21 September 2011 Static high-irradiance solar concentration by gradient-index optics
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Novel solutions for realistic gradient-index (GRIN) lenses are presented, that create the possibility of nominally stationary photovoltaic concentrators capable of daylong averaged flux concentration levels of order 103. One transfers the burden of precision solar tracking from massive units on which numerous solar modules are mounted, to miniaturized mechanical components inside modules that are completely stationary. The best optical properties for this aim would appear to be perfect imaging - a case where imaging and nonimaging objectives coalesce because perfect imaging is non-trivially synonymous with attaining the fundamental limit to concentration. Our GRIN profiles surmount limitations of classical Luneburg solutions that resulted in GRIN lenses being deemed physically unattainable idealizations for sunlight. To wit, while preserving perfect imaging, our GRIN profiles eliminate the need for refractive indices near unity, markedly reduce the range of refractive indices required, and permit arbitrary focal length. They are also amenable to realistic materials and fabrication technologies. Raytrace simulations confirm that they offer an unprecedented solution to this problem - even accounting for chromatic aberration and misalignment. Eliminating massive precision tracking of large photovoltaic arrays in favor of precision cm-scale lens tracking inside the modules opens the possibility of rooftop CPV. The perception that high solar concentration is inseparably linked to massive trackers is supplanted here by a different paradigm.
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Panagiotis Kotsidas, Panagiotis Kotsidas, Vijay Modi, Vijay Modi, Jeffrey M. Gordon, Jeffrey M. Gordon, "Static high-irradiance solar concentration by gradient-index optics", Proc. SPIE 8124, Nonimaging Optics: Efficient Design for Illumination and Solar Concentration VIII, 81240I (21 September 2011); doi: 10.1117/12.892181; https://doi.org/10.1117/12.892181

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