Wastewater treatment plants (WWTPs) are essential components of urban infrastructure, serving to improve water quality, reduce environmental hazards, and facilitate water reuse. However, these facilities are energy-intensive, with aeration and pumping processes representing the majority of electricity consumption. The increasing operational demands and reliance on centralized grids highlight the need for integrating sustainable energy solutions. This study aims to evaluate the feasibility of deploying a grid-connected photovoltaic (PV) system to partially supply electricity for a large-scale WWTP in Pakdasht, Iran. The research utilizes detailed three-dimensional energy-economic modeling and PV*SOL Premium simulations to capture site-specific climatic, operational, and electrical load conditions. A systematic analysis of electrical loads, panel layout, inverter configuration, and environmental factors was conducted to optimize system performance while maintaining continuous operational stability. The novelty of this work lies in its integration of module-level loss modeling, including mismatch, bypass diode, and soiling losses—into a comprehensive operational simulation framework. Despite previous studies on renewable energy in WWTPs, gaps remain in quantifying both spatial and temporal variability of PV system performance in large-scale facilities. Results indicate that a 3.63 MWp PV system can generate approximately 6.27 GWh annually, covering 28% of the plant’s total electrical demand. The system achieves a specific yield of 1,726 kWh/kWp and an annual performance ratio of 81.3%, demonstrating stable energy output across seasons.