Design, Construction, and Test of Solar Still

Executive Summary

Solar distillation is an effective method of obtaining clean and portable water to primary schools for hand-washing purposes and prevention of diseases such as COVID-19 in community schools with limited clean water resources. A single slope asymmetrical improved still was designed to take advantage of the pure, free solar energy that is available in the region where the device will be used.  During the design, production, and testing process, the project gave priority to the factors and design concepts that will optimize the daily productivity at a minimum cost. All various aspects that promote clean water output were taken into account and analyzed. These included the effect that the surface of the still container has on productivity, the impact of the amount of sunlight on efficiency, and potential effectiveness of improved using a movable external reflector. The final design added several features that increased output capacity to 15.5 liters within 4 hours. This project was a great experience on the importance of the sun as a source of energy.

Table of Contents

Introduction. 4

The Need for the Device and Audience. 5

Investigating and Designing. 6

Initial Sketches and ‘Fit for Purpose’ Statement 6

Concentrating Collector Solar Design. 7

Mexican Project Design. 7

The Rain Maker Device. 8

The Wicking System.. 8

Final Sketches. 9

Design Consideration. 10

Justification of the Design. 11

Production Plan Flow Chart and Safety Guidelines. 12

Production Plan Flow Chart 12

Safety Guidelines. 12

Production Process. 13

Construction Details. 13

Assemblage. 14

Finishing. 14

Analysis of Evidence of Performance Data. 15

Evaluating Effectiveness and Efficiency. 15

Modification to Improve Efficiency. 16

Financial Analysis. 18

Evaluation/Reflection Video. 18

Concept Map. 19

Conclusion. 20

Reference List 22

Design, Construction, and Test of Solar Still

Introduction

Global warming and climate change have become one of the most debated issues in the 21^st century. The future of humanity has been questioned with the rising water levels and natural disasters that have resulted from continued global warming. It has required that every human and governments around the world consider the existing energy reserves. It is interesting to note that human activities such as the burning of fossil fuels to meet their energy needs have played a significant role in contributing to the dilemma of global warming. There is an increasing need to minimize the risks associated with continued global warming and climate change by considering alternative clean energy sources.

Most importantly, it is essential to conserve non-renewable energy sources through clean, renewable sources such as wind, thermal, and solar. Another reason why renewable sources of energy are critical for the world today is the reliance on fossil fuel. The use of fossil fuel poses a great danger to the continued development of economies due to the fluctuations in oil prices and conflicts arising from oil exploitation and trade (Miller, n.d.). Solar energy is obtained from the power from the sun. It can produce approximately 1.8×1011MW, the power that is a thousand times larger than all domestic and commercial clean1010 is the entire world (Appropedia, 2017). That makes solar energy a sustainable single source of energy for the present and future generations. It is also freely available and environmentally cleans source of energy; hence has a great potential in mitigating the effects of global warming and climate change (Appropedia, 2017). Solar distillation is a process of evaporation and condensation aimed at purifying water. Solar still is and equipment that could be used to purify water at a high-efficiency level and low costs. This paper aims to design, construct, and test solar still that will be used to purify hand-washing water for students in primary schools at a low cost and high-efficiency levels.

The Need for the Device and Audience

In this health period, pandemics such as Corona Virus Disease 2019 (COVID-19) and similar diseases require strict adherence to World Health Organization guidelines, including frequent hand washing using clean water and soap. Therefore, easy access to uncontaminated clean water is an integral part of fighting infectious diseases and maintaining a healthy daily life (Service, 2017). Currently, almost every water source found globally is contaminated with impurities and chemical substances that make its direct use of a health hazard. It means that it is not proper to use the water directly as it is naturally found as it may contain some impurities that can prevent its safe use and consumption by humans and animals.

Unavailability of healthy handwashing and drinking water has been reported in learning institutions, particularly in primary schools. Due to their interactions and daily activities, primary children are very active and thus at a higher risk of touching contaminated surfaces during their playing and interactions at school. Due to funding issues, many primary schools are ill-equipped to provide proper sanitation for students, including clean and uncontaminated water points (Service, 2017). The conventional means of providing uncontaminated and pure water points include the use of electricity and other sources of energy, such as boiling using coal to purify the available water. That not only adds to the costs of operations in primary schools but also depletes our sources of non-renewable energy. Thus, it puts our planet at risk of not having sufficient energy for generations to come. It is in addition to contributing to global warming and associated adverse effects that have continued to devastate many communities around the world. That underscores the great need to use clean and cheap energy to ensure that our primary school-going children access uncontaminated clean water for handwashing in schools.

