ACKNOWLEDGEMENT:

ALLAH ALMIGHTY, the only single source of certainty and knowledge for us in this universe. We are very much thankful to ALLAH ALMIGHTY for bestowing us with this report. Heartiest thank to Mr. Qasim Ali Tatla, our project advisor, with full fledge respect and protocol whose towering personality always enlightens the passions to achieve our goals! Whose kind counseling tips and courteous attitude always backed us up to go on conquering the horizons of knowledge and skills. Also regards to, other faculty members of Mechanical department, for affectionate and respectful attitude towards us.

Table of Contents ACKNOWLEDGEMENT:........................................................................................................... 1

1. Abstract:................................................................................................................................. 6

2. Introduction: .......................................................................................................................... 7

2.1 Need: ..................................................................................................................................... 7

2.2 Renewable Energy resources of Pakistan: ............................................................................ 7

3. Literature Review: ................................................................................................................ 9

3.1 Background Research:...................................................................................................... 9

3.2 Early commercial adaption: ............................................................................................. 9

3.3 Currently Working Plants based upon Parabolic trough collectors. ..................................... 9

3.4 Solar Radiations: .............................................................................................................. 9

3.4.1 Direct radiation: ........................................................................................................... 10

3.4.2 Diffuse radiation: ......................................................................................................... 10

3.4.3 Reflexed radiation: ....................................................................................................... 10

3.4.4 Global radiation: .......................................................................................................... 10

3.5 Solar Collectors:.................................................................................................................. 10

3.5.1 Current Solar Concentration Technologies:................................................................. 11

3.6 Parabolic Trough Technology: ........................................................................................... 11

3.6.1 Working Principle: ....................................................................................................... 11

3.6.2 Suitable Materials for Collector: .................................................................................. 12

3.6.3 Suitable Materials for Absorber: .................................................................................. 12

3.6.4 Evacuated Tube Absorbers: ......................................................................................... 13

3.6.5 Heat Transfer Fluids: ................................................................................................... 13

3.6.6 Thermal Storage: .......................................................................................................... 14

3.6.7 Optimum solar Flux Extraction: .................................................................................. 14

3.6.8 Tracking System: ......................................................................................................... 14

3.6.9 Parabolic trough power plant Layout: ........................................................................ 14

4. Aims and Objectives: .......................................................................................................... 15

5. Methodology: ....................................................................................................................... 16

5.1 Calculations of Geometrical Parameter: ........................................................................ 16

5.2 Software Based Designing: ............................................................................................ 18

5.3 Experimentation: ............................................................................................................ 20

6. Results: ................................................................................................................................. 21

6.1 Case-I ............................................................................................................................. 21

6.2 Case-II ............................................................................................................................ 21

6.3 Case-III ........................................................................................................................... 22

6.4 Case-IV........................................................................................................................... 23

6.5 Case-V ............................................................................................................................ 23

6.6 Case-VI........................................................................................................................... 24

6.7 Case-VII ......................................................................................................................... 25

7. Conclusion: .......................................................................................................................... 26

8. Future Perspectives:............................................................................................................ 26

9. References ............................................................................................................................ 27

List of Figures:

Figure 2.1 Pakistan Direct Normal Solar Radiations Annual Figure. ........................................... 7

Figure 2.2 Estimated Renewable Energy Share in Global Final Energy Consumption (2011) [1]

......................................................................................................................................................... 8

Figure 2.3 Renewable power capacity ........................................................................................... 8

Figure 3.1 Components of Solar Radiation .................................................................................. 10

Figure 3.2 Schematic Of Concentrating Solar Power Units ....................................................... 11

Figure 3.3 Components and Concentration of rays at the focal point of Parabolic Trough ........ 12

Figure 3.4 Configuration of Evacuated Receivers ...................................................................... 13

Figure 3.5 Schematic of a Parabolic Trough power plant with a thermal storage syst ................ 14

