# Numerical and Parametric Analysis for Enhancing Performances of Water Photovoltaic/Thermal System
## 4 Conclusions  
This work proposes an improved dynamic numerical model for PV/T system based on the heat balance equations established for each layer and solved in MATLAB software. The main obtained outputs of the PV/T model are respectively the temperatures and the electrical and thermal power used for evaluating the advantages of using the PV/T system instead of PV conventional one. Figure 8: Comparison of PV and PV/T temperatures. Figure 10: Comparison of PV and PV/T electrical efficiency. Figure 9: Comparison of PV and PV/T electrical power. This developed model was built regarding the other models presented in literature [37] and validated through comparison of the three layer PV model with the NOCT model and using the equations of the cooling unit, derived from a previous PV/T model validated experimentally in [24]. Consequently, results revealed good agreement. Thus, the model is considered a useful tool for other research works aiming to investigate the PV/T system and analyze its energy yield. Thereafter, the PV/T model was used to investigate the effect of the water velocity and thickness on the cooling of the PV cells. Next, the improved PV/T model with optimum parameters values was applied in case operating conditions of Iasi, Romania, where the input variables, e.g., solar irradiance and ambient temperature, were given by PVGIS data [36]. Important conclusions of this work can be drawn as below:  
* The effectiveness of the developed PV/T model based on the three layer PV model tested at different of solar irradiance and ambient temperature was proven. * Inlet water temperature had a significant effect on the cooling of the PV panel. A lower PV temperature was noted when the inlet temperature was about 20 \({}^{\circ}\)C.
* As the water velocity ranged from 0.010 to 0.035 m/s, the cooling process improved. A lower PV temperature was obtained for water velocity of 0.035 m/s. * The temperature of the PV panel decreased while increasing the water film thickness from 3 mm to 7 mm and started increasing by 10 mm. * Optimal cooling of the PV cells (27.7 \({}^{\circ}\)C) was ensured, adopting optimum values of water velocity and thickness of 0.035 m/s and 7 mm, respectively, at inlet temperature of 20 \({}^{\circ}\)C.
* The improved PV/T model showed a better electrical performance (316.56 W) compared with the conventional PV panel (258.8 W). Furthermore, an important gain of 1334.5 W of thermal production was obtained. Therefore, the PV/T system designing based on the optimum functional parameters can be an efficient way to produce electrical and thermal energy simultaneously where the electrical and thermal efficiency can reach 19.07% and 80.3%, respectively. Moreover, similar results found in literature [20; 21] show economic advantages for implementing such systems in the same climate conditions, where the investment return can be up to 4.25 years with a 75% subsidy in the initial investment and six PV/T modules installed [38]. Future works foresee experimental programs for developing the PV/T model using a real experimental PV/T prototype that is installed on the roof of the Building Services Department, \"Gheorghe Asachi\" Technical University of Iasi, Romania, in order to consider more climatic parameters, such as the wind speed and direction, which also affect the electrical and the thermal energy outputs of the PV/T system. Conceptualization, C.E.F, S.V.H., N.C.C. and B.H. ; methodology, C.E.F. and B.H. ; software, C.E.F. ; validation, C.E.F, S.V.H. and E.F.T. ; formal analysis, C.E.F, S.V.H. and M.L.C. ; investigation, C.E.F, N.C.C., S.V.H., B.H., E.F.T. and M.L.C. ; resources, N.C.C. and M.L.C. ; data curation, C.E.F, N.C.C. and B.H. ; writing--original draft preparation, C.E.F. and S.V.H. ; writing--review and editing, C.E.F. and N.C.C. ; supervision, N.C.C. and B.H. ; project administration, N.C.C. ; funding acquisition, N.C.C. All authors have read and agreed to the published version of the manuscript.