Polar bear fur informs optimization strategies for textile based solar collectors

I am glad to announce my first biomimicry publication in the journal Energy and Buildings and would like to give a short overview of it. The paper is titled “Solar Heat Harvesting and Transparent Insulation in Textile Architecture Inspired by Polar Bear Fur” and summarizes the main findings of my master’s thesis that I finalized in 2012. I was a biomimetics student at the Carinthia University of Applied Sciences in Austria during that time but did the experimental part of the thesis within an internship at the Institute of Textile Technology and Process Engineering in Denkendorf (ITV Denkendorf), Germany.

The research focus of the paper is on the optimization of a textile-based solar collector system that could build the envelope of future textile-based buildings. Conventional solar collectors are usually built from heavy, rigid materials but alternative materials such as textiles allow for lightweight and material efficient solar collector system design. The proposed collector was inspired by the heat harvesting mechanism of polar bear fur. The polar bear is known for its efficient heat trapping properties, enabled by a dense fur of transparent and hollow hair that lets light pass through to the bear’s skin. The skin of the polar bear is black and absorbs light passing though the transparent fur. The emitted heat is trapped close to the bear’s body, due to a dense underfur including several air cavities for insulation. These principles were adapted to create a multi-layer arrangement of technical textiles and foils. Two transparent ETFE-membranes were used as the upper layers of the system. ETFE is known for its insulating properties but also lets light pass through due to its transparency. Underneath the ETFE-membranes a 1 cm thick air-permeable spacer fabrics textile provides space for an air-buffer. Underneath the spacer fabrics layer a black silicon layer analogous to the polar bear’s skin absorbs the majority of the incoming light. The emitted heat is trapped inside the system due to the air-buffer within the spacer fabrics layer as well as the heat insulating material properties of ETFE. Underneath the black silicon absorber an additional layer of insulation foam minimizes heat loss to the environment. For the purpose of heat transfer, an air flow was generated by a fan inside the air-permeable spacer fabrics layer. The air inside this layer heats up while it moves along the collector and can be piped to a thermo-chemical energy storage system for long-term retention of thermal energy. This concept could inform new self-sufficient, textile-based buildings that harvest all of their energy during summer months and spend this energy during winter. The ITV Denkendorf built a successful prototype building based on the principles described.

The main goal of the study was to test different parameter changes such as air-flow velocities, irradiation intensities and material arrangements on the output temperature of the collector. Temperatures up to 150 C° could be generated using the proposed system. It was also shown that the proposed system is totally independent from ambient temperatures and would work even in sub-zero temperatures if direct solar radiation is available. In the paper, I also discuss further biomimetic strategies that could be considered for additional energetic optimization such as the trapping and guiding of diffuse light via optical fibers or antireflective surface coatings inspired by the moth-eye effect, for example. If you are interested in learning more you can access my paper on ScienceDirect.

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