Multi-objective optimization of a solar-driven polygeneration system based on CO2 working fluid.

• A solar-driven polygeneration unit with CO 2 as the working fluid is investigated. • Initial optimization in steady-state conditions and secondary dynamical analysis. • The payback period is found to be around 6.4 years and the total efficiency is 55%. • The use of an extra ORC can be used for enhancing electricity production. • The exergy efficiency with ORC is found 23.63%, while without 23.37%. The object of this study is the investigation of polygeneration plants utilizing solar energy in order to produce power products on the scale of a few MW. Parabolic trough collectors are used in order to exploit solar irradiation and to provide the generated heat to the polygeneration/trigeneration cycle in a high-temperature range (500–570 °C). The plants under consideration additionally consist of a storage tank, a Brayton cycle with s-CO 2 , a LiBr-H 2 O absorption chiller and also the installation of a suitable thermodynamic organic Rankine cycle (ORC) cycle is examined in order to utilize waste heat for further power generation. The systems are first investigated for operation under steady-state conditions and then for dynamic conditions on an annual basis. Based on the final annual results of the plants, the plant in which ORC was not used shows annual electrical, exergy and energy efficiencies equal to 18.33%, 23.37% and 54.91% respectively, while the plant in which ORC was used similarly shows 19.05%, 23.63% and 49.00%. According to economic analysis, the payback period was found at 6.37 years without ORC and 6.51 years with ORC. Taking into account the operational and techno-economic results of the plants it can be concluded that the plants produce satisfactory energy products ensuring also the economic viability of the investment. [ABSTRACT FROM AUTHOR]