The effect of irradiance mismatch on a semi-dense array of triple-junction concentrator cells

A method to determine the effect of cell-to-cell non-uniformity on CPV module performance is applied to a high-concentration photovoltaic system, comprising a linear semi-dense array of 5 series-connected 1 cm(2) triple-junction concentrator cells (lattice-matched GaInP/GaAs/Ge). Characteristic irradiance distributions were obtained by Monte Carlo ray-tracing of the concentrator optical system. Spatial apodizing filters were then produced such that, when illuminated with a spatially uniform radiation source, the desired irradiance distribution is obtained behind the filter. An equivalent circuit model of the array was developed and fitted against reference uniform irradiance measurements at concentrations ranging from 10x to 1678x. The fitted model was then validated vis-a-vis measurements under non-uniform irradiance imposed by the filters at concentrations from 99x to 494x. Both experimental and simulated results show a characteristic stepped I-V behavior associated with irradiance mismatch in series-connected arrays. Under the worst-case conditions of irradiance mismatch over the array, the efficiency drops to 28.5% as compared to 39% for the case of perfect uniformity. Due to the translational symmetry of the primary concentrator, a redesign of the module with parallel cell interconnects enables to mitigate the effects of irradiance mismatch. The methods provide an experimentally verifiable approach to determine the effect of irradiance mismatch on concentrator solar cell arrays without the need for prototyping of the concentrator optics. They may further be applied to determine the underlying characteristics and properties of cells and arrays subjected to nonuniform irradiation. (C) 2013 Elsevier B.V. All rights reserved.