A solar-aided coal-fired power system (SACFPS) model with five load conditions (100%, 85%, 75%, 50%, and 40%) was built based on thermodynamic and thermoeconomic theories. SACFPS is a combination of a parabolic trough solar power system and a 660 MW coal-fired generation plant. The solar contribution evaluation method was introduced into the model to calculate the generation share of the solar power system. Results show that solar contribution decreases after an initial increase as effective solar normal irradiation increases. Optimization strategies, adjusting heat transfer fluid flow rate, have been proposed to maintain solar contribution at a high level. Thus, SACFPS with five load conditions has been optimized. This study also establishes a generation revenue function to evaluate the economics of SACFPS. Income generation of SACFPS after optimization is significantly higher than that without optimization. (c) 2015 Elsevier Ltd. All rights reserved.