The article deals with the regulation of frequency comprising of interconnected dual area solar thermal system by employing PID and multi staged PID controller as secondary controller. A recently invented evolutionary algorithm called invasive weed optimization algorithm (IWOA) technique is used to tune the constraints of recommended controllers. To verify the supremacy of the controller a disturbance of 0.01 p.u. in control area-1 and a time delay of 0.7sec was introduced in both the areas. Investigation suggests that multi staged PID controller performs better in terms of settling time and magnitude of oscillation as compared to traditional PID controller. IWOA optimized multi staged PID controller attain the nominal values during large alteration in system condition and parameters.