Hybridisation of solar and geothermal energy in both subcritical and supercritical Organic Rankine Cycles

A supercritical Organic Rankine Cycle (ORC) is renowned for higher conversion efficiency than the conventional ORC due to a better thermal match 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 geo-thermal 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 super-critical ORC to explore the benefit from the potential synergies of such a hybrid platform. The figure of merit analysis indicates that the hybrid plant produces a maximum of 15% and 19% 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.