Exergoeconomic and multi-objective optimization of a solar thermochemical hydrogen production plant with heat recovery

A solar hydrogen production plant based on a four-step copper-chlorine (Cu-Cl) thermochemical cycle is presented and analyzed in this paper. The integrated system includes a pressurized solar power tower, gas turbine unit, phase change material (PCM) for thermal energy storage (TES), Cu-Cl cycle, regenerative steam Rankine cycle (SRC), and a heat recovery unit. A predictive model is developed for energy, exergy, and exergo-economic analyses of the proposed system. A parametric study is also conducted to investigate the effect of major parameters on the system performance. The system is optimized with a non-dominated sorting genetic algorithm-II (NSGA-II) considering exergy efficiency and product cost per unit exergy as the two objective functions. The results indicate that the energy and exergy efficiencies of the overall system are 48.2% and 45%, respectively, while the total product cost per unit of exergy is found to be $10.97/GJ. The integrated solar system produces hydrogen, electricity, and steam at a rate of 0.1 kg/s, 50.49 MW, and 13.93 kg/s, respectively. Pareto solutions for multi-objective optimization indicate that the optimal design point of the system has an exergy efficiency and total product cost per unit of exergy of 50.1% and $11.94/GJ, respectively.