摘要
A supercritical Organic Rankine Cycle (ORC) is renowned for higher conversion efficiency than the conventional ORC due to a better thermal match (i.e. reduced irreversibility) presented in the heat exchanger unit. This improved thermal match is a result of the obscured liquid-to-vapor boundary of the organic working fluid at supercritical states. Stand-alone solar thermal power generation and stand-alone geothermal power generation using a supercritical ORC have been widely investigated. However, the power generation capability of a single supercritical ORC using combined solar and geothermal energy has not been examined. This paper thus investigates the hybridisation of solar and geothermal energy in a supercritical ORC to explore the benefit from the potential synergies of such a hybrid platform. Its performances were also compared with those of a subcritical hybrid plant, stand-alone solar and geothermal plants. All simulations and modelling of the power cycles were carried out using process simulation package Aspen HYSYS. The performances of the hybrid plant were then assessed using technical analysis, economic analysis, and the figure of merit analysis. The results of the technical analysis show that thermodynamically, the hybrid plant using a supercritical ORC outperforms the hybrid plant using a subcritical ORC if at least 66% of its exergy input is met by solar energy (i.e. a solar exergy fraction of >66%), namely producing 4-17% more electricity using the same energy resources. Exergy analysis shows that with a solar exergy fraction of more than 66% the exergetic efficiency of the hybrid plant is about 27-34% for the supercritical hybrid plant and 23-32% for the subcritical hybrid plant. The figure of merit analysis indicates that the hybrid plant produces a maximum of 15% (using a subcritical ORC) and 19% (using a supercritical ORC) more annual electricity than the two stand-alone plants. Economically, the hybrid plant using the supercritical ORC has a solar-to-electricity cost of approximately 1.5-3.3% less than those of the subcritical scenario.