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Name of the student  : Sohel Miah Present Address        :  Department of Mechanical & Chemical Engineering (MCE) Islamic University of Technology (IUT) Name of the Supervisor     : Prof. Dr. Md. Abdur Razzaq Akhanda Name of the Department   : Mechanical & Chemical Engineering (MCE) Programme                        : M.Sc. Engg (M) Tentative Title: Comparative Study of Hybrid Photovoltaic Thermal solar systems using Trapezoidal, Saw tooth forward and Saw tooth backward ribbed surfaces opposite to absorber plate during the months of February-June in IUT campus, Bangladesh. Background and present state of the problem: Photovoltaic cells convert 5-15% of the incoming solar radiation into electricity, with the greater percentage converted into heat. The solar radiation converted into heat increases the temperature of the PV modules, resulting in the drop of their electrical efficiency. This undesirable effect can be partially avoided by applying a suitable heat extraction mode with a fluid circulation, keeping the electrical efficiency at a satisfactory level. Furthermore, this extracted heat can be utilized for heating air and/or water. For this purpose Hybrid photovoltaic/thermal (PV/T or PVT) solar systems may be introduced. The PV modules that are combined with thermal units, where circulating air or water of lower temperature than that of PV modules is heated constitute the Hybrid PVT solar systems and provide electrical and thermal energy, increasing, therefore, the total energy output from PV modules. A Hybrid PVT solar system consists of a PV modules coupled with water and/or air heat extraction devices which convert the absorbed solar radiation into electricity and heat. This system is simple and suitable for building integration for providing hot water/air depending on the season and the thermal needs of the buildings. The improved PVT systems have aesthetic and energy advantages and could be used instead of separate installation of plain PV modules and thermal collectors.Water cooled PVT systems are practical systems for water heating in domestic buildings but their application is limited up to now.Air cooled PVT systems have already been applied in buildings integrated usually on their inclined roofs or facades. This system keeps the electrical output at sufficient level covering building space heating needs during winter and ventilation needs during summer avoiding also building overheating. In order to improve the energy performance of the photovoltaic system, much effort has been given on the research and development of a hybrid PVT (photovoltaic-thermal) technology using water as the coolant. The fin performance of the thermal absorber is known to be one crucial factor in achieving a high overall energy yield of the collector. Design and performance improvements of hybrid PV/T systems with water or air as heat removal fluid have been carried out at the University of Patras including modifications that contribute to the decrease of PV module temperature and to improve the total energy output (electrical and thermal) of the PV/T systems. Design concepts, prototypes and test results for water and air-cooled PV/T systems with and without additional glass cover are extensively presented in Tripanagnostopoulos et al., 2002a. Also PV/T solar water heaters of ICS (Tripanagnostopoulos et al., 1998) and of thermosiphonic (Tselepis and Tripanagnostopoulos, 2002) type have been studied. The diffuse reflector is suggested to increase both electrical and thermal output of PV/T systems (Tripanagnostopoulos et al., 2002a) and LCA results for PVT/water (Tripanagnostopoulos et al., 2005) and PVT/air (Tripanagnostopoulos et al., 2006) systems, compared with standard PV modules, give an idea about the positive environmental impact of the suggested systems.Several publications are referred to investigations on air heating solar collectors. The simpler modification that is suitable for application in the air channel of the PVT/air systems is the roughened opposite air channel wall surface (Prasad and Saini, 1991; Bhavnani and Bergles, 1990), by which up to about 30% heat extraction increase can be achieved. Better results give the addition of several type ribs in the air channel (Han and Park, 1988; Gupta et al., 1993). More efficient is considered the mounting of vortices (Turk and Junkhan, 1986; Biswas and Chattopadhyay, 1992; Zhu et al., 1995; Tiggelbeck et al., 1993; Brockmeier et al., 1993 and Fiebig, 1997), which contribute to about four times better performance in heat transfer. Three alternative modes of placing the water heat exchanger inside the air channel were tested (Tripanagnostopoulos et al., 2007), with the water heat exchanger at PV rear surface giving the best results for the combined water and air heat extraction. For the improvement of air heat extraction, three low cost modifications that increase the heat exchange surface in the air channel were tested to determine system performance. The design of an experimental PVT/dual system, both air and water circulation with modifications in the air channel is presented by Rezwan (2011). Four experimental setups with Triangular, Semicircular, Rectangular and Flat ribbed surfaces have been studied in IUT campus, Gazipur, Bangladesh from February to March, 2010. Natural convection is applied instead of forced convection to increase the system net electrical output and thereby the overall system efficiency. All setup are of same capacity, projected area, water heat extraction method and average depth. Objectives with specific aims: The objectives of this study are to carry out an experimental investigations to compare the performances of four PVT collectors having three different ribbed surfaces and a flat plate opposite to each absorber plate. All collectors will be of same capacity, same projected area, and same average depth. Tests will be carried out in IUT campus from February, 2012 to May, 2012. Possible Outcome: Performance study each PVT collector carries out and Results obtained will be compared with available information in the literature. Methodology The PVT system can effectively operate at locations in low latitudes where favorable weather conditions exists, or marginally in medium latitudes to avoid freezing. This system needs special arrangement for air and water circulations through the rear surface of the PV panel. This is made by combining air and water heat extraction methods together. The concepts of designing such an arrangement are given below. 	Water circulation and the heat extraction can be done by flowing water through pipes in contact with a flat sheet placed in thermal contact with the PV module rear surface. 	For air circulation an air channel is usually mounted at the back of the PV modules. Air of lower temperatures than those of the PV modules, usually ambient air, is circulating in the channel and thus both PV cooling and thermal energy collection can be achieved. The usual heat extraction mode is the direct air heating from PV module rear surface by natural or forced convection and the thermal efficiency depends on channel depth. The heat extraction by natural airflow depends on the temperature difference between the inserting air in the channel and the PV module. The operation of PVT systems with high rate of forced airflow gives satisfactory results regarding heat extraction. In natural airflow the flow rate is not usually so much high as in forced airflow applications. The smaller channel depth with high flow rate increases heat extraction, but it increase pressure drop, which reduces the system net electrical output in case of forced air flow, because of the increased power of the fan. In applications with natural convection, the smaller channel depth decreases air flow and these results to an increase of PV module temperature. In these systems large depth of air channel of minimum 0.1m is necessary along with natural convection. Considering these factors, in this project Natural Convection is applied instead of forced convection to increase the system net electrical output and thereby the overall system efficiency. Temperature distribution over the flat/ribbed surface opposite to absorber plate will be measured by using 36 S.W.G Chromel-Alumel thermocouples. Inlet and outlet temperatures of water, temperature of the air inside the air channel and the ambient temperature will also be measured by using these types of thermocouples. Experimental Setup: Four experimental setups are to be used with almost similar size except the shape of the RIBs as shown in the Figure 1. Each set up essentially consists of a hybrid PVT collector and a storage tank. Each collector a fabricated in a wooden box of size (100 67  21) cm. The inner part of the box is insulated by glass wool. At the inner bottom of the box, ribbed surface is placed. An absorber is placed in the middle part of the box on top of which a set of copper pipes are installed for water circulation. At the top of the wooden box a PV panel is placed which a shown in Figure 2. Three different ribbed surfaces such as Trapezoidal rib, Saw tooth forward rib, Saw tooth backward rib and a Flat plate are used in the experiment which are shown in the Figure 3. Each of the set ups is placed where there is no obstacle to sunshine and is faced towards the south with an inclination angle of 23.8 which is the appropriate angle to collect maximum available radiation in IUT campus, Bangladesh. 36SWG Chromel-Alumel thermocouples are used to measure the temperatures. These are placed in the water inlet, water outlet, absorber plate, PV panel and bottom side of ribbed surface. In these ways five different temperature measures. For measuring the Voltage and Current, used voltmeter.

