Energy and Exergy Analysis of a Solar Dish Stirling Heat Engine with Bottoming Organic Rankine Cycle

Abstract

Effective utilization of solar thermal energy is one of the thrust full areas of research for a sustainable future. Stirling engines are a promising technology which is widely used to produce kW level electric power from solar energy using parabolic dish concentrators. However, due to design imperfections, typical Stirling engines approximately have 51% heat loss. This energy can be utilized for additional power generation via coupling an organic Rankine cycle (ORC) with a waste heat recovery unit. The previous investigations shown a 41.5% overall efficiency of combined Stirling-ORC systems and adding ORC to Stirling cycle can improve power output and efficiency by 4% and 8%, respectively. However, these systems have not yet been coupled with solar thermal energy, and its real-time feasibility has to be evaluated energetically and exergetically. In the present investigation, a typical solar parabolic dish system is considered as a heat source to the Stirling heat engine. The effect of real-time solar irradiation and absorber temperature on performance of solar Stirling-ORC system has been quantified. It was found that 48% of the total energy lost by the Stirling cycle can be recovered by combining it with ORC. With the intention of design emphasis, a component wise exergy destruction rate is evaluated and illustrated. Further, a selection criterion for working fluids of ORC is also evolved.