The aim of this study is to investigate the seasonal effect of dust on the degradation of PV modules deployed in two different climate areas, Perth, Western Australia, a temperate climate region and Nusa Tenggara Timur (NTT), Indonesia, a tropical climate region. Results revealed that PV performance varied with season. In Perth, the performance of PV modules which was maximal in the beginning of summer decreased significantly at the end of the season. The performance then increased back approaching the initial position at the end of autumn and reached a peak at the end of winter. Similar reduction to the summer's performance was accounted by the modules at the end of spring. Meanwhile, in NTT, the performance of PV modules was maximal in the beginning of wet season, dropped slightly at the end of the season and decreased significantly at the end of dry season. Degradation of all modules in the two sites was more affected by dust compared to the non-dust related factors. The degradation is important information for future PV design in both areas, especially in NTT which accounted greater values than the typical dust de-rating factors. (C) 2017 Elsevier Ltd. All rights reserved.