Solar Cells, Fly’s Eyes, and the Archimedes Death Ray

Solar power is an increasingly popular topic as the need to develop sustainable sources of “clean” energy grows. The April 2011 issue of Optics and Photonics News (OPN) has an interesting article on research being done to improve solar cells by incorporating the features of compound fly’s eyes.  See "Insect Eyes Inspire Improved Solar Cells" on pages 39-43 for more information. 

The article begins with “a short history of solar power”. It mentions the legend that Archimedes set enemy ships on fire during an attack on Syracuse, presumably by focusing the sun’s rays using reflectors. Interestingly enough, there have been three episodes of Discovery Channel’s MythBusters on the “Archimedes Death Ray”. In the first episode in 2004 it was declared a myth after determining that the size of the mirror needed would be unrealistically large and would not be able to raise the temperature of wood enough to start a fire. Viewers were then challenged to devise a means of showing that the myth was plausible. In 2005, MIT students set fire to a wooden ship 100 feet away using 127 flat mirrors arranged in a parabola to focus the sunlight. (http://www.wonderbarry.com/deathray.html,http://history.howstuffworks.com/ancient-greece/archimedes-death-ray2.htm) They were invited onto the show to recreate what they had done. However, in the end it took too long for the fire to start and only worked with a stationary ship much closer than what was described in the legend. Therefore, the myth was again declared “busted”. A third episode was done in 2010 with President Barack Obama challenging the MythBusters to once again revisit the myth. This time 500 high school students each aimed a mirror. In spite of the extra mirrors a fire could not be started under the conditions in the legend and the myth was busted a third time.

Legends aside, modern-day use of solar power could be improved by designing solar cells to collect as much sunlight as possible and by increasing the efficiency of silicon solar cells. To address these challenges the authors’ research, as described in OPN, involves making the field of view of a solar cell as large as possible and minimizing reflections at the air-to-solar cell interface by using features found in a compound fly’s eye. They have used numerical simulations to demonstrate an increase in efficiency by modeling the curved, textured, outer surface of a compound eye on the surface of a solar cell. They have also formulated a nanomanufacturing method for replicating multiple copies of corneal “biotemplates”. Developing this capability would allow actual fly’s eye corneal layers to be replicated multiple times, perhaps to form an array placed over a solar cell. Overall they are working towards duplicating a fly’s eye as realistically as possible in 3D to maximize solar cell light collection and efficiency.

This is yet another example of how optics found in nature can be adapted and applied to solve real-world problems. Perhaps one day (soon?) fly’s eye solar cells will be commonplace.