1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 115-122 © IAEME
115
DESIGN, FABRICATION AND PERFORMANCE EVALUATION OF A LOW-
COST PARABOLIC TROUGH COLLECTOR WITH COPPER RECEIVER
Amit Kumar Pandey, Dr. Ajeet Kumar Rai, Vivek Sachan
MED, SSET, Sam Higginbottom Institute of Agriculture Technology and Sciences,
Allahabad (U.P.), India
ABSTRACT
In the present work, an attempt has been made to design, fabricate & evaluate the
performance of Parabolic Trough Collector (PTC) to produce hot water. The Supporting stand of
concentrator is made of mild steel & reflector is made of acrylic sheet with a rim angle of 45o
and
aperture area of 2.14 m2
and with a concentration ratio of 12.59. The receiver pipe is made of pure
copper. The thermal performance of the PTC was determined according to ASHRAE 93-1986
(RA 91). The maximum instantaneous thermal efficiency of 52.35% is obtained. The total cost of the
parabolic trough collector is calculated as Rs 7,000.
Keywords: Parabolic Trough Collector, Acrylic Mirror, Copper Receiver.
INTRODUCTION
Parabolic Trough Concentrator (PTC) is a solar concentrator technology that converts solar
beam radiation into thermal energy. A cylindrical parabolic trough is a conventional optical imaging
device used as a solar concentrator. It consists of a cylindrical parabolic reflector and a metal tube
receiver at its focal plane. The receiver is blackened at the outside surface covered by concentrator
and rotated about one axis to track the sun`s diurnal motion. The heat transfer fluid flows through the
absorber tube, gets heated and thus carries heat.
Such concentrators have been in use for many years. The aperture diameter, rim angle and
absorber size and shape may be used to define the concentrator. The absorber tube may be made of
mild steel or copper and is coated with a heat resistant black paint. Selective coatings may be used
for better performance. Depending on the temperature requirement different heat transfer liquids may
be used. Reflectors may be of anodized, aluminium Mylar or curved silvered glass. Since it is
difficult to curve a very large, mirror strips are sometimes used in the shape of parabolic cylinder.
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ISSN 0976 – 6340 (Print)
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Volume 5, Issue 5, May (2014), pp. 115-122
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2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 115-122 © IAEME
116
The reflecting part is fixed on a light weight structure. The concentration ratio for a cylindrical
absorber varies from 5 to 30.
The major energy losses from a concentrator-receiver assembly for normal incidence are
losses during reflection from reflecting surface and convection loss from the receiver to surrounding.
Efforts are made to use high reflecting materials and to reduce convection. Twisted types are used in
the absorber tube to cause large heat transfer from the absorber to working fluid.
A cylindrical parabolic trough may be oriented in any of the three directions: East-west,
north-south or polar. The first two orientations although simple to assemble, have higher incidence
angle cosine losses. The polar configuration intercepts more solar radiation per unit area as compared
to other modes and thus gives the best performance.
DESIGN CONSIDERATIONS
The Parabolic Trough Solar Concentrator, we present here, has the following innovative
characteristics: low cost of manufacturing materials, light and strong structure, and easy
construction. In order to reduce the construction expenses, two commercially available Acrylic
Mirror Sheets of the size (0.92 m * 1.22 m) and 1 mm thickness were used. They were placed
longitudinally; this in turn determined the size of the PTC. An Acrylic Mirror Sheet is chosen, since
it reflects 80% of sunlight. As part of the design of the PTC, the Mirror Sheets are not cut or rolled;
the Mirror Sheets are installed on the structure without modification, the parabolic profile is given by
the shape of the ribs and the weight of the sheets as they rest on said ribs.
Design Parameters of PTC
In order to determine the dimensions of the PTC, the following parameters were considered:
a rim angle of 45o
( r = 45o
) and the width of the acrylic sheet S = 1.22 m. Based on these two
parameters, it is possible to determine the aperture of the parabola, Wa:
ܹ௔ ൌ
2ܵ ‫݊ܽݐ‬ ቀ
߮௥
2 ቁ
ሺsec ቀ
߮ଶ
2
ቁ ൅ tan ቀ
߮௥
2
ቁ ൅ ln ሺsec ቀ
߮ଶ
2
ቁ ൅ tan ቀ
߮௥
2
ቁሻሻ
And, focal length, f:
݂ ൌ
ܹ௔
4 tan ቀ
߮௥
2 ቁ
On the other hand, the geometric concentration ratio (C) for a tubular receiver is given by:
‫ܥ‬ ൌ
ܹ௔
ߨ‫ܦ‬௢
Where, Wa is the width of the collector and Do is the outer diameter of the receiver. For the
manufacture of the receiver, a commercially available copper tube with outer diameter (Do) of 0.03
m is used. Table 1 gives a summary of the PTC key features.

