Energy and exergy performances of a TiO2-water nanofluid-based hybrid photovoltaic/thermal collector and a proposed new method to determine the optimal height of the rectangular cooling channel

Abstract

Abstract An energetic and exergetic analysis of a hybrid photovoltaic-thermal solar collector (PV/T) with a rectangular channel through which a water-TiO2 nanofluid circulates is made. A three-dimensional model with the actual boundary conditions of the hybrid collector is simulated under ANSYS Fluent. The results of the simulations are presented in the form of figures and tables with, among other parameters, the overall energetic η (%) and exergetic efficiencies e (%), thermal and electrical efficiencies, exergetic losses due to heat transfer and friction, as well as the entropy generation in the system. A comparison of the hybrid (PV/T) with a rectangular channel to that with absorber (sheet-and-tube type) shows from the 1st and 2nd laws of thermodynamics perspectives different performances. Among the obtained results, the water-TiO2 based-(PV/T) hybrid collector presents no substantial advantage over the water-based (PV/T). Besides, to determine the height of the heat exchanger with a rectangular cross-section, a novel method is proposed and fully-explained. The obtained value corresponds to the point of inflection of the curve (η(%)–e(%)) vs. H, and for the case study, it is found to be similar (1.1% difference) to that calculated using the Bejan and Sciubba (1992) formula.