Optical investigation of a sun simulator for concentrator PV applications.

In photovoltaics (PV), sun simulators are used to reproduce outdoor conditions in a lab environment such as irradiance level, light uniformity and spectral distribution. Concentrator (C)PV applications additionally require the sun simulators to provide rays with an angular distribution similar to that of the sun rays. However, different factors in CPV sun simulator setups make it difficult to achieve the perfect sun like angular distribution. This is mainly caused by the unavailability of appropriate light sources. Therefore, we investigated in this work, to which deviations such a non-ideal light source can lead and which impact is expected at the measurement of a CPV module. For this, two ray tracing models are presented - one for the simulation of natural sunrays, another one for the simulation of sun simulator conditions. The models are validated based on measurements and subsequently used to simulate the impact on a typical CPV module with silicone-on-glass Fresnel lenses. Here, significant deviations to outdoor conditions are found.

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

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.