Comparative study of supercritical CO2 brayton cycles for solar towers plants in arid climates: Design and off-design performance

Abstract

Concentrated Solar Power plants offer significant potential for sustainable energy generation, but their efficiency is often constrained by extreme ambient conditions and limited water resources in arid climates. This study examines the design and off-design performance of simple and recompression supercritical CO₂ Brayton cycles across various power scales, focusing on their integration into CSP tower plants in Morocco. The objective is to evaluate the impact of scaling on cycle efficiency, turbomachinery design, compare the performance of both cycles and identify optimal parameters to enhance performance in challenging environments. A detailed parametric sensitivity study of both cycle configurations was conducted to determine the optimal total recuperator conductance for improving cycle efficiency. For model validation, the results were compared with the National Renewable Energy Laboratory model. The solar field design was developed using the System Advisor Model at large scale. Off-design conditions were analyzed to assess the effects of varying ambient conditions and heat transfer fluid temperatures on cycle performance. The design analysis demonstrates that scaling up significantly improves thermal efficiency for both cycle configurations. The study identified optimal recuperator conductance values for simple and recompression cycle, leading to thermal efficiencies of 40.1 % and 45 %, respectively. Validation against the SAM model showed strong agreement, with relative errors under 3 %. Solar field design results indicate that the recompression cycle requires 12 % less heliostat field area than the simple cycle. Additionally, off-design analysis revealed that the simple cycle is more adaptable to arid climates, maintaining similar efficiency as recompression cycle at higher ambient temperatures.