Thermal Energy Storage Versus Biomass Hybridization for Firm Solar Power: Annual Off-Design and Uncertainty-Based Design of a Concentrating Solar sCO2 Combined Cycle in Tropical Climates

High direct normal irradiation and a large residual stream from oil-palm processing make the Colombian Caribbean an attractive site for firm renewable power, yet the balance between thermal energy storage (TES) and biomass backup for supercritical CO2 (sCO2) plants in tropical climates remains unresolved. This work evaluates a 120 MWe solar tower plant based on a re-heated recompression sCO2 Brayton cycle bottomed by a dual-pressure organic Rankine cycle (DORC) and hybridized with palm biomass. A Python 3.12/CoolProp 8.0 design model supplies temperature-dependent performance maps to an 8760 h quasi-steady dispatch layer with dry-cooling ambient coupling and part-load derating. Solar multiple, storage capacity, biomass capacity fraction and turbine inlet temperature are sized simultaneously with NSGA-II against levelized cost of electricity (LCOE) and capacity factor (CF), subject to a regional feedstock availability of 210 kt/yr, and the selected design is propagated through Monte Carlo simulation and Sobol analysis; biomass heat supplies 36–43% of the delivered electricity across the selected designs. The combined cycle attains 51.25% thermal efficiency at the 720 °C salt limit, while the cost-optimal designs deliver 47.9–49.6% at the turbine inlet temperatures selected, of which the bottoming cycle contributes 2.13 percentage points. The feedstock constraint is active along the Pareto front except at its fully firm corner: optimal designs saturate the biomass budget and reach firmness with solar multiples of 2.9–3.5 and 7–10 h of storage. Capacity factor rises from 0.888 to 0.998 for an LCOE penalty of 2.6% (108.5 to 111.3 USD/MWh), while the levelized cost spans P50 = 107 to P90 = 122 USD/MWh and the discount rate alone accounts for 78% of its variance. Near-baseload operation is therefore inexpensive for this class of plant, and financing terms rather than component costs govern its economic risk.