Figure 5.1 Visualization of Solar Beam Angle ............................................................................ 17

Figure 5.2 Relationship between absorber diameter and rim angle ............................................. 17

Figure 5.3 3D Modeling in Pro_E ................................................................................................ 18

Figure 5.4 Ground supports and trough supporting trusses ......................................................... 19

Figure 5.5 Cross-section of Evacuated annular tube .................................................................... 19

Figure 6.1 Experimentation with Aluminum trough and black absorber .................................... 21

Figure 6.2 Experimentation with Silver coated collector and black absorber tube .................... 21

Figure 6.3 Experimentation with Aluminum foil trough and black absorber tube ...................... 22

Figure 6.4 Experimentation with Aluminum Silver metal sheet collector and black absorber tube

....................................................................................................................................................... 23

Figure 6.5 Experimentation with Aluminum Silver metal sheet and black absorber tube .......... 23

Figure 6.6 Experimentation with Mirrors as reflecting surface and evacuated glass tube .......... 24

List of Tables: Table 3.1 List of Power Stations using Parabolic Trough Collectors. [2] [3] _______________ 9

Table 3.2 Suitable Materials for collector. [4] ______________________________________ 12

Table 3.3 Suitable Materials for Absorber. [4] _____________________________________ 12

Table 3.4 Heat transfer fluids with application in solar parabolic trough fields. [6] _________ 13

Table 5.1 Summary of PTC key features. _________________________________________ 18

Table 6.1 Experiment data for temperature rise in Case-I _____________________________ 21

Table 6.2 Experiment data for temperature rise in Case-II ____________________________ 22

Table 6.3 Experiment data for temperature rise in Case-III ____________________________ 22

Table 6.4 Experiment data for temperature rise in Case-IV ___________________________ 23

Table 6.5 Experiment data for temperature rise in Case-V ____________________________ 24

Table 6.6 Experiment data for temperature rise in Case-VI ___________________________ 24

Table 6.7 Experiment data for temperature rise in Case-VII ___________________________ 25

1. Abstract:

This report presents the designing of a parabolic trough collector with a rim

angle of 80° and discusses the experimentation on an existing parabolic trough collector unit with

a rim angle 90°, length 32 inch and aperture area 1152 inch2. The purpose of experimentation is to increase the temperature of hot water through absorber by hand layup method using different techniques including different coatings, mirrors and evacuated glass tube round the absorber. Designing has been done considering optimum values and materials as in case of commercial units. On available PTC unit, effects of ambient temperature, air velocity, different coatings and evacuated glass tube have been explained numerically and graphically. Overall, report explains the thorough designing and improving techniques for hot water generation by a hand layup method.

2. Introduction:

2.1 Need:

Energy has become the highest concerning word as for government’s point of view. As the population of the world going on increasing, the non-renewable resources are declined Day by day (e.g. fossil foils). Scientist’s estimated 50% increase in worldwide energy consumption in 2030 and 70% to 100% in 2050. The bio and fossil fuels cannot overcome this energy crisis in future. Each year, the sun sends over a billion terawatt hours of energy to the Earth, which is equal to 60,000 times the world's electricity needs.so, the world is moving towards the solar energy. Renewable energy resources are becoming many valuables due to continuously decrease in conventional energy sources. Sun energy which is sometimes called as solar energy is the largest treasure of renewable energy. All over the world, especially in our country most of the time in a year sun provides a good exposure (see figure 1). The use of sun for lightning during day time and heating in winter season is not a new concept. This was done from centuries. But due to increasing energy problems World is shifting toward utilizing renewable energy resources.

