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Abstract The potential to improve the performance of molten salt solar power tower system (SPT) is explored through the proposal of CO 2 -based binary mixture cycle in the present study. The feasibility of using xenon and butane as the additives to the S-CO 2 cycle are discussed from the perspective of thermodynamic analysis. The detail parametric study is performed to reveal the effects of crucial parameters on the performance of 4 system configurations. Furthermore, the systematic comparison is conducted for 4 cycle layouts adopting CO 2 /xenon, CO 2 and CO 2 /butane separately to illustrate the mechanism of performance improvement of SPT system coupled to CO 2 -based binary mixture cycle. The optimal performance of the SPT system is also demonstrated. Finally, the best performance system layout and suitable additives are recommended. The results indicate the following issues. Adding xenon into S-CO 2 cycle can obviously improve the overall thermal efficiency and exergy efficiency. While the effects of butane as an additive are converse. The inter-cooling CO 2 /xenon cycle is recommended as the most suitable layout coupled to the SPT system, and the exergy efficiency is 1.18%∼1.32% higher than that of the SPT system with S-CO 2 inter-cooling cycle. Detail exergy loss fraction distribution illustrates that the receiver is the highest exergy loss part and followed by the heliostat field, and butane as an additive is beneficial to reduce the receiver exergy loss for its smaller temperature difference. The study can provide a novel way to improve the SPT system performance and give a clue to the addition of CO 2 -based binary mixture in power cycles particularly for the application of SPT system. Highlights • Improvement on SPT performance is explored via using CO 2 -based mixture cycle. • Effects of key parameters on SPT with various CO 2 -based mixture cycle are analyzed. • Systematic comparison of different system layouts is performed. • Optimal additive and cycle configuration are recommended for SPT. [ABSTRACT FROM AUTHOR]

• Effects of key parameters on performance of CO 2 -based mixture cycles are revealed. • Comprehensive performance evaluation method is proposed based on η exe, SPT - w -Δ T MH. • Trade-off relations for 3 performance metrics are found based on Pareto fronts. • Optimal cycle configuration, operating parameters and additive are recommended. This study provides an exploration on improving the performance of solar power tower (SPT) plant via integrating with the CO 2 -based mixture Brayton cycle, and proposes a comprehensive comparison method. The effects of the crucial parameters on the SPT system are firstly revealed. Then, a comprehensive evaluation method is proposed based on 3 performance metrics including exergy efficiency, specific work and temperature difference of the main-heater, which are used to assess the thermodynamic performance and the compatibility between the thermal storage system and power cycle. Finally, the trade-off relationships of these metrics are found. The optimal layout, additive and operating parameters are also pointed out based on the comparative results to meet different design requirements. The findings show that the effects of crucial parameters on the performance of SPT system are not monotonous and individual criterion cannot comprehensively evaluate the system performance. Using xenon as an additive can yield excellent performance with higher exergy efficiency and better compatibility between cycle and thermal storage system than the CO 2 alone. While the ability to generate specific work is decreased to 105–112 kW·kg−1 with xenon-added that compares to the inter-cooling S-CO 2 cycle (121–130 kW·kg−1). When the exergy efficiency is required higher than 33%, the inter-cooling CO 2 /xenon cycle is the primarily recommended layout for its large specific work and good compatibility between the thermal storage system and cycle. The findings provide a novel way to improve the efficiency of SPT system as well as the compatibility between the cycle and thermal storage system. [ABSTRACT FROM AUTHOR]

In this perspective paper, the present status and development tendency of concentrating solar power (CSP) are analyzed from two aspects: (1) Potential pathways to efficient CSP through improving operation temperature to above 700 °C; (2) Technologies for efficient solar collection, thermal storage, and power generation at >700 °C. Based on the analyses, barriers on the way to the high-temperature CSP are summarized. They are: (1) the lack of methodology for heliostat design and field layout optimization, (2) significant performance degradations of solar-thermal conversion, heat storage and transfer in receiver and thermal energy storage due to high temperature, (3) the lack of suitable supercritical CO 2 (S–CO 2) Brayton cycle for CSP and mature design methods for S–CO 2 components. To overcome these issues, perspectives on following three aspects are proposed. Firstly, optimization approaches for optimal heliostat size and layout, and game-changing techniques for heliostat structure design should be brainstormed. Secondly, receivers and thermal storage devices designed through efficiency-improving approaches and fabricated by durable materials should be developed to maintain efficient and reliable operation. Thirdly, the developments of novel S–CO 2 cycle and corresponding key components are eagerly desired to achieve efficient thermal-electric conversion. Perspectives from this paper would present possible approaches to efficient CSP. • Present status and perspectives of concentrating solar power are analyzed. • Approaches to optimal heliostat size, structure, and layout shall be brainstormed. • Efficient high-temperature receivers and heat storage devices shall be developed. • Developments of novel S–CO 2 cycle and its key components are eagerly desired. [ABSTRACT FROM AUTHOR]