Chapter 1 Introduction

Water is a basic necessity of man along with food and air. Fresh water resources
usually available are rivers, lakes and underground water reservoirs. About 71% of
the planet is covered in water, yet of all of that 96.5% of the planet's water is found
in oceans, 1.7% in groundwater, 1.7% in glaciers and the ice caps and 0.001% in
the air as vapor and clouds, Only 2.5% of the Earth's water is freshwater and
98.8% of that water is in ice and groundwater. Less than 1% of all freshwater is in
rivers, lakes and the atmosphere. Moreover, typical purification systems are easily
damaged or compromised by disasters, natural or otherwise. This results in a very
challenging situation for individuals trying to prepare for such situations, and keep
themselves and their families safe from the myriad diseases and toxic chemicals
present in untreated water. Everyone wants to find out the solution of above
problem with the available sources of energy in order to achieve pure water.
Fortunately there is a solution to these problems. It is a technology that is not only
capable of removing a very wide variety of contaminants in just one step, but is
simple, cost-effective, and environmentally friendly. That is use of solar energy.

1.1 History
Solar distillation is a tried and true technology. The first known use of stills
dates back to 1551 when it was used by Arab alchemists. Other scientists and
naturalists used stills over the coming centuries including Della Porta (1589),
Lavoisier(1862), and Mauchot (1869)[3]. The first "conventional" solar still
plant was built in 1872 by the Swedish engineer Charles Wilson in the mining
community of Las Salinas in what is now northern Chile (Region II). This still
was a large basin-type still used for supplying fresh water using brackish feed
water to a nitrate mining community. The plant used wooden bays which had
blackened bottoms using logwood dye and alum. The total area of the
distillation plant was 4,700 square meters. On a typical summer day this plant
produced 4.9 kg of distilled water per square meter of still surface, or more
than 23,000 litres per day. Solar water Distillation system also called “Solar
Still”. Solar Still can effectively purify seawater & even raw sewage. Solar
Stills can effectively removing Salts/minerals {Na, Ca, As, Fe, Mn} ,Bacteria {
E.coli, Cholera, Botulinus}, Parasites ,Heavy Metals & TDS.

1.2 ABOUT SOLAR ENERGY

The sun radiates the energy uniformly in all direction in the form of
electromagnetic waves. When absorbed by body, it increases its temperature. It
is a clean, inexhaustible, abundantly and universally available renewable
energy[1].
 Solar energy has the greatest potential of all the sources of renewable energy
and if only a small amount of this form of energy could be used, it will be one
of the most important supplies of energy, especially when other sources in the
country have depleted. This solution is solar water distillation. It is not a new
process, but it has not received the attention that it deserves. Perhaps this is
because it is such a low-tech and flexible solution to water problems. Nearly
anyone is capable of building a still and providing themselves with completely
pure water from very questionable sources. 3.8x1024 joules of solar radiation is
absorbed by earth and atmosphere per year. Solar power where sun hits
atmosphere is 1017 watts and the total demand is 1013 watts. Therefore, the
sun gives us 1000 times more power than we need. If we can use 5% of this
energy, it will be 50 times what the world will require. The energy radiated by
the sun on a bright sunny day is 4 to 7 KWh per m2 [2].

1.3 Solar Still Evolution

Solar still technology has gradually been improved over the past decade along the
Border. The greatest problem for the first generation stills designed by EPSEA in
the mid-1990’s (an improvement on the original McCracken solar still) was that
when they dried out, the inner membrane silicone lining would outgas. This in turn
deposited a fine film on the underside of the glass, causing the water droplets to
bead up and fall back into the basin rather than trickle down the glass to the
collection trough and thus still water production drops dramatically (about 80% or
more drop). The first still used a food grade silicone and were made out of
plywood and concrete siding. It was found that the stills (3’ x 8’) were often
producing far more water than the users needed, especially in the summer. As time
evolved, a second generation solar still was developed made out of aluminum and
smaller (3’ x 6’ and 3’ x 3’). The still was lighter, but still expensive to build.
Fig. 2. First generation concrete sided EPSEA solar still built in 1995 that has been
operational for over a decade for the Eby family in Hueco Tanks, Texas. This still
uses a food grade rated silicone membrane.
Finally, a third generation still was developed by SolAqua (3’ x 4’) and used ABS
plastic outer shell. The outgassing problem was solved using new proprietary
materials for solar stills that eliminated outgassing problems while earning a NSF
rating for water contact for human consumption. These smaller stills can easily be
paralleled for larger families. SolAqua was granted its first patent in July, 1999 in
the U.S. on material and manufacturing techniques, and has additional patents
pending in the U.S., Mexico, and Europe. The technology has now evolved to the
point where with large manufacturing volumes (thousands versus hundreds of
manufactured units), still costs could be greatly reduced by a factor of three or
more in the future.

1.4Project Overview
Devikulam is a sparsely populated community situated in eastern India. The 320
locals struggle daily to obtain the necessary quantities of water to sustain their
everyday lives. Currently the small town relies upon a 30,000L water tank, 3 bores
(one of which is saline and another which is not currently functional) and the local
pond for their daily water supplies.
Access to safe drinking water is a fundamental human right and an indispensable
component for maintaining a positive quality of life. The Pitchandikulam Forest
Organisation, working in the Kauveli Bioregion (South-East India), had identified
that the village of Devikulam has inadequate access to a safe water supply.
Engineers Without Borders, paired with the Pitchandikulam Forest Organisation,
are in collaboration to find an environmentally sustainable and culturally
acceptable solution for the water crisis in Devikulam.

1.5 Project Aims and Report Contents

The aim of this project is to provide the community of Devikulam with a reliable
supply of uncontaminated drinking water. It is highly desirable to treat the local
water to a level equal to, or greater than, the levels set by the World Health
Organisation (WHO). It is imperative that the solution is:
 Cost effective;
 Environmentally sustainable;
 Socially, economically and culturally acceptable and;
 Perceived as being beneficial.
 1.5 OBJECTIVE OF THESIS

The designed model produces2.5 litres of pure water from 14 litres of dirty
water during six hours. The efficiency of plant is 74.37%. The TDS(Total
Dissolved Solids) in the pure water is 81ppm.

Distillation is one of many processes available for water purification, and sunlight
is one of several forms of heat energy that can be used to power that process. To
dispel a common belief, it is not necessary to boil water to distill it. Simply
elevating its temperature, short of boiling, will adequately increase the evaporation
rate. In fact, although vigorous boiling hastens the distillation process it also can
force unwanted residue into the distillate, defeating purification.
Solar Distillation is by far the most reliable, least costly method of 99.9% true
purification of most types of contaminated water especially in developing nations
where fuel is scarce or too expensive. Solar distillation is used to produce drinking
water or to produce pure water for lead acid batteries, laboratories, hospitals and in
producing commercial products such as rose water. Conventional boiling
distillation consumes three kilowatts of energy for every gallon of water, while
solar distillation uses only the free pure power of the sun. Expensive filtration and
deionizing systems are even more expensive to purchase and use and will not
totally purify the water by removing all contaminants. No additional heat or
electrical energy is required in our still and even after the sun sets, distillation
continues at a slower pace into the night. Recently, we‟ve been experimenting with
a unique optional solar energy booster using our top quality

“Sola Reflex reflector” to increase the water vaporization by increasing the

temperature on the internal fluid heat absorber. This will add efficiency and
increases the amount of daily pure water production. Solar still is possibly the
oldest method of desalination of water. Its principle of operation is the greenhouse
effect; the radiation from the sun evaporates water inside a closed glass covered
chamber at a temperature higher than the ambient. The saline water is fed on a
black plate in the lower portion of the solar distiller. The heat of the sun causes the
water to evaporate and water vapour condenses to form purely distilled droplets of
water when it reaches the cool transparent leaning surface made of glass or plastic

.
 Chapter 2 Design Goals

Based on the project statement, several design goals have been developed in order
for this device to be successful.