1 Figure 2.1 Pakistan Direct Normal Solar Radiations Annual Figure.

2.2 Renewable Energy resources of Pakistan:

Figure 2.2 explains the renewable energy share with global energy consumption which is almost 19 percent of the total. Biomass, biofuel, hydropower, wind, solar and geothermal technologies are the major contributors of this share. 1

NREL ASSOSIATION with the help of USAID CORPORATION

Figure 2.2 Estimated Renewable Energy Share in Global Final Energy Consumption

(2011) [1]

Figure 2.3 Renewable power capacity

While in figure 2.3, growth trend for renewable technologies can be seen from 2000 till 2014. CSP technology didn’t draw much growth in early years of 2000s but later it showed significant growth as it is clear from the graph.

3. Literature Review:

3.1 Background Research:

Concentrating Solar Power technology is introduced during 18’s. Mr. Auguste Mouchout is the first person that use the Parabolic trough technique to produce steam for steam engine in 1866. The first patent for solar collector is invented by Mr. Battaglia in Genoa, Italy in 1886. Later on John Ericson developed many CSP units for the irrigation, refrigeration and locomotion.

3.2 Early commercial adaption:

Solar Energy utilization techniques are not present research but scientists are working from many years to utilize solar energy.

1897: “Frank Shunam”, a US Engineer and pioneer of solar energy develop a small solar engine which worked by reflecting solar energy on the boxes which are filled with fluid which has boiling point less than water.

1912 - 1913: Shuman built a first world’s largest Solar Thermal Power Station in Madi Egypt. He used parabolic troughs to power a 45-52 engine that pumped more than 22,000 litres of water per minute from the Nile River to adjacent cotton fields. [2]

3.3 Currently Working Plants based upon Parabolic trough collectors.

There are many plants which are working and contributing a lot of energy in the world’s total power production such as Table 3.1 List of Power Stations using Parabolic Trough Collectors. [3] [4]

3.4 Solar Radiations:

Sun irradiation can be described as the flux of energy that the earth receives from the sun. This energy arrives as a set of waves at different frequencies, some of which are detectable by the human eye and another part, such as infrared rays, cannot be detected by the human eye. A classification of the types of irradiation can be made according to the way an object receives the sun’s rays.

Sr. No Year of development

1 2014

2 2014

3 2014

4 2014 Solaben Power Plant ( Spanish)

Genesis Solar Energy project

Solana Generating Station

Capacity (MW)

200

250

250

354

Plant

California

3.4.1 Direct radiation:

It is the unaltered radiation that comes directly from the sun without going through any changes on its way. It is characterized by its projection of a defined shade of those objects that intercept its path.

Figure 3.1 Components of Solar Radiation

3.4.2 Diffuse radiation:

Part of the sun irradiation that crosses the atmosphere is absorbed and reflected by clouds, dust particles in the air, trees, mountains etc. As a consequence of this, this type of radiation goes in all directions. It does not produce shades on objects. Horizontal surfaces receive it more than vertical ones because they are exposed to the entire sky vault; whereas the vertical surfaces are only exposed to half of it.

3.4.3 Reflexed radiation:

This is the radiation that is reflected by a surface. Its quantity depends on the surface’s reflection coefficient.

3.4.4 Global radiation:

As its name indicates, this is the sum of the above mentioned radiations.

3.5 Solar Collectors:

A solar thermal collector is a collector to collect heat by absorbing sun light. A collector is a device for converting the energy in solar radiation into a more useful or storable form. The energy in sun light is in the form of electromagnetic radiation from the infrared to the ultraviolet wavelength. The solar energy striking the Earth’s surface depends upon weather condition as well as location and surface tilt angle but overall it’s average value is 1000 W/m2 with clear sky and surface directly perpendicular to the sun rays.

3.5.1 Current Solar Concentration Technologies:

a. Parabolic Trough b. Fresnel Lenses c. Parabolic Dish d. Power Tower

Figure 3.2 Schematic Of Concentrating Solar Power Units

3.6 Parabolic Trough Technology:

3.6.1 Working Principle:

Parabolic trough-shaped mirror reflectors are used to concentrate sunlight on to thermally efficient receiver tubes placed in the trough focal line. In these tubes a thermal transfer fluid is circulated, such as synthetic thermal oil. Heated to approximately 400°C by the concentrated sun’s rays, this oil is then pumped through a series of heat exchangers to produce superheated steam. The steam is converted to electrical energy in a conventional steam turbine generator.

