Performance evaluation of parabolic trough solar collector with solar tracking tilt sensor for water distillation

Abstract

The distilled water production by the application of the parabolic trough solar collector technology has its significant importance that still needs further exploration. The current study represents the modification of parabolic trough solar collector, with the using of solar tracking tilt sensor with the continuous water circulation rate of 0.22 kg/s to enhance the productivity of the parabolic trough solar collector, and the tracking system consisting of low-speed 12 V motor units of 0.75 r/min and torque of 50 N m was found suitable for the tracking mechanism. The collector received 476 W/m² with the highest amount of distilled water up to 6675 ml/h m² during the months of August and the 121°C temperature was recorded during the experiment. The efficiency was noted 31% for the month of August due to the highest absorbing solar irradiance. It was concluded from the results that the tested values of pH and EC in distilled water were decreased from the initial values with the process of distillation through parabolic trough solar collector. Further, from the results, it was concluded that the PTSC was working efficiently with the highest amount of distilled water with the solar tracking tilt sensor and higher efficiency from 08:00 AM to 16:00 PM during the daytime. Furthermore, recommended by the results of the experiment that the amount of distilled water produced significantly depends on the amount of energy input on the concentrator. At last, the distilled water quality was measured and the results were found acceptable for the standard of the Environmental Protection Agency.

Keywords

Parabolic trough solar collector solar tracking tilt sensor efficiency desalination an electric motor converter

Introduction

Renewable energy had played a vital role to fulfill the energy demands across the globe. By 2050, the energy demand could be tripled because of the global population increasing day by day and expansion of the developing countries.¹ Renewable energy, that is solar, wind, biomass, waves, and geothermal, is acceptable for the key source of future using on the earth.² Among these resources, the solar energy is found to be the cheapest, unconstrained, and easy adaptation by the human beings.³ It is the radiant heat and light from the sun, which is harnessed for the using of different sources and technologies, that is heating, photovoltaic, solar thermal energies, and artificial photosynthesis.⁴ The total solar radiation (insolation) falls on the earth every year from the sun is approximately 174,000 TW⁵ as measured in the upper atmosphere.⁶

Water is a vital source of life on earth.⁷ There is an urgent need for clean, pure, and distilled water in many countries for the use of different purposes.^8,9 Mostly, the water resources are brackish and contain harmful bacterial species and ions, such as Na, Ca, Mg, Zn, and so on, which cannot be used directly. These brackish water resources cannot be used directly for the industries, hospitals, schools, and so on and thereby the pure water demand goes higher as reported by Duffie and Beckman.¹⁰ El-Sebaii and El-Bialy¹¹ reported that the active solar still increased the productivity of about 10 l/m²day with the thermal efficiency of 80% as compared to the passive solar still of 8 l/m²day and 57% thermal efficiency of the thickness of 3 mm glass covers applied. Another study by Eltawil and Omara¹² reported that the condensation rate and water productivity of the solar collector increased with the decreasing of inlet water and the surface temperature of the air. Fahad et al.¹³ strongly observed that the increasing temperature of the glass is directly proportional to the increase of water productivity of the collector for 17–23%. Fahim et al.¹⁴ observed from the experiment that the efficiency of conventional solar still to 71.5% was increased with the base slope angle of 30° and noted the output productivity of about 114%.

Parabolic trough (PT) solar distillation is one of the well-proven technologies, which can be used on a commercial scale to produce high power steam generation¹⁵ and such a system of small-scale version produced heat at the temperatures up to 150°C, which is required by all the small factory and hospital, that is refrigeration, sterilization, instruments washing, and so on.¹⁶ The performance of a solar collector can be improved greatly by using the solar tracking system, which concentrates a direct solar beam onto the focal point and it depends on the axis of a solar reflector.^17,18 The researcher has investigated the compression of different tracking modes as reported in Gowtham et al.¹⁹ and Okoye et al.²⁰ These studies’ results showed that the two-axis tracking system causes the highest system energy and improves the solar energy contribution. Gustavo et al.²¹ reported that the using of two-axis solar tracking system consumes more energy than the single-axis tracking system due to the extra control power.