2.1 Solar Power

The abundance of solar energy available in Somalia is an untapped renewable
resource that can be harnessed for the proposed device. Other sources of energy
such as fossil fuels are expensive, limited, and simply not available in many parts
of Somalia. Somalia’s abundant solar radiation is a highly effective and completely
renewable resource.

2.2 Affordability
It is unrealistic to expect the average Somali, who makes 50 USD a month, to buy
a distilling device for anything more than 10 USD. Since it may not be possible to
manufacture the device for this little, the device will need to be targeted towards
aid organizations like the Red Cross and CARE (Cooperative for Assistance and
Relief Everywhere). This device has the potential to make an enormous impact in
the daily lives of people without access to a reliable source of safe drinking water.
However, if the cost to manufacture the distiller is too high, organizations will be
unable to purchase it.

2.3 Output
The device should be able to produce two to four gallons of clean drinking water
per day. This would be enough water to hydrate a small family on a daily basis. A
higher output may require electricity and/or heat exchangers, and would require a
larger than practical evaporation surface. Aspects such as these would make the
device expensive and impractical.

2.4 Size
The goal of the distiller is to minimize size while maximizing the output of clean
drinking water. In addition, the device must be portable and moveable by a
maximum of two people. The amount of solar energy available in a region, along
with the desired output, will theoretically dictate the overall size of the device.
However, the size of the device could be minimized by experimentally testing and
optimizing specific design factors incorporated into the distiller.

2.5 Practicality
All of the contaminants contained in the feed water will remain in the distiller after
the water has evaporated. Therefore the device must be easy to clean, since
frequent cleaning will be a requirement for efficient operation. Also, the device
should be easy to level when being installed to ensure uniform water
depth. This will allow for a more efficient operation.

chapter 3 Water Distillation

3.1 Water Distillation

The process of water distillation involves heating water to the point of
vaporization, at which point the water will undergo a phase change from liquid to
vapor. The water vapor then condenses onto a cooler surface where it can be
collected. Any contaminants contained in the original feed water (such as salt, silt,
and heavy metals) will remain in the distiller basin. The collected water vapor is
now free of all prior contaminants and is fit for consumption. Refer to Figure 3
below.

Figure 3: Distillation Illustration

3.2 Basic Concept of Solar Powered Water Distillation

A solar powered distillation device will contain three basic components: a basin in
which the contaminated water is contained, a surface above said feed water for the
water vapor to condense onto (i.e. a glass pane), and a catch basin for the distilled
water to drain into. During operation of the distiller, solar energy is collected by
the feed water. When enough energy is absorbed by the water, the water undergoes
a phase change. The water vapors then rises and comes into contact with the cooler
transparent, inclined surface. Here the vapor once again goes through a phase
change from vapor back to liquid. The water then condenses and runs off the
transparent inclined surface into a collection bin. The distillation process rids the
contaminated water of any impurities and most commonly found chemical
contaminants within the environment. These contaminants are left behind in the
basin. This process is illustrated in Figure 4 below.

Figure 4: Basic Solar Powered Water Distiller

3.3 Research of Periodicals

There are numerous periodicals and formal research papers on solar water
distillation that were evaluated for useful information and ideas. Many ideas were
obtained from these papers. In this section, useful information and features are
outlined from each periodical.

3.3.1 The Effect of Water Depth

In this periodical different water depths were used in the basin of a simple
asymmetrical distiller. The amount of water output for each water level was
measured daily over a time period of one year in New Delhi, India. The effect of
increasing basin absorptivity was also tested during this span of time. The results
show that the daily water output is consistently greater for a shallower water depth.
The shallowest water depth used was 2 cm, while the largest water depth used was
18 cm. Above a depth of 8 cm, it was discovered that output remains constant. The
output for the 2 cm water depth was over 30% more than the water depth of 18 cm.
However, the deeper water levels did yield a higher water temperature. This is
mostly due to the higher heat capacity of a larger body of water. Higher basin
absorptivity was also found to lead to a greater water output.
In conclusion, the majority of solar radiation is absorbed in the first 2 cm of water
depth. Also, the basin absorptivity is a major factor in the design of a solar still.
These two pieces of information are highly valuable for increasing water output.

3.3.2 The Effect of Different Designs

In this periodical two different solar still designs are compared. The first design is
an asymmetrical still with mirrors on the walls (Figure 5). The second design is a
symmetrical still (Figure 6). The water output of the asymmetrical still was
measured to be 30% higher than the symmetrical version. The asymmetrical design
operated at a higher temperature. This is mostly due to the mirrors on the side and
back walls. The mirrors reduced heat energy loss and reflected all incoming solar
radiation towards the basin. Since the asymmetrical design has three insulated
walls where the mirrors reside, there is less area for heat energy to escape. The
symmetrical design has more area where heat loss occurs. In conclusion, the
asymmetrical solar still with mirrors is a superior design with greater efficiency
and higher overall water output.

Figure 5: Asymmetrical Solar Still Design

 Figure 6: Symmetrical Solar Still Design

3.3.3 Comparison between a Single-slope Still vs. a Pyramid-shaped Still

Configuration
In this paper, the single-slope still design received better efficiency and economical
performance ratings than the more complex, pyramid-shaped still design. The
researchers chose Aswan, Egypt, which has a latitude of 24°, for the location of
their experiment. While both designs had equivalent basin areas, the pyramid-
shaped still had a greater glass area, which caused more heat to be lost to the
environment. The pyramid-shape resulted in 8% less solar energy to be received by
the basin during the winter and 5% more solar energy to be received by the basin
during the summer. However, because of the pyramid-shaped still had a greater
glass area, the daily yield of the single-sloped still was 30% greater in the winter
and 3% greater in the summer. Additionally, the estimated cost of water for the
single-sloped still was about .03 $/L. In conclusion, the basic asymmetrical still
design is more efficient and less expensive.

3.3.4 Enhancing Single Solar Still Productivity

In this article, various enhancements are discussed that can increase overall clean
water output, as well as other information that is useful for the design of a solar
still. Once again the idea of using the smallest water depth possible is explored. As
the water depth increases, the output of the still steadily declines. A small decrease
from 3.5 cm to 2 cm increased output 26%. For areas with large amounts of solar
radiation near the equator, it was found that an angle around 23° for the glass is
optimal. This angle works well with the angle of the incoming solar radiation.

In the experiments conducted, it was also discovered that about 16% of the water
output occurred at night, without solar radiation. This is due to the increased
temperature difference between the water and glass cover, as well as the overall
decrease of heat capacity. It was also found that a sprinkler (cooling film) applied
to the outer layer of glass will lead to a substantial increase in clean water
production. The sprinkler lowers the temperature of the glass and increases the
temperature difference between the water and glass, thus increasing production.

