A novel auto-cascade low-temperature solar Rankine cycle system for power generation

► We have proposed a novel auto-cascade low-temperature solar Rankine cycle (ALSRC) system. ► The exhaust steam of expander is utilized twice and reclaimed more effectively. ► The zeotropic mixture Isopentane/R245fa is employed in this system. ► The thermal efficiency of ALSRC system can be higher than that of SSLSRC system. ► The system parameters are investigated and the most important ones are found. A novel auto-cascade low-temperature solar Rankine cycle (ALSRC) system is proposed. Compared to the single stage low-temperature solar Rankine cycle (SSLSRC) system, the ALSRC system is different because it consists of two solar collectors, two expanders, a regenerator, and an internal heat exchanger (IHE). The working fluid for the ALSRC is the zeotropic mixture Isopentane/R245fa. The main advantages of the ALSRC system is that heat from the exhaust stream of the expanders are reclaimed twice, once using an IHE and another time using a regenerator. System parameters such as regeneration, mixture composition, the outlet temperature of the low temperature solar collector, and the inlet temperature of two expanders are investigated to determine their effects on thermal efficiency. Results showed that with a regenerator, the thermal efficiency of the ALSRC system using a mixture of 0.32 R245fa by mass was significantly higher than that of the SSLSRC system. It was determined that regeneration, the mixture composition, and the outlet temperature of the low temperature solar collector are all important factors that affect the system’s thermal efficiency.