Exergy and energy analysis of a regenerative organic Rankine cycle based on flat plate solar collectors

In current study, a low temperature organic Rankine cycle (ORC) based on flat plate solar collectors with storage tank is considered. Due to low cost applications, water at ambient pressure is used in both the tank and collectors. Also, the cooling is done by water in ambient temperature. Energy and exergy analysis is used to evaluate the performance of the system under various conditions to find the main sources of exergy destruction and the potential to improve them. Some parameters including exergetic efficiency, thermal efficiency, exergy destruction rate, fuel depletion ratio and irreversibility ratio are investigated. Exergy efficiency and exergy destruction ratio are calculated for the overall system according to the second law of thermodynamics based on daily efficiency. Exergy analysis of each sub-system leads to the choice of the optimum physical parameters for minimum local exergy destruction ratios. Four different working fluids are considered including R245fa, R134a, pentane and toluene to evaluate the system. Results show that the solar collector, thermal storage tank and the vapor generator are the main sources of exergy destruction respectively. Also a parametric study shows that there is an optimum daily exergy efficiency based on turbine inlet temperature. Under the same load, pentane has the best performance followed by R245fa, toluene and R134a. The corresponding daily exergy efficiencies are 24.08%, 22.53%, 22.09% and 21.76%.