The design of broadband, wide-angle interference filters for solar concentrating systems

The optical performance of spectrally selective interference filters for wide-angle solar applications is addressed. A radially variable interference filter is proposed that can maintain acceptable efficiency over its entire surface in solar concentrating systems with a wide field of view. By applying ray tracing methods and a mapping technique, the angle at which the greatest proportion of energy is incident can be determined at as a function of position on the filter surface. The resulting angular distribution is used to design the interference filter with a tapered thickness profile for optimum performance according to the changing mean angle. The method has been applied for the optimisation of a spectral beam splitter in a hybrid photovoltaic/thermal central receiver system. Two types of interference filters are compared: the discrete multilayer and the rugate filter. Results for bandpass and bandstop configurations are presented, and the performance and practical issues associated with each solution are discussed. (c) 2005 Elsevier B.V. All rights reserved.