This project aims to design, construct, and test a solar-powered water distillation device used by primary school-going children in schools. The device needs to achieve high efficiency at a minimal cost if it meets cost-cutting and high-performance objectives. This device should meet the hand-washing needs of one classroom of 20 primary school-going children using approximately 30 liters of water every day. This solar water distillation device should allow these primary school students to maintain a constant water supply, with a very safe structure that is easy to clean and interact with between class lessons.

Investigating and Designing

Initial Sketches and ‘Fit for Purpose’ Statement

For this solar water design to meet the purpose of the selected audience, the following design requirements must be addressed in the initial sketches.

• The water distillation device must be powered by solar energy.
• The device must be able to produce between 4-6 gallons of clean and uncontaminated water every day.
• The device must be affordable to the community-based organization that wishes to supply them to primary schools.
• The device must be portable from one place to the other by two people.
• The device must be able to maintain high performance and efficiency levels.
• All the parts of the device must be able to be cleaned frequently by simple processes.

Several design concepts were considered for this solar-powered water distillation device for primary school-going children. Various beneficial designs were identified through the search for similar products and patents. The design concepts used in these specified designs were critically investigated. Practical ideas have been combined to develop the desired design concept that would meet the needs of hand-washing solar still for primary school-going children.

Concentrating Collector Solar Design

The first design concept that was investigated was concentrating on collector solar still. It applies parabolic mirrors that focus the sunlight rays onto the evaporation vessel that is enclosed. The advantage of this design is that it results in too high temperatures for high-efficiency levels (Solar Water Distiller, n.d.). However, this design has several drawbacks, including the high cost of construction and maintenance, as parabolic mirrors are very high. The design requires to be used in regions with strong sunlight (Durkaieswaran & Murugavel, 2015). Thirdly, this design, as it is composed of mirrors and other fragile materials, is not very ideal for use by the active primary school-going children as it is delicate.

Mexican Project Design

It uses a basic design concept that is asymmetric and consists of an enclosed basin at the bottom and slightly tilted glass at the top allowing incident solar to access the water contained in the basin. The concept interesting to the current design is that it uses glass as a surface to condense the water vapor. However, the design was deemed inefficient for the current project as the basin’s outer walls lacked insulations (Kumar, Kumar, Prakash, Kaviti 2015). The design was ineffective for the current project because it required significantly strong sunlight to heat the entire volume of water contained in the still. That was because the design required that all water be collected once in the device (see figure 1 below).

Figure 1: Mexican Solar Still

The Rain Maker Device

This device, known as Rainmaker 550, follows the design of the Mexican device mentioned above. However, it was considered to have one advantage of the Mexican type because of insulated wall surfaces’ inclusion. It makes sure that the heat absorbed by the still is retained for higher performance and efficiency. However, it was noted that this still retained the disadvantage of requiring the entire volume of water contained in the vessel to be heated once (See figure 2 below).

Figure 2: Rain Maker550

The Wicking System

Another design concept that was investigated here is Tilted Wick Still. The beneficial design aspect of this design discovered is the capillary action that allowed the distribution of feed water over the thin layer’s entire wick surface. That provides broad surface area exposure to the sunlight and thus maximizes sunlight intensity. This concept allows higher temperatures within the thin layer and makes the device efficient in distilling contaminated water. However, this design has some disadvantages because it is very costly and requires very complicated insulation processes (All About Water Filters, 2018). Also, it has high maintenance costs because the cloth used in the wick needs specialist cleaning to remove the sediments that have built up (See figure 3 below).

Figure 3: Tilted Wick Still

Final Sketches

Following further investigation, many beneficial concepts were discovered, and concepts impractical to the current project and were dismissed. Some of the concepts found helpful and applicable to the current device include maintenance if a constant water level, the increased surface area of the basin to ensure maximum exposure to the sunlight, and to ensure that heat is retained within the walls of the basin by insulating the walls of the still. Additionally, lenses were also found to be beneficial in ensuring that the incident light is concentrated. However, due to its cost implications and its construction complexity, this idea was discarded. Wicking system was also dismissed because it required a relatively high level of maintenance.

The final design concept adopted for this project is improved asymmetrical still, which was enhanced by adding some features that were considered beneficial from the investigation conducted. These features were added to enhance the efficiency of basic designs using concepts discovered from other designs. The following features were incorporated to improve the still’s efficiency.

Additional Features are below:

• Insulation on the sidewalls of the still to retain heat energy within the device
• Small float valve that regulates water to amount to height levels of about 2 centimeters to allow effective heating.
• Partitioned basin to permit smaller volumes or water bodies is preferably heated rather than heating the entire volume of the basin once.
• A flexible and insulated door for easier cleaning of the partitions and expulsion of salt debris.
• A preheated input reservoir using the solar absorbed during the entire day to ensure that solar radiation is maximized within the device.
• A solid structured stand that is constructed ergonomically to take minimal space in front of primary classes.
• Mirrored basin walls to concentrate all light to the water rather than allowing light absorption into the wall’s materials.

