Solar powered cascade system for sustainable deep-freezing and power generation - exergoeconomic evaluation and multi-objective optimization for tropical regions

Abstract

The global initiative to decarbonize the refrigeration sector aims to provide cooling energy while reducing CO2 emissions. In India, the majority of urban industrial refrigeration systems are powered by fossil fuel based electricity, which increases consumption of fossil fuel and it contributes to global warming. To address this issue, two unique solar thermal operated cooling configurations, the Simple Cascade System (SCS) and the Recuperative Cascade System (RCS), were designed to fulfil urban industrial cooling energy demands. The surplus electricity generated by these systems is transferred to the on-site grid. Ethane, n-butane, and R1233zd(E) were selected as working fluids due to their low global warming potential (GWP). Among them, the RCS system with R1233zd(E) demonstrated the highest energy and exergy performance, benefiting from its superior thermodynamic properties and effective utilization of internal heat. In New Delhi, the R1233zd(E) operated RCS system achieved the highest cooling and electricity outputs at 54 kW and 20 kW, respectively. Although the R1233zd(E) operated RCS system incurred higher costs, the performance improvement outweighed the increase in cost. To assess the system sustainability in terms of exergy utilisation, a new indicator sustainability index (SI) was developed and established with values of 1.1. Increasing the evaporator temperature enhanced the system performance but also raised total plant cost, while raising the system condenser temperature had the opposite effect. The multi-objective optimization assessment for RCS configuration indicated an optimal objective value of an energy utilization ratio (EUR) of 0.16, an exergy efficiency of 8.7 %, and a capital cost of 20 $/h.