In the realm of renewable energy, concentrated solar power (CSP) systems are at the forefront, offering a pathway to sustainable electricity generation, particularly when integrated into combined cycles. A standout innovation in this field is Direct Steam Generation (DSG), a technology that directly converts solar energy into steam. DSG’s departure from conventional CSP systems that rely on thermal oils makes it a significant change. This study compares two vital heat transfer fluids, the common Dowtherm A (a thermal oil) and the advanced DSG, to assess their efficiency and performance, particularly within integrated solar combined cycles (ISCCs). Here, our findings reveal that DSG outshines Dowtherm A in exergy efficiency, a vital metric for thermal system performance. This discovery challenges prior assumptions and underscores DSG’s potential to boost the overall efficiency of CSP systems. Significantly, the operational complexities associated with the need to pressurize thermal oil to prevent boiling at high temperatures, a drawback in Dowtherm A-based systems, are mitigated by DSG. The lower pressure drop in DSG systems makes them more efficient and cost-effective. In a broader context, our research contributes to the ongoing quest for optimal solar power plant performance. It highlights the critical role of heat transfer fluids in enhancing the efficiency and sustainability of integrated solar combined cycles. As renewable energy progresses, innovative technologies like DSG could revolutionize solar energy use, steering us toward a cleaner, more sustainable energy future. T hese insights are not limited to CSP alone; they have broader implications, potentially advancing renewable energy technologies across diverse applications and industries.