Optical analysis of deviations in a concentrating photovoltaics central receiver system with a flux homogenizer

Abstract

The application of a kaleidoscope as a flux homogenizer to a concentrating photovoltaics system with a central receiver is investigated. The optical setup of a primary dish-type concentrator, a secondary homogenizer optics, and a photovoltaic receiver is simulated using ray tracing. The influence of various deviations from the ideal-namely sunshape (circumsolar radiation), shading, tracking error, and shape of the primary optical concentrator-on the performance of the homogenizer is analyzed quantitatively using the optical efficiency and the normalized standard deviation as a measure of inhomogeneity. Flux distributions for different progressively increasing deviations are discussed qualitatively. Experimental validation of the simulation is presented. It is demonstrated that the performance of the homogenizer is not particularly sensitive to sunshape. If sufficient length is provided, the homogenizer effectively compensates for tracking error, misalignment, and shape deviations of the primary concentrator. Yet despite the presence of the homogenizer, shading due to the holder of the receiver significantly affects the flux distribution at the receiver.

A review of concentrated photovoltaic-thermal (CPVT) hybrid solar systems with waste heat recovery (WHR)

“…The linear coefficients of thermal and electrical outputs were obtained from multi-linear regression on measured data, which is similar to the quasi-dynamic method EN 12975-2: 2006 applied for solar thermal collectors. The influences of solar circumsolar ratio, shading, tracking error, deviations in the shape of the parabolic surface, and the homogenizer length were simulated using the ray-tracing method [184]. It was demonstrated that if sufficient length is provided, a kaleidoscope homogenizer compensates well for non-ideality factors of the primary concentrator.…”

Experimental Validation of Double Paraboloid Reflection for Obtaining Quasi-Homogeneous Distribution of Concentrated Solar Flux

“…Several homogeniser configurations are well documented in the CPV field. For instance, prism-based, working on the principle of total internal reflection [10]; mirror-based, working on multiple reflections using several mirrored facets [9,[11][12][13]; or those that are lens-based, such as the Köhler homogeniser [14], or domed homogenisers, as in [15,16].…”

Optical analysis of light management for finger designs in CPV systems

“…18,19 Consequently, secondary optical elements, such as homogenizers, are employed to improve the homogeneity of the round focused flux that results from the primary concentrator. 20 However, although the solar flux can be effectively "homogenized" with this strategy, it is at the expense of the angular distribution of the incident light which increases during this process. Figure 1 schematically depicts PV systems under concentrated sunlight conditions with and without homogenizers and shows the flux distribution and angular distribution of corresponding CPV system on the solar cell surface.…”

“…Directly imaging the Sun onto the front surface of the solar cell results in a concentrated non‐uniform flux distribution, 17 which can lead to a non‐uniform photon‐generated current density and a consequent voltage drop arising from series resistance power losses in the emitter and contact/metal resistance losses of the solar cell 18,19 . Consequently, secondary optical elements, such as homogenizers, are employed to improve the homogeneity of the round focused flux that results from the primary concentrator 20 . However, although the solar flux can be effectively “homogenized” with this strategy, it is at the expense of the angular distribution of the incident light which increases during this process.…”