• System-level technoeconomic analysis of CO2-mixture cycles with variable operation for Gen2 CSP. • Lower efficiency cycles with high ΔT beat high efficiency cycles in annual LCOE analysis. • CO2-COS in recompression with intercooling achieves minimum LCOE of 103. 6 /MWh. • Translated off-design principles into SAM format with hybrid pressure operation modes. • Variable operation outperforms constant operation by 3–4 /MWh across all 13 cycles. This study evaluates the thermodynamic optimization and system-level annual performance of CO 2 -mixture power cycles for Gen2 concentrating solar power plants under variable off-design operation. Starting from multi-objective optimization that identified Pareto-optimal solutions across five cycle configurations and twelve dopant options, thirteen cycles are selected to explore two strategic questions: whether compromise solutions between thermal efficiency and primary heat exchanger temperature difference yield better LCOE, and how to optimally utilize additional temperature gains from CO 2 -mixtures. For cycles offering temperature differences above 177°C, parallel “adjusted” and “normalized” configurations test whether additional temperature gains should reduce thermal storage costs or primary heat exchanger sizing. A key methodological contribution involves translating existing off-design operational principles into System Advisor Model’s user-defined power cycle format while employing a hybrid operational strategy combining fixed and sliding pressure modes. Variable operation consistently outperforms constant operation by 3–4 /MWh. Annual simulations for a 100 MW plant in Seville demonstrate that 53%CO 2 -47%COS mixture in recompression with intercooling achieves the minimum LCOE of 103. 6 /MWh, outperforming higher-efficiency CO 2 -mixture and pure CO 2 cycles. A precompression cycle with 55%CO 2 -45%COS mixture achieves the lowest total capital cost and second-lowest LCOE of 104. 2 /MWh despite moderate thermal efficiency through reduced thermal storage costs, suggesting extreme temperature gains can compensate for lower efficiency. While the trade-off between thermal storage and primary heat exchanger cost reduction remains inconclusive for Gen2 systems, with “adjusted” configurations experiencing higher annual molten salt pumping power consumption than “normalized” configurations of the same cycles, it presents promising potential for Gen3 applications.
Mutlu et al. (Mon,) studied this question.