Analysis of photovoltaic (PV) and photovoltaic/thermal (PV/T) systems using the exergy method

In this paper, analyses of photovoltaic (PV) and photovoltaic/thermal (PV/T) systems, based on the exergy method are presented. To this aim, explicit electrical and thermal models are developed and used to characterize each system. Furthermore, energy and exergy balances are combined in order to identify the different sources of exergy losses involved in both thermal and electrical energy fluxes. Electrical current and voltage reduction factors are defined and used to express the exergy as well as its destruction in PV/T system, while two thermodynamic diagrams are proposed to visualize these losses. The first one illustrates exergies expended, produced and destroyed during the conversion of solar radiation. The second one allows individual effects of both electrical potential and current losses to be explicitly revealed. The proposed methodology is applied to study a PV/T system operating under different environmental conditions, i.e., solar intensity and ambient temperature, where irreversibility in addition to energy and exergy efficiencies are calculated and analyzed.