Recording and analysis of off-axis multiplexed volume holographic lens for wavelength selective wide acceptance angle operation in concentrator photovoltaics

Photovoltaic (PV) conversion is highly wavelength-dependent. The efficiency of a PV system is maximum when converting photons of energy close to the bandgap energy of solar cells. In a spectral-splitting solar cell system, an appropriately designed holographic lens provides wavelength-selective performance to disperse and concentrate a specific spectral region of solar radiation with appreciable diffraction efficiency. However, for holographic lenses, the angular range over that diffraction efficiency remains appreciable is limited. To overcome the difficulties associated with the limited acceptance angle (angular selectivity) of a single holographic lens, an investigation on the design aspect of a multiplexed off-axis holographic lens has been made for the collection and concentration of sunlight effectively over a wide angular range with appreciable diffraction efficiency. Processing parameters for a typical thick-phase holographic lens have been optimized to get the maximum value of the acceptance angle. Based on the theoretical design, a multiplexed hologram consisting of four angularly multiplexed holographic lenses of equal fringe spacing has been recorded. Experimental curves for the variation of diffraction efficiency with the angle of reconstruction have been presented to show the effectiveness of such multiplexed lens for solar tracking. Simulation results for the multiplexed holographic lens are also presented, which shows a good agreement with the experimental results. Results show that such off-axis multiplexed holographic lenses can advantageously be used for wavelength-selective performance with appreciable diffraction efficiency over a wide angular range.