Figure 3.3 Components and Concentration of rays at the focal point of Parabolic Trough

3.6.2 Suitable Materials for Collector:

To achieve the maximum collector efficiency, selection of most appropriate material is very important. The material should posses

High Reflectivity Low absorptivity

Table 3.2 Suitable Materials for collector. [5]

3.6.3 Suitable Materials for Absorber:

As for as the absorber materials are concerned, they should possess High absorptivity Low Reflectivity High Thermal Conductivity Table 3.3 Suitable Materials for Absorber. [5]

Sr. No Matterial Desnsity Temperature

1 Steanless Steal 7.93 115

2 Glass Mirror 2500 120

3 Polished Aluminium 2.7 110

4 Silver Mirror Film 2100 100

5 Acrylic Mirrors 2400 85

Thermal Conductivity

1.05

16.2

215

1.15

1.1

Sr. No Matterial Desnsity Temperature

1 Aluminium Tube 2.65 125

2 Glass Tube 2500 120

3 Copper Tube 8920 90

4 Steanless Steel Tube 7.93 120

Thermal Conductivity

16.2

400

1.05

210

3.6.4 Evacuated Tube Absorbers:

These this technology, the absorber is covered with evacuated glass tube. It has the following benefits over the other choices The glass tube is transparent to solar short wave radiation but not to thermal long wave

radiation also glass is stronger than the alternative transparent plastic materials. Glass can hold vacuum better than any other material. The out gassing rate from a Bake-Pyrex glass is such that Pressure should be less than 0.1 N/m2

per 300 years which is 1012 times longer than a copper tube. [6] This technology is used to reduce convection losses. The vacuum also allows thermal expansions.

Figure 3.4 Configuration of Evacuated Receivers

3.6.5 Heat Transfer Fluids:

Parabolic trough solar collectors utilize a heat transfer fluid that flows through the receiver to collect the solar thermal energy and transport it to the power block. The type of heat transfer fluid used determines the operational temperature range of the solar field and thus the maximum power cycle efficiency that can be obtained. In good solar climates, Parabolic trough plants without thermal storage can produce an annual capacity factor of approximately 25%. Table 3.4 Heat transfer fluids with application in solar parabolic trough fields. [7]

2 Mineral oil, e.g., Caloria

3 Water, pressurized, +glycol

4 Water/steam

5 Silicon oil

6 Nitrate salt

7 Ionic liquids

8 Air

Synthetic oil, e.g., Biphenyl-

diphenyloxide13 – 395

Sr. No

1

–25 – ˃100

Temperature

Range (°C)

–10 – 300

Fluid

0 – ˃500

40 – 400

183 – ˃500

220 – 500

–275 – 416

High receiver pressure required and thick-wall tubing

Odorless, nontoxic, expensive and flammable

High freezing temperature, high thermal stability and corrosive

Organic methyl-imidazole salts, go thermal properties, very costly and no mass product

Low energy density, only special Industrial process heat applications

Relatively high application temperature and flammable

Relatively inexpensive and flammable

Only low-temperature Industrial process Heat applications

Properties

3.6.6 Thermal Storage:

One of the potential advantages of parabolic trough technologies is the ability to store solar thermal energy for use during non-solar periods. For the storage of heat salts Mostly “Potassium Nitrate and Sodium Nitrate” having Melting points 200 °C. Adding thermal storage allows the plant capacity factor to be increased from normal range which is 25% to 50% or more.

3.6.7 Optimum solar Flux Extraction:

The maximum solar flux is obtained we the solar ray strikes perpendicular to the surface of solar collector. So, to gain the optimum flux extraction

The parabolic trough should be due South facing. The slope angle of the parabolic trough should be equal to the latitude value of the

particular location.

