A multi objective optimization of CO₂-mixture based power cycles for concentrating solar power applications

This study presents a multi-objective optimization framework for CO₂-mixture based power cycles in Gen2 concentrating solar power applications, targeting 550 °C and 50 °C maximum and minimum cycle temperatures. A unified computational approach integrates 14 dopants with 5 cycle configurations (Simple Recuperated, Precompression, Recompression, Partial Cooling, and Recompression with Intercooling) using multi-objective controlled elitist genetic algorithms to simultaneously optimize thermal efficiency and primary heat exchanger temperature difference as surrogates for solar field and thermal energy storage costs. The methodology enables seamless evaluation of both supercritical and transcritical cycles through pressure–temperature phase envelope integration, revealing that transcritical CO₂-mixtures consistently outperform supercritical configurations for both pure CO₂ and CO₂-mixtures. The thermodynamical analysis shows that cycle complexity does not guarantee efficiency gains when CO₂-mixtures are used, as simple layouts can outperform complex configurations in thermal efficiency while complex layouts primarily benefit from temperature difference improvements in the primary heat exchanger up to 80 °C when CO₂-mixtures are used. Multi-criteria decision making analysis incorporating weighted thermal efficiency (60 %), temperature difference (20 %), and power block costs (20 %) identifies 66 % CO₂-34 % SO₂ mixture in Recompression with Intercooling layout as the most optimal, achieving 43 % thermal efficiency, 211 °C temperature difference, and 923 $/kWe power block costs that is below the critical economic viability threshold for Gen2 power blocks. Additional comparative analysis between CO₂-mixture and pure CO₂ based cycles investigating the utilization of additional temperature differences through primary heat exchanger offers further advantages in reducing the power block costs for recompression-type cycles when CO₂-mixtures are used, demonstrating power block costs as low as 766 $/kWe.