Nearly half of the insident solar radiation to the photovoltaic (PV) units will be converted to heat, which leads to a high operating temperature, cell structural damage, and the lifetime reduction. Therefore, an effective cooling method for these units is vital. The present work is the first experimental study on the influence of the twisted tapes (clockwise and counter-clockwise), which are inserted in riser tubes, on the performance of a photovoltaic thermal system from energy, exergy, and entropy generation viewpoints. In the indoor experiments, working fluid (pure water) with various flow rates ranged from 0.019 to 0.036 kg/s passed through the collector, where heat fluxes of 300, 500, 700, and 900 W/m2 were applied on the surface of photovoltaic units. Thanks to utilizing twisted tape inserts with the flow rate of 0.019 kg/s, the average surface temperature decreased by 1.4, 1.2, 1.7, and 0.6 ◦C, respectively, under heat fluxes of 900, 700, 500, and 300 W/m2. In addition, the overall energy efficiency of the photovoltaic thermal system, using clockwise and counter-clockwise twisted tapes, increased by 7.37 and 68.97%, respectively, compared to that of the conventional photovoltaic thermal system and PV unit. From exergy viewpoint, the photovoltaic thermal system using twisted tapes experienced higher overall efficiency (14.86%) compared to that of the conventional photovoltaic thermal system (13.57%) and PV unit (11.57%). Furthermore, lower entropy generation belonged to the photovoltaic thermal system with twisted tape inserts.

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