## 1 Introduction  
The energy crisis is becoming a formidable challenge for the world, as depletion of fossil fuel reserves is increasing rapidly [1]. In fact, a rise in population coupled with a high rate of energy consumption in the industrial sector and in residential buildings is exacerbating this problem. Furthermore, the world is seeing a further expansion in its infrastructure. The substantial use of fossil fuels is meanwhile increasing global greenhouse gas emissions. Therefore, it is important to address the aforementioned energy crises by replacing fossil fuels with sustainable energy resources. Solar energy is considered the most promising substitute in the context of sustainability, unlimited availability, and diversity of its usage [2]. Sunlight consists of different wavelength spectra that enables it to produce heat and electricity. The light spectrum ranges that are favorable to photovoltaic (PV) solar cells are utilized for generating electricity [3], while the remaining wavelength ranges that cause heat are best suited for solar thermal collectors. By integrating a photovoltaic module with a solar thermal collector, the capacity to utilize the whole sunlight spectrum can be achieved [4]. Therefore, by providing simultaneous production of heat and electricity, the photovoltaic/thermal (PV/T) system is considered the best option thus far. Higher overall energy performance with limited physical space makes the PV/T system even more appealing. The development of high quality and efficiency PV solar cells took a number of years, as various researchers and scientists contributed their time and knowledge. In the middle 1970's, scholars reported on theoretical and experimental work for PV/T technology. [PERSON] [5] was among the pioneers who in 1976 investigated the energy performance of PV/T systems for residential buildings. In the late 1970's, [PERSON] [6] analyzed the PV/T collector through the famous Hottel-Whillier model for thermal analysis, by modifying it according to hybrid solar collector suitability. Further, [PERSON] [7] accessed the technical feasibility of the hybrid PV/T system; since then, the research and development work on PV/T design has continued to change and evolve as the demand arises. The benefits of PV/T technology can be identified through a life cycle cost analysis based on the energy and exergy of the proposed system's configurations. Taking into consideration initial cost, annual savings, and return on investment, energy and exergy analyses of the double and single pass PV/T air collectors have been carried out by [PERSON] and [PERSON] [8]. On the basis of experimental findings from different locations, they concluded that the life cycle cost of the PV/T system is affected greatly by the heat exchanger design and the climatic conditions. A comparative exergy evaluation of a PV/T system using (PCM) phase change material/water as coolants in comparison with a reference PV module was presented by [PERSON] et al. [9]. The proposed PV/T system was also assessed further for economic feasibility in the context of possible commercialization. They proposed that in the long run the PV/T system is more economical compared to the reference PV module. There are several heat transfer fluids, but water and air are commonly used coolants for harvesting heat from the PV module. An enormous amount of research work has been carried out on the aforementioned coolants with the intention to maximize the usage of solar energy [10; 11]. [PERSON] et al. [12] investigated and compared the performance of a PV/T system with seven design configurations of liquid fluid carrier absorbers. Under varied operating and climatic conditions, the spiral flow design outperformed its rivals with the highest thermal efficiency and electrical efficiency. The low thermal conductivity problem in the case of air can be overcome by introducing a double pass air channel, where both the top and rear surfaces of the PV module exchange heat with the circulating air.