Analysis of solar still system

SUMMER INTERNSHIP-II
ANALYSIS OF SOLAR STILL SYSTEM
Faculty Mentor : Satayu C. Travadi (Assistant Professor)
Submitted By : Ronak Suthar (17ME097)
Pratik Tanwar (17ME098)
Duration : 17th April to 31th May
DEPARTMENT OF MECHANICAL ENGINEERING
1

 What Is SOLAR STILL SYSTEM ?
• Solar Still System distills water with substances dissolved in it by using the heat of
the sun to evaporate water so that it may be cooled and collected by purifying it.
• In a Solar Still, impure water is contained outside the collector, where it is
evaporated by sunlight shining through clear plastic or glass.
• They are used in areas where drinking watre is unavailable, so that clean water is
obtained from dirty water or from plants y exposing them to sunlight.
2

 Principle :
• The solar still system mainly works on the principle of evaporation and condensation.
• A solar stills distills water with substances dissolved in it by using the heat of sun to
evaporate water so that it may be cooled and collected, thereby purifying it.
• They are used in areas where water is unavailable, so that clean water is obtained
from dirty water or from plants by exposing them to sunlight.
• 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 into water again as it cools
and can then be collected.
• This process leaves behind impurities, such as salts and heavy metals, and eliminates
microbiological organisms. The end result is pure distilled drinking water.
3

 Working :
• Solar stills distill water using the two main scientific principles of the water cycle -
Evaporation and Condensation.
• Evaporation : It acts as a mechanism to separate pure water from the impurities. The
dirty water is left to sit in the sun, allowing it to absorb solar energy.
• The water begins to heat up as the energy is absorbed. As the temperature rises, water is
converted to steam - the purified water is that needs to be collected.
• Solar stills assume that all impurities have higher boiling points than that of water, so
certain contaminated water with impurities having a lower boiling point than water are
not suitable.
4

Cont..
• Condensation : The is the second cardinal step
of the distillation process. Once the evaporated
seam hits the glass ceiling, it begins to
condensate as it loses energy in the form of
heat.
• The condensed steam results in pure water
droplets. The water droplets flow down to the
empty water trough due to gravity as the glass
ceiling is angled downwards.
• The pure water collected in the empty trough is
free form minerals, bacteria and other
substances which are unable to evaporate with
the water.
5

 Types of Solar Stills :
• Solar distillation systems can be classified as passive and active. Solar radiation is
the input energy of the passive solar stills, but the efficiency of the system is low.
• Attempts have been made to increase the efficiency and productivity by
preheating the saline water in solar stills. This method is called active solar
distillation. In the case of active solar distillation, an additional source of thermal
energy is required for faster evaporation inside the same passive solar still.
• The additional source may be a solar energy based system or thermal energy
contained in hot water which is discharged by other industries. There are many
different ways to make a solar still and different materials that can be used. Listed
are the various types of passive solar water distillers.
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Types of Solar Still
Active Type Passive Type
Single Effect
Multi Effect
Basin Type
Wick Type
Multi Week Type
Diffusion Type
Greenhouse
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 Advantages :
• Provide a maintained pH level which is very close to natural water as compared to
other water purifiers.
• Very cheap there is no cost of extra energy once you are solar still is manufactured
you will get benefits without extra cost.
• Less hazardous because there is no any mechanical equipment.
• Works on free energy which we get from the sun hence there is a record of CO2
emission.
• Water taste is claimed to be very good if we compare it other purifiers.
8

 Disadvantages :
• The solar still doesn’t break down the bacteria’s.
• Sun still produce a low quantity of water.
• This process is very time consuming.
• In solar still, boiling process of water does not occur.
• Large top glass may attract the bugs and insects.
9

 Components of Solar Still :
• A basin : The basin contains the saline (or brackish) water that will undergo distillation.
As such, it must be waterproof and dark (preferably black) so that it will better absorb
the sunlight and convert it to heat. It should also have a relatively smooth surface to
make it easier to clean any sediment from it.
• A support structure : Support structures form the sides of the still as well as the basin,
and support the glazing cover. As noted earlier, some materials used in forming the basin
also form the still support structure while other still configurations demand separate
structures, especially to hold the glazing cover.
• A transparent glazing cover : After the pan, the glazing cover is the most critical
component of any solar still system.It is mounted above the basin and must be able to
transmit a lot of light in the visible spectrum yet keep the heat generated by that light
from escaping the basin.
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• A distillate trough (water channel) : The distillate trough is located at the base of the tilted
glazing. It serves to collect the condensed water and carry it to storage. It should be as small as
possible to avoid shading the basin.
• In addition to these, ancillary components may include :
1. Insulation (usually under the basin)
2. Sealants
3. Piping and valves
4. Facilities for storage
5. An external cover to protect the other components from the weather and to make the
still esthetically pleasing
6. A reflector to concreate sunlight
11

 Materials :
• Basin : For the basin aluminum coated with silicone rubber is the best option. The
durability of basins made with this material increased into the 10- to 15-year range.
• Support Structure : The primary choices for support structures are wood, metal,
concrete, or plastics. In most cases the choice of material is based upon local availability.
Use of metal frame is practically limited to aluminium and galvenized steel. Silicon rubber
is not adhere with galvenized steel so aluminium is suitable for support structure.
• Glazing Cover : Tempered glass is the best choice in terms of wettability and its capability
to withstand high temperatures. It is also three to five times stronger than ordinary
window glass and much safer to work with.
12

