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

Himanshu Manchanda,Mahesh Kumar

doi:10.1186/s40807-015-0019-8

Abstract

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/m2/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/m2 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.

Highlights

With the growing demand of energy, environmental concern and fast run out of non-renewable energy sources, it becomes necessary to use the renewable energy sources for various applications
The analysis showed that the economic feasibility of a solar still desalination system becomes more justified, if environment degradation costs associated with fuel-based desalination are acknowledged
It was concluded from the study that inclined solar still design with wick and weir, lower water depth, still orientation, condensing cover cooling, and energy storage materials significantly improve the distillate output of the system

Summary

Background

With the growing demand of energy, environmental concern and fast run out of non-renewable energy sources, it becomes necessary to use the renewable energy sources for various applications. Solar still productivity improves with lower water depth, condensing cover inclination equal to latitude of place, with energy storage materials, sun tracking system, reflectors, flat plate collector, and phase change material Numerous operational parameters such as free surface area of water, water glass temperature difference, and inlet water temperature. (DSS), and single slope dou- and water depth the effect of DSS and SSDAS solar still gives higher distil- still, 10° tilt angle and 0.02 m ble effect asymmetrical still (SSDAS), basin area—1 m2, with different orientations and design parameters late output than symmetrical water depth gives higher double slope still yield These results condensing cover inclinaare concluded only for one tion—10°, 30°, and 45°. In stepped solar still with and daily efficiency without internal reflectors, of SS with and without respectively reflectors is not increased significantly (3 %)

Rajaseenivasan and Murugavel Double slope single and

Findings

Conclusion