ISSN: 2394-3122 (Online) Impact Factor: 3.471 Volume 3, Issue 7, July 2016
SK International Journal of Multidisciplinary Research Hub
Journal for all Subjects
Research Article / Survey Paper / Case Study Published By: SK Publisher (www.skpublisher.com)
Performance Evaluation of Concentric Collector Solar Thermal Systems by using Different Reflectors
K. Manoj Kumar1
Dept of Electrical & Electronics Engg MITS
Madanapalle, India
K. V. R. B. Prasad2 Dept of Electrical & Electronics Engg
MITS Madanapalle, India
Abstract: This paper presents the method of improving the performance of concentric collector solar thermal systems (CCSTS) by using different reflectors. In solar thermal system (STS) with concentric collectors, a reflector plays a key role to extract thermal energy from solar radiation. The heat generated using concentrated solar radiation is depends upon the effectiveness of the solar reflectors. This paper aims to show the implementing two different types of reflectors in CCSTS.
Glass and Aluminum are used as reflecting materials to reflect the solar radiation on to the collector. The thickness of glass is as thin as possible to reduce double absorption during the transmission of the incident solar radiation. In this paper, the glass reflectors with thickness 1.5mm, 2mm and aluminum reflectors are considered to analyze the performance of CCSTS with hardware implementation. From the results obtained, 1.5 mm thickness glass reflector has better reflectivity among the three but Aluminum reflector is cost effective.
Key Words: Concentric Collector Solar thermal system (CCSTS), glass reflector, thickness, Aluminum reflector, reflectivity.
I. INTRODUCTION
In 21st century, usage of renewable energy increases day by day. Solar energy is a primary source of renewable energy. It is free, clean, safe, and abundant in nature. In recent years, the development and utilization of solar energy technology have become an essential strategy in so many countries for sustainable development. From solar energy, power is generated in two ways through solar photovoltaic systems and solar thermal systems. The solar energy output depends on irradiance, temperature and atmospheric conditions. STS is used to produce heat [1]-[2]. Using STS, power can also be generated with concentrated solar power (CSP) thermal systems.
In STS, the thermal energy is generated by using CCSTS [3].In this system, reflector plays a major role to produce the heat at the collector. The reflectors are used to focus solar energy on to the collector [4]. The magnitude of reflected radiation is a function of wavelength and special distribution of the incident radiation. The heat generated using concentrated solar radiation depends upon the effectiveness of the solar reflectors. The reflectors must have some characteristics, such as low-cost, high reflectance-ratio and better weather ability. The performance of the reflector can be improved by either improving the reflectance or by reducing the cost of the reflector.
To improve the reflectivity of the glass reflector, thickness of the reflector can be reduced to avoid double absorption during the transmission of the incident solar radiation over a wide a spectrum and withstand the strength specifications [5].
To reduce the cost of the reflector, the low cost reflecting materials like aluminum is used as a reflector [6].
In this paper, the generation of heat in STS is improved by reducing the thickness of glass reflector. The thickness of glass reflector is reduced from 2mm to 1.5mm for improving the performance of the CCSTS. Later, the aluminum foil is used as reflecting material to reflect the solar radiation on to the collector. Here, a parabolic dish model is used to collect the solar
Volume 3, Issue 7, July 2016 pg. 6-11 radiation from reflectors to the collectors. The performance of the three reflectors is analyzed by using hardware implementation. The results obtained for different reflectors were analyzed. From the results, it is observed that the 1.5mm thickness glass reflector is having high reflectivity and aluminum is cost effective for certain applications in which cost of the system is main perspective.
II. MODEL DESCRIPTION
Fig 1. Parabolic dish model.
Parabolic dish model is shown in Fig.1. It consists of a parabolic dish shaped concentrator or reflector that reflects solar radiation on to the receiver placed at the focal point of the dish. The dish usually tracks the sun in with the help of a t racking system [7]. This tracking system is either manual or automatic. Currently researches focus on solar dish (SD) and generators to produce electricity. The main advantages of SD systems include high efficiency and modularity which is suitable for dist ributed generation. In this model, orientation of solar collector (SC) in space is the main factor influencing the quantity of absorbed solar radiation energy [8]. In the case with optimal angles of a solar collector, we will have the maximum of solar radiant energy.
