The authors previously proposed and experimentally investigated a new standalone desalination system that is composed of a parabolic trough collector put under conventional solar still. In this study, an unsteady theoretical model is developed using the energy balance equations for the main components of the system to investigate the effect of different parameters on the performance of the new solar still. The model is used for calculation of productivity, and the absorber, saline water, and the glass cover tem-peratures. Results obtained using the present model are compared with the experimental results and a good agreement is observed between them. Moreover, as the experimental study was limited to the winter period, to thoroughly understand the new system performance at different climates conditions, its performance in four seasons is considered. Results show that in Kerman weather conditions, on average the present solar still system produces 0.961 L of freshwater per day in summer which is 55% more than the yield in winter for the Fixed parabolic trough collector. For the parabolic trough collector with tracking systems, the system would produce 1.266 L per day in summer. (C) 2020 Elsevier Ltd. All rights reserved.