The objective of this study is to achieve a higher solar-to-electricity conversion efficiency through solar fossil hybrid thermal power systems compared to a solar-only power plant. The study reveals the thermodynamic details for the improved solar-to-electricity efficiency in a solar hybrid power plant. A correlation was established to describe the main factors influencing the thermodynamic performances, including higher collector efficiency, higher turbine efficiency and upgraded energy level of the moderate-temperature solar heat. This proposed mechanism can be applied to effectively integrate solar and fossil-fired energy in a power system. The studies took typical fossil-fired power plants to hybridize with solar heat in three approaches: preheating the feed water before it entering the boiler for coal-fired system; heating for generation of saturate steam or superheated steam in gas-fired combined cycle. The results indicate that the moderate-temperature solar and fossil hybridization technology can provide a promising direction for efficient utilization of low-grade solar heat. (C) 2017 Elsevier Ltd. All rights reserved.