Comparison of sCO2, CO2 mixture, and steam Rankine cycles for CSP with components sizing: implications for cost and flexibility

While all commercial concentrating solar power (CSP) plants with central receivers are equipped with the steam Rankine power cycle, supercritical CO2 (sCO2) cycles are seen as a promising advancement. They offer higher efficiencies and more compact turbomachinery at high temperatures compared to the steam Rankine cycle, however, sCO2 cycles face challenges related to high pressures and temperatures, which increase material demands and the mass and cost of heat exchangers. As the need for flexible electricity generation grows, the thermal inertia of the power block, linked to its metal mass, becomes increasingly important. This study examines and compares the component sizes, material usage, and economic and flexibility impacts of sCO2, CO2 mixtures, and steam Rankine cycles for commercial-scale CSP applications. All cycles are designed with the same thermal energy input, keeping the solar field and thermal storage constant. Heat exchanger designs, including primary heaters, recuperators, and air-cooled units, follow the ASME Code and are modeled using Aspen Exchanger Design & Rating. Since no commercial sCO2 turbines exist at this scale, turbine design parameters are estimated using a developed simplified approach. Results are compared with existing studies to assess component-level and system-level implications in terms of cost, performance, and flexibility.