Solar still,A water Purifying Technique Project Report
Submitted in partial fulfillment for the award of the degree of
Bachelor of Technology
RAJASTHAN TECHNICAL UNIVERSITY, KOTA
Guided By: - Submitted By: -
Mr. Kapil Jain Aman Agrawal
Lecturer,Mech.Deptt. Bharat Ajwani
Vit (East), Jaipur Ashok Kumar Meena
Kirodee Lal Meena
Manoj kumar Nagar
B.Tech. IV Yr. VIII Sem
DEPARTMENT OF MECHANICAL ENGINEERING
VIVEKANANDA INSTITUTE OF TECHNOLOGY (EAST)
VIT Campus, NRI Road, Jagatpura, Jaipur-303012
2. Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration Page ii
We take this momentous opportunity to express our heartfelt gratitude, ineptness
& regards to vulnerable and highly esteemed guide, Mr. Rahul Goyal, Head of
Department of Mechanical Engineering, Vit (East) for providing us an opportunity
to present our project on “SOLAR STILL”.
We with full pleasure converge our heartiest thanks to Our project guide
Mr. kapil jain,Lecturer,Department of mechanical engineering, Vivekananda
institute of technology(East) and to Project coordinator Mr. Bhanu Pratap Singh,
Lecturer, Department of Mechanical Engineering for their invaluable advice and
wholehearted cooperation without which this project would not have seen the
light of day.
We attribute hearties thanks to all the faculty of the department of ME
and friends for their valuable advice and encouragement.
Ashok Kumar Meena
Kirodee lal Meena
Manoj kumar Nagar
3. Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration Page iii
This is to certify that Aman Agrawal, Amit upadhyay, Bharat ajwani, Ashok
Kumar meena, kirodee lal Meena,Manoj Nagar; Students of IVth
Semester Mechanical Engineering of Vit (East), Jaipur during the academic
session 2012-13 is working for his project under my guidance entitled “Solar Still”
in the partial fulfillment for award the degree of Bachelor of Technology in
Mechanical Engineering from Rajasthan Technical University, Kota.
Their Work is Found…………….
Project Guide Project Coordinator
Mr. Kapil Jain Mr. Bhanu Pratap Singh
Deptt. Of Mechanical Engg. Deptt. Of Mechanical Engg.
Vit (East), Jaipur Vit (East), Jaipur
4. Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration Page iv
Title Page No
CHAPTER 1 INTRODUCTION………………………………….………... 2
CHAPTER 2 WATER PURIFICATION…………………………………... 3-4
2.1 WATER PURIFICATION………………………… 3
2.2 OPTIONS FOR WATER PURIFICATION…….. 4
2.3 BENEFITS OF DISTILLATION………………… 4
2.4 NEEDS OF WATER PURIFICATION…………… 4
CHAPTER 3 SOLAR WATER DISTILLATION………………………….. 5 -6
CHAPTER 4 BASIC CONCEPT OF SOLAR WATER DISTILLATION…. 7-8
4.1 SUPPLY FILL PORT……………………..……….. 7
4.2 OVERFLOW PORT…………………………..……. 8
4.3 DISTILLED OUTPUT COLLECTION PORT..…… 8
CHAPTER 5 WORKING OF SOLAR STILL………………………………. 9-10
CHAPTER 6 DESIGN OF SOLAR STILL…………………………………. 11-16
6.1 DESIGN OBJECTIVES …………………………. 11
6.2 DESIGN CONSIDERATIONS………….………… 11
6.3 SOME PROBLEMS WITH SOLAR STILLS ……… 12
6.4 CONCEPTS FOR MAKING A GOOD SOLAR STILL 12
6.5 DESIGN TYPES AND THEIR PERFORMANCE…… 13
CHAPTER 7 CAPABILITIES……………………………………………….. 17
5. Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration Page v
CHAPTER 8 USER EXPERIENCES……………………………………..…. 18-19
CHAPTER 9 COST ANALYSIS & MATERIALS……………………………… 20-23
CHAPTER 10 BERKAD’S APPLICATIONS……………………………………. 24-27
CHAPTER 11 WATER PURIFIERS…………………………………………..…. 28-32
CHAPTER 12 SOLAR PANELS…………………………………………..…. 33-34
CHAPTER 13 WOULD A SOLAR STILL SUIT OUR NEEDS?……….……… 35
CONCLUSIONS ……………………………………….……………… 36
REFERENCES ………………...………………................................ 37
6. Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration Page vi
Figure Page No
Fig.1.1 Basic concept of Solar Water Distillation 08
Fig.1.2 Working of Solar Still 09
Fig.1.3 Layout of Solar Still Plant 10
Fig.1.4 Components of Solar Still 16
Fig. 1.5 Passive Solar Still Design 22
Fig. 1.6 Design Drawing of Solar Still, Dimensions in cm. 23
Fig. 1.7 Berkads practical Application 25
The purpose of this project is to design a water distillation system that can purify water
from nearly any source, a system that is relatively cheap, portable, and depends only on
renewable solar energy.
The motivation for this project is the limited availability of clean water resources
and the abundance of impure water available for potential conversion into potable
water, In addition, there are many coastal locations where seawater is abundant but
potable water is not available. Our project goal is to efficiently produce clean drinkable
water from solar energy conversion.