3.3.5 Conclusion to Periodical Research

A great deal of important information was discovered during research of
periodicals:
• Water depth was found to be one of the main factors of clean water production. It
is important to maintain a water depth of 2 cm or less.
• An asymmetrical design was found to be the most inexpensive and efficient type
of solar still.
• The optimal angle of the glass for regions near the equator was found to be
around 23°.

• The largest temperature difference possible between the glass and water will lead
to increased water production.

• The greatest absorptivity possible for the basin will lead to the maximum water
output.
• Minimizing heat loss is a key to increased production.

3.4 Patent Research

A patent search revealed numerous designs and ideas related to the use of solar
power to distill water.
Many of the patents which emerged during the search are currently not being
manufactured, and are simply outlined ideas and concepts. Other patents were too
complex in geometry or operation, and were impractical for a cost effective device.

3.4.1 Solar Collection System with Radiation Concentrated On Heat Absorber

Vanes
This patent contained a few key ideas such as the use of Fresnel lenses to increase
the efficiency and overall production of the distiller by focusing the incoming
radiation onto a trough of water. The second idea that this patent introduced was
the use of individual water troughs instead of a large water basin in the distiller. At
the base of the troughs were tightly spaced vanes that utilize the capillary action of
water to increase the surface area of the water being exposed to the incoming solar
radiation, further increasing overall efficiency. By using troughs, the distiller is
able to maximize available surface area and minimize water volume in the distiller.
As shown in Figure 7 below, each trough has a Fresnel lens focusing energy onto
the water. When applying the ideas outlined in this patent to the design goals listed
in Section 2 of this paper, it becomes apparent that incorporating the Fresnel lenses
and the vanes in each trough would defeat our requirements of a low cost and
practical device.
 Figure 7: Multiple Effect System with Fresnel Lenses (cross
section)

3.4.2 Solar Water Distillation System

One elaborate patent available outlines the utilization of electrical power
generation to aid in increasing the fresh water output. Through the use of heat
exchangers and a complicated water plumbing system (refer to Figure 8), the phase
changes from water to water vapor can be completed and maintained at a constant
rate. Although this patent outlines a design that increases the overall water output
of the system, the construction of heat exchangers, complicated plumbing, and
electrical power generation lead to a device that is simply too expensive and
impractical to be utilized in the areas that would require such a device.
 Figure 8: Complex Solar Distillation System

3.4.3 High Output Solar Distillation System

This patent describes a useful multiple effect system. The term “multiple effect”
refers to a system designed in such a way that evaporated water from one surface
condenses on the bottom of another surface and subsequently transfers thermal
energy to the second surface which also contains evaporating water. The design
uses an inclined wicking system in an enclosed area, similar to a basic distiller, to
supply a constant feed of water through the still. The saturated wick allows for
some of the feed water to be vaporized for condensate and the rest of the feed
water run out of the distiller as hot water. Figure 9 shows the multiple wicks
absorbing solar radiation. The design is simple, cost effective, but less efficient as
it does not convert all of the feed water to distilled water.

Figure 9: Multiple Effect Wicking System

3.4.4 Method and Apparatus for Solar Distillation

This device uses a more traditional single basin design, but again uses a water
wicking system. The wick system maintains a constant feed rate that can be
predetermined based on the wick size. It also introduces the idea of preheating the
feed water to increase efficiency, and creating a vapor circulation system inside the
distiller to further increase efficiency. However, as with all wicking systems, the
ability to clean the still effectively is compromised because each of the wicks
would have to be cleaned with water at the end of each day of use. Refer to Figure
10.
Figure 10: Single Basin Wicking System

3.4.5 Patent Search Conclusion

Patents of many different solar distillers exist, from simple one step single basin
designs, to multi-step heat exchangers. However most of the patents outlined
contained aspects that made the design unfit to meet the design goals of this
project. Many beneficial ideas were outlined such as utilizing a water feed system
to eliminate any required user interaction during the course of the day. Also, the
idea of limiting the total volume of water in the still at any single time should help
increase the efficiency of the still by constantly heating a small volume of water as
opposed to having to heat a larger volume.
The small market for a commercial solar still appears to be filled by devices that
are built on an “as needed” basis instead of being purchased. Many patents
incorporate new ideas, however no patent seems to address the need for an
efficient, easy to maintain, simple, cost effective design. Overall, the potential for
an effective solar distiller is something that many neglect to realize or utilize
effectively.

3.5 Market Search

A product search for a solar powered water distillation device produced a small
handful of actual products. During this research it has become evident that the
market for such a device is not a strong one. When the need arises for a solar
powered water distillation device, instead of buying a ready made product, an
improvised distiller is usually constructed on site. This is probably because the
typical area in need of a water distillation device is a low income area and the local
population simply cannot afford to spend upwards of $400 on a device
.
3.5.1 The Watercone
The Watercone is possibly the simplest design for a solar water distiller. It is a
plastic molded hollow cone with a spout at the top and a lip on the inside of the
cone at the bottom to collect the distillate as it runs down the inside of the cone
(see Figure 11).

Figure 11: The Watercone

The Watercone is also the most versatile device on the market. It is portable,
lightweight, has no moving parts, and easy to clean and maintain. However the
Watercone does have a few shortcomings. One of which is its low output of fresh
water (less than half a gallon per day). This amount would not prove adequate for a
small family. The other major drawback of the Watercone is that is it constructed
of plastic instead of glass. The cohesive properties of water cause it to bead up
much more regularly on plastic than it would on glass. This leads to an effect
demonstrated in Figure 11. Instead of the water running off the plastic surface, it
simply beads up and blocks the incoming solar radiation from reaching the water in
the bottom of the still. Also, the Watercone is not currently in mass production,
demonstrating that the market for such a device is weak.

3.5.2 The Rainmaker

The Rainmaker (Figure 12) is the only product currently on the market available
for purchase. The product features a tempered glass condensing surface, weighs
about 70 pounds, and claims efficiencies of about 0.8 gallons of water output per
kWhr/m2.

Figure 12: The Rainmaker 550TM

The key disadvantage to The Rainmaker 550TM is its high cost of $480. This
amount is simply not affordable to be able to market this device to the families and
communities that would benefit most from the device.

3.5.3 El Paso Solar Energy Association

In 1995, the El Paso Solar Energy Association (EPSEA) in conjunction with the
State of Texas and the State Energy Conservation Office constructed solar
distillation devices that were to be targeted to the low income communities that
reside along the Texas/Mexico border. These communities typically have limited
access to fresh drinking water and are not able to afford a solar distillation device
to provide the needed water. Through these organizations, the cost of each solar
still was reduced to about $50 for each family who was willing to buy one. The
estimated cost of these solar distillers was between $650 for an 18 ft 2 distiller up to
$850 for a 24 ft2 distiller (see Figure 13).

Figure 13: EPSEA Solar Still

3.5.4 Market Search Conclusion

The market for a solar powered water distiller is not strong enough to support a
variety of products. Currently, when the need for a solar water distiller arises, it is
met by simply constructing a still from readily available materials. The few
products and plans currently available are too expensive to be implemented in
areas where the distillers are needed the most. In order for a device to be successful
in this market, the most practical method would be to make the device affordable
to an aid organization, such as the Red Cross, which would then be able to supply
the stills to low income families and communities.

