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

Benjamin Fritz,Markus Guttmann,Ruben Hünig,Gábor Horváth,Guillaume Gomard,Ádám Pereszlényi,Uli Lemmer,Marc Schneider,György Kriska,Ádám Egri,Oksana Ostroverkhova

doi:10.1371/journal.pone.0243296

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.

Highlights

A properly textured front surface of photovoltaic solar panels should allow the following characteristics: (i) A low sunlight reflectance irrespective of the illumination conditions and a high absorption of the collected light in the photovoltaic active layer, both leading to a high energy yield [1,2,3]. (ii) Radiative cooling that improves the power conversion efficiency and the reliability of the solar panels [4, 5]. (iii) Self-cleaning, which decreases the maintenance costs associated to the removal of soiling particles [6,7,8]
In this work we demonstrate that microtextured photovoltaic cover layers can strongly reduce their attractiveness to the mayfly species Ephemera danica (Muller, 1764) and horseflies (Diptera: Tabanidae), two typical polarotactic aquatic insect taxa [29] functioning as indicators of polarized light pollution
Photovoltaic cover layers form the interface between solar modules and their environment

Summary

Introduction

A properly textured front surface of photovoltaic solar panels should allow the following characteristics: (i) A low sunlight reflectance irrespective of the illumination conditions and a high absorption of the collected light in the photovoltaic active layer, both leading to a high energy yield [1,2,3]. (ii) Radiative cooling that improves the power conversion efficiency and the reliability of the solar panels [4, 5]. (iii) Self-cleaning, which decreases the maintenance costs associated to the removal of soiling particles [6,7,8]. Aquatic insects in general (belonging to the following orders with aquatic or semiaquatic species: Coleoptera, Collembola, Diptera, Ephemeroptera, Hemiptera, Hymenoptera, Lepidoptera, Mecoptera, Megaloptera, Neuroptera, Odonata, Plecoptera, Trichoptera) have evolved to identify water bodies by the horizontal polarization of water-reflected light [22, 23]. This strategy can result in a maladaptive attraction of polarotactic aquatic insects to smooth artificial surfaces like the glass/plactic covers of solar panels, because these surfaces can reflect a similar polarization pattern as water surfaces [23, 30, 31]. This effect is harmful for the aquatic insect populations concerned, and is called polarized light pollution [30]

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