This article presents automatic generation control (AGC) of an interconnected two-area hybrid thermal system with additional power generation from dish-Stirling solar thermal system (DSTS) and wind turbine system (WTS). Each area is equipped with Integral (I), Proportional-Integral (PI), and Proportional-Integral-Derivative (PID) as secondary controllers to regulate power output of thermal system and maintain the power balance. This facilitates maintaining the frequency close to its nominal value. Biogeography-based optimization (BBO) technique is used for simultaneous optimization of controller parameters. System dynamics are evaluated with step load perturbation and random load perturbation in Area1. The performance of PID is found improved in comparison to I and PI controller in terms of settling time, peak deviation and magnitude of oscillation. Investigation shows that BBO optimized PID controller parameters obtained at nominal conditions are robust enough and not necessary to optimize for wide changes in renewable energy sources, area capacity ratio, system loading, and inertia constant (H). Thus, integration of DSTS and WTS for AGC of interconnected system is safely attributed. (C) 2016 Elsevier Ltd. All rights reserved.