Chapter 4 Literature Search

 4.1Water Purification
“Water purification is the process of removing contaminants” (Kostoff et. al 2007),
from a water source so to be used for drinking, washing and industrial purposes.
Purification occurs to limit the levels of certain components of the water so to
reduce the potential associated health risks. “The world health organisation has
identified 752 substances that may be present in tap water” (Sutherland 2008), and
it is many of these elements that purification aims to remove. From “minerals,
fungi, and viruses” to “parasites, viruses and organic matter” (Kostoff et. all 2007)
the levels of these elements need to be reduced to minimal quantities for water to
be classified drinkable. Water purification techniques have evolved with advancing
technology over the past decades, from “simple systems based on the imitation and
adaptation of naturally occurring processes” (Brissaud 2006), such as sand filters,
to complex multi stage purification techniques that use such techniques as
“coagulation, flocculation and deionization” (Kostoff et. al 2007). Many different
techniques are still operational around the world depending on the country’s
economic situation and needs.

4.1 Existing Purification Techniques

Presently there are many different techniques that are used to purify water for a
variety of applications. Most purification systems aim to purify water to the
standards of the World Health Organisation so that it can be used as a source of
drinking water. A combination of reverse osmosis, and filtration is one of the main
ways in which water is purified in modern day times .“Reverse osmosis is a
membrane based demineralization technique used to separate dissolved solids”
(Kucera 2010) from water. By using permeable selective membranes and pressure
the system is able to “overcome the ‘osmotic pressure’ allowing water to cross the
membrane from high concentration to low” (McIlvaine 2008). This process is used
to remove ionic contaminants and other dissolved solids form the water.

4.2 Filtration
Filtration is a method of purification used to extract turbidity and sediments from
the contaminated water supply. Sand filters are the most commonly used method of
filtration before reverse osmosis and other such technologies were developed, and
it was successful because it followed a natural system, where water is “filtered
through sand in fresh lakes” (Cartwright 2006). The process of filtration involves
the pores of the filtrate; the size of the pores determines the effectiveness of the
purification system. As the water is gravity fed through the filter, sediment and
turbidity are ‘caught’ in the pores between the filtrate, removing them from the
water source. However, this lead to the ‘filter becoming ‘backed up’ due to the
accumulation of contaminants in the filtrate pores, leading to a reduction in the
systems efficiency (Wotton 2002). This is overcome through a backwash technique
developed to remove the contaminants and sediments caught within the filtration
system, restoring it to its original working state.

Table 3 Strengths and Weaknesses of Filtration (adapted from APEC Water

Systems n.d)

4.3 Solar Distillation

Solar distillation is the technique of harnessing the suns energy (heat) to vaporize
water; it is a traditional method for water purification. The concept of purification
by distillation is simple, water generally has the lowest boiling point out of all the
contaminants, by using the heat of the sun the water can be vaporized before any of
the other particulates. By capturing the vaporized water, a purified water supply
can be established, as all of the original contaminants have been left behind in the
original position. Water has a enthalpy of vaporization of 40.65 KJ/mol (Kucera
2010), meaning that at 373.15oK (100 oC) 40.65KJ/mol is required to transform
liquid water into gas. During distillation all this energy is required from the heat of
the sun, and during direct sunlight the energy produced by the sun can be up to
590.4 KJ/hour/m2 (Qiblaway et. al 2007). From this it can be seen that it is feasible
to gain purified water from distillation as the sun provides all the energy that is
required and it comes at no cost. However, there are always complications that
arise during this process, problems like heat transfer and sun exposure. Much heat
is generally lost through absorption from other materials; this absorption decreases
the amount of heat being transferred to the water and in turn the volume of water
being vaporized.

Table 4 Strengths and Weaknesses of Solar Distillation (Lof, 1961)

Strengths Weaknesses
potential for expansion from modular limited flow rate
design
removes salinity, turbidity and bacteria requires solar energy
environmentally sustainable removal of healthy minerals
mechanically maintainable
cost effective

It is the particulates and sediments in the water which are responsible for the
diseases and the reason why the World Health Organisation set drinking water
standards so to minimize the risk of potential health detriments. Demonstrated
below in Table 3, are the drinking water standards set by the World Health
Organisation. There are secondary affects that are also associated with the
consumption of contaminated drinking water. It is know that contaminated
drinking water is the main cause of diarrheal disease, plus the fact that Devikulam
has “low levels of sanitation” (EWB 2011) that ultimately leads to the significant
health and hygiene risks to the local inhabitants.

The problem associated with drinking contaminated water resonates with the fact
that levels of sanitation are low within the Devikulam community. This brings
health risks that could have detrimental effects on the surrounding community and
is the reason why the drinking water standards set by the World Health
Organisation need to be adhered to
Chapter 4 Design and Working of Solar Still
Many different designs and theories were evaluated. After this preliminary
research, it was concluded that a simple asymmetrical distiller, similar to that
shown in Figure 4, is the most efficient and inexpensive solardistiller design. In
order to improve the overall design and to remain innovative, numerous attributes
and features from other designs and periodicals were also added. In this section,
the final design will be described, as well as the specific features that make this
design unique and efficient.
6.1 Design objectives for an efficient solar still:-

For high efficiency the solar still should maintain:-

 A high feed (undistilled) water temperature.

 A large temperature difference between feed water and condensing surface
 Low vapour leakage.

A high feed water temperature can be achieved if:-

 A high proportion of incoming radiation is absorbed by the feed water as

heat. Hence low absorption glazing and a good radiation absorbing surface
are required.
 Heat losses from the floor and walls are kept low
 The water is shallow so there is not so much to heat.

A large temperature difference can be achieved if:-

 The condensing surface absorbs little or none of the incoming radiation

 Condensing water dissipates heat which must be removed rapidly from the
condensing surface by, for example, a second flow of water or air, or by
condensing at night.

6.2 Design Considerations:-

Here in my model to increase efficiency I have used zinc matt as basin plate and
painted it black so as to increase my efficiency and output of potable water. Using
this material as basin plate gave an efficiency of 98.12% which is an achievement
of my research work. This model was constructed and analysed in JNV
CHONKARWARA, BHARATPUR(RAJASTHAN).
Different designs of solar still have emerged. The single effect solar still is a
Relatively simple device to construct and operate. However, the low productivity
of the Solar still triggered the initiatives to look for ways to improve its
productivity and Efficiency. These may be classified into passive and active
methods. Passive methods include the use of dye or charcoal to increase the solar
absorbtivity of water, applying good insulation, lowering the water depth in the
basin to lower its thermal capacity, ensuring vapor tightness, using black gravel
and rubber, using floating perforated black plate, and using reflective side walls.
Active methods include the use of solar collector or waste heat to heat the basin
water, the use of internal] and external condensers or applying vacuum inside the
solar still to enhance the evaporation/condensation processes, and cooling the glass
cover to increase the temperature difference between the glass and the water in the
basin and hence increases the rate of evaporation.
Single-basin stills have been much studied and their behavior is well understood.
The efficiency of solar stills which are well-constructed and maintained is about
50% although typical efficiencies can be 25%. Daily output as a function of solar
irradiation is greatest in the early evening when the feed water is still hot but when
outside temperatures are falling. At very high air temperatures such as over 45ºC,
the plate can become too warm and condensation on it can become problematic,
leading to loss of efficiency
.
6.3 Some problems with solar stills which would reduce their
efficiency include:-
 Poor fitting and joints, which increase colder air flow from outside into the
still
 Cracking, breakage or scratches on glass, which reduce solar transmission or
let in air.
 Growth of algae and deposition of dust, bird droppings, etc. To avoid this
the stills need to be cleaned regularly every few days
 Damage over time to the blackened absorbing surface.
 Accumulation of salt on the bottom, which needs to be removed
periodically.
 The saline water in the still is too deep, or dries out. The depth needs to be
maintained at around 20mm.