Cont...
• Distillate Trough : Basins lined with butyl rubber or EPDM can have their liners
extend beyond the basin to form the trough. This method is inexpensive to
implement and provides a corrosion-free channel.
13

 Literature Review :
• 1. A. Muthu Manokar concluded that in high water levels, the maximum temperature of the basin water,
vapour and water is recorded in the late afternoon hour between 15hrs and 18hrs whereas lower levels are
attained from the middle of the afternoon. Also, the largest temperature (83.9 C) of the solar still is recorded
in the inner wall surfaces while the lowest temperature is recorded at the bottom of the still (32.2 C).
• 2. Krishna PV, Shrideva V and Priya BH stated that Solar distillation is one of the best methods for waste
water treatment. For a single slope solar distillation unit east from 9:30am to 12:30pm then west from
12:30pm to 5:30pm is the direction in which maximum efficiency was obtained. For both copper
electroplated Aluminium basin and Aluminium basin with black paint 3 litres volume of waste water showed
the maximum efficiency.An Aluminium basin with black paint showed better efficiency when compared to
that of a copper electroplated Aluminium basin. The efficiency has increased from 54.66 to 65.63 by
replacing a copper electroplated Aluminium basin with an Aluminium basin with black paint.
• 3. Sadhana stated that the productivity is decrease from morning to evening for a less water level whereas
for high water level the productivity is increase from morning to evening.
• 4. B.S.Nijmeh stated that a glass cover that is no more than 5 to 7 centimeters from the water surface will
allow the still to operate efficiently. Conversely, as glass-to-water distance increases, heat loss due to
convection becomes greater, causing the still's efficiency to drop.
DEPARTMENT OF MECHANICAL ENGINEERING 14

Cont...
• 5. S. Kharparde and P.P.Pande conclude that a solar still should be built in a way that will get the water as hot
as possible, and keep it as close to the glass as possible. This is achieved by keeping the glass cover at a
minimum distance from the water surface, which in practical terms, falls between 5 and 7 cm, and by
minimizing the depth of water in the pan, to about 1.5 cm.
• 6. J.I.Orisaleye, S.O.Ismail and A.A.Ogundare stated that the basin should be made from aluminum coated
with silicon rubber. The durability of basins made with this material increased into the 10- to 15- year range.
For the hundreds of stills one company sold using this material, the coating was all done by hand. With
production roll coating equipment, the basin's durability could probably be increased even more.
• 7. Shyam Verma and Devendra Singh concluded that ordinary window glass is the best choice for glazing
cover rather other materials. Except that it has an oily film when it comes from the factory, and must be
cleaned carefully with detergent and/or ammonia. If you choose glass as a glazing material, double-strength
thickness (i.e., one-eighth of an inch, or 32 millimeters) is satisfactory.
DEPARTMENT OF MECHANICAL ENGINEERING 15

 Design Parameters :
• The slope of glazing cover should be less about 20 to 25 degree due to three main
factors.
 The higher the slope, the more glass and supporting materials are needed to
cover the basin.
 Higher slope increase the volume and weight of still utimately it increases
the shipment cost.
 Higher slope can increase the volume of air inside the still , which lowers the
efficiency of the system.
• The glass cover that is no more than 5 to 7 cm from the water surface will
allows the still more efficiently. Because more distance increase the
convenction will plummet the efficiency.
16

Cont...
• It is clear that a solar still should be
built in a way that will get the water as
hot as possible, and keep it as close to
the glass as possible. This is achieved
by keeping the glass cover at a
minimum distance from the water
surface, which in practical terms, falls
between 5 and 7 cm, and by
minimizing the depth of water in the
pan, to about 1.5 cm.
17

Cont...
• Apart from that, The basin liner is made of galvanized iron sheet of0.5 × 1 m2
with maximum height of 288mm, and 1.4 mm thickness. The basin surfaces are
painted with black paint to absorb the maximumamount of solar radiation
incident on them.
• In addition to this, the bottom and sides are insulated with 25 mm thick thermo
cool and 12.5 mm thick wood with thermal conductivity 0.015 W/m K and 0.055
W/m K respectively.
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 Analysis of various parameters :
19

Cont...
• From the 1st graph, we can see that In the morning hours (9.00 – 10.00hrs), the
glass temperature is higher than the water and vapour temperature causing small
productivity due to the small energy absorbed by the water at this period.
• From the 2nd graph, we can see that water depth should be 10 or 20 mm because
it gives higher vapour temperature around 75 degree to 80 degree.
• From the 3rd graph, it is mandatory to keep water depth 20 or 40 mm to get more
output. But, at 40 mm water depth output will decrease in a huge amount in the
evening time.
20

Cont...
• Finally, from the last graph, we can get more than 80 % efficiency through 20 mm
depth of water.
• For higher water levels, the efficiency slowly increasing from morning and it will
reach maximum in the late evening. Between 17hrs and 18hrs, 50mm and 60mm
water levels are given more than 100% efficiency; due to the output of distillate
water energy (Qd) is much higher than the solar radiation (I) input during this
period.
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 Cost Analysis :
No. Parts Cost (Rs.)
1 Total cost of aluminium box 1500
2 Cost of carbon black paint 100
3 Cost of tempered glass 1000
4 Cost of reflector 2000
5 Cost of insulation and sealing (Silicon glue) 2500
6 Cost of hoisting mechanism and other auxillaries 500
7 Cost of labour and machining 600
8 Cost of temperature sensor 2200
9 Cost of other parts (Table, Base, Piping etc) 500
10 Net cost of the Project 12400/-
22

THANK YOU
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