Optimization of a hybrid energy plant by integrating the cumulative energy demand

Abstract

This paper deals with the optimal design of a hybrid energy plant, which can include the following energy systems: solar thermal collector, photovoltaic panel, hybrid photovoltaic/thermal solar system, combined heat and power system, organic Rankine cycle, absorption chiller, air source heat pump, ground source heat pump and thermal energy storage. Three different configurations are analyzed. In the first configuration, the abovementioned systems are considered with the exception of the hybrid photovoltaic/thermal solar system and organic Rankine cycle. In the second configuration, a hybrid photovoltaic/thermal solar system is also included and in the third configuration the use of an organic Rankine cycle as the bottoming cycle of the combined heat and power system is evaluated. The optimization goal is to minimize the primary energy demanded throughout the manufacturing and operation phase of the hybrid energy plant. The challenge of non-linear life cycle inventory scaling of energy systems is also addressed. A tower located in northern Italy is selected as a case study and two different approaches are evaluated. The first approach consists of solving the sizing optimization by minimizing primary energy consumption only during the operation phase, while in the second approach primary energy consumption is minimized throughout the life cycle of the plant by integrating the life cycle assessment into the optimization process. The results show that, if life cycle assessment is integrated, the optimal sizes of plant components are different and the primary energy saving throughout the life cycle is always higher. With reference to the LCA integrated approach and compared to the first configuration, the use of a hybrid photovoltaic/thermal solar system instead of separate solar thermal collector and photovoltaic panels is more efficient and may allow a primary energy saving of about 4%. Furthermore, compared to a conventional plant, the primary energy saving achievable with the first configuration is approximately 14%, while the primary energy saving increases to about 17% for the second and third configurations.