This work develops a method for the optimal design of a solar-assisted combined heat and power (CHP) system, in which the solar thermal central receiver subsystem and the steam power cycle subsystem are integrated to meet the real-time requirements of steam and power from production process. A mathematical model with the objectives of minimum total annual cost (TAC) and environmental impact (EI) is formulated to optimize the configuration and the size of the major equipment units, and schedule the dynamic operation of entire system. This model accounts for the hourly variability of Direct Normal Irradiance (DNI) and the electricity load in a typical day, as well as the power losses caused by the partial load operation of steam turbines. Based on the presented model, the optimum level of solar capacity is determined through a comprehensive analysis considering the trade-off between TAC and EI of the system. At last, a case study is illustrated and the results are elaborated to demonstrate that the desired system configuration can be obtained by application of the proposed model.