An experimental study on small scale sea water desalination unit through solar power in Cox’s Bazar, Bangladesh

Fresh water is the basic requirement of human life. Water for drinking purpose, industrial and agricultural purposes demands ample quantity of fresh water. The solar desalination systems have the advantage of low maintenance and operational cost. In spite of high investment cost of solar stills, they are friendly to the nature. In the present article, a modified stepped solar still has been designed, fabricated and tested. The modification includes fabricating steps on which small earthen lamps are placed. The maximum temperature on the steps was found to be 67oC. In case of conventional solar still the maximum temperature recorded was 53oC. The maximum temperature of water at the steps was 26.41% higher than the basin temperature of conventional solar still. The maximum productivity of the modified solar still was 326.66% higher than conventional solar still. The optimum water input flow was found to be 250 ml/hr. I. Introduction Fresh water is primary requirement of human race. Water for drinking purpose and other industrial and agricultural purposes demands large quantity of fresh water (1). The solar desalination systems have the advantage of low maintenance and operational cost. Although solar stills have high investment cost, they are compatible with the environment (2). About 6.3 billion people are living on earth in which 400 million people are at living in water scarce areas which would rise to four billion by mid-century (3). The fabrication of solar still is simple and can be constructed by locally available materials and unskilled people. Solar stills are widely used for desalination in small scale. (4). According to an estimation, about 97% of available water sources are saline and/or consist of harmful bacteria and 2% are in the form of frozen glaciers and polar ice. Hence, only 1% of the earth's water can be used for drinking and domestic purposes (5).The arising requirement for water is primarily due to the increase of population and fast growth of industries (7). The heat energy of sun can be used in solar collectors, solar cooking, desalination and cooling systems (8). Generally, for steam generation, water heating processes and CPCs are used, as they are capable of producing higher temperatures in comparison of flat plate collectors, they can also be used for desalination purpose (9).Most of the arid, remote and semi-arid regions are lack natural fresh water in the southern part of the country and are dependent heavily on underground water for drinking purpose (10). Higher productivity is obtained in multiple-effect diffusion solar still (MEDS) (11). Solar stills are largely used for water purification in rural and remote areas with limited demand and low population when the potential of brine water sources and solar energy are available (12). II. Literature review There has been a lot of work in the field of solar stills to enhance its performance. Researchers have improved the performance by various means such as change in geometry, employment of mirrors in various orientation, use of waste heat etc. Park et al. (2016) designed a multiple-effect diffusion (MED) hybrid solar still with dual heat sources of solar thermal energy and waste heat. Performance tests with waste heat were performed with three operational parameters: (1) the seawater level in the basin (2) the seawater flow rate to the wick and (3) the amount of heat input into the hybrid still. It was observed that the productivity of the hybrid still increases with the increasing heat input, which recorded productivity of 18.02 kg/m 2 at waste heat amount of 22.37 MJ/d. The maximum productivity of distillate was obtained at the lowest seawater level with the experiment including waste heat source. The maximum performance of the MED solar still was achieved at the operation condition obtaining maximum productivity at the second effect plate (13). El-Agouz modified a stepped solar still using a storage tank for salt and sea water with continuous water circulation. Investigation was made on effect of installing a storage tank and cotton black absorber for modified stepped solar still on the distillate productivity. The indication was given by the results that, the productivity of the modified stepped still was higher than conventional solar still by 43% and 48% for sea and salt water with black absorber respectively, while 53% and 47% of sea and salt water, respectively with cotton absorber. The daily efficiency for conventional solar still was 20% lower than the modified stepped still. At a feed water flow rate of 3 LPM for salt water and 1 LPM for sea water, maximum efficiency of modified stepped still was obtained (8).

Enhancement of pyramid solar still productivity using absorber plates made of carbon fiber/CNT-modified epoxy composites

Modeling an active solar still for sea water desalination process optimization

In this research project two solar still plants have been fabricated; single and double slope still plants. The exergy and exergy efficiency concepts have been applied for the comparative analyses of both solar stills. Experimental readings, i.e. various temperatures, amounts of distilled water and solar radiations have been taken for solar stills at different time intervals in Indore (22° 43′ 4.51″ N and 75° 49′ 59.88″ E). The percentage variations in the different parameters, i.e. increments in temperature, increments in quantity of water, thermal efficiencies, rates of exergy at inlet/outlet and exergy efficiencies have also been calculated for stills at various solar intensities and time intervals. After experimental and comparative analyses, better outputs have been shown at 14:50 PM for double slope and 14:45 PM for single slope plant due to the cumulative effects of solar radiations on the still plants. During this period thermal/exergy efficiencies, i.e. 46.630/1.949% and 47.259/3.389% were found the best. The performance of single slope solar still has been found better, and 14:30 to 14:50 PM time interval has been recorded superior for the distillation of water through still plants where percentage increments of the performance evaluating parameters were enhanced.

Solar energy as a sustainable and accessible energy source can be harnessed and converted to electrical energy using photovoltaic modules. Solar Photovoltaic (PV) systems show tremendous promise as sustainable, environmentally friendly and low-cost electricity sources. Solar energy can also be applied to produce potable water using solar distillation still. In this study, water production performance of four low-cost solar stills with different arrangements of PV module-DC heater and sea sand layer in the solar still basin was evaluated. Four types of double slope single basin solar distillation stills with similar shapes were fabricated. A stainless steel basin with length 50 cm, width 30 cm and depth 8 cm was used in each solar still. The still configurations differed based on inclusion of 2 cm depth of sea sand layer in the basin and use of a 50 Watts PV-DC heater. A comparison of the cumulative water production among these solar stills showed that the integrated system that included sea sand in the solar still basin and also used PV-DC heater was the most effective; producing two times the water produced by a conventional solar still. The integrated solar still can be employed in coastal and rural areas with lack of clean water and electricity supply.

