This document summarizes the design, fabrication, and testing of a modified single slope solar still. Key findings include: 1) The still was tested in Allahabad, India and found that a glass condensing cover produced 64% more distillate than a PVC cover. 2) Temperature measurements showed the glass cover reached higher temperatures than the basin water, with the largest difference occurring in the afternoon. 3) Over six days of testing, the still produced an average of 2.25 liters of distillate daily, with an efficiency as high as 39%. 4) The total fabrication cost of the still was estimated at 10,600 rupees, with a payback period of

1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME
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DESIGN, FABRICATION AND TESTING OF A MODIFIED SINGLE
SLOPE SOLAR STILL
Ajeet Kumar Rai*, Pratap Singh, Vivek Sachan, Nripendra Bhaskar
Mechanical Engineering Department
Sam Higginbottom Institute of Agriculture Technology and Sciences, Allahabad
ABSTRACT
In the present work a single slope single basin solar still was designed fabricated, and
its performance was tested in the Allahabad climatic conditions. An effort is also made to
find the effect of condensing cover material on the performance of solar still. It was found
that over the hours of experimental testing that the condensing cover made up of glass gives
64% more distillate than the condensing cover made up of polyvinyl chloride. Cost
calculations are also performed to find the payback period of the system.
Keywords: Slope Solar Still, heat transfer coefficients.
INTRODUCTION
A solar still is a device by which distilled or portable water can be produced from
saline water, such as seawater brackish water. Solar still are normally used to provide a small
scale of portable water needed in remote isolated location, where there is plenty of solar
energy source of saline water are available [1].
A conventional basin type solar still is simply an air tight basin that contains a
shallow layer of saline water, a sloped top cover of a transparent material usually glass to
solar radiation and side metal frame walls[2]. Solar distillation is a technology with a long
history. The first known-application of solar stills was in 1872. When a still at laslina on the
northern deserts of Chile started its three decades of operation to supply a mining community
with drinking water. Most stills built and studies since then have been based on the same
principles, though many variations in geometry, materials, methods of construction, and
operation have been incorporated [3]. The cost of building and operating a conventional still
is relatively low compared to those involving sophisticated designs. However, the
conventional or standard basin type solar still [5-8] proven to have a low thermal efficiency
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2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
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with low daily distillate productivity [4]. The efficiency and yield of the conventional solar
still depend on different factors: the design and functionality of the still, location, weather
conditions, etc. [5]. Their low thermal efficiency is due to the considerable shadow caused by
the walls of the basin that tend to decrease the absorption of solar radiation that could have
been used for water distillation process. In order to improve the performance of conventional
solar stills, several other designs have been developed, such as the double-basin type [6],
multi-basin [7,8], inverted trickle [9], multi-effect [10], regenerative [11], with reflectors
[12]. Kalogirou [13] presented an excellent review on various types of passive and active
solar stills. Among these types are the single-slope with passive condenser, double
condensing chamber solar still, vertical solar, and conical solar still. In this paper, a
modification in design of a single slope solar still is presented and its performance is
evaluated in Allahabad climatic condition. The condensing cover made-up of glass cover is
replaced with a PVC material.
Design of the solar still
The photograph of the modified single slope solar still are shown in figure 1.The still
mainly consists of the basin and absorber plate carrying the saline water, the cover, and the
support structure as shown in Fig.1. The basin of the still (tray) and absorber plate, and the
collector were all fabricated using Galvanised Iron. The basin contains the absorber
aluminium plate which has a surface area of 1×1 m2
. A hole with diameter of approximately
30 mm was drilled into the tray to provide accessibility of saline water into the basin during
initial filling and bottom section of basin was insulated to reduce thermal losses to the
surroundings. The absorber was coated with black paint to maximize absorption of the
incident solar radiation on the basin. The two different condensing covers, located on the top
of the solar still unit, was made of two different material(a) A glass cover and (b)A
transparent PVC sheet. The side walls are made of using two 5 mm thick glass plates
separated by 2 cm air gap. The side walls are made of glass to capture more diffuse radiation
and the air gap is provided to minimize heat loss from sides. The distillate output from the
still was frequently collected using a plastic container placed under the nozzle outlet part of
the collector.
Fig 1 photograph of the modified design single slope solar still