6.4 Concepts for making a Good Solar still:-

The cover can be either glass or plastic. Glass is preferable to plastic because most
plastic degrades in the long term due to ultra violet light from sunlight and because
it is more difficult for water to condense onto it. Tempered low-iron glass is the
best material to use because it is highly transparent and not easily damaged (Scharl
& Harrs, 1993). However, if this is too expensive or unavailable, normal window
glass can be used. This has to be 4mm think or more to reduce breakages. Plastic
(such as polyethylene) can be used for short-term use. Stills with a single sloping
cover with the back made from an insulating material do not suffer from a very low
angle cover plate at the back reflecting sunlight and thus reducing efficiency. It is
important for greater efficiency that the water condenses on the plate as a film
rather than as droplets, which tend to drop back into the saline water. For this
reason the plate is set at an angle of 10 º to 20º.
The condensate film is then likely to run down the plate and into the run off
channel. Brick, sand concrete or waterproofed concrete can be used for the basin of
a long-life still if it is to be manufactured on-site, but for factory-manufactured
stills, prefabricated Ferro-concrete can be used. Moulding of stills from fibreglass
was tried in Bharatpur(Rajasthan) but in this case was more expensive than a brick
still and more difficult to insulate sufficiently, but has the advantage of the stills
being transportable. By placing a fan in the still it is possible to increase
evaporation rates. However, the increase is not large and there is also the extra cost
and complication of including and powering a fan in what is essentially quite a
simple piece of equipment. Fan assisted solar desalination would only really be
useful if a particular level of output is needed but the area occupied by the stills is
restricted, as fan assistance can enable the area occupied by a still to be reduced for
a given output.
6.5 Design types and their performance:-

1. Single-basin stills have been much studied and their behavior is well
understood. Efficiencies of 25% are typical. Daily output as a function of
solar irradiation is greatest in the early evening when the feed water is still
hot but when outside temperatures are falling.
2. Multiple-effect basin stills have two or more compartments. The
condensing surface of the lower compartment is the floor of the upper
compartment. The heat given off by the condensing vapour provides energy
to vaporize the feed water above. Efficiency is therefore greater than for a
single-basin still typically being 35% or more but the cost and complexity
are correspondingly higher.
3. In a wick still, the feed water flows slowly through a porous, radiation-
absorbing pad (the wick). Two advantages are claimed over basin stills.
First, the wick can be tilted so that the feed water presents a better angle to
the sun (reducing reflection and presenting a large effective area). Second,
less feed water is in the still at any time and so the water is heated more
quickly and to a higher temperature. Simple wick stills are more efficient
than basin stills and some designs are claimed to cost less than a basin still
of the same output.
 4. Emergency still - To provide emergency drinking water on land, a very
simple still can be made. It makes use of the moisture in the earth. All that is
required is a plastic cover, a bowl or bucket, and a pebble.
5. Hybrid designs - There are a number of ways in which solar stills can
usefully be combined with another function of technology. Three examples
are given:
 Rainwater collection:-By adding an external gutter, the still cover can be
used for rainwater collection to supplement the solar still output
 Greenhouse-solar still:-The roof of a greenhouse can be used as the cover of
a still.
 Supplementary heating: - Waste heat from an engine or the condenser of a
refrigerator can be used as an additional energy input. After going through
the various existing designs of solar stills there are a few facts that come to
picture:
 The efficiency of single stage still is around 25%.
 The efficiency of multistage stills is higher than 35%.
 Mostly people use three staged stills because for more stages the cost
outweighs the utility.
 Most of the losses can be attributed to heat transfer losses.

Thermal losses are mostly in form of conduction and convection and very little by
radiation – owing to low temperatures. So we can assume radiative losses to be
negligible. Also the cost of a solar still which produces reasonable amount of
purified water is high. The cost of water produced by the still is high. This fact
attributes to almost negligible penetration of solar stills in Indian villages. While
persuing and pondering about the ways to reduce costs the first factor that comes to
mind is why not increase the efficiency. But as we all know this is much easier said
than done. After giving it a considerable thought we came up with a design that
can greatly improve the efficiency of a solar water distillation system by
minimizing thermal losses.

4.2 Overall Design Outline

The base of the solar still is made of G.I. box of dimension (4’ x 2’ x 10 cm). This
box is embedded into another box of wood shown in figure 1. Here length L= 65
cm, Breath B= 125cm, Height H= 30 cm. and at opposite side = 13 cm, Angle Θ =
150 . This also contains same box of thermocol inside it between the G.I box and
wooden box. The thermocol is having 15 cm thickness. The channel is fixed such
that the water slipping on the surface of the glass will fall in this channel under the
effect of gravity. A frame of fibre stick is fixed with the wooden box so that glass
can rest on it. This completes the construction of the model. The holes for the inlet
of water, outlet of brackish water and outlet of pure water is made as per the
convenience. We have made the outlet of brackish water at right bottom of the
model (seeing from front of the model), outlet of the pure water at the end of the
channel and inlet at the right wall above the outlet.

Figure 18: Overall Design

4.3 Basin Design
It is the part of the system in which the water to be distilled is kept. It is therefore
essential that it must absorb solar energy. Hence it is necessary that the material
have high absorbtivity or very less reflectivity and very less transmitivity. These
are the criteria’s for selecting the basin materials. Kinds of the basin materials that
can be used are as follows: 1. Leather sheet, 2. Ge silicon, 3. Mild steel plate, 4.
RPF (reinforced platic) 5. G.I. (galvanised iron).
We have used blackened galvanised iron sheet(K= thermal conductivity=
300W/m0C) (3mm thick).( SIZE:: 4’ X 2’ X 10 cm BOX OF G.I.).

4.4 Side Walls:

It generally provides rigidness to the still. But technically it provides thermal
resistance to the heat transfer that takes place from the system to the surrounding.
So it must be made from the material that is having low value of thermal
conductivity and should be rigid enough to sustain its own weight and the weight
of the top cover (refer fig.no.2). Different kinds of materials that can be used are:
1) wood , 2) concrete, 3) thermocol, 4) RPF (reinforced plastic). For better
insulation we have used composite wall of thermocol (inside) and wood (outside).
(Size:: wood(k= thermal conductivity=0.6W/m0C):-- 8 mm thick, thermocol(k=
thermal conductivity=0.02W/m0C):--- 15 mm thick).

Figure.2 Side Walls for Solar Still.

3.2.3 Top Cover: The passage from where irradiation occurs on the surface of the
basin is top cover. Also it is the surface where condensate collects. So the features
of the top cover are: 1) Transparent to solar radiation, 2) Non absorbent and Non-
adsorbent of water ,3) Clean and smooth surface. The Materials Can Be Used Are:
1) Glass, 2) Polythene. We have used glass (3mm) (figure 3)thick as top cover
having rubber tube as frame border. (size: ---- 4’ x 2’cm).
 Figure.3 Solar Still Glass with Cover
3.2.4 Channel: The condensate that is formed slides over the inclined top cover
and falls in the passage, this passage which fetches out the pure water is called
channel. The materials that can be used are: P.V.C., 2) G.I. , 3) RPF . We have
used P.V.C channel (figure.4)(size:: 4.5’ X 1” cm).

