Abstract <p>A comparative numerical computational fluid dynamics (CFD) study is carried out to improve the design and overall performance of a locally manufactured flat-box photovoltaic (PVT) collector at low cost. The numerical study shows that the design of the solar collector in the form of a flat-box with internal blades (fins and perforated baffles) integrated with the absorber, has the maximum enhanced efficiency. The longitudinal fins increase the heat transfer area without significantly affecting the turbulence of the flow, while the transverse perforated baffles contribute to an increase of the time for the water to stay within the flat-box collector, thus increasing water temperature. Experimental assessment shows that the proposed design achieves a worthy increase in the water temperature compared to the ambient temperature. In concerning to photovoltaic (PV) module, measurements show that the temperature of the integrated PV module is higher than the temperature of the separate PV module at limited water flow of 500 mL/min. Consequently, the integrated solar module produces a reduced voltage and a reduced current. Indeed, for the limited water flow, the temperature of the absorber remains high, resulting in some heat being transferred from the absorber to the PV module and aggravated performance. In contrast, the performance of integrated PV module has been slightly improved at water flow of 1200 mL/min due to the reduction of PV module temperature. As a result, the integrated flat-box PVT systems have a critical value of water flow to improve the performance of the PV module.</p>