A novel analytical performance investigation of varying water depth in an active multi-stage basin solar still in addition to optimization of water depth in a single stage basin still

Factors affecting basin type solar still productivity: A detailed review

The lack of safe and clean drinking water sources is one of the problems faced in most rural communities in Zambia. Water in these communities is mostly obtained from shallow wells and rivers. However, this water might be potentially contaminated with harmful substances such as pathogenic bacteria and therefore, unsafe for drinking. Solar water distillation represents an important alternative to palliate problems of fresh water shortages. Solar water stills can be used to eliminate harmful substances from contaminated water by treating it using free solar energy before it can be consumed. Therefore, there is a need to improve solar still performance to produce a greater quantity of safe drinking water. One possible method to improve performance is through adding reflectors to solar stills. Reflectors improve performance by increasing the quantity of distillate by about 22.3 % at a water depth of 15 mm and about 2 9% at a water depth of 10 mm when compared to the distillate produced from a still without reflectors. The water produced using solar stills with reflectors was tested and adhered to World Health Organization (WHO) drinking water standards. This implies that solar distillation with reflectors could be adopted at a larger scale to produce safer drinking water at a reduced cost.

Modifying performance of solar still, by using slices absorber plate and new design of glass cover, experimental and numerical study

Performance of solar still units and enhancement techniques: A review investigation

In the present purely experimental work, we tested a solar distiller with a simple slope in the region of El-Oued located in the south-east of Algeria, during the winter then the summer seasons at the same place. Dimensions of the studied device are (1000 x 500 mm), while the depth of the water to be distilled is 1 cm, the glazing thickness is 4 mm, and the tilt angle with respect to the horizontal is 10 °.The aim of this work is to compare distillation between winter (January) and summer (May) to show that weather factors such as solar radiation, ambient temperature and humidity are influential on the distiller productivity. The amount of distilled water in winter was about 119 ml per day. However, that in summer was 1127 ml per day in total, so it is an increase of more than 9 times the production of distilled water.

Clean water is essential for good health which influences the social and economic development of any nation. However, there is limited access to safe water on a global scale. This challenge can be overcome through a multi-faceted approach, including the development of appropriate technologies for water treatment and decision-making tools. Solar distillation is one of the commonest non-conventional methods for improving the quality of water. In this vein, the most widely-exploited solar distillation system is a conventional solar still, which has a thin layer of saline water in a shallow basin with a transparent cover over the water and one or two slopes. The productivity of a solar distillation system is influenced by design, climatic and operational factors, with solar radiation being the most influential meteorological parameter. It is therefore necessary to optimize solar radiation that effectively reaches the base of the solar still. Previous attempts have sought to improve the design characteristics of conventional solar stills through the consideration of system geometry and optical properties of construction materials. One of the important geometric parameters is the ratio (R) of length to width (aspect ratio) of the still base. For a single-slope solar still (SSS), R has been examined in preceding studies. Nevertheless, there is a paucity of information on the aspect ratio of a double-slope solar still. In this study, a state-of-the-art software (ESP-r) was used to simulate the variation of effective insolation with R for a double-slope solar still (DSS) in the east-west and north-south orientations and a SSS facing south. Meteorological data captured at the University of Strathclyde and Guantanamo Bay was employed in this analysis. Simulation results show that the optical performance of a DSS was lower (in both orientations) than that of a SSS at both sites. The DSS collected more solar energy in the east-west orientation than north-south orientation, for a given value of R. In addition, effective insolation increased with R to an optimum level for both the DSS and SSS. Approximate optimum values of R were 3.0 and 2.0 for the University of Strathclyde and Guantanamo Bay respectively. However, the optimum value of R was not sensitive to the orientation of the DSS at the two sitesFurther, the DSS and SSS exhibited the same optimal value of R at a specific site. . It appears that R significantly affects solar collection in DSS.

Potable water is essential for human existence. In addition, the quantity of potable water is limited. On the other hand, saline water is available, but it is not considered potable. Solar energy is utilized to convert saline water into potable water through a process called solar desalination. Solar stills are devices used to convert saline water into potable water using solar energy; however, the quantity of potable water produced is low. This review paper shows the use of evacuated tubes to increase the water temperature and hence increase the potable water from solar stills. Various researchers have worked on solar stills with evacuated tubes, as discussed in this review. The study concluded that evacuated tubes are among the most crucial components for increasing the amount of drinkable water produced by solar stills.

Techniques used to improve the performance of the stepped solar still—A review

Due to the scarcity of potable water in some places and inability of available natural sources to fill the growing need for supplies of safe drinking water in addition to the high cost of energy used in saline water desalination. Pollution of fresh water resources by industrial wastes has heightened the problem. Solar energy is one promising solution to meet these ever-increasing demand clean and eco-friendly techniques should be used like solar distillation. This study is done to find the effect of PCM on solar distillation in a double slope solar still. The principle of pure water production from saline water using different designs of a solar water distillation technique is the same. A phase change material is a substance with high heat of fusion which, on melting and solidification is capable of storing and releasing a large amount of energy. In a double slope solar still, solar distillation was performed and the distillate output collected was recorded without using PCM. Some modifications were made to the solar still. Solar distillation was again performed in the solar still with different PCM. The amount of the distillate collected changes with many factors. The selection of PCM is an important step in the project. There are various things to consider before choosing a PCM. The theoretical model of the solar still system is developed. Through the various experiments performed on the solar still, various analysis were shown.