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Abstract This paper presents a review of the exergy and sustainability index of solar thermal systems. The review includes exergy analyses of solar collectors, solar drying systems and photovoltaic thermal (PVT) systems. Solar collectors, the most essential components of solar thermal systems, receive solar energy and convert it into thermal energy. The PVT collector is a popular means of harvesting solar energy. A PVT collector can generate electrical and thermal energies simultaneously. Experimental and theoretical approaches for a PVT air collector with a ∇-corrugated absorber are investigated in this study. A steady-state energy analysis of the PVT air collector is performed to predict photovoltaic (PV) and air outlet temperatures. Experimental results are in close agreement with the results of the theoretical study. The percentage errors of PV and air outlet temperatures between experimental and theoretical values are 5.49% and 3.75%, respectively. The PVT exergy efficiency of the PVT air collector with a ∇-corrugated absorber is 13.36% and 12.89% for the theoretical and experimental study, respectively. Furthermore, a sustainability index is proposed. The sustainability index of the PVT air collector is 1.168 and 1.148 for the theoretical and experimental study, respectively. Highlights • The theoretical approach of photovoltaic thermal (PVT) air collector with ∇-corrugated absorber is presented. • The predicted results are consistent with the results obtained from the experiments. • The exergy and sustainability index for various mass flow rates and solar radiations are obtained. • The exergy and sustainability index of solar thermal systems are reviewed. [ABSTRACT FROM AUTHOR]

Photovoltaic–thermal (PVT) collectors can generate electrical and thermal energy simultaneously. The combination of these two technologies can reduce the required space, time installation and use of materials. PVT air collector present increased total efficiency by increasing solar radiation amount. This review presents the concepts and descriptions, as well as previous works conducted on thermoelectric (TE). A theoretical study of PVT-TE air collectors is also performed. Mathematical models are proposed and solved using iterative process based on the matrix inversion method. An improvement in energy yields can be obtained using TE solar collector technology because TE devices increase the energy conversion efficiency of the system. The annual cost (AC) and annual energy gain (AEG) of PVT-TE air collectors are determined. The cost–benefit ratio or AC per AEG (AC/AEG) is presented for different combinations of mass flow rate and number of TE to increase the feasibility of users in selecting the optimal design features that correspond to minimum AC/AEG. [ABSTRACT FROM AUTHOR]