Abstract:
Heat produced in solar thermal collectors is of low grade which can not be effectively recovered using conventional Rankine cycle systems. Organic Rankine cycle (ORC) is a suitable candidate for low grade heat energy resources. ORC exploits organic fluids operating the cycle at low temperatures. A detailed model of a saturated solar ORC system, using evacuated flat plate photovoltaic thermal collector as a direct vapor generator, is presented in this work. Simulation study is performed for five working fluids to investigate the performance of the system under different pressure ratios and 3 different solar collector configurations (Simple flat plate collector (FPC), Flat plate photovoltaic-thermal (FPV-T) collector, Evacuated flat plate photovoltaic-thermal (EFPV-T) collector). Simulation results revealed that Rankine cycle efficiency and system’s thermal efficiency increases when pressure ratio of the cycle is increased while collector thermal efficiency was decreasing with increasing pressure ratio. Results for the 3 collector configurations showed a drop in system performance in case of FPV-T collector configuration while it significantly enhanced in EFPV-T collector configuration. In EFPV-T collector configuration, fluid R600 obtained a maximum net work output and Rankine cycle efficiency of 556.4W and 12.44% respectively. Simulation results for system overall performance revealed that fluid R245fa exhibited the maximum system overall power output of 76.81 W/m2 and overall electrical efficiency of 8.24%, followed by R601 with system overall power output of 75.97 W/m2 and overall electrical efficiency of 8.13%,in case of EFPV-T collector configuration at 3.5 pressure ratio. However, high global warming potential of R245fa and high flammability of R601 makes it less attractive.