Distillation is one of many processes that can be used for water purification. This
requires an energy input as heat, electricity and solar radiation can be the source of
energy. When Solar energy is used for this purpose, it is known as Solar water
Distillation. Solar Distillation is an attractive process to produce portable water using
free of cost solar energy. This energy is used directly for evaporating water inside a
device usually termed a „Solar Still‟. Solar stills are used in cases where rain, piped, or
well water is impractical, such as in remote homes or during power outages. Different
versions of a still are used to desalinate seawater, in desert survival kits and for home
water Purification. For people concerned about the quality of their municipally-supplied
drinking water and unhappy with other methods of additional purification available to
them, solar distillation of tap water or brackish groundwater can be a pleasant, energy-
efficient option. Solar Distillation is an attractive alternative because of its simple
technology, non-requirement of highly skilled labour for maintenance work and low
The use of solar thermal energy in seawater desalination applications has so far
been restricted to small-scale systems in rural areas. The reason for this has mainly
been explained by the relatively low productivity rate compared to the high capital cost.
However, the coming shortage in fossil fuel supply and the growing need for fresh water
in order to support increasing water and irrigation needs, have motivated further
development of water desalination and purification by renewable energies.
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
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.
3.1 Water Purification:-
It is the process of removing undesirable chemicals, biological contaminants,
suspended solids and gases from contaminated water. The goal is to produce water fit
for a specific purpose. Most water is purified for human consumption (drinking water),
but water purification may also be designed for a variety of other purposes, including
meeting the requirements of medical, pharmacological, chemical and industrial
applications. In general the methods used include physical processes such
as filtration, sedimentation, and distillation, biological processes such as slow sand
filters or biologically active carbon, chemical processes such
as flocculation and chlorination and the use of electromagnetic radiation such
as ultraviolet light.
3.2 Options for water purification:-
There are four possible ways of purifying water for drinking purpose:-
3. Chemical Treatment
4. Irradiative Treatment
Considering the areas where the technology is intended to be used we can rule
out few of the above mentioned methods based on the unavailability of materials or
costs. Chemical treatment is not a stand alone procedure and so is irradiative treatment.
Both can act only remove some specific impurities and hence can only be implemented
in coordination with other technologies.
This analysis leaves us with two methods – Distillation and Filtration. By weighting the
Positive and negatives of both the methods we decided to go by the first one. The most
Important considerations were that of complexity, higher maintenance and subsequent
costs coupled with need of other sophisticated supporting equipments.
3.3 Benefits of Distillation:-
Finally we decided to go by distillation method owing to the following benefits:-
1. It produces water of high quality.
2. Maintenance is almost negligible.
3. Any type of water can be purified into potable water by means of this process
4. The system will not involve any moving parts and will not require electricity to
5. Wastage of water will be minimum.
3.4 Needs and Specifications of water purification:-
Our project centers on converting the roughly 99.6% of water that is, in its natural
form, undrinkable, into clean and usable water. After researching and investigation, we
outlined our needs to be the following:-
1. Efficiently produce at 2 gallons of potable water per day minimum
2. Able to purify water from virtually any source, included the ocean
3. Relatively inexpensive to remain accessible to a wide range of audiences
4. Easy to use interface
5. Intuitive setup and operation
6. Provide clean useful drinking water without the need for an external energy
7. Reasonably compact and portable
Our aim is to accomplish this goal by utilizing and converting the incoming
radioactive power of the sun's rays to heat and distill dirty and undrinkable water,
converting it into clean drinkable water. A solar parabolic trough is utilized to effectively
concentrate and increase the solid angle of incoming beam radiation, increasing the
efficiency of the system and enabling higher water temperatures to be achieved.
SOLAR WATER DISTILLATION
Solar energy is a very large, inexhaustible source of energy. The power from the sun
intercepted by the earth is approximately 1.8×1011
MW., which is many thousands times
larger than the present all commercial energy consumption rate on the earth. Thus in
principle, solar energy could supply all the present and future energy needs of the world
on a continuous basis. This makes it one of the most promising of all the unconventional
energy sources. In addition to its size, solar energy has two other factors in its favor.
Firstly, unlike fossil fuels and nuclear power, it is an environmentally clean source of
energy. Secondly, it is free and available in adequate quantity.
Solar water distillation is a solar technology with a very long history and
installations were built over 2000 years ago, although to produce salt rather than
drinking water. Documented use of solar stills began in the sixteenth century. An early
large-scale solar still was built in 1872 to supply a mining community in Chile with
drinking water. Mass production occurred for the first time during the Second World War
when 200,000 inflatable plastic stills were made to be kept in life-crafts for the US Navy.
The energy required to evaporate water, called the latent heat of vaporisation of
water, is 2260 kilo joules per kilogram (kJ/kg). This means that to produce 1 litre (i.e.
1kg as the density of water is 1kg/litre) of pure water by distilling brackish water requires
a heat input of 2260 kJ. This does not allow for the efficiency of the system sued which
will be less than 100%, or for any recovery of latent heat that is rejected when the water
vapour is condensed. It should be noted that, although 2260 kJ/kg is required to
evaporate water, to pump a kg of water through 20m head requires only 0.2kJ/kg.
Distillation is therefore normally considered only where there is no local source of fresh
water that can be easily pumped or lifted.
