A mini review of techniques used to improve the tubular solar still performance for solar water desalination

In this work, we have selected three number of stepped type solar stills of the same overall dimensions 620 mm (W) × 808 mm (L) but with different absorber surface areas due to the variation in the shape of the basin surface. The other design parameters like depth of water, thickness of glass cover, insulation thickness, type of condensing cover, absorbing material provided over the basin, and angle of inclination of the still were kept constant to study the effect of shape of the absorber surface over the distillate yield obtained. The shape of the absorber surface provided in the basins of solar stills A, E and F was flat, convex and concave respectively. When the convex and concave type stepped solar stills are used, the average daily water production has been found to be 56.60% and 29.24% higher than that of flat type stepped solar still respectively. Also an economic analysis was made. The payback period of flat type, convex type and concave type stepped solar still is 823 days, 525 days and 637 days respectively. Thus, the convex type solar still gives the returns within the least possible time as compared to other two types of stepped solar stills. The laboratory tests were conducted to test the quality of water after distillation. The tests indicate that the quality of water in terms of pH, electrical conductivity, total hardness, TDS, Alkalinity, Nitrates etc. is well within the desirable limits as prescribed by WHO for Indian specific conditions.

Advanced designs of solar desalination systems: A review

Nowadays freshwater needs were covered by fossil fuel-based desalination systems in many areas over the world. However, fossil fuels’ excessive burning results in rapid depletion and pollution of the local environment as well as threat to life sustainability. Therefore, through the last few decades the scientific community focused on the systems relying on solar energy in seawater desalination as a clean alternative. Stepped solar stills, which convert solar energy to the required heat for producing freshwater in seawater desalination, are paid much attention. This article provides a comprehensive analysis of stepped solar stills’ development. Performance enhancement techniques, desalinated water production, efficiency and maximum theatrical production are discussed. This work aims to keep researchers and concerned scientific community abreast of stepped solar stills’ improvements. Such stills of low construction and running costs can meet the freshwater daily needs for small communities in coastal areas, islands and rural areas especially in Mideast. In conclusion, this review clarified that the stepped type solar stills still need multiple improvements to enhance their production efficiency and freshwater quantity. Further attention should be paid to the design of modified stills to attain better and efficient solar heat absorption as well as evaporation of seawater.

In the following experimental study modifications were carried out into a stepped solar still, considerably increasing the distilled water productivity. Objective function in present study is the comparison between of an active stepped solar still provided with modifications in a new water cooling circulation depending upon an active mode by means of a PV cell incorporated for a stepped solar still, with a conventional solar still without water circulation. In the study the results of glass cover temperature, basin temperature, and fresh water productivity are collected for both stepped solar stills. Also, the solar radiation rate for a period of June 2018 to November 2018 have been carried out in order to optimize the stepped still performance and its yield as well. It was found that, these additions and modifications highly enhance the evaporation and condensation, so distillate yield was augmented. It was found that, daily distilled water productivity reached about 7.21 l/m2 day for the stepped solar still with water circulation. While corresponding value was 4.45 l/m2 day for the conventional stepped solar still at the same water depth (2) cm at summer times and 6.41 l/m2 day for the stepped solar still with water circulation and 3.5 l/m2 day for the conventional stepped solar still at winter times also at the same water depth. The increase in daily distillate water productivity for a stepped solar still with a PV and water circulation is about 78.24 % higher than that of a conventional stepped solar still. Moreover, the average efficiency of daily freshwater productivity is 42.84 % for a stepped solar still with water circulation, while it was 37 % for a conventional stepped solar still, at the same water depth 2 cm at summer and 40.5 % for a stepped solar still with water circulation and 34 % for a conventional stepped solar still at winter times. The present study held under the climate conditions of Egypt at Faculty of Engineering-Tanta University, Egypt.

Stepped solar Stills: A comprehensive review of Design, Performance, and optimization strategies for sustainable water desalination

Five different solar stills (SSs) have been tested in this experimental study. Hemispherical SS, tubular SS, pyramid SS, double slope SS, and conventional SS are the five SS systems. The primary goal is to determine which SS will perform more effectively at the testing location. Initially, the SSs were evaluated with no changes and the outcomes were contrasted with those of the conventional SS. Secondly, exterior reflectors have been added to four SSs. Third, hemispherical SS and tubular SS with reflectors have been utilized with phase change material (PCM) combined with Ag-Nanoparticles. Lastly, tests using reflectors, fan, and external condensers have been conducted on the hemispherical SS and tubular SS. The findings showed that the increase in productivity for hemispherical SS, tubular SS, pyramid SS, and double slope SS without modifications are 107 %, 97 %, 66.5 %, and 30 % greater than that of conventional SS, respectively. Furthermore, the results depicted that employing reflectors improved the productivity rise for tubular SS, hemispherical SS, pyramid SS, and double slope SS to be higher than conventional SS's productivity by 168 %, 153 %, 113 %, and 85 %, respectively. Besides, the effect of employing PCM-Ag with hemispherical SS and tubular SS (with reflector) is increasing their productivity to be 202 % and 212 % higher than conventional SS's production, respectively. Also, the hemispherical SS and tubular SS with reflector, fan, and a condenser showed 217 % and 236 % higher productivity than conventional SS. The actual cost of producing water for the conventional SS, hemispherical SS, and tubular SS with reflectors and fan is 0.0244, 0.012, and 0.013 $/L, respectively.

