Grid frequency stability has become a major issue due to abrupt integration of PV generation into conventional thermal grids. The reason is solar intermittency. This paper proposes an integrated Optimal Power Flow (OPF) and Automatic Generation Control (AGC) strategy employing a Fractional Order PID (FOPID) controller optimized using the Gazelle Optimization Algorithm (GOA). The suggested algorithm has been tested on the IEEE 30-bus system under hybrid thermal–solar operation. Simulation results reveal that the GOA–FOPID controller significantly enhances frequency regulation and system economy compared to traditional PID and other evolutionary algorithm. The proposed method achieves a 15–20% reduction in total generation cost ($511.9/h vs. $583.5/h), a 35–40% decrease in power loss (6.39 MW vs. 10.44 MW), and a 45–50% reduction in emission level (0.12 t/h vs. 0.26 t/h). Moreover, voltage deviation improves from 1.1153 p.u. to 0.4188 p.u., ensuring enhanced dynamic response with minimal overshoot and faster settling. These results confirm the superior adaptability and stability of the GOA–FOPID approach for frequency control in solar-integrated power systems.