The purpose of this paper is to investigate theoretically the performances of a photovoltaic-thermal solar collector by applying three different geometrical shapes of fluid circulation channels (circular tube, half tube and square tube) and using pure water and Ethylene glycol-water (EG-W) mixture as heat transfer fluids. The computational model developed is based on thermal balance equations. Predicted results show that half tube design provides best photovoltaic cooling effect and highest efficiency compared to others geometries. At 0.04kg/s mass flow rate, the use of half tube increases thermal efficiency by 1.17% and 2.6% compared to circular and square tubes respectively. Moreover, for the same comparison, an enhancement of 0.53% and 1.16% is obtained for electrical efficiency. It is found that the use of pure water as working fluid improves the thermal and electrical yields by 4.5% and 1.85% respectively referred to EG-W mixture. The thermal effect of using the both working fluids is investigated at different flow rate. It is found that EG-W mixture causes higher energy losses due to the pressure drop in comparison with water especially for high flow rate. Furthermore, the impact of photovoltaic/thermal collector design parameters on the electrical and thermal performances has been analyzed and discussed. (C) 2020 Elsevier Ltd. All rights reserved.