all-weather energy harvester based on a non-planar dielectric architecture to induce controlled changes in thermal and electrostatic fields (Fig. 1 b, upper image).First, the high transmittance of the non-planar structure is able to focus sunlight to induce rapid in-plane temperature fluctuations within a pyroelectric element.The change in polarization of the pyroelectric leads to the generation of a charge, where the current is proportional to the rate of temperature change (d T/ d t ) (Fig. 1 b, lower left).Second, the curved and textured nature of the nonplanar dielectric leads to the spreading and separation of raindrops to produce rapid changes in droplet-solid contact area (d S/ d t ); see lower right Fig. 1 b.The rapid change in droplet area acts to enhance the triboelectric output as a result of liquid-solid contact electrification.By taking this hybrid approach, this harvester was able to produce an enhanced electrical output due to a combination of a solar-induced pyroelectric response and raindrop-induced triboelectric effects.
As observed in Fig. 1 c [ 4 ], their experimental results showed that the non-planar-based energy harvester enhanced pyroelectric output power by 174% at 0.2 sun, which surpassed conventional planar pyroelectrics that produce a more uniform thermal field.In addition, power generation from impacting rain droplets was increased by 65% compared to planar devices, which were less effective in facilitating droplet spreading and separation events.
Natl Sci Rev , 2023, Vol. 10, nwad218 The non-planar dielectric was designed to optimize the pyroelectric and triboelectric outputs by carefully tailoring its potential for sunlight transmission, sunlight concentration, and increasing droplet dynamics.The final structure was based on a transparent conical layered structure, which included polydimethylsiloxane (PDMS) as a conical lens to focus sunlight onto the pyroelectric element, a thin indium tin oxide (ITO) layer to act as a transparent conductor to collect the triboelectric charge, and a thin outer dielectric layer of hydrophobic polytetrafluorety hy lene (PTFE) that makes contact with the raindrops.The geometry of the conical lens was optimized to maximize the temperature fluctuations (d T/ d t ) in the pyroelectric, while the outer hydrophobic PTFE surface was optimized to improve droplet spreading (d S/ d t ) and charge transfer between the water droplet and the dielectric, without compromising the transmission of sunlight.The microscopic surface morphology and roughness of the PTFE also helped to enhance the triboelectric contribution.The pyroelectric energy harvesting element was based on a ferroelectric polyvinylidene fluoride (PVDF) film which was coated with carbon nanotubes (CNT) that acted as both an electrode and a solar absorber with desirable solar-to-heat conversion efficiency.
Outdoor testing of the non-planar dielectric for adaptive weather harvesting was undertaken, where the system is i l lustrated in Fig. 1 d and e.In an outdoor setting, the temperature fluctuations were driven by both confined solar illumination and wind-/humidity-driven heat convection.Ambient convective heat variations also allow for power generation during night-conditions where solar cells are clearly unable to operate.
This innovative research provides a novel approach to all-weather energy harvesting, where the use of additive manufacturing provides a route for scalability.Potential applications can be the supply of power to sensor networks and the Internet of Things (IoT) [ 5 ].

Figure 1 .
Figure 1.All-weather non-planar energy harvester.(a) Potential weather scenarios, where heat and wind induce pyroelectric effects, while rain droplets induce triboelectric effects.(b) Mechanism for a non-planar dielectric to produce rapid non-uniform temperature fluctuations ( dT/dt , left) and rapid changes in droplet-solid contact area ( dS/dt , right).(c) Comparison of output power for both planar and non-planar approaches.(d) Deployment of scaleable harvester, and corresponding (e) image of non-planar energy harvester; Scale bar: 2 cm [ 4 ].