A comprehensive decade review and analysis on designs and performance parameters of passive solar still

The simplest and easily accessible type of solar distillation is passive solar still which utilizes freely and abundantly available sun energy for removal of salinity/impurity from saline/brackish water. The main drawback of passive solar still is its lower efficiency and distillation output. Different designs of passive solar stills are fabricated and tested by various researchers to meet water demand economically. Concave wick basin pyramidal-shaped solar still was observed to produce 4.0 l/m/day average distillate with a cost of 0.065$/l. Double basin solar still showed an average of 85 % higher yield than single basin still. Stepped type, inclined, tubular, pyramidal, spherical, and hemispherical shapes were considered an efficient designs of passive solar still. Numbers of parameters such as water depth, solar radiation, ambient conditions, condensing cover material, its cooling and direction, internal and external reflectors, sun tracking system, wicks, thermal and energy storage materials were outlined which highly affect the performance of solar still. Water depth of 0.04 m and condensing cover inclination to latitude of the place were observed optimum operational parameters. A distillate output of 4.3 l/m was collected with cotton gauge top cover cooling to V-type solar still. Increase of 75 % in productivity and 56 % in daily efficiency was observed with internal reflector stepped solar still. An improvement of 380 % was observed in stepwise basin solar still integrated with sun tracking system. Despite large efforts carried out on passive solar distillation, there are some challenges like bulkiness, high initial cost, and optimization of spacing between condensing cover and water surface of inclined still, thermophysical properties of basin material, flow rate, insulation material and its thickness, which need to be improved to make this technique efficient in practical utilization. This review paper mainly presents the results of previous work carried out on the designs, operational and process parameters affecting distillation, cost analysis, further scope of improvement in preceding work along with their limitations. The decade reviews on solar stills based on different context authored by many researchers have also been summarized. Moreover, this review paper will help the researchers to understand the basics of solar still with the need, developments and challenges in passive solar distillation to improve its thermal performance.