3.6.8 Tracking System:

Tracking systems are required for collectors to follow the sun in order to concentrate the direct solar radiation onto the small receiver area. High concentration ratio collectors cannot work without a tracking system. Various forms of tracking mechanisms, varying from simple to complex, have been proposed. They can be divided into two broad categories. One is Mechanical and other one is Electrical/electronic systems. The electronic systems generally exhibit improved reliability and tracking accuracy. These can be further subdivided into the following: Mechanisms employing motors controlled electronically through sensors that detect the magnitude of the solar illumination. Mechanisms using computer controlled motors with feedback control provided from sensors measuring the solar flux on the receiver. The parabolic trough is single tracking technology.

3.6.9 Parabolic trough power plant Layout:

Figure 3.5 Schematic of a Parabolic Trough power plant with a thermal storage syst

4. Aims and Objectives:

The major task behind this research work is to increase the efficiency of the parabolic trough collector. We adopted different techniques and methodologies for the completion of this task. Following sequence is adopted to 3D Designing on Pro_E.

Most appropriate materials for fabrication.

Different selective surfaces for collector.

Use of Evacuated Glass Tube for absorber.

Experimentation by Hand layup method.

5. Methodology:

5.1 Calculations of Geometrical Parameter:

Based on two parameters of parabolic trough collector (PTC), the rim angle which

is 80r and width of collector it is possible to determine the aperture of parabola. [8]

2)(8

12

tan

f

a

f

a

r

(1)

Above equation gives another way of mechanical design if we take two parameters, rim angle and

aperture of parabola according to the prototype requirement.

2tan

2secln

2tan

2sec2 rrrrfS (2)

This equation further proceeds to calculate the width of collector S based upon focal length value

obtained from the first equation.

2tan

2secln

2tan

2sec

2tan2

rrrr

r

a

S

W (3)

This equation is the alternate way of calculation taking rim angle and collector width as selected values.

2tan4 r

aWf

(4)

Equation gives the value of focal length. The absorber tube must have a sufficient diameter to permit a high intercept factor. The intercept factor is the ratio of the total reflected radiations to the reflected radiations that hit the absorber surface. On the other hand, diameter should not be as large to have more thermal losses. For ease of our calculations we assume intercept factor of value 1 means there are no slope errors or microscopic errors on the collector surface. The necessary absorber diameter to reach an intercept factor of 1 depends upon the distance of the absorber tube from the collector surface and the solar beam angle.

Figure 5.1 Visualization of Solar Beam Angle

The distance between the collector and the absorber is different for the different points on the collector surface and is maximum for mirror rim and the absorber. So we take the rim of the parabola to determine the absorber diameter. [9]

Figure 5.2 Relationship between absorber diameter and rim angle

r

D

abs

a

d

sin

2sin

(5)

Geometric concentration ration can be calculated by the following formula

o

a

d

WC

(6)

The optical efficiency is expressed by [10]

costan1 fagro A (7)

Where θ is the angle of incidence. ϒ is the intercept factor and Af is the geometric factor. In case of the normal incidence optical efficiency is reduced to

agro (8)

Table 5.1 Summary of PTC key features.

5.2 Software Based Designing:

Based upon the above calculated Parameters as shown in Table 5.1, we design the parabolic trough in Pro_E Wildfire 4.0.

