Comprehending thermal system limits is crucial for enhancing and optimizing energy systems. Finite-time thermodynamics reveals a relationship between efficiency and maximum power output. This study explores the theoretical boundaries of direct steam generation in concentrated solar power plants. We use a finite-time approach, considering heat transfer irreversibilities from the heat source, including linear and radiative resistance models, alongside classical thermodynamics. We compare these findings with the estimated efficiency based on design operating conditions. The proposed solar power plant employs an optically optimized linear Fresnel reflector field with direct steam generation, linked to two 10 MW Rankine cycles featuring two and three steam extractions. Meticulous power block optimization minimizes entropy generation within the cycle to maximize exergy efficiency. Concurrently, solar field optimization aims to surpass the FRESDEMO solar field's intercept factor. Our results indicate that the estimated efficiency aligns closely with the theoretical maximum predicted by finite-time thermodynamics, especially the radiative resistance model, with the lowest relative error. This insight offers a valuable tool for designing highly efficient future solar power plants.