Design Consideration

In designing this device, there were critical factors that were taken into account. That included the strength, efficiency, productivity, size, maintenance costs, safety, service life, simplicity, operability, and cost of materials. Also, other factors that were important in the design of this device were the instantaneous and overall efficiencies, and general heat transfer within the entire device system (Hansen, Narayanan, & Murugavel, 2015). The overriding factors included the cost-effectiveness, maintenance, and ease of operation by the primary students.

Figure 4: Final Design

Volume

The volume of the still was obtained working out the required volume as shown below

=

=  = 0.4275m³

Hence, 0.4275 x 1000 = 427.5Litres

Justification of the Design

This single slop design solar still with partitioned basin is better and preferred for the current project because of the following reasons:

• As shown in figure 4 above, the various partitions added ensures that not the entire volume in the basin is heated all at once thus increases the efficiency of the device
• It has a top glazing cover that allows efficient sun radiation to reach the water in the partitions.
• It has mirrors at the sides of each partition to focus maximum light energy onto the water surface and, therefore, no heat through wall absorption.
• The insulation also prevents heat absorption by the walls of the system.
• The design is made from locally available and cheap materials, making it affordable to the community sponsors.

Production Plan Flow Chart and Safety Guidelines

Production Plan Flow Chart

The production plan flow chart is presented as shown below

Safety Guidelines

The safety guidelines that were followed during the production of this single slope solar still include the following:

• All construction equipment was taken out in an open leveled surface.
• No liquid or substance was tested during and after the construction.
• The industrial hand gloves were inspected for integrity and tears before being used throughout the construction process.
• The parts of the device were fitted carefully to follow the partitions’ length and height, and more significant consideration was given to the mirrors’ angles.
• The silicone that was used in glass fitting was considered for compatibility issues.
• During the welding, protection goggles were used to protect the eyes from flying particles.
• All pieces of steel, glass and insulators used were properly disposed of after the construction.

Production Process

It involved the fabrication process where different parts of the device were put together to form a single component. Several steps were followed in the full construction of the single-slope solar still. They are highlighted below.

Construction Details

A large mild steel sheet was measured through a measuring tape to construct the still basin. The scriber was then used to mark the dimensions required for the basin that included 1500 mm by 1900 mm and 17 mm. The marked sheets were then cut out carefully using a hack saw. The final basin was welded using a welding machine to form the basin.

Plywood was used to construct the sidewall. The plywood was measured using the tape measure, which was then joined and nailed together. To build the top glass cover, which was estimated to the desired measurements and cut using a glass cutter. The PVC pipes were measured and marked with a scriber to construct the channels. The marked points were then cut and affixed to various specific positions firmly. The collector that was used in this device was a standard collector that was obtained from a supplier.

Assemblage

Following the successful purchasing and fabrication of all parts into place, the assembling of various components was done in procession. The insulation of the side walls was done. Then, the basin was placed inserted. Next, the channel was then fixed on the sides. The glass was them fixed on the top to cover the entire still. Then the connectors were connected to the channels.

Finishing

Following the completion of assembling, the finishing was done by dressing the rough edges of glass and metal using sandpaper and file. The entire walls of the still were then painted to protect the still from corrosion and give it an attractive look.

Figure 5: Finished Device

Figure 6: Finished Device

Analysis of Evidence of Performance Data

Evaluating Effectiveness and Efficiency

The testing of this device for effectiveness and efficiency was done in August. The varying amount of water was put into the device, with each volume recorded.  The amount of water filled into the still was 15 liters, 20 liters, and 25 liters. The output was also recorded for each amount, respectively and was recorded as below. The testing time was 4 hours. The maximum temperature that was achieved during this test was 65⁰C.

Table 1: Volume of water obtained in Testing

From the data obtained above, it is clear that the maximum output of clean water is collected when 40 liters of water is put into the device.

Therefore, it follows that the volumetric efficiency of this device could be calculated as

ηv  = 12.4/40 ×100

ηv = 31 %

The distilled water’s pH was 6.26, which is within the range recommended by the World Health Organization, which is between 6.50 and 8.50.

Modification to Improve Efficiency

Several actions could be taken to improve efficiency. The solar still should be able to maintain a high temperature of the feedwater, a large temperature difference between the condensing surface and the feed water, and a relatively low vapor leakage To achieve high efficiency (Rajaseenivasan, Tinnokesh, Kumar, & Srithar, 2016). However, modifying the solar still to attain all these aspects involves a high cost and beat the logic of maintaining a low cost and efficient solar still.