Various studies were conducted to develop low cost parabolic solar collector (PSC) for the production of distilled water which can be used in the moderate temperature. Solar desalination is an environmentally friendly and cost-saving process, competitive with other conventional desalination techniques.^20,22 Desalination is one of the techniques which is suitable for the production of distilled water and it has received great attention as an alternative solution to distilled water production.⁴ The energy required to evaporate water from liquid to gas state is 627 W/kg.²³ Solar desalination is a promising technique and an alternative way for the production of distilled water.¹¹ There are several solar designs that have been proposed for the production of distilled water. But parabolic trough solar collector (PTSC) was found to be more significantly applicable to the production of distilled water.²³ Jinesh et al.²⁴ reported that the two-axis sun-tracking system increased the efficiency of PTSC and increased the production of distilled water. Jozef et al.²⁵ reported that the design of a single-axis tracking system is suitable for the PTSC in moderate temperature application in remote areas.

In this study, PTSC of 2.53 m² areas is used to supply the heat to the absorber which produces distilled water at a temperature of 130°C. The purpose of the study was to investigate the single-axis solar tracking mechanism for the production of distilled water by using PTSC and also finding out the efficiency of the collector. The Figure 1 shows the flow chart of the experiment.

Figure 1.

Flowchart of the experiment.

Material and methods

Description of PTSC

The experiment was conducted for the purpose of producing distilled water with the application of single-axis solar tracking mechanism in PTSC. The PTSC was made from the aluminum (galvanized) stainless steel sheet in the shape of a PT, which was used for reflecting the sun rays to one focal point (receiver). The cross-sectional area 2.53 m² of the PT was calculated by using equation (1) reported by Fahim et al.¹⁴ and Jozef et al.²⁶

Art = Drt \times Lrt

(1)

Design specification of the parabola

Parabola was designed according to the concentration of the sun rays falling on the PSC. Parabola is the locus of a point that moves from a fixed point and fixed line as shown in Figure 2. The fixed line is called D (directrix) and the fixed point F (focus) and the length FR equals the length RD. While the axis of the parabola is the line perpendicular to the directrix and passing through the focus (F) line as showed and vertex is the point where parabola intersects its axis at point V (midway between the focus and directrix).

Figure 2.

Design specification of parabola.

Figure 2 shows that if the origin is taken at the vertex “V” and the x-axis along the axis of parabola, then the equation of parabola becomes is equation (2), while when the origin is shifted to the focus “F,” with the vertex to the left of the origin, the equation of parabola becomes is equation (3). The software named as Parabolic Calculator 2.0 version is also used for finding of focal line of PT as shown in Figure 3 and reported by Jozef et al.²⁵

y^{2} = 4 f x

(2)

y^{2} = 4 f (x + f)

(3)

Figure 3.

The steel frame of the parabola.

Two-axis tracking PTSC was designed to produce the distilled water at a pressure close to the ambient and the design of the collector consists of the four main parts: (a) PT reflector, (b) solar receiver, (c) power supply and control system, and (d) solar tracking system.

a. PT reflector

The PT reflector was made from a steel frame with an aperture width of 1.04 m, length of 2.44 m, rim angle (Ø) of 75°, and length of focal point (f) 0.4 m was used, while the reflecting surface sheet was used in this study with the dimension of 0.0005 m × 2.44 m × 1.04 m stainless steel sheet type of aluminum (430BA) and the frame was fabricated from the steel as demonstrated in Figure 3, and this diagram frame allows the testing of different reflecting surfaces.

b. Solar receiver

The receiver consists of black painted aluminum pipe length of 2.60 m with the diameter of 0.02 m that is fixed on the 0.4 m focal points of the parabola, which was used for the distillation purposes. It absorbed the reflected rays from the reflecting PT in the form of thermal energy and then heat up the water and convert into vapors form. The width of the receiver was estimated from the width of the solar flux in the focal line of the collector and the total flux (W/m²) can be evaluated by segmenting the solar energy reflected by each segment can be determined by using equation (4). The area and volume of the receiver were 1632.8 m² and 816.4 cm³, respectively, calculated with the use of the following equation (5) reported in Julián et al.²⁷ The method reported by Kaluri and Ganapathisubbu²⁸ was used for the determination of total flux of the parabola, while W_img was the image width depending on the local rim angle of the parabola and equation (6) was used for the determination of the flux pattern (W/m²) in the focal point of the parabola

