In the present study, two solar stills were assembled and experienced to evaluate the yield and energy performance of an improved passive solar desalination system compared to a conventional one. The improved still is incorporated with a latent heat thermal energy storage medium and a parabolic solar concentrator. A parabolic solar concentrator was added to concentrate and increase the amount of solar irradiance absorbed by the still basin. Paraffin wax was applied as phase change material (PCM) in the solar still bottom plate. In the current study also, the effect of impure water profundity inside the still on still's accumulated yield have been assessed. The following study involved a mathematical analysis for calculation of the exergetic proficiency as an efficient tool for the optimization, and yield evaluation of any energy systems and solar stills as well. Experimental research conducted in steady days of summer and winter at six different values of impure water profundity inside the solar still basin. The salinity of the impure water tested was about 3000-5000 ppm, while the salinity for the resulted drinkable water was about 550-500 ppm. The performed outcomes revealed that during summer, exergetic efficiency is higher than its qualified value in winter with approximately (10-15%) for the same water profundity. Results also disclosed that, the exergetic efficiency is higher when the water profundity in the basin is lower with approximately (6-9%). The experimental findings reveals that, the solar still with PCM and parabolic concentrator is higher in the daily freshwater yield in summer with an amount of (55-65%) and in winter with an amount of (35-45%) compared to the usual solar based still. The current work performed during January 2016 as a winter season, and July 2016 as a summer season from 8:00 am to 6:00 pm under the climate conditions of Tanta city-Egypt. (C) 2017 Elsevier Ltd. All rights reserved.