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A vector based freeform approach is proposed for the geometrical reverse design of reflecting solar concentrators. The effect of solar cone angle of incident vectors is taken into consideration in the method based on three-dimensional freeform optics. The method developed is a closed-loop program and did not need any other commercial software. According to the transmission pattern of solar concentrators, the source-target mapping should be initially established prior to constructing an initial geometry formed by discrete points using the Geometric Construction Method. The freeform surface is generated by connecting several triangular flat elements defined by these points and then the Monte-Carlo ray tracing was conducted. The freeform surface can then be further optimized through feedback modifications. Finally, the optimal shape is obtained when the design examples are the off-axis freeform reflectors with target circular/rectangular receivers for the use of Concentrated Photovoltaic. This method provides a practical approach for improving the optical performance of solar concentrators. [ABSTRACT FROM AUTHOR]

The conventional imaging solar concentrators normally obtain a Gaussian distribution on the receiving surface. The aperture size of a thermal receiver (TR) is always limited primarily to the high concentration area, discarding the edge part to be lost. The current study proposes a novel free-form Cassegrain concentrator (FFCC) for PV/T combining utilization. The remaining heat flux by the edge of focal spot is directed by the secondary mirror for electric generation. The profile of secondary reflector is constructed by the geometric construction method (GCM), aiming at achieving high concentration for the TR and uniform flux distribution for the PV receiver (PVR). The energy transmission characteristics of FFCC, including the incident vectors and heat flux distribution on the TR/PVR are both investigated. The effects of changing the receiving locations, PV/T dividing ratio, etc. are analyzed. The sun size/solar conic angular is also considered for practical use. The GCM method and simulation results in this article can provide a reference for the PV/T solar energy system and free form surface design. [ABSTRACT FROM AUTHOR]