Research Article Effects of Nonuniform Incident Illumination on the Thermal Performance of a Concentrating Triple Junction Solar Cell Fahad Al-Amri 1 and Tapas Kumar Mallick 2 1 College of Technology, P.O. Box 7650, Dammam 31472, Saudi Arabia 2 Environment & Sustainability Institute, University of Exeter, Penryn Campus, Cornwall TR10 9EZ, UK Correspondence should be addressed to Fahad Al-Amri; alamrifahad@hotmail.com Received 24 February 2014; Revised 20 May 2014; Accepted 21 May 2014; Published 16 June 2014 Academic Editor: Mark van Der Auweraer Copyright © 2014 F. Al-Amri and T. K. Mallick. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A numerical heat transfer model was developed to investigate the temperature of a triple junction solar cell and the thermal characteristics of the airfow in a channel behind the solar cell assembly using nonuniform incident illumination. Te efects of nonuniformity parameters, emissivity of the two channel walls, and Reynolds number were studied. Te maximum solar cell temperature sharply increased in the presence of nonuniform light profles, causing a drastic reduction in overall efciency. Tis resulted in two possible solutions for solar cells to operate in optimum efciency level: (i) adding new receiver plate with higher surface area or (ii) using forced cooling techniques to reduce the solar cell temperature. Tus, surface radiation exchanges inside the duct and Re signifcantly reduced the maximum solar cell temperature, but a conventional plain channel cooling system was inefcient for cooling the solar cell at medium concentrations when the system was subjected to a nonuniform light distribution. Nonuniformity of the incident light and surface radiation in the duct had negligible efects on the collected thermal energy. 1. Introduction Nonuniformity of the incident illumination in concentrated photovoltaic (CPV) systems occurs as a result of using concentrating optics that refect or refract light fux on the solar cell surface. Te optimal optical system design would concentrate radiation on the solar cell surface in a uniform distribution. However, existing concentrators condense the majority of the incident fux onto a limited area of the cell surface, and most areas of the cell receive the remaining small amount of radiation. Tis situation produces a highly nonuniform irradiance distribution on the photovoltaic cells. Tis nonuniformity has two main efects on the solar cell: (i) electrical impacts, such as high ohmic drops and the fow of an internal current, and (ii) thermal impacts, such as increased temperatures in some regions of the cell that cause hot spots and drastically reduce the overall efciency and power output. Tis reduction of power limits the viability of photovoltaic cells as an alternative energy source. Previous studies reported thermal behavior of the CPV solar cells, such as Min et al. [1] and Cotal and Frost [2] who developed a theoretical thermal model for predicting the temperature of a multijunction solar cell based on passive cooling systems. Vincenzi et al. [3] used a silicon wafer with microchannels circulating water directly beneath the cells as an active cooling system. Moshfegh and Sandberg [4] performed both a numerical study and an experimental study of the fow and heat transfer characteristics of natural air convection behind solar cells. Te results demonstrated that surface radiation signifcantly afects the temperature and conversion efciency of the solar panel. Bhargava et al. [5], Garg and Adhikari [6], and Hegazy [7] analyzed the performance of hybrid photovoltaic/thermal (PV/T) air heating collectors and reported the efects of diferent design and controlling parameters on system performance. Al-Amri and Mallick [8, 9] recently developed a numerical heat transfer model for predicting the maximum cell temperatures of multijunction concentrating solar cell systems that were actively cooled by water-forced and air-forced convection. Te maximum cell temperature was strongly dependent on the inlet velocity and the channel width. Teo et al. [10] experimentally investigated an active cooling system for Hindawi Publishing Corporation International Journal of Photoenergy Volume 2014, Article ID 642819, 12 pages http://dx.doi.org/10.1155/2014/642819