Feasibility research on a hybrid solar tower system using steam and molten salt as heat transfer fluid

As a high solar concentration technology, the solar tower power (STP) system is an appealing approach to generate high-grade thermal energy and achieve high thermal-to-electric efficiency. In this study, the authors notice the solar flux distribution characteristic of the central receiver and combine the advantages of lower average operation temperature of the direct steam generation (DSG) loop and higher efficiency of the molten salt (MS) loop. A hybrid solar tower system that involves steam and MS as the heat transfer fluids is proposed for improving the thermal efficiency of STP systems. The receiver of the hybrid system is divided into two sections, which are respectively designed for the MS and DSG loop, namely MS-DSG system. By comparing the DSG-MS system to the traditional system, the DSG-MS system demonstrates significant heat loss reduction of 31.8 GWh in Lhasa and 34.5 GWh in Tonopah, and the corresponding electricity outputs are improved by 6.22% and 5.82% with a MS receiver panel number of 8. The steam outlet quality of the DSG loop is insensitive to the overall performance of the systems. It is indicated that the steam quality can be adjusted for ensuring two-phase heat transfer stability and safe operation of the receiver. Moreover, the hybrid system also gives a flexible adjustment of thermal energy storage capacity by optimizing receiver panel number for different heat transfer fluid loop.