Achieving a stable equilibrium between produced power and consumed power remains a critical challenge in present-day power systems, especially with the developing incorporation of renewable energy sources, such as solar photo-voltaic (SPV) systems. This study exhibits a graphical method-based D-Decomposition approach to design a controller with Proportional-Integral controller with Derivative Filter (PIDF) for load frequency control (LFC) single area. Design of LFC via the proposed approach also extends to a two-area power system, which includes both a SPV system and a thermal reheat power plant.