The main objective of current work is to scrutinize the performance of unglazed photovoltaic thermal system (PVTs) and transparent glazed photovoltaic thermal system (GPVTs) from energy and exergy standpoints using four different operating fluids consisting of deionized water, GNP/water, SWCNT/water, and MWCNT/water nanofluids with a mass concentration of 0.05%. Sunny and stable days with the clear sky of September and October are selected as the suitable actual conditions. The outdoor experiments are carried out from 9:30 to 16:00. The results reveal that in the GPVTs, although using a transparent glass cover has an undesirable effect on the surface temperature, electrical output power, and electrical efficiency, the concurrent effect of the glass cover and nanofluid considerably increases the thermal and overall efficiencies. Among all studied operating fluids, the GNP/water and SWCNT/water nanofluids would be more efficient in terms of energy and exergy performances. Regarding the energy viewpoint, the overall efficiencies of GPVTs/MWCNT, GPVTs/SWCNT, and GPVTs/GNP are higher by 12.32%, 17.02%, and 22.65%, respectively, compared to those of PVTs with deionized water. Moreover, from the exergy viewpoint, the overall efficiencies of PVTs/water, PVTs/MWCNT, PVTs/SWCNT, and PVTs/GNP are higher by 1.42%, 1.68%, 1.93%, and 2.32%, respectively, compared to those of the PV unit.

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