Energy and Buildings 42 (2010) 2184–2199 Contents lists available at ScienceDirect Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild Exergetic performance assessment of a solar photovoltaic thermal (PV/T) air collector F. Sarhaddi ∗ , S. Farahat, H. Ajam, A. Behzadmehr Department of Mechanical Engineering, Shahid Nikbakht Faculty of Engineering, University of Sistan & Baluchestan, Zahedan 98164-161, Iran article info Article history: Received 2 November 2009 Received in revised form 16 March 2010 Accepted 8 July 2010 Keywords: Solar photovoltaic thermal (PV/T) air collector Exergy efficiency Computer simulation abstract In this paper, an attempt is made to evaluate the exergetic performance of a solar photovoltaic thermal (PV/T) air collector. A detailed energy and exergy analysis is carried out to calculate the thermal and electrical parameters, exergy components and exergy efficiency of a typical PV/T air collector. Some corrections are done on related heat loss coefficients. An improved electrical model is used to estimate the electrical parameters of a PV/T air collector. Further, a modified equation for the exergy efficiency of a PV/T air collector is derived in terms of design and climatic parameters. A computer simulation program is also developed to calculate the thermal and electrical parameters of a PV/T air collector. The results of numerical simulation are in good agreement with the experimental measurements noted in the previous literature. Finally, parametric studies have been carried out. It is observed that the modified exergy efficiency obtained in this paper is in good agreement with the one given by the previous literature. It is also found that the thermal efficiency, electrical efficiency, overall energy efficiency and exergy efficiency of PV/T air collector is about 17.18%, 10.01%, 45% and 10.75% respectively for a sample climatic, operating and design parameters. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Renewable energies are going to be a main substitute for fossil fuels in the coming years for their clean and renewable nature. Solar energy is one of the most significant renewable energy sources that world needs. The major applications of solar energy can be classified into two categories: solar thermal system, which con- verts solar energy to thermal energy, and photovoltaic (PV) system, which converts solar energy to electrical energy. Usually, these sys- tems are used separately. In the solar thermal system, external electrical energy is required to circulate the working fluid through the system. On the other hand, in the PV system, the electrical efficiency of the system decreases rapidly as the PV module tem- perature increases. Therefore, in order to achieve higher electrical efficiency, the PV module should be cooled by removing the heat in some way. In order to eliminate an external electrical source and to cool the PV module, the PV module should be combined with the solar air/water heater collector. This type of system is called solar photovoltaic thermal (PV/T) collector. The PV/T collector produces thermal and electrical energy simultaneously. Besides the higher overall energy performance, the advantage of the PV/T collector system lies in the reduction of the demands on physical space and ∗ Corresponding author. Tel.: +98 541 2426206; fax: +98 541 2447092. E-mail address: fsarhaddi@eng.usb.ac.ir (F. Sarhaddi). the equipment cost through the use of common frames and brack- ets as compared to the separated PV and solar thermal systems placed side-by-side. The main part of a building integrated photovoltaic thermal (BIPVT) system is PV/T air collector. The energy payback time (EPBT) of a PV/T air collector lies between 10 and 15 years depending on insulation and the performance of it. If the performance of a PV/T air collector can be increased, the energy payback time can be reduced. Therefore, the performance evaluation of a PV/T air collector is important. The performance of a PV/T air collector parametrically depends on climatic, operating and design parameters such as ambient temperature, solar radiation intensity, wind speed, solar cell temperature, back surface temperature, inlet and outlet air temperature, inlet air velocity, open-circuit voltage, short-circuit current, maximum power point voltage, maximum power point current, the length and width of PV/T air collector, overall heat transfer coefficient, etc. It can be evaluated in terms of the first and second law of thermodynamics. Its evaluation based on the first and second law of thermodynamics is known as energy efficiency and exergy efficiency, respectively. The energy analysis has some deficiencies [1,2]. Fundamentally, the energy concept is not sensitive with respect to the assumed direction of the process, e.g., energy analysis does not object if heat is considered to be transferred spontaneously in the direction of increasing temperature. It also does not distinguish the quality of energy, e.g., 1 W of heat equals 1 W of work or electricity. Energy 0378-7788/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2010.07.011