To improve the frequency stability in an interconnected power system including renewable energy sources, the control actions need to be more robust and efficient. For this reason, this study proposes a new optimised proportional-integral-derivative (PID) controller coordinated with redox flow batteries (RFBs) for the enhancement of load frequency control (LFC) of power system concerning large penetration of wind power generation. The PID controller parameters were obtained using a recently developed meta-heuristic optimisation algorithm named Grey Wolf optimiser. To show the effectiveness of the proposed control strategy, the interconnected two-area IEE Japan East 107-bus-30-machine power system was investigated for the simulation. The system dynamic responses were obtained considering load change in area-1 and large wind farm integration in area-2. A comparative study of performance of the proposed strategy with some well-known optimisation techniques was performed. Furthermore, the sensitivity analysis of the proposed controller was also examined by varying the penetration range of the integrated wind farm. Dynamic responses obtained from the simulation satisfy the LFC requirements. In addition, the results reveal that the frequency control concept-based optimised PID controller coordinated with the RFB will enhance the frequency stability in terms of settling time, peak undershoot, and peak overshoot.