Comparing the performance of passive and active double and single slope solar stills incorporated with parabolic trough collector via energy, exergy and productivity

An experimental work is presented on comparing the performance of passive and active single slope (SS) and double slope (DS) solar stills without and coupled with parabolic trough collector (PTC). The comparison is based on still freshwater productivity, and energy and exergy efficiencies. This work is performed at hot (summer) and cold (winter) climate conditions under meteorological conditions of upper Egypt. Results illustrate that the freshwater productivity and efficiency of the solar stills with or without PTC in summer is greater than winter. Moreover, DS still has greater freshwater productivity, energy and exergy efficiencies than SS. The maximum freshwater productivity increases by about 6% in case of using DS still with PTC (DS + PTC) instead of SS with PTC (SS + PTC). Coupling PTC with SS still rises its daily yield by 115% and 85% and its average daily energy efficiency by 38.3% and 49.1% in summer and winter, respectively. The maximum average daily energy efficiency of the DS + PTC system is 49.09% and its total efficiency is 22.96% with an increase of 16.5% and 5%, respectively compared to SS + PTC. The average daily exergy efficiency of the DS only and DS + PTC in summer increases by 3.3% and 2.6%, respectively compared to the corresponding SS. (C) 2019 Elsevier Ltd. All rights reserved.