3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME
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Test site meteorological environment
The new single slope solar still was tested under Allahabad (25.
450
N, 81.850
E)
climatic condition in typical summer month. Allahabad is characterized by two distinct
seasons: a very hot season (March–June) and cold season (November -February). The hot
months are typically characterized by high solar insolation. The hot months average
temperature of Allahabad range from 300
C to 430
C. The cold month’s average temperature
range from 30
C to 140
C .
Experimental Procedure
Experiments were conducted at Allahabad (U.P.), India (25°28’N, 81°54’E) in the
month of April. The condensing cover of the single sloped still was kept with their glass
covers facing south, so as to obtain maximum radiation throughout the day. Initially 2 cm
basin water depth was taken. Readings of solar intensity, ambient air temperature and the
temperature of basin water, glass cover, inside air were recorded. Hourly and daily distillate
output was measured directly from the graduated bottles.Two different sets of experiments
were conducted. These were (1) Performance of still with condensing cover made of glass
and (2) Performance of the still with condensing cover made of PVC. Copper – constantan
thermocouples were installed and used to measure the temperature of water, condensing
cover, basin, atmosphere and anemometer used to measure wind speed.
RESULTS AND DISCUSSION
Numbers of experiments were conducted on every set of experiment. Typical results
of the variation of the ambient temperature, cover temperature, saline water temperature and
basin temperatutes during representative days of testing are shown in fig.4. At the start in the
early morning and at the end in the evening the basin water temperatures and glass cover
temperatures of both the still match very closely, but the difference increases and attains
maximum value in the afternoon. This difference in the time for the maximum values of solar
radiation and that of basin water temperature is due to the higher thermal inertia of the basin
water mass. Fig .2 shows the solar intensity on particular day 15-03-2013 .The maximum
intensity of 1060 w/m2
is received at 13:00 hrs.
Fig.2 Variation in solar intensity on 15-03-2013
Fig .3 shows the wind speed on particular day of 15-03-2013. The maximum wind speed of
1.1 m/s is observed at 11:30 hrs.

4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME
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Fig. 3 Variation in wind speed on 15-03-2013
Fig. 4 shows the temperature of glass, water, atmosphere and basin. Initially at 8:30 hrs glass
temperature is higher than water temperature.
Fig. 4 Variation of temperature with time
Fig.5 shows convective heat transfer coefficient for Present model and Dunkle model. The
maximum value of Convective heat transfer coefficient for Present model is obtained at 4:30
in the evening time.
Fig. 5 Variation of convective Heat Transfer Coefficient

5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME
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Fig.6 shows evaporative heat transfer coefficient for present model and Dunkle model.
Evaporative heat transfer coefficient for present model is higher than Dunkle model.
Fig.6 Variation in Evaporative heat transfer coefficient
Fig 7 shows the variations in theoretical distillate and experimental distillate.
Fig. 7 Comparison of theoretical and experimental distillate yield
Fig 8.The Total daily distillate yield from the still as a function of daytime during the four
days of testing

6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME
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Cost estimation
Typically, in designing a solar still for a primary application to provide a small scale
of portable water needed in remote isolated location, the objective is to maintain the cost
minimal.
Table1: Cost estimation for the component of fabricated single slope solar still
Component Cost (Rs )
G.I. basin 4500
Glass(5mm thickness) 4700
Support legs 600
Coating &primer 100
Cost estimation for various component used in the in-house fabrication of the single slope
solar still is given in Table1.The cost of the single slope still glass is Rs 4700. The cost of
labour work was estimated Rs 700.The total cost of the fabricated still, including labour, was
approximately Rs 10600. It should be noted that the solar still here was fabricated for
research purpose and not for commercial use . It is expected that the cost would significantly
decrease if a large number of still are fabricated for commercial purpose. With zero
maintenance cost the payback period will be less than one year.
CONCLUSIONS
In this work, a modified single slope solar still was designed, fabricated and
experimentally tested during daytime for six days under outdoors of Allahabad climatic
conditions. It was found that over the hours of testing in data, the daily distillate produced
from the still ranged from approximately 2.25 litre of absorber area. The daily efficiency of
the still reached as high as 39%. The payback period is less than one year.
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