3.2.5 Supports for Top Cover: The frame provided for supporting the top cover is
an optional thing. I.e. it can be used if required. We have used fibre stick as a
support to hold glass (size :: 5 mm X 5mm). The only change in our model is that
we have to make the model as vacuumed as possible. So we have tried to make it
airtight by sticking tape on the corners of the glass and at the edges of the box from
where the possibility of the leakage of inside hot air is maximum.
 Figure.5 Working model of solar distillation system

4.5.1 Collection Mechanism

In order to collect the distillate, the angled glass is positioned so that the distillate
drops directly into the angled Lexan collection mechanism seen below in Figure
22. Distillate condensates on the bottom surface of the glass, runs down to the
bottom edge of the glass, drops into the collection mechanism, and flows into the
output tank through a vinyl hose.

Figure 22: Collection Mechanism

4.5.2 Output Tank
The output tank receives and holds distillate, and has a capacity of 5 gallons. The
output tank is removable and hangs on a hook attached to the bottom of the frame,
which will keep the distillate from absorbing solar radiation (see Figure 23). In
order to construct the output tank, a 5 gallon gasoline tank was painted black and
the nozzle was replaced with a screen with a hole for the vinyl output hose.

Figure 23: Output Tank

4.6 Design Overview
Solar energy enters the device through the inclined glass surface. Mirrors reflect all
radiation towards the basin. Highly insulated basin minimizes heat loss. Several
small bodies of water heat up and evaporate from basin and then condense onto
cooler glass surface. Float valve keeps water in basin at a constant 1.5 cm
throughout the day. Clean water runs down glass surface and feeds into collection
mechanism, which then feeds into removable output tank. Salt residue is wiped
away at the end of the day.
The energy varies depending on the time of the day and also due to seasonal and
climatic changes. For high efficiency the solar still should maintain a high
temperature of the feed (un-distilled) water which can be obtained if a high
proportion of the incoming radiation is absorbed by the feed water as heat. Hence a
system with low absorption glazing and a good radiation-absorbing surface are
required. There is also a need to keep heat losses from the floors and walls low and
make the water shallow enough so that there is less to heat. The same time keep the
temperature of the condensing surface low. The basin liner was painted black to
increase the capacity of solar radiation absorption. As a control, the other still was
painted black on all the internal surfaces of the walls including the basin liner to be
consistent with the designs of current conventional solar stills.
 Table 1. Design parameters of the Solar Still

Temperatures were recorded every two hours from 08:00 - 16:00 hrs.
Temperatures of the feed water and that near the condensing surface were
recorded using four Emil Yellow-back mercury thermometers with a tolerance of
0.3°C on each of the stills, two located in such a way that the thermometers are in
contact with the feed water to measure the its temperature and two located near the
glass condensing surface to measure the temperature of the condensing surface.

Solar Still Operation

Water to be cleaned is poured into the still to partially fill the basin. The glass
cover allows the solar radiation to pass into the still, which is mostly absorbed by
the blackened base. This interior surface uses a blackened material to improve
absorption of the sunrays. The water begins to heat up and the moisture content of
the air trapped between the water surface and the glass cover increases. The heated
water vapor evaporates from the basin and condenses on the inside of the glass
cover. In this process, the salts and microbes that were in the original water are left
behind. Condensed water trickles down the inclined glass cover to an interior
collection trough and out to a storage bottle. Feed water should be added each day
that roughly exceeds the distillate production to provide proper flushing of the
basin water and to clean out excess salts left behind during the evaporation
process. If the still produced 3 litres of water, 9 litres of make-up water should be
added, of which 6 litres leaves the still as excess to flush the basin.
Single basin- Single slope solar still

The impure saline feed water goes into the solar still and the sun's rays penetrate a
glass surface causing the water to heat up through the greenhouse effect and,
consequently, evaporate. When the water evaporates inside the solar still, it leaves
all contaminants and microbes behind in the basin. The evaporated and now
purified water condenses on the underside of the glass and runs into a collection
trough and then into an enclosed container. In this method the salts and microbes
that were present in the original feed water to the solar still, are left behind.
Additional water fed into the solar still flushes out concentrated waste from the
basin of solar still to avoid excessive salt deposition in the basin. A solar still
effectively eliminates all water-borne pathogens, salts and heavy metals that other
huge methods cannot do. Solar still technologies bring immediate benefits to users
by reducing health problems associated with water-borne diseases. For solar still
users, there is also a sense of satisfaction in having their own trusted and easy to
use water treatment plant on-site at home. As a thumb rule, solar still production is
a function of solar energy (insolation) and ambient temperature. Figure 3
diagrammatically shows the principal energy exchange mechanisms in a basin-type
double slope solar still. Solar radiation is absorbed on the black bottom of the basin
generally known as basin liner. However, there are several reflection losses from
the cover surfaces, the water surface, and the bottom itself. There may also be
some absorption of solar energy in the cover of the solar still.
Fig. 2. Basin-type single slope passive solar still.
Chapter 5 OBSERVATIONS AND ANALYSIS OF EXPERIMENTAL
RESULTS
As we can observe from the table that distillate productivity was less during the
morning hours after sunrise but as the temperature increased the productivity of
distillate also increased considerably. The distillate productivity was also there
after sunset because water in the basin has absorbed heat during the daytime and
continues to evaporate till the water temperature in the basin cools down.
The productivity of distillate water corresponds favorably with the theoretical
analysis obtained in Figure. Their maxima taken place at 12:00 h, where solar
radiation intensity and the temperature of water inside the still are high, are 1.6 and
1.5942 kg/m2h for practical and computed values respectively giving an efficiency
of 99.64%.

The experimental results obtained show that it corresponds favorably with the
theoretical analysis and the productivity of the still increases with the intensity of
solar radiation and the temperature of feed water. As we can observe from the table
and figure that distillate productivity was less during the morning hours after
sunrise but as the temperature increased the productivity of distillate also increased
considerably. The distillate productivity was also there after sunset because water
in the basin has absorbed heat during the daytime and continues to evaporate till
the water temperature in the basin cools down.

Figure 7. Distillate flow rate verses time.

Figure 6. The impact of the wind velocity on the temperature of water inside the
still.
Impact of the wind velocity on the temperature of water inside the still:

Figure 6 shows the variation of temperature of water inside the still with the wind
velocity taken from 7:00h– 12:00 h. The increasing in wind velocity, leads to an
increasing production in distilled water, as well as to a better cooling of the inner
and the outer glass sides, followed by an important temperature difference between
the water and the inner side of the glass, where this difference is of great interest,
as it represents the cooling agent of the glass and where the external heat losses by
convection can reach their maximum, as the coefficient of external heat exchange
is dependent on the wind velocity according to the relation.The experimental result
of distillate of water from the constructed still is presented in Figure 7.

