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Development Of High Efficiency Holographic Solar Concentrator

In this report, we present the experience gained up-to-date in the development of holographic solar concentrators. The techniques used in the generation of high efficiency dielectric volume-holograms of the transmission type are presented in detail. These techniques facilitate the manufacturing of holographic lenses with diffraction efficiency in the order of 97%. In order to achieve the high efficiency, the research team has developed sensitizing and film development procedures for dichromated layers whose scattering losses are comparable to those of the unexposed gelatin layer. The manufacturing of the dichromated gelatin layers is performed in-house (30 x 40 cm2) and can easily be extended to large apertures. The layering procedure is a continuous process and is limited at present only by the travel of the motor-driven table top. The reproducibility of the film-thickness for a batch of manufactured 30 x 40 cm2 holographic plates is better than ± 1 μm. The film-thickness variation of the gelatin film averaged over the entire surface of a holographic plate is in the order of 0.2 Pm/cm. Theoretical and experimental results are presented for some relevant parameters that control the diffraction efficiency of the concentrator. Emphasis is placed on the problems encountered when a multiple lens-system (stack) is generated in a single gelatin layer or in an integrated multi-layer hologram.