In the present paper the performance of solar chimney power plants based on second law analysis is investigated for various configurations. A comparison is made between the conventional solar chimney power plant (CSCPP) and the sloped solar chimney power plant (SSCPP). The appropriate entropy generation number and second-law efficiency for solar chimney power plants are proposed in this study. Results show that there is the optimum collector size that provides the minimum entropy generation and the maximum second-law efficiency. The second-law efficiency of both systems increases with the increasing of the system height. The study reveals the influence of various effects that change pressure and temperature of the systems. It was found that SSCPP is thermodynamically better than CSCPP for some configurations. The results obtained here are expected to provide information that will assist in improving the overall efficiency of the solar chimney power plant. (C) 2013 Elsevier Ltd. All rights reserved.