22 October 1993 Design and optimization of a holographic concentrator for two-color PV operation
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The subject matter of this research project is to develop, manufacture and field test a spectrally dispersing solar collector system using a holographic solar concentrator in conjunction with spectrally matched advanced solar cells for photovoltaic power generation. The advantage of a holographic solar concentrator as compared to a conventional one is seen in the overall reduction of investment cost and in the possibility to generate inexpensive solar electric power. In this paper we present the techniques specifically developed for the design and manufacturing of efficient holographic optical elements and holographic lens stacks that are used in the fabrication of bandwidth matched solar concentrators for VIS and NIR photovoltaic operation. The lens stack separates the white light radiation into several spectral ranges that are focussed onto photocells possessing corresponding spectral characteristics. Contrary to previously published arrangements, we present here the concept and the design characteristics of a holographic concentrator that allows positioning of the cell in a plane parallel to the lens aperture. The initial idea of using two lenses recorded in the same aperture or same holographic layer focussing onto two off-axis foci proved to be of limited value due to the off-axis focussing that introduces strong reflection and aberration. Here we present a new concept in which the two lenses are shifted in the plane of the aperture so that each lens-cell configuration exhibits axial geometry. Both lenses are designed as axially corrected holographic stacks that include a lens and a correction grating. The design minimizes the cross coupling between the two holographic systems. Stack layouts for AlGaAs/GaAs and GaAs/Si combinations are discussed. Cross-coupling effects and aberrations involving the IR lens are minimized. Experimental diffraction efficiencies are fitted with non-cosinusoidal refractive index modulation showing best performance for 100 by 100 mm2 aperture. The theoretical predictions are compared with the first experimental results.
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Ernst Ulrich Wagemann, Klaus Froehlich, Jochen Schulat, Hartmut Schuette, and Christo G. Stojanoff "Design and optimization of a holographic concentrator for two-color PV operation", Proc. SPIE 2017, Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XII, (22 October 1993); doi: 10.1117/12.161965; https://doi.org/10.1117/12.161965

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