Figure 1: Schematic diagram of each experimental setup.

Figure 2: Details of Hybrid Collector.

(a) Trapezoidal rib                                                 (b) Saw tooth forward rib

(c) Saw tooth backward rib                                (d) Flat plate

Figure 3: Test specimens. (All dimensions in mm)

10. References

Battisti, R., Tripanagnostopoulos.Y., 2005. PV/Thermal systems for application in industry. In: Proceedings of (CD-ROM) of 20th European Photovolatic Solar Energy Conference, 6-10 June 2005, Barcelona, Spain, paper 6CV.2.3.

Chow TT, Pei G, Fong KF, Lin Z, Chan ALS, Ji J, 2008. Energy and exergy analysis of photovoltaic-thermal collector with and without glass cover. Applied Energy, 2008 [in press; on line 9 June 2008]

Chow TT, He W, Ji J, Chan ALS, 2007. Performance evaluation of photovoltaic-thermosyphon System for subtropical climate application. Solar Energy, 81(1), 2007, 123-130.

Chow TT, Ji J, He W, 2007. Photovoltaic-thermal collector system for domestic application. ASME Journal of Solar Energy Engineering, 129, May 2007, 205-209.

Chow TT, He W, Ji J, 2006. Hybrid photovoltaic-thermosyphon water heating system for residential application. Solar Energy, 80(3), 2006, 298-306.

Chow TT, Chan ALS, Fong KF, Lo WC, Song CL, 2005. Energy performance of a solar hybrid collector system in multi-story apartment building. Journal of Power and Energy, Proceedings of the Institution of Mechanical Engineers Part A, 219(1), 2005, 1-11.

He Wei, Chow Tin-Tai, Ji Jie, Lu Jianping, Pei Gang, Chan Lok-shun, 2006. Hybrid photovoltaic and thermal solar collector designed for natural circulation of water. Applied Energy, 83(3), 2006, 199-210.

He W, Ji J. Chow TT, 2007. An experimental study of façade-integrated photovoltaic/water-heating system. Applied Thermal Engineering, 27(1), 2007, 37-45.

Ji Jie, Chow Tin-Tai, He Wei, 2003. Dynamic performance of hybrid photovoltaic/thermal collector wall in Hong Kong. Building and Environment, Vol. 38(11), 2003, pp.1327-1334.

Tripanagnostopoulos.Y, 2007. Aspects and improvements of hybrid photovoltaic/thermal Solar energy systems. Solar Energy 81 (2007) 1117–1131.

M.R.Karim, M.A.R. Akhanda, 2011. Study of a hybrid photovoltaic thermal (PVT) solar systems using different ribbed surfaces opposite to absorber plate. Journal of Engineering and Technology (JET), Vol.09, No.01, June 2011.