• Off-design performance of sCO 2 and CO 2 mixture cycles. • Detailed design and off-design models of recuperator and air cooler/condenser. • Overall solar tower power plant techno-economic performance optimization. • The optimum cooler/condenser air design temperature is not exceeded 96.8% of hours. • Optimum air-cooled cooler/condenser approach temperature is the lowest one (5°C) The next generation of concentrated solar power plants is expected to utilize supercritical CO 2 cycles as power block. These systems can be further enhanced by using dopants to increase the critical temperature and move towards transcritical cycles, allowing for higher power cycle efficiency and lower cost. Air-cooled condensers, usually used in new plants, have significant impact on power cycle and plant performance. This work aims at investigating the influence of air-cooled cooler/condenser design parameters on the technoeconomic performance of solar tower plant with sCO 2 and CO 2 mixture power cycles. Simple recuperated cycles using sCO 2 and CO 2 mixture with silicon tetrachloride (SiCl 4 ) are modeled at design and off-design conditions and integrated in the solar tower power plant model. The optimum cooler/condenser design parameters are determined for Seville, Spain by varying minimum cycle temperature, cooler/condenser approach temperature, solar multiple, and thermal energy storage size. Results show that CO 2 mixture cycles at the design point have on average 3.9 and 4 percentage points higher thermal and electric efficiency than an sCO 2 one. Moving to the annual overall analysis, the optimum ambient air design temperature, for both the solutions, is 35°C (a value 5°C below the maximum and not exceeded 96.8% of hours during the year), while the optimum cooler/condenser approach temperature is the minimum considered, equal to 5°C. At the same time, CO 2 mixture cycle has 8.4% lower levelized cost of electricity compared to the sCO 2 one at both the base and optimum solar multiple, lower thermal energy storage size and is less sensitive to the ambient air design temperature changes.
Naumov et al. (Sat,) studied this question.