3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 115-122 © IAEME
117
Table 1: Specifications of PTC
Rim Angle ( r) 45o
Focal Length (f) 0.0051 m
Aperture Width (Wa) 1.1861 m
Diameter of Receiver Tube (Do) 0.03 m
Length of Parabola (L) 1.82 m
Effective Aperture Area (Aa) 2.09 m2
Concentration Ratio (C) 12.59
Reflectivity of collector (ρ) 0.9
Absorptivity of receiver tube (α) 0.8
Transitivity of receiver tube (τ) 0.8
Intercept Factor (γ) 0.92
Therefore, the sacrifice in optical efficiency is small, while the increment in concentration
ratio and aperture area is significant. This allows savings in reflective materials cost.
Fabrication of PTC
The PTC is constructed in a very simple manner. It consists of a parabolic trough, a receiver,
and a support structure. The detailed description of each part is given below:
1. Parabolic Trough
The proposed trough collector consists of low-cost Acrylic Mirror Sheet of 1 mm thickness,
which has undergone a careful deformation process that was necessary to bring it to parabolic shape.
The material is easily available and can be given requisite shape. For the easy manoeuvrability of the
collector system, the aperture width of the trough is taken 1.18m and its focal length is 0.0051 m.
The aperture area of the reflecting surface is 2.14m2
. To maintain the parabolic shape intact, cross-
ribs made of cast iron are provided on the back surface. The trough collector is then mounted on
stand made of cast iron. The specific mirror sheet is economic, light and has a high reflectivity
coefficient of 0.80. The environmental stability of the reflective surface was monitored for 12
months.
2. Receiver
The purpose of the designed parabolic trough collector was to heat water at atmospheric
pressure and temperature. The desired process was carried out in the receiver placed concentrically
along the focal line of the collector. Out of many shapes thought of, from circular to square, circular
section was finalized. The reason being easy availability and less area coverage to avoid shading on
the reflector. The circular pipe made of Copper (Cu) is used for the purpose. Copper makes a good
conductor of heat because of its free electrons that can quickly pass on the energy that is applied to it.
The size of the Receiver was decided based on two factors viz. (i) Local availability of channel
section, and (ii) Concentration ratio desired. The final Receiver dimensions are taken as outer
diameter 0.03m and length 2.13m.
3. Collector Support Structure
For collector`s stability and accuracy, a rigid supporting structure is designed and made with
rigid iron strips. The structure frame is supported to the rotation axis of the parabolic reflecting

4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 115-122 © IAEME
118
surface. It is used for the rotation of the horizontal axis for daily tracking of the sun. For test purpose
and cost reduction, the unit is designed for easy manual tracking.
EXPERIMENTAL SETUP
The experimental setup of the parabolic trough solar collector consists of a collector, a
storage tank of capacity 30 litres, and a receiver pipe of length 2.13 m with two valves at both ends.
The water supply tank is located above the receiver`s pipe level to allow the heating fluid to flow
naturally without pumping system. The storage tank is filled from main water supply. The water inlet
and outlet temperature of the absorber tube, the ambient temperature, the reflector temperature, the
temperatures at inlet/outlet/middle surface of the receiver, the solar radiation intensity and the wind
velocity are continually measured during the experiment. The outdoor experimentation was carried
out in the month of March and April 2014. The testing system is oriented North-South to capture
maximum insolation as shown in figure 1.
Fig. 1: Experimental Setup of parabolic trough concentrator
PERFORMANCE OF PARABOLIC TROUGH COLLECTOR
The purpose of the performance analysis is to develop an empirical mathematical model that
characterizes the performance of the solar field under different operating conditions for the system
under study. The parameters that will be used to estimate the performance are the solar field
efficiency and the useful heat output from the solar field.
Optical Efficiency
The optical efficiency ηo is defined as the amount of radiation absorbed by the absorber tube
divided by the amount of direct normal radiation incident on the aperture area. The optical efficiency
when the incident radiation is normal to the aperture (θ = 0o
) is given as:
ߟ௢ ൌ ߩሺ߬ߙሻߛ
Thermal Efficiency
For solar collectors in general, the collector overall efficiency ηc is defined as the ratio
between the useful output Qu [W] delivered by the collector to the global irradiance I [W/m2
]
incident on the collector aperture area Aa [m2
]

