Bioreplicated coatings for photovoltaic solar panels nearly eliminate light pollution that harms polarotactic insects

Abstract

Many insect species rely on the polarization properties of object-reflected light for vital tasks like water or host detection. Unfortunately, typical glass-encapsulated photovoltaic modules, which are expected to cover increasingly large surfaces in the coming years, inadvertently attract various species of water-seeking aquatic insects by the horizontally polarized light they reflect. Such polarized light pollution can be extremely harmful to the entomofauna if polarotactic aquatic insects are trapped by this attractive light signal and perish before reproduction, or if they lay their eggs in unsuitable locations. Textured photovoltaic cover layers are usually engineered to maximize sunlight-harvesting, without taking into consideration their impact on polarized light pollution. The goal of the present study is therefore to experimentally and computationally assess the influence of the cover layer topography on polarized light pollution. By conducting field experiments with polarotactic horseflies (Diptera: Tabanidae) and a mayfly species (Ephemeroptera: Ephemera danica), we demonstrate that bioreplicated cover layers (here obtained by directly copying the surface microtexture of rose petals) were almost unattractive to these species, which is indicative of reduced polarized light pollution. Relative to a planar cover layer, we find that, for the examined aquatic species, the bioreplicated texture can greatly reduce the numbers of landings. This observation is further analyzed and explained by means of imaging polarimetry and ray-tracing simulations. The results pave the way to novel photovoltaic cover layers, the interface of which can be designed to improve sunlight conversion efficiency while minimizing their detrimental influence on the ecology and conservation of polarotactic aquatic insects.

Polarized Light Pollution of Fixed-Tilt Photovoltaic Solar Panels Measured by Drone-Polarimetry and Its Visual-Ecological Importance

“…The polarized light pollution (PLP) of smooth (shiny) and dark (especially black) artificial surfaces can be reduced or eliminated in the following ways [4,8]: (i) Making the surface rough (matt) results in it reflecting light diffusely with all possible angles of polarization α, the consequence of which is the considerable decrease in the net degree of linear polarization d of reflected light. The rougher (matter) the surface, the lower the d. Photovoltaic solar panels and other black reflectors with rough cover surface can have quite small PLP, but the reduction in PLP depends on both the surface mattness and the species of polarotactic aquatic insects concerned [9,11]. (ii) According to Umow's law [34], darker surfaces reflect light with lower degrees of linear polarization d. Thus, upon making a polarized-light-polluting surface bright (especially white), its reflected d significantly drops, and, thus, its PLP drastically decreases [4].…”

“…Since the oviposited eggs irremediably perish due to dehydration [7], this phenomenon can endanger the local insect population concerned. Therefore, in the last few decades, researchers have thoroughly mapped the sources of PLP in order to understand the hazards with which aquatic insects are confronted in their optical environment [8][9][10][11].…”

“…The PLP associated with photovoltaic solar panels is of particular importance, because several studies have indicated that these panels can attract polarotactic aquatic insects to lay their eggs upon them [9,11]. Furthermore, the PLP of solar panels can be a possible indirect cause of bat-panel collisions [17,18]: the polarotactic insects attracted by the polarization of panel-reflected light can lure insectivorous bats [13], which consume these deceived insects.…”

“…With this equipment, we measured the reflection-polarization characteristics of fixed-tilt photovoltaic solar panels from the viewpoint of flying polarotactic aquatic insects, which are the most endangered targets and potential victims of such panels. According to Száz et al [9] and Fritz et al [11], these photovoltaic solar farms offer relevant PLP for water-loving polarotactic insects. In this work, we present the reflection-polarization patterns and the temporal change in the polarized light pollution of solar panels measured from two orthogonal viewing directions between sunrise and sunset on a sunny and an overcast day, and we discuss their visual-ecological importance.…”

How the morning-afternoon cloudiness asymmetry affects the energy-maximizing azimuth direction of fixed-tilt monofacial solar panels

“…Until now we have dealt with fixed-tilt monofacial solar panels having a smooth, Fresnel-reflecting (R > 0) cover surface. Nowadays, solar panels with an anti-reflective (matte) cover surface are gradually spreading [22][23][24][25]. The reflectivity of such matte covers is very small: 0 < R ≪ 1.…”