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• Cogeneration system proposal for a building in Pisa for sized and undersized modes. • Energy costs of the proposed system are evaluated and contrasted for Iran and Italy. • Proposed system payback period is obtained and analyzed for Iran and Italy by NPV. • For under-sized system, electricity cost is about 37% more than in sized system. • If natural gas price is taken the same as Iran, the payback period reduces by 6.4%. The objective of the present paper is sizing of a technically optimum and economically feasible cogeneration system to supply heating, cooling and electricity to a reference building in the city of Pisa, Italy, for different months of the year. This cogeneration system is proposed in two operational modes, sized and under-sized, so that the effect of natural gas and electricity consumption costs on the system design can be achieved. To this end, the amount of energy consumption and cost of various types of the proposed cogeneration systems based on reciprocating engines are computed and compared. Afterward, in the proposed systems, for understanding the effect of the costs of the energy carriers in different countries on the rate of payback period, a comparison is conducted on the payback period between Iran and Italy. In the end, a sensitivity analysis is performed in Iran and Italy to survey the effect of any change in the cost of investment, natural gas, and electricity on the payback period. The results indicated that although the costs of gas and electricity are comparatively lower, the payback period is longer for Iran, which can be blamed on Iran's higher discount rate (~50%). The results of sensitivity analysis showed that if the natural gas cost in Italy equals that of Iran, there would be a 6.4% reduction in the payback period and if the electricity cost consumption in Iran is taken equivalent to the cost of electricity in Italy, a decrease of 25% will appear in the payback period. [ABSTRACT FROM AUTHOR]

• Sizing and operation optimization of a hybrid energy plant. • Integration of life cycle assessment into optimization. • Non-linear life cycle inventory scaling of energy systems. • Estimation of the operational primary energy and cumulative energy demand. 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. [ABSTRACT FROM AUTHOR]