Human beings need 1 or 2 litres of water a day to live. The minimum requirement
for normal life in developing countries (which includes cooking, cleaning and washing
clothes) is 20 litres per day .Yet some functions can be performed with salty water and a
typical requirement for distilled water is 5 litres per person per day. Therefore 2m2
solar still are needed for each person served. Solar stills should normally only be
considered for removal of dissolved salts from water. For output of 1m3
/day or more,
vapour compression or flash evaporation will normally be least cost.
Solar distillation systems can be small or large. They are designed either to serve
the needs of a single family, producing from ½ to 3 gallons of drinking water a day on
the average, or to produce much greater amounts for an entire neighbourhood or
village. In some parts of the world the scarcity of fresh water is partially overcome by
covering shallow salt water basins with glass in greenhouse-like structures. These solar
energy distilling plants are relatively inexpensive, low-technology systems, especially
useful where the need for small plants exists. Solar distillation of potable water from
saline (salty) water has been practiced for many years in tropical and sub-tropical
regions where fresh water is scare. However, where fresh water is plentiful and energy
rates are moderate, the most cost-effective method has been to pump and purify.
Solar distillation is a relatively simple treatment of brackish (i.e. contain dissolved
salts) water supplies. In this process, water is evaporated; using the energy of the sun
then the vapour condenses as pure water. This process removes salts and other
impurities. 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. It is recommended that drinking water has 100 to 1000 mg/l of salt
to maintain electrolyte levels and for taste. Some saline water may need to be added to
the distilled water for acceptable drinking water.
Generally, solar stills are used in areas where piped or well water is impractical.
Such areas include remote locations or during power outages .Distillation are therefore
normally considered only where there is no local source of fresh water that can be
easily pumped or lifted. One of the main setbacks for solar desalination plant is the low
thermal efficiency and productivity. In areas that frequently loss power, Solar stills can
provide an alternate source of clean water. A large use of solar stills is in developing
countries where the technology to effectively distill large quantities of water has not yet
BASIC CONCEPT OF SOLAR WATER DISTILLATION
The basic principles of solar water distillation are simple yet effective, as distillation
replicates the way nature makes rain. The sun's energy heats water to the point of
evaporation. As the water evaporates, water vapor rises, condensing on the glass
surface for collection. This process removes impurities such as salts and heavy metals
as well as eliminates microbiological organisms. The end result is water cleaner than
the purest rainwater. The SolAqua still is a passive solar distiller that only needs
sunshine to operate. There are no moving parts to wear out.
The distilled water from a SolAqua still does not acquire the "flat" taste of
commercially distilled water since the water is not boiled (which lowers pH). Solar stills
use natural evaporation and condensation, which is the rainwater process. This allows
for natural pH buffering that produces excellent taste as compared to steam distillation.
Solar stills can easily provide enough water for family drinking and cooking needs.
Solar distillers can be used to effectively remove many impurities ranging from
salts to microorganisms and are even used to make drinking water from seawater.
SolAqua stills have been well received by many users, both rural and urban, from
around the globe. SolAqua solar distillers can be successfully used anywhere the sun
The SolAqua solar stills are simple and have no moving parts. They are made of
quality materials designed to stand-up to the harsh conditions produced by water and
sunlight. Operation is simple: water should be added (either manually or automatically)
once a day through the still's supply fill port. Excess water will drain out of the overflow
port and this will keep salts from building up in the basin. Purified drinking water is
collected from the output collection port.
4.1 Supply Fill Port:
Water should be added to the still via this port. Water can be added either manually or
automatically. Normally, water is added once a day (in the summer it's normally best to
fill in the late evening and in the winter, in the early morning). Care should be taken to
add the water at a slow enough flow rate to prevent splashing onto the interior of the still
glazing or overflowing into the collection trough.
4.2 Overflow Port:
Once the still basin has filled, excess water will flow out of this port. SolAqua
recommends three times daily distilled water production to be allowed to overflow from
the still on a daily basis to prevent salt build-up in the basin. If your still produced 2
gallons of product water then you should add 6 gallons of fresh feed water through the
fill port. If flushed like this on a daily basis, the overflow water can be used for other
uses as appropriate for your feed water (for example, landscape watering).
4.3 Distilled Output Collection Port:
Purified drinking water is collected from this port, typically with a glass collection
container. Stills that are mounted on the roof can have the distillate output piped directly
to an interior collection container. For a newly installed still, allow the collection trough to
be self-cleaned by producing water for a couple of days before using the distillate output
Fig.1.1 Basic concept of Solar Water Distillation
WORKING OF SOLAR STILL
Fig.1.2 Working of Solar Still
Solar stills are called stills because they distill, or purify water. A solar still
operates on the same principle as rainwater: evaporation and condensation. The water
from the oceans evaporates, only to cool, condense, and return to earth as rain. When
the water evaporates, it removes only pure water and leaves all contaminants behind.
Solar stills mimic this natural process.
A solar still has a top cover made of glass, with an interior surface made of a
waterproof membrane. This interior surface uses a blackened material to improve
absorption of the sun's rays. Water to be cleaned is poured into the still to partially fill
the basin. The glass cover allows the solar radiation (short-wave) to pass into the still,
which is mostly absorbed by the blackened base. The water begins to heat up and the
moisture content of the air trapped between the water surface and the glass cover
increases. The base also radiates energy in the infra-red region (long-wave) which is
reflected back into the still by the glass cover, trapping the solar energy inside the still
(the "greenhouse" effect). 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. There are no
moving parts in Solar still and only the sun‟s energy is required for operation.
