## 1 Introduction  
Photovoltaic thermal solar collectors have gained attraction in renewable energy systems, as they allow the conversion of solar radiation into both electrical and thermal energy. These collectors could be utilized for a variety of applications in the industrial and building sectors, such as the provision of domestic hot water (DHW) [1], air-conditioning [2], desalination [3], solar cooling [4], polygeneration systems [5] and industrial heat production [6, 7, 8]. The two main types of solar collectors are the concentrating and the non-concentrating collectors [9]. Collectors from both types have been examined numerically and experimentally, considering the thermal, the electrical and the optical operation. The non-concentrating PV/T solar collectors have been studied and investigated in various studies in the literature. [PERSON] et al. [10] created a mathematical model regarding the dynamic simulation of how a water system with a flat plane PV/T absorber works, which was verified with regards to its validity via indoors empirical data from experiments. They examined the slope effect and the effect of the collector's connection on the electrical and the thermal operation of this system, which was installed on a vertical facade in a building. They found that the type of connection for the solar PV/T had a greater impact on the thermal operation than on the electrical operation, and the optimum tilt angle was 40\({}^{\circ}\). [PERSON] and [PERSON] [11] performed an exergetic and energetic study of a PV/T system in different locations and then optimized the design with regard to the exergy efficiencies. [PERSON] et al. [12] established a numerical simulation for the analysis of hybrid solar collectors. With the developed model, they investigated the effect of a few parameters (solar radiation, water temperature at the inlet and the glazing covers number) on the collector's thermal operation performance. Moreover, they studied the monthly thermal and electrical operation of the collector considering the climatic conditions of Tunisia, where they found that the maximum electrical power was 8119 kWh/m\({}^{2}\) while the maximum thermal energy was 49,440 kWh/m\({}^{2}\). [PERSON] et al. [13] researched the impact of low-emissivity coating, based on silver, on the electrical and thermal performance of a flat plane PV/T collector. A numerical model considering the energy balance was created and validated with results coming from experiments. The study shows that the coating reduced the heat losses by 8% with a minimal effect on the electric performance, compared with the same collector without the coating. [PERSON] et al. [14] developed a simulation model for an uncovered PV/T collector which took into consideration the main parameters affecting the collector efficiency, a model which was also validated using empirical results. [PERSON] et al. [15] created a numerical model to investigate different geometries for the flow channels, which was then studied experimentally and compared to a conventional PV module. The main conclusion was that the spiral flow collector presented the highest electrical performance of 9.1%. [PERSON] et al. [16] performed a 3-dimensional computational fluid dynamics analysis (CFD) study on different absorber geometries. An absorber with rectangular channels achieved better thermal performance than the reference case of a commercial hybrid collector with flat elements. While solar thermal concentrated collectors have been studied extensively [17; 18], few works in the literature have been found that consider hybrid concentrated collectors. [PERSON] et al. [19] proposed a methodology for the characterization, simulation and evaluation of a concentrated hybrid collector. Then, they applied it to a collector with a parabolic reflector and compared the results with conventional PV modules and a conventional solar collector. A dynamic theoretical model was developed by [PERSON] et al.