Nanofluids, which are new generation cooling fluids, have been found to improve the heat transfer coefficient and enhance the system performance in recent years. In this observation, TiO2/water nanofluid (with 0.5 wt% and 1 wt% TiO2) is used as a coolant to investigate the photovoltaic thermal (PVT) collector under solar radiation intensities of 500, 700 and 900 W/m(2) and mass flow rates ranging from 0.012 kg/s to 0.0255 kg/s. At high solar radiation, the thermal energy efficiency is high but is inversely proportional to the electrical energy efficiency due to the increment in PV surface temperature. The energy efficiency of 1 wt% TiO2 nanofluid-based PVT collector is 85%-89% compared with 60%-76% of water-based collector at 0.0255 kg/s. The improvement in exergy efficiency of 1.0 wt% TiO2 is 6.02% compared with that of water-based collector at the mass flow rate of 0.0255 kg/s. In addition, a new theoretical approach model is developed to compare the theoretical and experimental results of the TiO2/water nanofluid-based PVT collector. Considerably close agreement between the new theoretical approaches and experimental is obtained with an accuracy of 97.6%-99.2%. (C) 2019 Elsevier Ltd. All rights reserved.