The still is filled each morning or evening, and the total water production for the
day is collected at that time. The still will continue to produce distillate after sundown
until the water temperature cools down. 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.
Fig.1.3 Layout of Solar Still Plant
The most important elements of the design are the sealing of the base with black
DESIGN OF SOLAR STILL
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
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:-
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
6.3 Some problems with solar stills which would reduce their
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
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
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 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
Botswana 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:-
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.
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.
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
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.
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.
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:
a) Rainwater collection:-By adding an external gutter, the still cover can be used for
rainwater collection to supplement the solar still output.
b) Greenhouse-solar still:-The roof of a greenhouse can be used as the cover of a
c) 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:
1. The efficiency of single stage still is around 25%.
2. The efficiency of multistage stills is higher than 35%.
3. Mostly people use three staged stills because for more stages the cost outweighs the
4. Most of the losses can be attributed to heat transfer losses.
5. 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
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.
The equations governing the heat transfer rates are:-
Q = - k A dT / dx
Q = h A ( Tsurface- Tambient )
Both the losses are greatly dependant on the area and temperature difference between
the medium i.e., water and ambient. Hence if we can reduce temperature of the whole
system we can reduce the heat loss and hence improve the efficiency.
But reducing operating temperature will come at the cost of lower rated of evaporation
and consequently lower rated of condensation leading to slower distillation. So now the
problem boils down to increasing the rated of evaporation at lower temperature.
(Mass loss rate) / (Unit area) = (Vapor Pressure - Ambient Partial Pressure) * sqrt (
The Vapor Pressure of a liquid at a given temperature is a characteristic property of that
liquid. Vapor pressure of a liquid is intimately connected to boiling point.
Vapor Pressures are influenced by Temperature logarithmically and this relationship is
defined with the Clausius Clapyron Equation:
Log P2 / P1 = Delta H vaporization [ 1 / T1 - 1/T2] / 2.303 ( R)
R = universal gas law constant = 8.31 J/mol-K = 8.31 X 10-3 Kj / mol-K
P1 and P2 = vapor pressure at T1 and T2
T1 and T2 = Kelvin Temperature at the initial state and final state
At 373K the pressure is 1 atm.
We all know that boiling takes place when the ambient temperature equals that of the
vapor pressure of the liquid. This means that we can increase the rate of evaporation by
reducing the pressure of the vessel. This will ensure higher rates of evaporation even at
Constructing a solar water distiller using available utensils like plastic for casing,
aluminum for absorption of heat, glass and the thermocol for insulation. Got the
temperature of water up to 60 degrees and 100 ml of distilled water in 4 hours.
Surface area: .12 mt square (1 sq feet)
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
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 point-
of-use (POU) technology with NSF (National Sanitation Foundation) certification for
arsenic removal, under Standard 62. Solar distillation removes all salts and heavy
metals, as well as biological contaminants.
Surveys were conducted on user satisfaction with project participants receiving cost-
shared solar distillers . Users were nearly unanimous that owning a solar still was good
for them. 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. Others valued the
independence and fascination they experienced from being involved in the production of
their own purified water. Most colonias residents often do not trust their local water
supply in those cases when there is one available (e.g., Columbus). 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 pilot projects 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 during the wintertime where some families had insufficient still water.
Generally, it appears that for most Border households about 0.5 m2 meter of
solar still is needed per person to meet potable water needs consistently throughout the
year. Those households with insufficient wintertime still water production typically 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, a solar still can 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 of 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 in all cases. Solar still savings were approximately $150 - $200 a year
per household instead of purchasing bottled water.
Solar still technology has gradually 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 expensive to build.
Compared to purchasing comparable quantities of bottled water, the average return on
investment on a solar still for a family is typically 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 northern Mexico families often 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.
COST ANALYSIS & MATERIALS
1. 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.
2. The main frame is composed of steel owing to its corrosion resistance, low weight,
long life and easy cleanability.
3. The outside of the complete distiller is coated with carbon black to increase
absorption of radiation.
4. The cover on the top is made of tempered glass so that the birds can‟t see their
reflection and hence avoid nuisance.
Total cost of Aluminium box = Rs 2700
Cost of crushed hay and sawdust = Almost free
Cost of carbon black paint = Rs 200
Cost of tempered glass = Rs 800
Cost of Reflector = Rs. 500
Cost of insulation and sealing = Rs. 250
Cost of the hoisting mechanism and other auxiliaries = Rs 500
Cost of labor and machining = Rs 600
Cost of transportation = 800
Cost of other parts = 450
Cost of Report Writing: Rs. 700 (Typing, Editing, Color Printing, Hard Binding)
Net cost of the Project = Rs 7500
The per-liter cost of solar-distilled water can be calculated as follows:
(a) estimate the usable lifetime of the still;
(b) add up all the costs of construction, repair and maintenance (including labor)
over its lifetime; and
(c) 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
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:
1. The outer box will be fabricated first. It will be made of double wall and will be filled
with glass wool to provide insulation.