5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 115-122 © IAEME
119
ߟ௖ ൌ
ܳ௨
‫ܣ‬௔ ‫כ‬ ‫ܫ‬௕
For a concentrating collector, the useful output Qu can be expressed as:
ܳ௨ ൌ ݉. ‫ܥ‬௣. ሺܶ௢ െ ܶ௜ሻ ൌ ‫ܣ‬௔. ‫ܫ‬௕. ߟ௢ െ ‫ܣ‬௔௕௦. ܷ௟. ሺܶ௔௕௦ െ ܶ௔ሻ
RESULTS AND DISCUSSION
Numbers of observations were taken on the system in the month of March & April 2014 in
the campus of SHIATS, Allahabad, Uttar Pradesh, India. Datas are plotted for a particular day.
Fig. 2: Variation of solar intensity with time
Figure 2 shows the variation of solar intensity with time. As it is expected, the maximum
intensity of 1020 W/m2
is obtained at mid noon.
Fig. 3: Variation of wind speed with time
0
1
2
3
4
5
6
WindVelocity(m/s)
Time of the day
Vw
0
200
400
600
800
1000
1200
SolarIntensity(w/m2)
Time of the day
I(t)

6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 115-122 © IAEME
120
Figure 3 shows the variation of wind speed with time, which is moderate except in the
evening time. System is capable of offering good resistance to wind.
Fig. 4: Variation of temperatures with time
Figure 4 shows the variation of water inlet into the receiver pipe, water outlet from the
receiver pipe and ambient temperatures with time of the day. It is clear from figure 2 and 4 that, due
to better solar intensity in the forenoon, water outlet temperature from the receiver pipe is higher
than in the afternoon. The blue line shows the water inlet temperature to the receiver from an
overhead tank, which is getting heated throughout the day and because of this the blue line, has a
tendency to move up in the graph. Till around 11 ‘o’ clock water temperature in the tank is at
atmospheric temperature and so, green line and blue line are closer to each other.
Fig. 5: Variation of temperature difference with time
Figure 5 shows the variation of temperature difference between inlet and outlet temperatures
with time of the day. As it is clear from figure, the maximum temperature difference of 47o
C was
obtained at 11:00 Hours.
0
10
20
30
40
50
60
70
80
90
Temperature(oC)
Time of the day
Twi
Two
Ta
0
5
10
15
20
25
30
35
40
45
50
Temperature(oC)
Time of the day
ΔT

7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 115-122 © IAEME
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Fig. 6: Variation of thermal efficiency with time
Figure 6 shows the variation of instantaneous thermal efficiency of the system with time of
the day. As it is clear from the figure, a maximum instantaneous thermal efficiency of 52.35% is
obtained at around 3:30 Hours.
Cost analysis of the system is also performed and it is obtained as Rs 7,000. Payback period
is also calculated and it is less than 2 years.
CONCLUSION
From the collected data, figures, graphs and tables, in relation with the analysis and
discussions, this research investigation can be concluded that, the fabricated PTC is quite efficient.
As the construction is very simple with locally available low cost materials, it could be manufactured
in any workshop. The maximum water temperature obtained from the PTC was 80o
C and a
maximum temperature difference from the inlet was 47o
C. Due to its low cost and simple
technology, it is affordable by the middle and lower middle class people of India.
NOMENCLATURE
ηo = optical efficiency ρ = Reflectivity
τ = Transitivity α = Emissivity
γ = Intercept Factor ηc = Thermal Efficiency
Qu = Useful Heat Output m = Mass Flow Rate
Cp = Specific Heat of Water To = Outlet Temperature
Ti = Inlet Temperature Aa = Aperture Area
Ib = Incident Solar Radiation Aabs = Absorber Area
Ul = Overall Heat Transfer Coefficient Tabs = Absorber Temperature
Ta = Ambient Temperature
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48
48.5
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49.5
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50.5
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51.5
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8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 115-122 © IAEME
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