The productivity of distillate water corresponds favorably with the theoretical

analysis obtained in Figure 4. Their maxima taken place at 12:00 h, where solar
radiation intensity and the temperature of water inside the still are high, are 1.6 and
1.5942 kg/m2h for practical and computed values respectively giving an efficiency
of 99.64%.A better efficiency of 98.12% has taken place at 12:00 h, which can be
explained by the existing, at this time, of a better intensity of solar radiation (1238
W/m2) as well as a better temperature of the feed water (69 0C) yielding an
important quantity of distillate water of about 1.5942 kg/m2 h.

The corresponding plots for the ambient, water and glass temperatures verses the
time of the day are displayed in Figure 2. The curves are essentially quadratic with
maxima occurring at 31.6, 69.0 and 45.0oC for ambient, water and glass
respectively. It was noticed that the temperatures of the water and glass increase to
maxima due to different heat flows (by convection, radiation and evaporation),
going up to the glass.

Figure 3 shows a plot of the hourly variation of saturated partial pressures of water
at water and glass temperatures, while plots of convective, evaporative coefficients
and distillate against time; and best characterization curves are shown in Figure 4.
Variation of instantaneous efficiency is shown in figure 7.
 Figure 7. Variation of the instantaneous efficiency.

The quality of water was tested before feeding to solar still distillation unit to
insure the feed-water quality and the distilled water from solar still was tested after
collecting the distillate to insure the quality. It is observed that the pH of the water
before distillation was slightly acidic. The pH of distilled condensate was 7.0
indicating neutral character. The TS, TDS, sulphates, phosphates and chlorides
were reduced to zero after the solar distillation in all the four solar stills (Table 3).
It insures that the distilled water is ‘Pure’ water.

Table 3: Physico-chemical parameters of feed-water and solar distillate in all

four units
 USER EXPERIENCES
Surveys were conducted by NMSU on user satisfaction with solar distillers and
found that project participants receiving cost-shared solar distillers for the pilot
EDA, EPA, and BorderPACT projects. Users were nearly unanimous that owning
a solar still was good. Some owners prized the idea of using alternative, clean
energy to achieve their purposes, while at the same time leaving only a small
“footprint” on the planet. All were very enthused about the economic benefits of
using a solar distiller. They found that paying a relatively low price for a still was a
favorable alternative to having to buy water on a regular basis with no end in sight
to this routine. Still others valued the independence and fascination they
experienced from being involved in the production of their own purified water.
Many colonias residents often do not trust their local water supply. While many
have noted a concern over local water supply color or odor, the overwhelming
characteristic that gains their attention is poor taste. There is a good deal of
concern with taste, and most of those interviewed noted that one of the reasons for
wanting a water purification system was to improve the taste of their local water
supply. Since many of the local water supplies are high in salts and minerals (e.g.,
iron or sulphur), they often have a marginal or poor taste. The solar stills were
considered useful by colonia residents to improve drinking water taste.

Solar distillers were able to meet all of the drinking and cooking water needs of a
household. Not all of the households receiving solar stills through the EPA pilot
project had stills optimally sized to meet all of their wintertime water production
needs, but about 40 percent of the households were completely satisfied with their
still water production. All households had sufficient water during the high
summertime production period, and it was the wintertime where some families had
insufficient still water. Generally, it appears that for most Border households about
one half square meter of solar still is needed per person to meet potable water
needs consistently throughout the year.

Most households with insufficient wintertime still water production had 0.35 m2 or
less of still area per person. Survey results clearly indicate that only about a third
of colonias residents are willing or able to pay the full price of the solar still up
front, because most simply could not afford the higher up-front capital cost.
However, interest mounted greatly when the possibility of financing was
mentioned. Thus, water districts and others interested in providing potable water to
Border colonias should consider offering an option for still financing. To bolster
interest, a clear, easy-to-follow breakdown of cost payback should be provided.
Prospective customers interest is peaked when they realize that even at full price,
the still could pay for itself in less than two years as compared to purchasing
bottled water. Some prospective customers would be delighted to know that
savings over a decade or more could be substantial and amount to thousands of
dollars. Almost all of those surveyed were using their solar stills regularly, thus
now meeting most or all their drinking water and cooking water supply needs via
solar distillation. Occasionally, still users had to supplement their still supply with
store-bought water, especially in the winter, when still production decreases to
about half of summertime production. Yet the need for purchasing bottled water
from a store was greatly mitigated by the availability of still-produced water in the
winter. Solar still savings are approximately $150 - $200 a year per household
instead of purchasing bottled water.
Solar still users show a highly favorable attitude towards the use of solar stills.
Most show a great deal of enthusiasm concerning their stills. Still users have a high
level of confidence in the water produced by their stills. In all cases interviewed,
users noted that they feel solar distilled water is safe to drink.
Table 2 quantifies household perceptions and overall satisfaction regarding solar
still use. Most notably is the concern for health, with nearly half of those surveyed
claiming that they wanted a solar still for the purpose of improved family health.
Of those responding “Other,” to this question, the majority desired a solar still
because of their commitment to environmental issues. Responses varied from “we
love solar” to “…trying to embrace permaculture.” A number of households also
responded that they had opted for a solar still to offset the cost of purchased
drinking and cooking water.
 TABLE 2: SOLAR STILL SATISFACTION

TABLE 3: SELECTED USER PERCEPTIONS

 COST ANALYSIS & MATERIALS
Materials:-
 The side and bottom walls need to be insulated. This can be achieved by
using multilayered insulator. Glass wool will be sand-witched between two
metallic plates.
 This will ensure negligible heat loss to the surroundings. The main frame is
composed of steel owing to its corrosion resistance, low weight, long life
and easy cleanability.
 The outside of the complete distiller is coated with carbon black to increase
absorption of radiation.
 The cover on the top is made of tempered glass so that the birds can‟t see
their reflection and hence avoid nuisance.
The per-liter cost of solar-distilled water can be calculated as follows:
 estimate the usable lifetime of the still;
 add up all the costs of construction, repair and maintenance (including labor)
over its lifetime; and
 divide that figure by the still's total expected lifetime output in liters.
Such a cost estimate is only approximate since there are large uncertainties in both
the lifetime and the yield estimates. Costs are usually considerably higher than
current water prices–which explains why solar backyard stills are not yet marketed
widely in India.

Assembling and manufacture:-

Fabrication of the whole unit is pretty straight forward and involves metal cutting,
welding, glass cutting, sealing, painting and drilling. All these processes can be
done at any local workshop using simple machines – lathe, drill, welding, milling
etc. The steps in the process of assembling are outlined as follows:
 The outer box will be fabricated first. It will be made of double wall and will
be filled with glass wool to provide insulation.
 The stages will be fabricated second the collector holes will be made at the
time of fabrication. Finally the stages will be assembled inside the outer
covering.
 The collector tubes are then made and attached to the lowermost stage.
 The holes are provided for
1. Collecting distilled water
2. Transporting saline water
3. To attach the pump
  The whole system is sealed using sealant to prevent the air from leaking in
from the atmosphere.
 The cost of construction for a passive solar still is considerably cheaper than
a more complex humidification/condensation flow through system. All that
is required is a large insulated box with solar absorbing material in the basin,
and a transparent glazing.
Because the box is not under any loading, most insulating foam boards such as
expanded polystyrene, extruded polystyrene, and polyisocyanurate board can
provide structural rigidity and no other materials will be needed. The cost of
construction components is listed below.

