This study focuses on the numerical simulation of heat transfer in a photovoltaic (PV) panel installed in Aparecida do Taboado (−20.086289, −51.115985), Brazil. Experimental data from an operational PV system are used to validate the simulation, showing good agreement with the results. A key novelty of this work is the introduction of an innovative serpentine heat exchanger design integrated on the rear side of the PV panel. This design features arranged square channels where water flows along a serpentine path, ensuring direct and extensive contact with the panel’s backside. The addition of the heat exchanger itself, but without any water flow, has a strong impact on the numerical results, increasing the maximum temperature, reducing the minimum, and also increasing the temperature gradient. The heat exchanger operating with a water volume flow of 150 ml/min reduces the maximum and minimum temperatures more effectively, and it may be an alternative to improve the PV’s efficiency. This cooling strategy not only boosts the energy conversion efficiency of the PV module but also may improve its long-term performance and durability compared to configurations without the heat exchanger. All simulations were conducted using Ansys Fluent, incorporating real-world data on solar irradiance, ambient temperature, wind speed, and humidity.