2. 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.
3. The collector tubes are then made and attached to the lowermost stage.
4. The holes are provided for
a. Collecting distilled water
b. Transporting saline water
c. To attach the pump
5. The whole system is sealed using sealant to prevent the air from leaking in from the
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.
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.
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.
Solar Radiation Absorber:
Another sheet of the same polycarbonate sheet used for the glazing can be
painted black and used as a solar heat absorber.
A picture of the passive solar still is shown below in Fig. 10, and dimensions are
shown in Fig. 11. The dimensions of the water refill port are arbitrary, or if tube filling is
chosen as the filling mode, it can be omitted. The actual catch for distill water is not
shown, but simply consists of a strip of polycarbonate fixed to the sloped glazing near
the bottom, to catch and direct the condensate out through the drip spout.
Berkads are a simple water supply option that is extensively used in Somalia
since the 1950‟s. A berkad is an artificial catchment that collects surface runoff that
results from intense rainfall episodes. They are usually lined with masonry and/or
concrete, and often include on one side a catch-pool that traps the coarse sediment.
Berkads are generally constructed in gently sloping areas, where low barriers are
sometimes present to direct runoff towards the catch-pool and then to the cistern.
During the intense rainfall episodes, berkads may fill up within several hours and last for
months throughout a dry period (Banks, 2008).They are the main water source for both
the human and livestock water needs. The studied berkads are on average 20 m long,
10 m wide and 3.5 m deep. Their volume thus is 700 m3.
When implementing a solar still system on the berkads it is essential that the
design is as simple as possible but still effective. Keeping in mind the economic and
logistic aspects, affordable and local materials should be used whenever possible.
Nevertheless, to guarantee a good functioning of the system, some parts need to be
For Budunbuto, a single slope solar still is preferred above a double slope solar
still, as having only one slope equals to having only one internal gutter which can be
easily connected to the drink water storage tank. To increase the solar interception, the
solar still needs an equator facing top cover, with the length therefore lined on an east-
west axis (this might be problematic for already existing berkads, which might not be
orientated properly). The top cover should be set at an angle of 10º, which is considered
to be the most accepted angle for a single slope solar still at this latitude (Khalifa, 2010).
It should be made either out of a 3-4 mm thick glass or a ultra-violet resistant polyvinyl
chloride (PVC) sheet. As mentioned above, glass is the preferred material as it
increases the efficiency of the solar still. When choosing for a glass cover, it is important
that the structure of the still is build to carry the weight of the relatively heavy glass. The
sides of the still should be closed in order to make the still airtight. This could be done
by using the same material chosen for the top cover. At the inlet of the surface runoff
water, a one way door should be placed (Figure 6). This would allow the surface runoff
water to flow into the berkad during periods of rainfall, as the door would then open
under the weight of the water, but it would remain shut during dry periods.
The condensed water should be collected in a gutter fixed along the lower edge
of the cover. On the outer side of the cover a similar gutter should be placed for the
collection of the rainwater. Both gutters should be placed on a small angle to let the
water run towards the airtight pipes that connect it to the drinking water tank. Both
gutters should also be made of a material that is not affecting the properties of the water
and so should the airtight pipes be. Particular attention needs to be used when installing
the rain water collection gutter, as factors as the weight of the water in the gutter and
the wind effects should be considered. It is also advised to add a gutter screen (e.g. a
simple mesh with a fine pattern), as debris from the roof may collect in the gutter,
The clean water storage tank should be placed in the immediate vicinity of the
berkad and should be properly closed, preventing any light from entering. It is advised
to place the drinking water tank in the ground (lower than the gutters), as in this way the
water would flow under gravity towards the tank.
A hand pump should be used for the extraction of the drinking water from the
tank, which should solely be used for human consumption. Another hand pump should
be used for the extraction of the water from the berkad, which should be used for animal
watering and other domestic use (washing, cooking, etc.).
Very important in the design of the system is that all the joints and fittings are
accurately isolated to prevent heat loss. For this reason, a one way valve could be
placed at connection point of the internal gutter and the pipe that goes to the drinking
Discussion and recommendations
The results presented above indicate that the implementation of a solar still on (already
existing and new) berkads is a feasible measure for the improvement of the water
quantity and quality in the village Budunbuto. Above this, it is generally agreed that solar
stills are a good option in remote areas where the water demand does not exceed the
200 m3/day (Tiwari et al., 2003 and Fath, 1998). However, the approach used is very
theoretical and abstract, what inevitably may have lead to some inaccuracies:
- The evaporation loss has been calculated based mostly on remotely sensed data,
which is available only at a large scale for the studied location. This is a source of
inaccuracy within the results of the Penman open water evaporation equation. However,
it is important to notice that due to the availability of this data it is actually possible to
make estimates over an otherwise data scarce region.
- The actual water consumption rate, and thus the amount of berkads needed with a
solar still system, might differ from what has been estimated. This because the water
consumption rates and the number of inhabitants of Budunbuto are also an estimation
based on the little information that is available.
- The theoretical approach used to estimate the output from the solar still is very
abstract and might be inaccurate. On the other hand, this seems the most reasonable
approach to use when estimating solar still output theoretically, as it is possible to make
assumptions for the efficiency of the system and the remaining parameters are all
- The solar still design as described above resulted to be the most suitable for
Budunbuto. However, as the approach used is very theoretical, it may not be the most
functional design in practice. Therefore it is recommended to test various simple solar
still designs during the pilot project. This could be done by constructing both single and
double slope solar stills, using plastic and glass top covers.