Figure 5.3 3D Modeling in Pro_E

Description Dimensions

parabolic length (L) 127 cm

parabolic aperture (Wa) 63.50 cm

Focal distance (f) 19 cm

Aperture area (Aa) 0.805 m2

Rim angle (ɸr) 80⁰

Inner diamiter of the reciever (di) 8 mm

Outer diameter of the reciever (do) 10 mm

Concentration ratio (C) 20.2

Optical efficiency 57%

Figure 5.4 Ground supports and trough supporting trusses

Figure 5.5 Cross-section of Evacuated annular tube

5.3 Experimentation:

Experimentation has been performed on a fabricated parabolic trough collector to further enhance the efficiency of the unit to get max possible temperature rise. Different coatings of high reflectivity like silver paint, aluminum silver sheet, aluminum foil and specially mirrors have been used. To minimize convective losses, a thin cover sheet covering all aperture area has been used. Moreover, an evacuated glass tube has been installed round the absorber to further decrease the convective losses. Results of these different techniques has been elaborated in next section in the form of tables and graphs. Parameters like tilt angle, day time and air velocity have been considered seriously. All experiments were performed by hand layup method.

6. Results:

6.1 Case-I

Aluminum trough and black absorber tube:

Figure 6.1 Experimentation with Aluminum trough and black absorber

Table 6.1 Experiment data for temperature rise in Case-I

6.2 Case-II

Silver coated collector and black absorber tube:

Figure 6.2 Experimentation with Silver coated collector and black absorber tube

°C

Time

Normal Water

Temperature

Ambient

Temperature

Experiment

Time Duration

Final Water

Temperature

°C

30 - 35

30 - 35

36

36

26

26

64

62

12:30 PM

2:00 PM

°C Minutes

Table 6.2 Experiment data for temperature rise in Case-II

6.3 Case-III

Aluminum foil and black absorber tube:

Figure 6.3 Experimentation with Aluminum foil trough and black absorber tube

Table 6.3 Experiment data for temperature rise in Case-III

30 - 35

30 - 35

60

58

38

36

26

24

1:00 PM

2:00 PM

Time

Ambient

Temperature

Normal Water

Temperature

Experiment

Time Duration

Final Water

Temperature

°C °C Minutes °C

2:30 PM 37 25 30 - 35 67

01::00 PM 38 26 30 - 35 68

Time

Ambient

Temperature

Normal Water

Temperature

Experiment

Time Duration

Final Water

Temperature

°C °C Minutes °C

6.4 Case-IV

Aluminum Silver metal sheet and black absorber tube:

Figure 6.4 Experimentation with Aluminum Silver metal sheet collector and black absorber tube

Table 6.4 Experiment data for temperature rise in Case-IV

6.5 Case-V

Mirrors as reflecting surface and black absorber tube:

Figure 6.5 Experimentation with Aluminum Silver metal sheet and black absorber tube

12:20 PM

36 26 30 - 35 7501::00 PM

36 26 30 - 35 77

Time

Ambient

Temperature

Normal Water

Temperature

Experiment

Time Duration

Final Water

Temperature

°C °C Minutes °C

Table 6.5 Experiment data for temperature rise in Case-V

6.6 Case-VI

Mirrors as reflecting surface and evacuated glass tube:

Figure 6.6 Experimentation with Mirrors as reflecting surface and evacuated glass tube

Table 6.6 Experiment data for temperature rise in Case-VI

12:15 PM 39 27 30 - 35 77

1:20 AM 37 26 30 - 35 78

Time

Ambient

Temperature

Normal Water

Temperature

Experiment

Time Duration

Final Water

Temperature

°C °C Minutes °C

2:15 PM 39 27 30 - 35 81

12:20 PM 39 27 30 - 35 81

Time

Ambient

Temperature

Normal Water

Temperature

Experiment

Time Duration

Final Water

Temperature

°C °C Minutes °C

Graph 6.1 Effectiveness of different techniques

6.7 Case-VII

Case-VI without cover sheet: Table 6.7 Experiment data for temperature rise in Case-VII

Graph 6.2 Graph depicting to effectiveness of Case-VI with different arrangements

0

10

20

30

40

50

60

70

80

90

Case-I Case-II Case-III Case-IV Case-V Case-VI

Tem

pera

ture

(°

C)