A comprehensive review of tubular solar still designs, performance, and economic analysis

Enhancing the performance of tubular solar stills for water purification: A comprehensive review and comparative analysis of methodologies and materials

Water is signified as the gift of nature. However, modern societies are in tremendous need of fresh water due to the abundant industrial sector and factory growth that is leading to more and more such natural resource pollution. Also, there are global arid and desert areas where there are fewer regular rainfalls besides groundwater scarcity. Additionally, although there are abundant water bodies, most of them are not suitable for domestic irrigation, and especially for drinking purposes since they are brackish or saline water. Thus, water desalination is essential with no impact on the environment. Solar desalination is proven to be a sustainable and reasonable way for producing potable water. Numerous sorts of solar stills are introduced, and the most exhibited one is the conventional type of solar still, that is, so-called basin solar still. However, the low productivity of such solar still is signified as its major concern. Researchers have made their efforts to improve the productivity of solar stills through various designs and operating parameters. This detailed review is mainly focused on the various types of solar stills, their analyses and the status of several solar distillers. Throughout the entire work, it is confirmed and recommended to enhance the performance through advanced modifications that are also discussed. Such modifications are including advanced designs such as pyramid triangular solar stills, tubular, double basins and hemispherical and spherical solar stills. Also, integrated systems stills are recommended, such as connected solar stills with photo voltaic cells (PVC) or solar collectors to increase productivity.

Solar distillation is a very economical process for the fresh water production, especially in arid and semi-arid areas where solar energy is abundant. Several types of solar stills have been designed and manufactured for a purpose to increase their performances. This work aims to study experimentally under outdoor conditions of Hodna’s region, two types of solar still, the first is an inclined solar still with different wick thicknesses (thick, medium and thin) operating in drop by drop system of feed water and the other is conventional. Four clear days of the April months have been chosen to experiment the solar stills performances. The results showed that the solar stills performances are notably influenced by design and operating conditions, as revealed by the daily production and efficiency values of the inclined solar still with thin wick which achieved 4.14 liter/m2.day and 46.66%, with an improvement of about 23.21% and 12.56 % respectively, compared to those of the conventional solar still, which reached 3.36 l/m2 and 34.1% respectively. In addition, the economic analysis illustrates that the low cost of one liter of distilled water and the quicker payback period at the same time are for the inclined solar still with a thin wick of about 0.011$/l and 77 days respectively.

Improvement techniques of solar still efficiency: A review

This study aims at improving a solar distillation still by comparing the performance of four types of double slope single basin solar stills to produce adequate amount of potable water in the areas with confined fresh water. These solar stills fabricated with similar shapes. In each solar still a stainless steel basin with the length of 50 cm, width of 30 cm and depth of 8 cm was utilized. The still configurations differed based on inclusion of 2 cm depth of sea sand layer in the basin, a layer of black paint in the basin and use of a 50 W PV-DC heater. The study was conducted to increase the potable water production under Malaysia tropical condition. A comparative research of cumulative water production among these solar stills showed that solar still with black painted basin was the more efficient; producing 234 %, 190% and 148% the potable water produced by a conventional solar still, solar still with sand layer in basin and solar still connected to a PV-DC heater, respectively.

Thermal models of solar still—A comprehensive review

Harnessing evacuated tube technology for enhanced solar still: A comprehensive review

Water is essential necessity on earth for the human beings. For drinking purpose Only 3% of earth's water can be used rest 97% is found in oceans and can't be fit for drinking or agriculture purpose. Many countries in the world facing severe water scarcity problem and can be major reason for war. By considering these problems solar stills came into existence but due to low productivity of pure water its use is limited. This field requires a special attention so many researchers put efforts in order to increase efficiency of stills by introducing different type of solar stills.. But in this paper active and passive type solar still with nano particles has been reviewed to increase efficiency and daily yield of the stills. In passive type solar stills, solar still with nano phase change material has 50.85% daily efficiency and still with CuO nano particles have daily efficiency of 34%.While in the case of active type solar stills when phase change material, nanoparticles integrated with various type solar still, the efficiency was increased by 73.8% over the conventional solar still. When the conventional solar still integrated with parabolic trough collector and 0.10% volume fraction of Al2O3 nanofluid for 2.5cm water depth in 1m² basin, there was 66% rise in productivity and 70% increase in thermal efficiency. It was observed that with decrease in water level in basin the productivity of pure water increases.