Chang [1] proposed a method to determine the gain of a tracked panel, rotated about a horizontal east west axis with continuous adjustment to minimize the angle of incidence, according to three kinds of radiation sources will be considered, i.e. the extraterrestrial radiation, global radiation predicted by empirical models under clear sky situation and global radiation observed in Taichung (phi=-24.2 degrees N), Taiwan. In this article, Chang [1] incorrectly calculated the daily variation of the solar azimuth angle. The mentioned error could have its influence on all other results. The present comments are focused on correcting the calculated solar azimuth angle by Chang [1] and to discuss the sensitivity of other calculated values to this observed error. (C) 2018 Elsevier Ltd. All rights reserved.