Abstract
Man’s harvesting of photovoltaic energy requires the deployment of extensive arrays of solar panels. To improve both the gathering of thermal and photovoltaic energy from the sun we have examined the concept of biomimicry in white butterflies of the family Pieridae. We tested the hypothesis that the V-shaped posture of basking white butterflies mimics the V-trough concentrator which is designed to increase solar input to photovoltaic cells. These solar concentrators improve harvesting efficiency but are both heavy and bulky, severely limiting their deployment. Here, we show that the attachment of butterfly wings to a solar cell increases its output power by 42.3%, proving that the wings are indeed highly reflective. Importantly, and relative to current concentrators, the wings improve the power to weight ratio of the overall structure 17-fold, vastly expanding their potential application. Moreover, a single mono-layer of scale cells removed from the butterflies’ wings maintained this high reflectivity showing that a single layer of scale cell-like structures can also form a useful coating. As predicted, the wings increased the temperature of the butterflies’ thorax dramatically, showing that the V-shaped basking posture of white butterflies has indeed evolved to increase the temperature of their flight muscles prior to take-off.
Highlights
Man’s harvesting of photovoltaic energy requires the deployment of extensive arrays of solar panels
Can we prove practically that the butterflies concentrate light, and heat, onto their thorax? Second, is there an optimum angle with which they accomplish this and which we would have to adhere to in solar concentrator design? Third, does the light reflected by the butterfly wings themselves match the input requirements of any given photovoltaic solar cell? Fourth, can whole butterfly wings be used directly to increase the output from a given solar cell? can specific sub-structures from the wing or bead-like coatings be used to achieve improved solar cell outputs?
As white butterflies of the family Pieridae are especially effective at early take-off on cloudy days, and can fly before other groups of butterflies in poor weather, we reasoned that this ability is due to the V-shaped posture they adopt with their wings while ‘thermal’ basking (Fig. 1a)
Summary
Man’s harvesting of photovoltaic energy requires the deployment of extensive arrays of solar panels. We tested the hypothesis that the V-shaped posture of basking white butterflies mimics the V-trough concentrator which is designed to increase solar input to photovoltaic cells. These solar concentrators improve harvesting efficiency but are both heavy and bulky, severely limiting their deployment. The white butterflies of the genus Pieris take flight before other butterflies on cloudy days when solar inputs to flight muscle warming are limited This ability to heat up quickly on cloudy days has been anecdotally suggested to relate to the V-shaped posture they adopt whilst basking in cloudy conditions, a process we here term ‘reflectance basking’. Can we prove practically that the butterflies concentrate light, and heat, onto their thorax? Second, is there an optimum angle with which they accomplish this and which we would have to adhere to in solar concentrator design? Third, does the light reflected by the butterfly wings themselves match the input requirements of any given photovoltaic solar cell? Fourth, can whole butterfly wings be used directly to increase the output from a given solar cell? can specific sub-structures from the wing (e.g. a mono-layer of removed scale cells) or bead-like coatings (e.g. a coating of nano-beads with the same orientation and properties of the pterin beads) be used to achieve improved solar cell outputs?
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