Cases

Comperison of different cases corresponding to their Temperatures

Final Water

Temperature

°C

50

62

81

Case-VI without Cover sheet and evacuated tube

Case-VI without Cover sheet

Case-VI with Cover sheet

Different Arrangements

0

10

20

30

40

50

60

70

80

90

Case-VI withoutCover sheet andevacuated tube

Case-VI withoutCover sheet

Case-VI with Coversheet

Tem

pera

ture

(°

C)

Different Arrangements

Comperison of different case-VI arrangements corresponding to their

Temperatures

7. Conclusion:

As it is clear from the graph 6.1 by introducing the evacuated tube maximum temperature is achieved as compared to the simple mat black coper tube. The reason is that we reduced the forced convection loses which ultimately results the water temperature to increase.

When we compare the parabolic trough with simple aluminum sheet and black copper absorber

with no cover sheet with the mirrored collector and evacuated absorber with a cover sheet the temperature difference if final water after 30 minutes is 32 °C which is a significant figure. This temperature difference is due to prevention in natural convection as well as forced convection.

Experimental results prevail that the overall parabolic trough efficiency strictly depends upon

the reflectivity of collector surface and absorptivity of receiver.

By hand layup method we cannot make the evacuated tube perfectly evacuated so, due to this minor fluctuation in readings may occur.

By using aluminum silver metal sheets instead of mirrors as collector surface we get almost

same temperature in both cases. Aluminum silver metal sheets are cheaper than the mirrors. In this way we can make this technology cost effective.

8. Future Perspectives:

As the parabolic trough collectors are used for steam generation so they can be used in existing steam power plants for the pre heating of the water and this leads to increase the efficiency of power plant by reducing the fuel consumption.

Introduction of thermal storage technology with nitrates (sodium, calcium, potassium, ….) made this technology more and more profitable and it became direct competitors of conventional power plants.

In agriculture sector photovoltaic technology is used which has high initial and maintenance

cost. By replacing it with concentration based parabolic trough technology because it has pay back potential. It’s initial cost is high but maintenance cost is very low.

9. References

[1] Renewables 2013, Global Status Report, Renewable Energy Policy Network for the 21 Century.

[2] Smith, Zachary Alden; Taylor, Katrina D., Renewable And Alternative Energy Resources, 2008, p. 174..

[3] "Concentrating Solar Power Projects in the United States," 17 February 2014. [Online]. Available: NREL.gov.

[4] "Concentrating Solar Power Projects in Spain," 17 February 2014. [Online]. Available: NREL.gov.

[5] Sri P. Mohana Reddy, Pathi Venkataramaiah and Devuru Vishnu Vardhan Reddy, "Selection of Best Materials and Parametric Optimization of Solar Parabolic Collector Using Fuzzy Logic," 26 October 2014.

[6] Weir, John Twidell and Tony, Renewable Energy Resources, Second ed., London: 1986, p. 137.

[7] David Kearney National Renewable Energy Laboratory1617 Cole Blvd., Golden, CO, "Advances in Parabolic Trough Solar Power Technology".

[8] A. Gama, C. Larbes, F. Yettou and B. Adouane, ""Design and realization of a novel sun tracking system with absorber displacement for parabolic trough collectors"," Renewable and sustain energy, p. 03, May 23, 2013.

[9] Matthias Gunther (Intitute for Electrical Engineering, Rotational energy conversion, University of Kassel, Wilhelmshoher Alee 73, 34121 Kassel), "Advanced CSP Teaching Materials Chapter 2 "Solar Radiation"".

[10] Yassine Denagh , Ilyes Bordja, Yassine kbar and Hocine Bensoussa, "Adesign method of an S-curved parabolic trough collector absorber with a three-dimentional heat flux density contribution," p. 10, July 23, 2013.

[11] Pilkington Solar International GmbH, 1996,Status Report on Solar Thermal Power Plants, ISBN 3-9804901-0-6, Ko ¨ln, Germany..