Zähr, M.; Friedrich, D.; Kloth, T.Y.; Goldmann, G.; Tributsch, H.: Bionic photovoltaic panels bio-inspired by green leaves. Journal of Bionic Engineering 7 (2010), p. 284-293
10.1016/S1672-6529(10)60252-1

Abstract:
In strong solar light, silicon solar panels can heat up by 70 ̊C and, thereby, loose approximately one third of their efficiency for electricity generation. Leaf structures of plants on the other hand, have developed a series of technological adaptations, which allow them to limit their temperature to 40 – 45 ̊C in full sunlight, even if water evaporation is suppressed. This is ac- complished by several strategies such as limitation of leaf size, optimization of aerodynamics in wind, limitation of absorbed solar energy only to the useful fraction of radiation and by efficient thermal emission. Optical and infrared thermographic measurements under a solar simulator and in a streaming channel were used to investigate the corresponding properties of leaves and to identify suitable bionic model systems. Experiments started with the serrated structure of ordinary green leaves distrib- uted over typical twig structures and finally identified the Australian palm tree Licuala ramsayi as a more useful bionic model. It combines a large area for solar energy harvesting with optimized aerodynamic properties for cooling and is able to restructure itself as a protection against strong winds. The bionic models, which were constructed and built, are analyzed and discussed.