<p>This paper presents a theoretical investigation of the combined effect of the nonlinear thermal absorption coefficient and artificial roughness of an absorbent tube on the dynamics of a conventional photovoltaic thermal (PVT) water panel. The roughness and the nonlinear absorption coefficient are localized inside the tubes of the absorbent plate and in the photovoltaic (PV) module, respectively. The analytical expressions for the temperature on each layer of our system are determined from the energy balance equation. The simulations of the analytical expressions obtained are performed in the MATLAB software environment by considering the contributions of roughness, nonlinearity, and their combined effects. The results of our numerical investigations under standard test conditions reveal that the combined effect leads to a greater temperature reduction in the PV module than when roughness and nonlinearity are considered separately. Furthermore, the combined effect induces a reduction in the maximum temperature of the PV module by about 9°C, leading to an improvement of about 0.39% in electrical efficiency.</p>