Economic Potential of Solar Thermal Power Plants With Direct Steam Generation Compared to HTF Plants

The direct steam generation (DSG) in parabolic trough collectors is a promising option to improve the mature parabolic trough solar thermal power plant technology of the Solar Energy Generating Systems (SEGS) in California. According to previous studies [1–3], the cost reduction of the DSG process compared to the SEGS technology is expected to be 8 to 25%. All these studies were more or less preliminary since they lacked detailed information on the design of collector fields, absorber tubes required for steam temperatures higher than 400°C and power blocks adapted to the specific needs of the direct steam generation. To bridge this gap, a detailed system analysis was performed within the German R&D project DIVA. Power blocks and collector fields were designed for four different capacities (5, 10, 50 and 100 MW_el) and different live steam parameters. The live steam temperature was varied between saturation temperature and 500°C, and live steam pressures of 40, 64 and 100 bar were investigated. To assess the different cases, detailed yield analyses of the overall system were performed using hourly data for the direct normal irradiation and the ambient temperature for typical years. Based on these results the levelized costs of electricity were determined for all cases and compared to a reference system using synthetic oil as heat transfer fluid (HTF). This paper focuses on two main project findings. First, the 50 MW_el DSG system parameter comparisons are presented. Second, the detailed comparison between a DSG and a SEGS-like 100 MW_el system is given. The main result of the investigation is that the benefit of the DSG process depends on the project site and can reach an 11% reduction of the levelized electricity cost (LEC).