Energy, exergy, economic and environmental (4E) evaluation of a solar-integrated energy system at medium–high temperature using CO2 as the parabolic trough collector (PTC) working medium

Abstract

This paper proposes a solar-integrated energy system at medium–high temperature (i.e., working temperature >300 °C) for power generation, desalination, and sodium hydroxide (NaOH) production. The system consists of four subsystems, including parabolic trough collector (PTC), organic Rankine cycle (ORC), multi-effect distillation (MED), and electrodialysis. The PTC system uses CO2 gas as the working medium to obtain medium–high temperature heat sources. The electrodialysis system electrolyzes the brine to obtain NaOH and HCl, thus avoiding environmental pollution. Energy, exergy, economic and environmental analysis were adopted to evaluate the system's performance, and six critical parameters were investigated. The results showed that the system production of desalinated water, NaOH, and HCl was 106.75 kg/h, 10.61 kg/h, and 48.46 kg/h, respectively, when the direct normal irradiance was 500 W/m2. The net output power of the ORC and the power consumption of the electroanalysis system reached 23.07 kW and 5.00 kW, respectively. The power consumption of the PTC compressor was 8.01 kW. The exergy destruction of solar collector accounted for the most significant proportion, reaching 76.98%. The exergy efficiency of the system reached 12.42%. Among the six different ORC working mediums (R134a, R152a, R600, R600a, R717, and Pentane), Pentane performed the best in the integrated system, while R134a performed the worst. The annual income of the system could reach 27,645 $, with a simple payback period and payback period of 8.62 years and 10.12 years, respectively. The net present value could reach 1,103,722 $. The system could reduce CO2 emissions by 5.64 tons per year. The research in this paper contributes to understanding the overall characteristics of solar-integrated energy systems when using gaseous working mediums to achieve medium and high-temperature thermal storage. It provides a reference for the development of more efficient solar-integrated energy systems.