Mid and low-temperature solar–coal hybridization mechanism and validation

• A new mechanism to reveal the improved efficiency in a solar-hybrid system was given.
• A case study was taken on a 200 MW coal-fired power plant hybridized with solar heat.
• The simulation results have a good agreement with the theoretical values.
• The theoretical improved efficiency can be considered as a reliable criterion.

A higher solar-to-electricity conversion efficiency was one of the major advantages of the solar-fossil hybrid systems, compared to the solar-only power plants. In this paper, a new mechanism to reveal the reasons for the improved solar-to-electricity efficiency in a solar-hybrid power plant was given. A correlation was built to describe the main influencing factors of its thermodynamic performances, including higher collector efficiency, higher turbine internal efficiency and upgraded energy level of the mid and low-temperature solar heat. This proposed mechanism can be used to integrate solar–coal hybridization system effectively. A case study was taken as the typical 200 MW coal-fired power plant hybridized with solar heat at approximately 300 °C, where the solar heat was used to preheat the feed water before entering the boiler. Furthermore, simulation results of this mid and low-temperature solar-hybridization system was conducted to prove the proposed mechanism. It is expected that the theoretical values have a good agreement with the simulation ones. The results obtained indicate that why development of mid and low-temperature solar–coal hybridization technology may provide a promising direction to efficient utilization of low-grade solar thermal energy, and provide the direction to enhance system performances of this kind of solar–coal hybrid power plants.