Thermodynamic study of a novel combined heat and power system integrated with solar energy

Combined heat and power systems crucially require high efficiency and flexibility because of the high penetration level of intermittent renewable power. The efficiency and flexibility of traditional combined heat and power systems are limited by their heating-controlled operation mode. Therefore, a heat-power decoupling technique with high energy utilization efficiency and flexibility is necessary. In this study, a novel combined heat and power system integrated with solar energy is proposed. Detailed analytical models based on thermodynamics laws are developed, and a 330 MW unit is used as an example to assess the comprehensive thermodynamic performance and operational flexibility of the proposed system. Results show that the average net energy efficiency of the novel system during daytime and nighttime can reach 54.68% and 55.75%, respectively. Meanwhile, the average net exergy efficiency of the novel system during daytime and nighttime can reach 38.73% and 38.83%, i.e., an improvement of 2.43 and 2.59 percentage points, respectively, compared with the traditional combined heat and power system. The peak-shaving ability of 97.80 MW can be improved, and 295.35 tons of standard coal per day can be saved using the novel system compared with the traditional combined heat and power system under the average rated heating load. This study provides a promising approach for utilizing solar energy to enhance the efficiency and flexibility of combined heat and power plants.