Reflective optics for redirecting convergent radiative beams in concentrating solar applications

Abstract We investigate optical characteristics of flat, ellipsoidal, hyperboloidal, and paraboloidal reflectors for redirecting convergent radiative beams common in concentrating solar applications. Optical simulations are performed with selected types of radiative sources including a generic uniformly-emitting spherical cap and a specific realization of a multi-source high-flux solar simulator. Two-dimensional ray-tracing simulations are conducted for an ideal optical system without optical imperfections consisting of a spherical cap source, a beam-redirecting reflector, and a target tailored to capture all radiation. System optical performance is evaluated in terms of output beam optical characteristics of rim angle, ray distribution and relative position to the input beam. Three-dimensional Monte-Carlo ray-tracing simulations are performed for a practical optical system with a realistic solar simulator as radiation source and the four beam-redirecting reflectors. We predict optical characteristics of resulting radiative power, spatial and directional flux distribution, optical efficiencies on specified flat and hemispherical targets, and clearance between simulator, reflector and target. From the model system with a solar simulator and exemplary parameters, it is concluded that the investigated four types of reflectors enable redirection of the horizontal-axis beam from the solar simulator to non-horizontal axis targets. The flat reflector enables the highest system optical efficiency of 97% at the expense of the smallest clearance between the source, the reflector and the reflected image. Curved reflectors render a larger degree of freedom to design the characteristics of the output beam. Thus, curved reflectors are suitable for applications that require large clearance between system components and/or high radiative flux output on cavity surface, but at the expense of lower system optical efficiency.