Thermo-economic assessment of an innovative power cycle for medium-temperature concentrated solar power plants

• Propane hybrid Rankine–Brayton (HRB) cycle proposed for parabolic-trough CSP plants. • Standardized annual techno-economic comparison with HRB–isobutane, steam Rankine, ORC–toluene and sCO 2 Brayton cycles. • HRB–propane delivers similar annual output but ∼1.3 % higher revenue than a state-of-the-art steam Rankine CSP plant. • HRB–propane cuts steam Rankine power-block cost by 9.8–28.6 % and LCOE by 1.2–4 %. • HRB–propane matches ORC–toluene profitability with lower pressure ratios and non-vacuum condensation. Medium-temperature parabolic-trough concentrated solar power (CSP) plants still rely mainly on superheated steam-Rankine cycles, which limit efficiency improvements and cost reductions. This study proposes and evaluates a propane-based hybrid Rankine–Brayton (HRB) power cycle as an alternative for CSP plants operating below 400 °C and benchmarks it against steam-Rankine, organic Rankine (toluene), supercritical CO 2 recompression Brayton and HRB-isobutane cycles. A two-stage assessment is performed. First, a non-standardized parametric analysis identifies efficiency optima under identical heat-source conditions. Second, a standardized comparison fixes the solar field, thermal energy storage (TES), and total design-point heat-exchanger size across the cycles; a genetic algorithm optimizes their distribution among components to maximize net power without relying on component-cost models. Annual simulations are performed using hourly meteorological and electricity-price data for Seville, with revenue-maximizing dispatch. Results show that HRB–propane achieves a similar annual energy yield to the steam-Rankine baseline while delivering 1.3 % higher revenue and reducing power-block costs by 9.8–28.6 %, thereby lowering levelized cost of energy (LCOE) by 1.2–4 %. Compared with ORC–toluene, HRB–propane offers similar profitability with lower pressure ratios and above-atmospheric condensation, reducing air-ingress risk and avoiding working-fluid vent losses associated with vacuum operation. These findings suggest that propane-based HRB cycles can improve the techno-economic performance of CSP plants below 400 °C, supporting their consideration for next-generation solar-thermal systems.