Multi-objective optimization of an integrated ocean thermal energy conversion system

Abstract

Low carbon, stability, and great capacity are the advantages of ocean thermal energy (OTE). Inadequate thermodynamics and exergoeconomic performances of ocean thermal energy power generation, however, impede its large-scaled commercial application. In that case, an integrated power generation, refrigeration, and desalination ocean thermal energy conversion (OTEC) system, where the deep cold seawater is reused, has been proposed to simultaneously produce the aforementioned diverse materials to cater the energy demands of remote tropical islands. Further, a reference point-based fast nondominated sorting genetic algorithm III (NSGA-III) is employed where the exergetic efficiency and levelized cost of energy (LCoE) are selected as the objective functions to obtain the optimal thermodynamics and exergoeconomic performances. The results display that a net output power of 4.36 kW, refrigeration capacity of 67.22 kW, and freshwater production of 13.31 t/d can be achieved when the flow rate of power subsystem is 1.0 kg/s. Moreover, compared to the single OTEC plant with an LCoE of 3.56 $/kWh, the integrated system's LCoE is only 0.31 $/kWh. Furthermore, the optimization result indicates that the ranges of the exergetic efficiency and LCoE are 10.93 %–40.56 %, and 0.091 $/(kWh) to 0.443 $/(kWh), respectively. Finally, decision-makers can choose any solution on the pareto frontier as operation values depending on specific preferences and criteria.