{\begin{matrix} Total flux = flux (1) + flux (2) + \dots + flux (n) = {\sum^{​}}_{i = 1}^{n} f lux (i) \\ flux (i) = [\frac{(\frac{I_{b}}{n})}{W_{img} L_{r}}] \end{matrix}

(4)

{\begin{matrix} A_{ab} = π \times D_{ab} \times L_{ab} \\ V_{ab} = π \times \frac{Da b^{2}}{4} \times L_{ab} \end{matrix}

(5)

flux pattern = L_{r} . (flux (i) W (i) + flux (i + 1) W 9 I) + \dots + flux (n) W (i)) = \sum_{i = 1}^{n} f lux (i)

(6)

Similarly, in general, the solar pattern flux at the different distance from the focal point of the parabola can be determined by using equation (7)

pattern (i) = [{\sum^{​}}_{i}^{n} flux (i)] \cdot [W (i) - W (i - 1)] \cdot L_{r}

(7)

c. Control and power supply

Figure 4 shows the closed-loop control system of the tracking sun around the East–West or North–South axis. This system consists of two DC motors, which were used for the rotating of PTSC with the current passing from the controller of the sun tilt sensor. The motors are attached to the pulley and then attached with collector with the help of a chain belt, while the speeds of motors are adjusted with the sensor rotation speed. Control systems determined the input and output of energy and also focus on the collector to the sun position angle.

Figure 4.

The tracking motor mechanism of PT (motor, sprocket, and chain system).

The PTSC model was presented with the tracking system consisting of low-speed 12 V motor units of 0.75 r/min and torque of 50 N m was found to be suitable for the tracking mechanism. A sprocket and chain system was used to connect the motor unit with the main tracking shaft of the PT, while the motor power consumed during the operation was measured to be 2.0 W as shown in Figure 4. The two-axis tracking system maintains the plane of the solar beam and always normal to the aperture of the PTSC. Thus, all the reflecting sun rays from collector surface were collected by the focal line receiver (absorber). The control tracking system is capable of achieving the tracking shaft radial displacement between 0.1 and 0.3°/min, so the solar tracking covers the maximum change in the solar elevation angle of 0.20°/min.

d. Solar tracking mechanism

Solar tracking tilt sensor was installed in the experimental setup with the absorber at one end. The average tracking precision of the solar tracking tilt sensor was ≤0.1° and set with the speed of rotation as between the 0.5 and 1°/s. Figure 5 shows the specification of solar tracking tilt sensor which is used for the tracking of the sun rays system in the experiment. The controller was used for controlling the single-axis direction of the collector, while the converter was used for the conversion of the AC power supply to DC power supply. Khaled et al.²⁹ and Maxime and Ole³⁰ reported that the accuracy of the tracking system depends on the solar irradiance magnitude with the deviation from zero is 0.2° and 0.05°.

Figure 5.

The specification of solar tracking tilt sensor. AC: alternating current; DC: direct current.

Mirza et al.³¹ and Mousazadeh et al.²² studied the different types of sun-tracking systems with their advantages and disadvantages and they reviewed that most of the efficient and popular sun-tracking device are in the form of polar-axis and azimuth/elevation types. The solar tracker has an average accuracy of about 0.05° to the essentially continuous tracking system used in the solar collector reported by Nafey et al.³² and Nagarajan et al.³³ Farahbod et al.¹⁶ and Odeh and Abu-Mulaweh³⁴ described the most commonly used two-axis sun-tracking systems which were applied in various solar energy systems and the accuracy of the tracking system highly relies on to be parallel with the zenith axis.

Experimental site location

The experiments were conducted at the College of Engineering, Nanjing Agricultural University, China with the 32.134°N latitude and 118.685°E longitude of 15 m high altitude. The experimental setup was used for water distillation through the performance evaluation of PTSC with the using of single-axis tracking mechanism. The site was perfect because it receives maximum solar radiance from morning to evening without the interference of any shadow of a structure. According to the metrological data for the year 2017 which were collected from the metrological station of Nanjing, China, the months from April to August 2017 were selected for the experiment with the help of metrological data as shown in Figure 6.