Although the above described inaccuracies are present, the information of this
report will provide a reliable guideline for the pilot project, during which the working of
the system will be tested. It is expected that the actual production rate of the solar still
will be within the range estimated and that the efficiency will most likely be around 15%.
However, to satisfy the water demand for animal watering and domestic use (about 35.5
m3/yr), more berkads are needed. These berkads obviously do not need a solar still
system, as the water does not need to be within the mineralogical and bacteriological
standard used for drinking water.
During the pilot phase of the project, it is advised to accurately measure both the
quantity and quality of the water produced by the still. The electrical conductivity, pH,
NO3- and the alkalinity of the water should directly be measured in the field. For the
analysis of the major cations and anions, it is advised to take 10 ml samples 13
filtered with a 0.45 μm membrane filter, which should then be sent to a water laboratory.
Also the bacteriological content of the water should be analysed, to make sure that the
bacteria and viruses are actually not present in the drinking water. These
measurements would certainly contribute to increase the knowledge regarding the
purification of contaminated water by using solar stills.
Once the working of the system has proven to be effective, it is important that the
water users are well informed about the solar still in order to ensure its correct
functioning and its sustainability. It is essential to emphasize that the solar still will only
produce the expected output when it is fully airtight. This means that the water inlet
should never be opened by the users to extract the water from the berkads as the hand
pumps should solely be used for that. The same holds for the drinking water tank which
should also never be opened. Another important point is that the maintenance of the
berkads is regularly carried out and that possible leaks are immediately detected and
repaired.Particular attention should be paid for the drinking water tank, which is
positioned in the ground, what makes it difficult to detect possible leaks.
The above described advisable design for the solar stills in Budunbuto is very
simple and (thus) not optimally efficient. It has been chosen to keep the design simple
because an increase in the efficiency and productivity of the still is usually coupled to an
increase in cost, which is an undesirable result. With this design, the solar stills
represent a low cost technology with low cost maintenance, which can be carried out by
History of drinking water filtration
During the 19th and 20th centuries, water filters for domestic water production
were generally divided into slow sand filters and rapid sand filters (also called
mechanical filters and American filters). While there were many small-scale water
filtration systems prior to 1800, Paisley, Scotland is generally acknowledged as the first
city to receive filtered water for an entire town. The Paisley filter began operation in
1804 and was an early type of slow sand filter. Throughout the 1800s, hundreds of slow
sand filters were constructed in the UK and on the European continent. An intermittent
slow sand filter was constructed and operated at Lawrence, Massachusetts in 1893 due
to continuing typhoid fever epidemics caused by sewage contamination of the water
The first continuously operating slow sand filter was designed by Allen Hazen
for the city of Albany, New York in 1897.
The most comprehensive history of water
filtration was published by Moses N. Baker in 1948 and reprinted in 1981.
In the 1800s, mechanical filtration was an industrial process that depended on the
addition of aluminum sulfate prior to the filtration process. The filtration rate for
mechanical filtration was typically more than 60 times faster than slow sand filters, thus
requiring significantly less land area. The first modern mechanical filtration plant in the
U.S. was built at Little Falls, New Jersey for the East Jersey Water Company. George
W. Fuller designed and supervised the construction of the plant which went into
operation in 1902.
In 1924, John R. Baylis developed a fixed grid backwash assist
system which consisted of pipes with nozzles that injected jets of water into the filter
material during expansion.
Types of filters:-
Water treatment plant filters
Types of water filters media filters, screen filters, disk filters, slow sand filter beds, rapid
sand filters and cloth filters.
Point-of-use filters for home use include granular-activated carbon filters (GAC) used
for carbon filtering, metallic alloy filters, microporous ceramic filters, carbon block resin
(CBR), microfiltration and ultrafiltration membranes. Some filters use more than one
filtration method. An example of this is a multi-barrier system. Jug filters can be used for
small quantities of drinking water. Some kettles have built-in filters, primarily to reduce
Point-of-use microfiltration devices can be directly installed at water outlets (faucets,
showers) in order to protect users against Legionella spp., Pseudomonas spp.,
Nontuberculous mycobacteria, Escherichia coli and other potentially harmful water
pathogens by providing a barrier to them and/or minimizing patient exposure.
Certification of Water Filters:-
Three organizations are accredited by the American National Standards Institute, and
each one of them certify products using ANSI/NSF standards. Each ANSI/NSF standard
requires verification of contaminant reduction performance claims, an evaluation of the
unit, including its materials and structural integrity, and a review of the product labels
and sales literature. Each certifies that home water treatment units meet or exceed
ANSI/NSF and Environmental Protection Agency drinking water standards. ANSI/NSF
standards are issued in two different sets, one for health concerns (such as removal of
specific contaminants (Standard 53, Health Effects) and one for aesthetic concerns
(Aesthetic Effects, such as improving taste or appearance of water). Certification from
these organizations will specify one or both of these specific standards.
