Thermal resistance correlation as a design tool of a natural convective heat sink with plate-fins for concentrating photovoltaic (CPV) module cooling is suggested. For this purpose, extensive experimental investigations are performed for various heat sink geometries, input power, as well as inclination angle. From the comparison between the proposed general correlation and the previous studies, it is shown that the proposed correlation predicts well the effects of inclination angle and fin spacing on the thermal performance of the natural convective heat sink with plate-fins. Also, optimal fin spacing strongly depends on the temperature difference as well as the inclination angle. The optimal fin spacing is significantly changed when the inclination angle is larger than 70 degrees. (C) 2012 Elsevier Ltd. All rights reserved.