III. DETERMINATION OF FOCAL PONT FOR THE PARABOLIC DISH
During installation identifying the correct focal point of the parabolic dish is very important. To calculate the Focal point (f), it is necessary to measure diameter (D) and depth of the dish (c).
Fig 2. Determination of focal point for parabolic dish.
Fig 2, represents the diagram of a parabolic dish for determining the focal point for the reflected solar radiation to harness the maximum heat from the reflectors [9].
From the Fig 2, the formula used to calculate focal point of parabolic dish is
Where f is focal point,
D is diameter of the parabolic dish and c is depth.
Volume 3, Issue 7, July 2016 pg. 6-11 IV. EXPERIMENTAL SETUP
In this paper three parabolic dishes of same area are considered to analyze the performance of STS. For the analysis two different reflecting materials are considered; one is glass mirror material and other is aluminum foil. For first parabolic d ish, glass mirror of 1.5mm thickness is used as a reflector. Glass is cut into small pieces and paste to it. For second parabolic dish, glass mirror of 2mm thickness is placed on it as a reflector. Finally, for third dish, aluminum foil of microns thickness is placed on it as a reflecting material. An open type storage vessel is placed at the focal point of each dish. Each vessel contains 600ml of water as collector. In this system absorber (or collector) is allowed to rotate with respect to sun to extract more solar radiation instead of rotating parabolic dish. The storage vessel (or collector) is rotated manually to extract more thermal energy.
(a) (b)
(c)
Fig 3 Experimental setup of (a) glass mirror reflector with 1.5mm thickness, (b) glass mirror with 2mm thickness and (c) aluminum reflector.
Fig 3 shows the experimental setup of three reflectors i.e., glass reflector of 1.5mm thickness and 2mm thickness along with aluminum reflector. The experimental setup is placed parallel to the earth axis. The thermometer is used to measure water temperature having a range of 00C to 3600C. The experimentation is carried out in the month of May 2016 for two different days. The water temperature readings are taken at an interval of 15 minutes in a span of hours.
Experiment Procedure:
The setup is placed under the sun and the storage vessel is rotated manually to track the focal point of the dish.
Storage vessel is filled with 600ml of water and takes readings of water temperature.
The readings are recorded for a span of hours at an interval of 15 minutes.
V. RESULTS
Validation of Experimental Setup
Testing is conducted during clear sky days in the month of May 2016 for about days. The test results were taken between 11:30 am and 1:00 pm. The data was recorded for every 15 minutes in the span of one and half hours. The thermometer is used to measure the water temperature.
Volume 3, Issue 7, July 2016 pg. 6-11 Table I shows the water temperature readings of three reflectors for day1.
S.
no
Time Ambient temperature (0C)
Water Temperature (0C)
Glass mirror Aluminum foil 1.5mm
thickness
2mm thickness
1 11:30 36 31 31 31
2 11:45 37 46 45 41
3 12:00 37 50 49 44
4 12:15 37 53 51 47
5 12:30 37 54 52 48
6 12:45 37 52 50 46
7 13:00 37 50 48 44
Table I: Day 1 water temperature readings
The emissive power of solar energy is calculated by using STEFAN-BOLTZMANN law
Where T= temperature of the surface (0K)
σ= Stefan Boltzmann constant
= 5.67x10-8 W/m2-k4.
The water temperature in storage vessel is measured in 0C, which is further converted into 0K by using the relation (273+temperature in 0C) to calculate the emissive power.
The results obtained are shown in Table I are represented in graphical representation and shown in Fig 4.
Fig 4. Temperature Variation of water on Day 1 for three different reflectors.
Table II shows the water temperature readings of three reflectors for day 2 between 11:5 AM to 1:05 PM.