Figure 6.

Average metrological data for the year 2017.

System testing

Figure 7 represents the testing platform of the PTSC that was developed and fabricated from the locally available material from the market and it allows the different outdoor tests, as well as different tracking axis, that is North–South or East–West axis with the continuous water flow with the rate of 0.022 kg/s. The distillation unit (DU) is made from glass and its length is 1 ft and attached with absorber pipe through the narrow pipe and it received water vapors from the absorber pipe through outlet opening jet. The water vapors cooled down with the low temperature of the continuous flow of cooled water in DU to become in the liquid state.

Figure 7.

Isometric view of test platform operating in sunny day.

Performance of parabolic solar trough collector

The performance of PTSC was evaluated with a quantity of distilled water during the experiment with the following equation (6) reported by Omara et al.³⁵ and Omara and Mohamed³⁶

Q = \frac{E \times G \times A}{2.3}

(8)

Solar irradiance

Solar irradiance is the amount of energy which falls on the collector per unit time per unit area of the collector and received in the form of thermal energy. The solar irradiance was recorded with the help of solar power meter (Model No: SM206) daily, weekly, and monthly basis.

The efficiency of the collector

The thermal efficiency of the collector is the ratio of heat available (input) to the collector by solar irradiance incident on the absorber of solar collector and output (distilled water) of the concentrator. The performance of the collector in terms of efficiency was evaluated with the using of the single-axis solar sensor and calculated with the using of following equation (9) studied by Nafey et al.,³² Nagarajan et al.,³³ and Pollerberg et al.³⁷

η = \frac{Mass of distilled water (kg) x 627 W / kg}{Solar energy (W)} \times 100

(9)

Results and discussion

Average solar irradiance

The solar irradiance was calculated with the help of mechanical device (Solar Power Meter, SM206) on monthly basis and the monthly average mean solar irradiance data were noted during the solar time from 08:00 AM to 16:00 PM as shown in Figure 8. The results were similar to the findings of Omara et al.³⁵ and Prakash and Velmurugan.³⁸ The graph showed that the highest mean value of solar irradiance 476 W/m² was noted for the August, while 275 W/m² was the lowest solar irradiance recorded for the month of April. The error bars graph shows the errors with stranded deviation in the months of the year with the solar time. The solar irradiance started increasing from 09:00 AM up to 16:00 PM solar time with the help of sun sensor using.

Figure 8.

Average means monthly solar irradiance.

Pollerberg et al.³⁷ and Ravi et al.³⁹ reported that starting off the daytime at 09:00 AM the solar irradiance was noted up to 610 W/m² and increased with the increase of ambient temperature of the collector. The solar irradiance started increasing from 12:00 noon sharp to 15:00 PM with the clearance of the day, in the months of April and May and the data were recorded 15 days and 17 days for the months of April and May, respectively. The reason was that the sun was not clear due to the rain and cloudy days in the months of April and May. The results are contradictory with the findings of Ravi et al.⁴⁰ and Ravishankar et al.⁴¹ as they reported that the collector works efficiently in the months of June, July, and August due to the brilliant sunshine and highest amount of solar irradiance.

Average mean monthly temperature

The mean range of temperature of the PTSC was noted during the experiment time for 9 h from 08:00 AM up to 16:00 PM for the months (April to August-2017) of the year. The results are contradictory with the findings of Odeh and Abu-Mulaweh,³⁴ Pollerberg et al.,³⁷ and Saad and Hosni⁴² as they noted that the temperature of the collector increased with the time of the day. Table 1 shows the relationship between the absorber and ambient temperature of the PTSC and the standard bars on the line graph represent the standard error of the data for the months of the year. The line graph showed that the average monthly ambient and absorber temperatures were found in direct association with each other.

Table 1.

Average monthly ambient and absorber temperature of parabolic trough solar collector.