Box Structure/Insulation:
Extruded polystyrene foam has the best combination of light weight, rigidity, and
low cost. Foam boards of 2” thickness measuring 4‟x8‟ can be purchased for
approximately $20 from sources such as Univfoam and Foam-Control. Three
boards are required for the construction a solar still with base dimensions of 1x2.25
m, with a 20º inclined slope glazing. The maximum side height is 0.50 m, the
minimum side height
is 0.14 m.

Glazing:
One solid piece of polycarbonate measuring 1x2.25m will be required for the
glazing. This can be purchased from sources such as Eplastics and USplastic for
around $70 for a 1/16” thick sheet measuring 4‟x8‟. The excess from this sheet
will be used to construct the catch for the distilled water.
 Chapter economics

Compared to purchasing comparable quantities of bottled water, the average return

on investment on a solar still for a family is typically only a couple of years.
Factoring in the health costs of contaminated water, payback for a solar still can be
immediate. Solar distillation is the cheapest way to clean water for a household and
is quite economical as compared to reverse osmosis and electric distillation. A
square meter for a single basin solar still costs about $400. Many families in the
U.S. colonias often spend from $8 to $12 per week on bottled water. Likewise, in
Mexico families typically spend $3 - $5 per week on purified water. This
represents an investment of anywhere from $150 to $600 per year for bottled
water. Thus, simple payback on a solar still strictly compared to purchasing bottled
water is typically within two to three years. The levelized energy cost of solar
distilled water is about US$.03 per liter, assuming a ten year still lifetime. The first
EPSEA stills have now been operating for a decade and are still going strong.
 CHAPTER-7
CAPABILITIES
A solar still operates using the basic principles of evaporation and condensation. The
contaminated feed water goes into the still and the sun's rays penetrate a glass surface
causing the water to heat up through the greenhouse effect and subsequently
evaporate. When the water evaporates inside the still, it leaves all contaminants and
microbes behind in the basin. The evaporated and now purified water condenses on the
underside of the glass and runs into a collection trough and than into an enclosed
container. In this process the salts and microbes that were in the original feed water are
left behind. Additional water fed into the still flushes out concentrated waste from the
basin to avoid excessive salt build-up from the evaporated salts.
A solar still effectively eliminates all waterborne pathogens, salts, and heavy
metals. Solar still technologies bring immediate benefits to users by alleviating health
problems associated with water-borne diseases. For solar stills users, there is a also a
sense of satisfaction in having their own trusted and easy to use water treatment plant
on-site.
Solar still production is a function of solar energy (insolation) and ambient
temperature. Typical production efficiencies for single basin solar stills on the Border
are about 60 percent in the summer and 50 percent during the colder winter. Single
basin stills generally produce about 0.8 liters per sun hour per square meter.
Given the smaller product water output for a solar still, the technology calls for a
different approach to providing purified water in that it only purifies the limited amounts
of water that will be ingested by humans. Water used to flush the toilet, take a bath,
wash clothes, etc. does not need to meet the same high level of purity as water that is
ingested, and thus does not need to be distilled.
Solar stills have proven to be highly effective in cleaning up water supplies and in
providing safe drinking water. The effectiveness of distillation for producing safe drinking
water is well established and long recognized. Distillation is the only stand alone
pointof- use (POU) technology with NSF (National
 conclusion

From the graph 1, we can conclude that the increase in temperature and hence the
evaporation is maximum in the period of 11:15 am to 1:30 pm. The maximum
temperature achieved is 530c which is at 1:30 pm. then the temperature decreases.
The aim of our experiment was to get pure water from the brackish water available.
The brackish water we have supplied was 14 litres and at the end of the experiment
we got 1.5 litres. The experiment was carried out in winter season. The TDS level
of purified water obtained is 81 PPM. So the water obtained is potable.
Theoretically, the experiment should fetch out 2.33 litres. So the efficiency of the
system is 6%. Distillation is a method where water is removed from the
contaminations rather than to remove contaminants from the water.Solar energy is
a promising source to achieve this .This is due to various advantages involved in
solar distillation. The Solar distillation involves zero maintenance cost and no
energy costs as it involves only solar enegy which is free of cost. It was found from
the experimental analysis that increasing the ambient temperature from 32°C to
47°C will increase the productivity by approx 12 to 23%, which shows that the
system performed more distillation at higher ambient temperatures. When inverted
type absorber plate was used thermal efficiency of single slope solar still was
increased by 7 %. It was observed that when the water depth increases from 0.01m
to 0.03m the productivity decreased by 5%.These results show that the water mass
(water depth) has an intense effect on the distillate output of the solar still system.

Solar still productivity can also increase by use of reflector by 3%. The use of the
mirror reflector will increase the temperature of the solar still basin; such an
increase in the temperature is because of the improvement in solar radiation
concentration. The solar radiation increase from 0 MJ/m2 /h to 6 MJ/m2 /h has
increased the productivity of the still by 15 to 32%. However the increase of the
solar radiation parameter will increase the solar energy absorbed by the basin liner.
The main disadvantage of this solar still is the low productivity or high capital cost
per unit output of distillate.This could be improved by a number of actions, e.g.
injecting black dye in the seawater,using internal and external mirror,using
wick,reducing heat conduction through basin walls and top cover or reusing the
latent heat emitted from the condensing vapour on the glass cover.Capital cost can
be reduced by using different designs and new materials for construction of solar
stills.
Advances have made to improve the evaporation rate of a capillary solar still by
changing the fiber and fabric. From multilayer thick fabric researchers move to
very thin fabric. Again the fiber used now is hydrophobic one rather than the
hydrophilic. This enhances the durability of still fabric. The design complicacy is
not desirable for the rural domestic applications. Hence, material developments
should be the point of focus for future research in this area. The simple
conventional solar still is more economical than active solar distillation system to
provide drinking for the domestic applications.A single sloped solar still receives
more radiation than adouble sloped solar still at low and high altitude stations.
Lower condensing cover angle yield is more compared to higher condensing cover
angle. Solar still productivity mainly depends on temperature difference between
water and glass.The effect of water flow over the glass cover has a significant
effect on the heat capacity of water mass in the basin.The still consisted of a
vertical conical shaped blackened cotton wick (representing absorbing/evaporating
surface) with good capillarity is increasing the yield. Energy storage medium
increases the solar still productivity and efficiency. An addition of black dye
increases the daily productivity and the efficiency of the system by about 10%.
Solar stills in combination with greenhouses could be designed to provide
technically feasible systems suitable forarid areas. In active solar distillation
system the optimum flat-plate collector inclination is 20° and the still glass-cover
inclinationis 15° for a solar still which provides maximum annual yield.The active
solar still is more suitable for commercial applications like distilled water for
selling purposes, extraction of essence from different seeds and green leaves use in
batteries, chemical laboratories etc.
Solar stills have a good chance of success in India for lower capacities which are
more than 20 km away from the source of fresh water and where the TDS of saline
water is over10,000 ppm.To decrease fresh water costs, efforts should be
undertaken in the following research topics: thermal storage studies, insulation
studies, thermo-optical studies for the condensingcovers, geometry and design
studies. From the above discussions various parameters involving the conventional
solar still productivity are identified.Inprinciple, solar energy can be used to
separate pure water from most of the natural contaminants, such as dissolved solids
(salts) and particles (dirt and algae).Solar distillation is most economically
effective when sunlight is allowed to pass through a transparent cover and into a
black evaporating pan with little pr no concentration of the sun rays.
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