S.
no
Time Ambient temperature
(0C)
Water Temperature (0C) Glass mirror Aluminum
foil 1.5mm
thickness
2mm thickness
1 11:30 36 31 31 31
2 11:45 37 47 46 42
3 12:00 37 51 50 46
4 12:15 37 55 52 47
5 12:30 37 53 50 45
6 12:45 37 51 48 44
7 13:00 37 49 47 43
Table II: Day 2 water temperature readings
0 10 20 30 40 50 60
11:30 AM
11:45 AM
12:00 PM
12:15 PM
12:30 PM
12:45 PM
1:00 PM
temperature of 1.5mm thickness glass reflector temperature of 2mm thickness glass reflector temperature of aluminum foil reflector ambient temperature
Volume 3, Issue 7, July 2016 pg. 6-11 The results obtained shown in Table II, are represented in graphical representation and shown in Fig 5.
Fig 5. Temperature Variation of water on Day 2 for three different reflectors.
From the results shown in Tables I and II, it is observed that 1.5 mm thickness glass reflector performance is better than the other reflectors. Among the other two reflectors, the 2 mm thickness glass reflector performance is better than the aluminum foil reflector.
Experimental setup details:
The details of experimental set-up used to conduct the experiment are shown below.
Aperture area of dish : 1877.33 cm2 Area of absorber : 947.88 cm2 Focal point of dish : 46.5 cm Concentration ratio : 1.98
Thickness of glass reflectors : 1.5mm and 2mm Ambient temperature : 31 0C
Attained maximum temperatures are For 1.5 mm thickness reflector : 540C For 2 mm thickness reflector : 52 0C For aluminum reflector : 48 0C
VI. CONCLUSION
In this paper, three different reflectors are used to analyze the performance of two glass reflectors, one having 2 mm thickness and the other having 1.5 mm thickness, along with the aluminum foil reflector were assessed by analyzing the result s.
From the results, it is observed that the 1.5 mm thick glass reflector has good reflectivity. Its weight is also low when compared with 2 mm glass reflector. On the other hand, the aluminum foil reflector has less reflectivity but its cost is low and weight is very low among the three reflectors. hence, 1.5 mm thick glass reflector may be preferred for best solar thermal applications which need high temperature whereas aluminum foil may be preferred for certain solar thermal applications where cost is main perspective.
0 10 20 30 40 50 60
11:30 AM
11:45 AM
12:00 PM
12:15 PM
12:30 PM
12:45 PM
1:00 PM
temperature of 1.5mm glass reflector temperature of 2mm thickness glass reflector temperature of aluminium foil reflector ambient temperature
Volume 3, Issue 7, July 2016 pg. 6-11 References
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6. Xiaoming Ling, Duowang Fan, Fan Yang, “A Study of the Organization and Performance of Thermally Evaporated Aluminum Reflector for Solar Energy System” In proceedings of IEEE, 2nd conference on Environmental Science and Information Application Technology, 2010.
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8. Jurgita Grigoniene and Mindaugas Karnauskas, “Mathematical modelling of optimal tilt angles of collector and sunray reflector,” ENERGETIKA, 2009.
9. G.D.Rai by Non-Conventional Energy Sources, Khanna publishers- 4th edition-2006.
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AUTHOR(S)PROFILE
K. Manoj Kumar, was born on November, 1993. He received his bachelor’s degree in Electrical and Electronics engineering from NBKR Institute of Science and Technology in 2010.
He is pursuing his post-graduation in Electrical Power Systems in Madanapalle Institute of Technology & Science from 2014.
K.V.R.B. Prasad, was born on august, 1972. He received his bachelor’s degree in Electrical and Electronics engineering from NBKR institute of science & Technology in 1993. He received his master’s degree in Electrical Power Systems from JNTU Anantapuram in 2005. He completed his Ph.D. in BITS, Pilani in 2012. He is working as professor in Madanapalle Institute of Science and Technology.