Time (h)	Months of the year, 2017
	April		May		Jun		July		August
	Amb. Tmp	Abs. Tmp	Amb. Tmp	Abs. Tmp	Amb. Tmp	Abs. Tmp	Amb. Tmp	Abs. Tmp	Amb. Tmp	Abs. Tmp
8:00 AM	28	90	31	90	34	95	32	85	36	95
9:00 AM	30	100	32	100	34	105	34	95	37	105
10:00 AM	34	105	34	105	35	110	36	100	37	110
11:00 AM	35	109	35	107	35	115	36	103	37	110
12: Noon	35	113	36	110	36	120	36	105	37	115
13:00 PM	35	113	36	113	36	120	36	105	37	120
14:00 PM	35	113	36	113	36	120	36	105	37	120
15:00 PM	35	108	36	113	36	110	36	105	37	120
16:00 PM	35	103	36	108	36	105	36	100	37	115

Note: Amb. Tmp denoted the ambient temperature and Abs. Tmp represent the absorber temperature.

The total average absorber temperature of the collector was recorded from 121, 117, and 113°C for the months of August, July, and June, respectively, due to the clear sunny days. The results were in agreement with the findings of Saban et al.⁴³ as they noted the temperature of the collector in the months of June–August up to 120°C with the 12:00 noon sharp. Similarly, in the months of April and May, the absorber temperature was noted least at the ambient temperature of the collector, due to the rain and cloudy days and also recorded the data for 15 and 17 days, respectively, in these two months. Jinesh et al.²⁴ and Mousazadeh et al.²² reported that the temperature of the collector was increased with the using of the solar sensor in the PTSC. Sethi and Dwivedi⁴⁴ studied the performance assessment of a PT collector; they fixed the inlet temperature of 27°C with the low flow rate and noted that the outlet temperature of the collector reached up to 123°C. The standard bar graph applied to the data with the standard error bars which showed that the data were fit to both the ambient and absorber temperature of the collector.

Performance of PTSC

The performance of collector was noted from the output of distilled water per hour for the months of the year from 08:00 AM up to 16:00 PM as shown in Figure 9. The highest distilled water was recorded for the months of August, July, and June 6675, 4851, and 3519 ml/h m², respectively. Shanmugasundaram and Janarthanan⁴⁵ revealed the solar distillation with different phase change materials; they noted that the output of collector increased with the increase of solar irradiance. The results were in agreement with the findings of El-Sebaii and El-Bialy¹¹ as they studied that output of the collector was increased with the increasing of condensation area of the collector.

Figure 9.

Distilled water per hour.

The performance of the collector was found higher as compared with the previous studies. Due to the clear sunny days with no wind, while in the months of April and May the performance of collector was low due to the lowest output of distilled water from 2858 and 3184 ml/h m², due to the 15 and 17 days data recording interval with the rainy, air blowing and cloudy days, respectively. The results were in disagreement with the findings of Arunkumar et al.,⁴ Fahim et al.,¹⁵ and Gustavo et al.²¹

The efficiency of PTSC

The thermal efficiency of the collector was the ratio of input heat available to the collector and output of distilled water of the PSC with the help of single-axis solar tracking system (sun sensor). The efficiency of the collector was calculated for the months of the year during solar timing from 08:00 AM to 16:00 PM as shown in Figure 10. The results were found similar to the findings of Ravi et al.⁴⁰ and Ravishankar et al.⁴¹ They had studied the tracking system for the increased efficiency of the collector. The line graph showed the inter-relationship between the efficiency and solar irradiance of the months of the year, while the standards bar represents the standard error between the months of the year. The efficiency of 31% was recorded as the highest efficiency for the month of August with the higher solar irradiance, while 19% efficiency was recorded as the lowest efficiency for the month of April. The graph showed that there was no difference between efficiency and solar irradiance, as it was calculated as a minimum with respect to the months of April and May, due to the fact about the demonstration, cloudy and rainy days.

Figure 10.

Comparison of solar irradiance and efficiency of the PTSC.

Saban et al.,⁴³ Sharshir et al.,⁴⁶ and Shashikanth et al.⁴⁷ concluded from the results that the efficiency of the collector has been increased with the increase of the absorber area of the collector. Another study by Shiva et al.⁴⁸ and Singh and Tiwari⁴⁹ conducted the experiment and concluded that efficiency of the collector was increased with the increase of solar irradiance, the area of the condensation, and the ambient temperature of the collector.