NSF International: The NSF Water treatment Device Certification Program requires
extensive product testing and unannounced audits of production facilities. The goal of
this program is to provide assurance to consumers that the water treatment devices
they are purchasing meet the design, material,and performance requirements of
Underwriters Laboratories: Underwriters Laboratories, Inc., is an independent,
accredited testing and certification organization that certifies home water treatment units
which meet or exceed EPA and ANSI/NSF drinking water standards of contaminant
reduction, aesthetic concerns, structural integrity, and materials safety.
Water Quality Association:The Water Quality Association is a trade organization that
tests water treatment equipment, and awards its Gold Seal to systems that meet or
exceed ANSI/NSF standards for contaminant reduction performance, structural integrity,
and materials safety.
Filters that use reverse osmosis, those labeled as “absolute one micron filters,”
or those labeled as certified by an American National Standards Institute (ANSI)-
accredited organization to ANSI/NSF Standard 53 for “Cyst Removal” provide the
greatest assurance of removing Cryptosporidium. As with all filters, follow the
manufacturer‟s instructions for filter use and replacement.
Portable water filters
Main article: Portable water purification
Water filters are used by hikers, by aid organizations during humanitarian
emergencies, and by the military. These filters are usually small, portable and light (1-2
pounds/0.5-1.0 kg or less), and usually filter water by working a mechanical hand pump,
although some use a siphon drip system to force water through while others are built
into water bottles. Dirty water is pumped via a screen-filtered flexible silicon tube
through a specialized filter, ending up in a container. These filters work to remove
bacteria, protozoa and microbial cysts that can cause disease. Filters may have fine
meshes that must be replaced or cleaned, and ceramic water filters must have their
outside abraded when they have become clogged with impurities.
These water filters should not be confused with devices or tablets that are water
purifiers, some of which remove or kill viruses such as hepatitis A and rotavirus.
The term water polishing can refer to any process that removes small (usually
microscopic) particulate material, or removes very low concentrations of dissolved
material from water. The process and its meaning vary from setting to setting: a
manufacturer of aquarium filters may claim that its filters perform water polishing by
capturing "micro particles" within nylon or polyester pads just as a chemical engineer
can use the term to refer to the removal of magnetic resins from a solution by passing
the solution over a bed of magnetic particulate.
In this sense, water polishing is simply
another term for whole house water filtration systems. Good materials to create a filter is
sand, gravel, activated carbon and window screens.
“The next world war-if ever-will not be over land, but on WATER. Globally more than
one billion people lack access to safe drinking water, nearly all of them in the
developing countries, including India”. Nearly one-third of the population worldwide live
in areas which are waterstressed. This figure is expected to increase further by a fold by
2025. Approximately 80% of diseases in India are caused by water borne micro
organisms. This is true in rural as well as urban India. However, awareness of health
risks linked to unsafe water is still very low among the rural population. The few who
treat water resort to boiling or use domestic candle filters. With more & more number
people are becoming conscious about contaminated drinking water; the demand for
water purifiers is rapidly rising especially in India. In the past few years, Indian water
purifier industry has seen an exponential growth of 22% CAGR (Compounded Annual
There are three types of Water Purifiers in the market:
1. Ultra Violet Based
2. Reverse Osmosis Based
3. Chemical Based
The UV segment constitutes more than 55% of the industry and has its key focus
area for water Purifier manufacturers because of higher margins it offer. The Indian
water purifier market has tremendous potential with a market size of approximately INR
1400 Cr ore. It is more evident from the fact that global majors such as Philips and
Hindustan Unilever have stepped in the area. In the years to come, we can expect to
see others entering the battle.
FEATURES OF A GOOD PURIFIER
It should retain natural quality of water
User friendly features.
Absolutely safe for drinking purpose as per WHO standards.
In-built storage tank
Avoids all contamination with last point purification.
ABOUT THE PRODUCT
WATER PURIFIER – PUREIT
Pure-it is the world‟ s most advanced in-home water purifier. Pure-it, a breakthrough
offering of Hindustan Unilever (HUL), provides complete protection from all water-borne
diseases, unmatched convenience and affordability. Pure-it‟ s unique Germ kill Battery
technology kills all harmful viruses and bacteria and removes parasites and pesticide
impurities, giving you water that is “as safe as boiled water". It assures your family
100% protection from all water –borne diseases like jaundice, diarrhoea, typhoid and
cholera. Pure-it not only renders micro-biological safe water, but also makes the water
clear, odorless and good-tasting. Pure-it does not leave any residual chlorine in the
output water. The output water from Pure-it meets stringent criteria for microbiologically
safe drinking water from one of the toughest regulatory agencies in the USA, EPA
(Environmental Protection Agency). The performance of Pure-it has also been tested
by leading scientific and medical institutions in India and abroad. This patented
technological breakthrough has been developed by HUL. Pure-it runs with a unique,
Germ kill Battery Ki that typically lasts for 1500 liters of water. Consumer will get 4 liters
of water that is as safe as boiled water for just one rupee. Pure-it in-home purification
system uses a 4 stage purification process to deliver “as safe as boiled water” without
the use of electricity and pressurized tap water.
Pure-it purifies the input drinking water in four stages, namely;
1. MICRO-FIBER MESH- Removes visible dirt.
2. COMPACT CARBON TRAP- Removes remaining dirt, harmful parasites &
2. GERM KILL PROCESSOR– uses 'programmed chlorine release technology‟
and its Stored Germ kill process targets and kills harmful virus and bacteria.
