Monthly Performance of a Photovoltaic Thermal System in Series with a Solar Thermal Collector in Laminar and Turbulent Regimes

Solar thermal (ST) collectors could only generate thermal power, while photovoltaic thermal (PVT) systems could provide both electricity and thermal power. However, the PVTs outlet temperature is usually not high enough for use in many applications such as space heating. Therefore, a new system called PVT system and ST collector in series (PVT-ST) is inducted to generate thermal power with higher outlet temperature and electricity. This paper explores the potential and feasibility of using PVT-ST under relatively hot and dry weather conditions in four cities of Tehran, Abadan, Baghdad, and Basra. To this end, the yearly performance of the system in terms of the first and second laws of thermodynamics is numerically evaluated. Moreover, the effects of the working fluid mass flow rate, in both laminar and turbulent regimes, on the module performance are investigated. Additionally, a comparative study is made between the PVT-ST, single PVT, and single ST systems. The working fluid regime analysis reveals that optimal thermal and electrical efficiency can be obtained in a turbulent regime. While the turbulent regime reflects better electrical exergy, the thermal exergy is dramatically decreased by raising the mass flow rate. Considering the mass flow rate of 0.0304 kg/s (turbulent regime) in July, the thermal efficiencies of the single ST, PVT-ST, and single PVT systems are 85.7%, 78%, and 72.9%, respectively. However, regardless of the mass flow rate, the PVT-ST system has the highest thermal exergy, peaking at 14.56 W/m2 at the lowest mass flow rate (laminar regime), which is double the thermal exergy of the single PVT. Finally, the annual study of the system performance in different cities illustrates that the maximum thermal power and exergy can be produced in Basra, averaging 375.72 and 1.46 W/m2. However, the maximum electricity production, with  an average of 77 W/m2 belongs to Baghdad.