Off-design modeling of radial turbines and system-level optimization for transcritical CO2-based mixture power cycles in parabolic trough CSP plants

Transcritical CO 2 -based mixture power cycles have shown promising potential for concentrated solar power (CSP) applications due to their improved thermodynamic performance and operational flexibility. However, the off-design behavior of radial turbines and their impact on system-level performance under variable solar conditions require further investigation. This study conducts off-design modeling and system-level optimization of a regenerative transcritical CO 2 -based mixture power cycle for parabolic trough CSP plants by developing a one-dimensional radial turbine model coupled with a system-level cycle simulation to predict turbine isentropic efficiency under varying operating conditions. Four working fluids, including pure CO 2 and CO 2 /R32 mixtures with mass fractions of 70/30, 50/50, and 30/70, are investigated, and the effects of working-fluid composition, turbine operating conditions, and off-design performance under representative seasonal scenarios are analyzed. The results indicate that CO 2 /R32 mixtures can enhance system performance compared with pure CO 2 under CSP operating conditions, with the CO 2 /R32 (30/70 wt%) mixture achieving the highest daily electricity generation efficiency on the autumn equinox and the highest daily electricity generation on the summer solstice. Through the coupled turbine and system optimization, the net power output is increased by 27.90–33.39% compared with non-optimized conditions. • Radial turbine model applies to transcritical CO 2 and CO 2 /R32 mixtures. • Systematic analysis covers turbine size, performance, and off-design conditions. • System-component optimization boosts net power output by 27.90–33.39%. • CO 2 /R32 (30/70 wt%) system peaks power at summer solstice, efficiency at autumn equinox.