4. POLISHER – Removes residual chlorine and all disinfectant by-products, giving
clearodorless and great tasting water.
5. BATTERY LIFE INDICATOR -Ensures total safety because when the germ kill
power is exhausted, the indicator turns red, warning you to replace the battery.
4.1 Solar Panel
A solar panel (also solar module, photovoltaic module or photovoltaic panel) is a
packaged connected assembly of photovoltaic cells. The solar panel can be used as a
component of a larger photovoltaic system to generate and supply electricity in
commercial and residential applications. Each panel is rated by its DC output power
under standard test conditions, and typically ranges from 100 to 320 watts. The
efficiency of a panel determines the area of a panel given the same rated output - an
8% efficient 230 watt panel will have twice the area of a 16% efficient 230 watt panel.
Because a single solar panel can produce only a limited amount of power, most
installations contain multiple panels. A photovoltaic system typically includes an array of
solar panels, an inverter, and sometimes a battery and or solar tracker and
FIG. Solar Panel
4.2 Theory and construction
Solar panels use light energy (photons) from the sun to generate electricity through the
photovoltaic effect. The majority of modules use wafer-based crystalline silicon cells or
thin-film cells based on cadmium telluride or silicon. The structural (load carrying)
member of a module can either be the top layer or the back layer. Cells must also be
protected from mechanical damage and moisture. Most solar panels are rigid, but semi-
flexible ones are available, based on thin-film cells.
Electrical connections are made in series to achieve a desired output voltage
and/or in parallel to provide a desired current capability. The conducting wires that take
the current off the panels may contain silver, copper or other non-magnetic conductive
transition metals. The cells must be connected electrically to one another and to the rest
of the system. Externally, popular terrestrial usage photovoltaic panels use MC3 (older)
or MC4 connectors to facilitate easy weatherproof connections to the rest of the system.
Bypass diodes may be incorporated or used externally, in case of partial panel
shading, to maximize the output of panel sections still illuminated. The p-n junctions of
mono-crystalline silicon cells may have adequate reverse voltage characteristics to
prevent damaging panel section reverse current. Reverse currents could lead to
overheating of shaded cells. Solar cells become less efficient at higher temperatures
and installers try to provide good ventilation behind solar panels.
Depending on construction, photovoltaic panels can produce electricity from a
range of frequencies of light, but usually cannot cover the entire solar range
(specifically, ultraviolet, infrared and low or diffused light). Hence much of the incident
sunlight energy is wasted by solar panels, and they can give far higher efficiencies if
illuminated with monochromatic light. Therefore, another design concept is to split the
light into different wavelength ranges and direct the beams onto different cells tuned to
those ranges. This has been projected to be capable of raising efficiency by 50%.
Currently the best achieved sunlight conversion rate (solar panel efficiency) is
around 21% in commercial products, typically lower than the efficiencies of their cells in
isolation. The energy density of a solar panel is the efficiency described in terms of peak
power output per unit of surface area, commonly expressed in units of watts per square
foot (W/ft2). The most efficient mass-produced solar panels have energy density values
of greater than 13 W/ft2 (140 W/m2).
Would a solar still suit our needs?
Human beings need 1 or 2 litres of water a day to live. The minimum requirement for
normal life in developing countries (which includes cooking, cleaning and washing
clothes) is 20 litres per day (in the industrialised world 200 to 400 litres per day is
typical). Yet some functions can be performed with salty water and a typical requirement
for distilled water is 5 litres per person per day. Therefore 2m² of still are needed for
each person served.
Solar stills should normally only be considered for removal of dissolved salts from
water. If there is a choice between brackish ground water or polluted surface water, it
will usually be cheaper to use a slow sand filter or other treatment device. If there is no
fresh water then the main alternatives are desalination, transportation and rainwater
collection. Unlike other techniques of desalination, solar stills are more attractive, the
smaller the required output. The initial capital cost of stills is roughly proportional to
capacity, whereas other methods have significant economies of scale. For the individual
household, therefore, the solar still is most economic.
For outputs of 1m³/day or more, reverse osmosis or electrodialysis should be
considered as an alternative to solar stills. Much will depend on the availability and price
of electrical power. Solar distillation Practical Action 5 For outputs of 200m³/day or
more, vapour compression or flash evaporation will normally be least cost. The latter
technology can have part of its energy requirement met by solar water heaters.
In many parts of the world, fresh water is transported from another region or location by
boat, train, truck or pipeline. The cost of water transported by vehicles is typically of the
same order of magnitude as that produced by solar stills. A pipeline may be less
expensive for very large quantities.
Rainwater collection is an even simpler technique than solar distillation in areas
where rain is not scarce, but requires a greater area and usually a larger storage tank. If
ready-made collection surfaces exist.
Distillation Purification Capabilities:-
Solar stills have proven to be highly effective in cleaning up water supplies to
provide safe drinking water. The effectiveness of distillation for producing safe drinking
water is well established and recognized. Most commercial stills and water purification
systems require electrical or other fossil-fueled power sources. Solar distillation
technology produces the same safe quality drinking water as other distillation
technologies; only the energy source is different: the sun.
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.
1) BOOK-Renewable Energy Sources By G.D.Rai