The modification that was adopted to achieve high efficiency was the addition of the external reflector. That is where an external reflector was added to the single-slope solar still to increase the incident solar energy into the still.  This external reflector ensures that a portion of solar radiation that is outside the solar still system is reflected onto the glass and into the water. It is critical to note that the sun’s position keeps changing frequently, and the system has a single inclined surface. Therefore, maximum efficiency in such a system could be increased when the external reflector is hinged carefully to the edge of the system in a manner that allows free movement of the mirror following the sun’s position. It increases the overall amount of incident solar energy radiated into the still, thus creating more efficient solar still. Following this modification, the following results were obtained.

Table 2: Volume of Water after Modification

As observed in the results, the maximum amount of water collected remains high, with the input of 20 liters of feed water. The volumetric efficiency of the still now becomes, before modification, as follows:

ηv = 12.4/40 ×100

ηv = 31%

After Modification using External Reflector

ηv = 15.5/40 ×100

ηv = 38.75 %

The results show that this system’s volumetric efficiency is 31% when 40 liters’ input is used within 4 hours. However, this efficiency could be significantly increased to 38.75% when an external reflector is attached to the still. The addition of this reflector resulted in,

[(38.75-31)/31] ×100

25% increase in volumetric efficiency.

Figure 7: Input Water versus Output Water

Financial Analysis

The cost of this device amounted to $340. This cost is affordable for the community organizations with funds allocated to handwashing, ranging between $ 1500 and $ 3400 per year. However, the costs could significantly drop local materials such as plywood and stand are obtained locally from the community. It is less expensive than purchasing commercially distilled water from a local supplier, and the long-term benefits outweigh the initial setup costs. Also, the low maintenance costs make this device worth an investment.

Evaluation/Reflection Video

Several lessons have been learned using this device. This project’s first important lesson is that water purification could be done using very simple evaporation and condensation process. The reason is that the impurities in the water cannot evaporate. The second lesson that was very insightful is the capabilities of sunlight as a source of energy. The sunlight is absorbed by both the water in the still and the container of the still. That results in the absorption of energy by the molecules and ions. With enough energy absorption, some water molecules can free themselves from the liquid and change to gaseous state, which then flies around within the still container. The free-flying gas molecules collide with the sides of the container and film. Eventually, they lose their energy to these surfaces and stick on container walls. The most important idea that I have obtained from the whole process is the role that energy plays in all of these. Energy is required for evaporation and is then released during condensation. Solar is our primary source of clean and renewable energy, which, when harnessed, could be very useful in various applications.

Concept Map

The concept map for this solar still device design, construction and testing are presented below.  

Conclusion

This project provides practical application and an exceptionally insightful reinforcement of solar energy theories as a renewable energy subject. This exercise involved the design, construction, and production of a solar device that could be used to purify water using solar as a source of energy. This project aimed to ensure that the device is cheap and efficient to allow community-based organizations to supply them to primary school children to promote hand-washing in schools. The materials used in this project are cost-effective and make solar energy more cost-efficient than other sources. By applying mathematical knowledge and solar energy knowledge, the device’s efficiency was improved by incorporating a reflector that enabled more solar energy to be focused on the device. That has been a very insightful experience that, when applied in other areas, could help humans solve their global warming and climate change issues in addition to conserving the energy sources for future generations.

Reference List

All About Water Filters, 2018. Ultimate guide to solar water distillers: solar water distillation 101. Available from http://all-about-water-filters.com/ultimate-guide-to-solar-water-distillation/ [26 August 2020].

Appropedia, 2017. Solar distillation. Available from http://www.appropedia.org/Solar_distillation [26 August 2020].

Miller, B., n.d., Water conservation & efficiency protects rivers and lakes. Available from https://westernresourceadvocates.org/water-conservation-efficiency/ [26 August 2020].

Durkaieswaran, P. & Murugavel, K. K., 2015. ‘Various special designs of single basin passive solar still – a review’, Renewable and Sustainable Energy Reviews, vol. 49, pp. 1048-1060.

Hansen, R. S., Narayanan, C. S., & Murugavel, K. K., 2015. Performance analysis on inclined solar still with different new wick materials and wire mesh’, Desalination, vol. 358, pp. 1–8.

Kumar, P. V., Kumar, A., Prakash, O., & Kaviti, A.K., 2015. Solar stills system design: a review. Renew. Sustain. Energy Rev., vol. 51, pp. 153-181.

Rajaseenivasan, T., Tinnokesh, A., Kumar, G. R., & Srithar, K., 2016. Glass basin solar still with integrated preheated water supply-theoretical and experimental investigation. Desalination, vol. 398, 214-221.

Service, R.F., 2017. Sunlight-powered purifier could clean water for the impoverished. Available from http://www.sciencemag.org/news/2017/02/sunlight-powered-purifier-could-clean-water-impoverished [26 August 2020].

Solar Water Distiller, n.d. The solar still. Available from http://www.i4at.org/surv/sstill.htm [26 August 2020].