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In this article, a comparative study is carried out between two equations for the exergy efficiency of photovoltaic thermal (PV/T) air collectors; the first equation is based on net output exergy and the second equation is in terms of exergy losses. The exergy efficiency equation parametrically is dependent on thermal and electrical parameters of PV/T air collector; therefore, improved thermal and electrical models are used to calculate them. Developing an exergy balance for PV/T air collector system, the various exergy components in PV/T system are introduced and two equations for the exergy efficiency of PV/T air collector are derived. A computer simulation program is also developed which is based on the used improved thermal and electrical models. In order to validate the simulation results, a typical PV/T air collector has been built and some experiments have been carried out on it. The results of numerical simulation are in good agreement with the experimental results. Finally, parametric studies have been carried out and the effect of design and climatic parameters on two exergy efficiency equations has been investigated. It is observed that the improved exergy efficiency obtained in this paper is in good agreement with the one given by the previous literature and it is better because it shows the portion of each of exergy losses in the exergy efficiency equation, directly.

The aim of the present study is the simultaneous optimization of thermal and electrical efficiencies of a solar photovoltaic thermal (PV/T) air collector. The analytical expressions for thermal parameters and thermal efficiency are derived by developing energy balance equation for each component of PV/T air collector. In order to calculate the electrical parameters and electrical efficiency of PV/T air collector the five-parameter current-voltage (I-V) model and a set of translation equations are used. An experimental setup for a typical PV/T air collector is built to measure its thermal and electrical parameters. The experimental validation of the used thermal and electrical models has been carried out by the measured data. It is observed that there is a good agreement between simulated and experimental results. Finally, the simultaneous optimization of the PV/T air collector has been carried out to maximize thermal and electrical efficiencies, simultaneously. Furthermore, the optimized ranges of inlet air velocity, duct depth and the objective functions in optimal Pareto front have been obtained.