The purity of distilled water

The tap water was tested before and after the distillation process with the EC meter (Model No: 4083) as shown in Table 2. The results showed that the values of pH and EC are decreased with the process of distillation. The results are in agreement with the findings of Gowtham et al.¹⁹ and Pollerberg et al.³⁷ They tested the distilled water before and after the process of the collector. It was concluded that the PTSC was recommended as the most suitable technique for the production of distilled water. The process for distillation involves boiling the water, allowing the steam to condense in a tube, and collecting the condensation in a container. There may be many substances dissolved in the water, and some of them may vaporize along with the water, but salts and other solid solutes are left behind. Sophisticated distillation techniques, that is PTSC can eliminate even the volatile solutes; the collected condensate should be free of any solutes and we would expect its pH to be 7. If we measure the pH immediately after distillation, that is probably what we will find, but it soon changes.

Table 2.

Parameters tested before and after the distillation process through parabolic trough solar collector.

S. no.	Parameters	Before	After
1	pH	7	5.8–7
2	EC	25.5–29.7 µS/cm	22.4–27.8 µS/cm

EC: electrical conductivity.

The pH of pure water before distillation is around 5.8, which makes it acidic. The reason is that water absorbs carbon dioxide and continues to do so until it comes into equilibrium with the atmosphere. In solution, carbon dioxide reacts with water to produce carbonic acid, which in turn releases hydronium ions into solution, which is equivalent to releasing free hydrogen ions.

2H₂O + CO₂ –> H₂O + H₂CO₃ (carbonic acid) –> H₃O⁺ (hydronium) + HCO₃⁻ (bicarbonate ions)

The pH value can vary from 0 to 14. Solutions with a pH between 0 and 7 are acidic, while those with a pH between 7 and 14 are basic. Pure distilled water should be neutral with a pH of 7, but because it absorbs carbon dioxide from the atmosphere, it is actually slightly acidic with a pH of 5.8. It takes about 2 h for a sample of distilled water to absorb all the carbon dioxide it can from the atmosphere and achieve its final pH.

The results were contradictory with the findings of Sharshir et al.⁴⁶ as they studied the purification of distilled water with the concentrating solar power technology and concluded that the distilled water is free from ions. The results were strongly agreement with the findings of Abo-Elkasem et al.,¹ Farahbod et al.,¹⁶ and Mousazadeh et al.²² as they reported that the distilled water prepared through collector was free from the impurities and the results were similar with the present study results. The results were in agreement with the findings of Soteris⁵⁰ and Vivar et al.⁵¹

Conclusion

The efficiency of PTSC was calculated with the consideration of solar irradiation and 31% was noted highest for the month of August with respect to higher solar irradiation, while the 19% was recorded minimum for the month of April because of lower solar radiation. Maximum distilled water was obtained from 4851 and 6675 ml/h m² in the months of July and August with the highest amount of solar irradiance, respectively. In the current study, a constant energy input of 627 W/m² had increased the distilled water production by 35%. Furthermore, from the experimental results, it was recommended that the PTSC had better efficiency during the daytime for 9 h, that is 08:00 AM to 16:00 PM. Considering the results, it was recommended that the amount of distilled water produced significantly depends on the amount of energy input on the concentrator. The results also showed that PTSC with sun tilt sensor has produced more distilled water and as free from impurities, that is Mg, Ca, Zn, and Na, and it was concluded that the single-axis solar tracking mechanism used in PTSC is the better technique for the production of distilled water with the condenser, because according to the study site location of the experiment.

Footnotes

Acknowledgements

First of all thanks to all the contributors and special thanks to the Chinese Government Scholarship Council for this great opportunity. This work was edited for proper English language, grammar, punctuation, spelling, and overall style by native English speaking editors at American Journal Experts.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Fahim Ullah is a Doctoral student of Nanjing Agricultural University, major in Agricultural Mechanization Engineering.

Min Kang, is a professor of Nanjing Agricultural University. His main research area are design of agricultural equipment, non-traditional manufacturing technology, numerical control machining.

Appendix

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