Search

The latest generation of concentrated solar power (CSP) systems uses supercritical carbon dioxide (s-CO2) as the working fluid in a high-performance recompression Brayton cycle (RcBC), whose off-design performance under different environmental conditions has yet to be fully explored. This study presents a model developed using the Engineering Equation Solver (EES) and System Advisor Model (SAM) to evaluate the operation of two solar-driven s-CO2 RcBCs over a year, considering meteorological conditions in northern Chile. Under design conditions, the power plant outputs a net power of 25 M W with a first-law efficiency of 48.3%. An exergy analysis reveals that the high-temperature recuperator contributes the most to the exergy destruction under nominal conditions. However, the yearly simulation shows that the gas cooler's exergy destruction increases at high ambient temperatures, as does the turbine's during off-design operation. The proposed cycle widens the operational range, offering a higher flexibility and synergistic turndown strategy by throttling the mass flow. The proposed cycle's seasonal first-law efficiency of 39% outweighs the literature cycle's 29%. When coupled to a thermal energy storage system, the proposed cycle's capacity factor could reach 93.45%, compared to the value 76.45% reported for the cycle configuration taken from the literature. [ABSTRACT FROM AUTHOR]

Exergy is a thermodynamic property that represents the quantification of the maximum useful work that can be extracted from a system interacting with the environment. Regarding solar radiation, radiative exergy has been a matter of study over the last 60 years where the main models applied describe the radiation as undiluted and diluted. The exergy of solar radiation is useful in the preliminary assessment of the performance of solar technologies, since the efficiency of the system depends directly on this value. The present paper describes a review of the main models reported in the literature considering these two approaches, analysing the main differences between the models and the main assumptions applied. A comparative analysis is carried out for the models of diluted and undiluted radiation, where the behaviour of every expression is discussed in detail. For the undiluted expressions, the behaviour of every model within a temperature range is analysed. For black-body radiation at a source temperature of 6000 K, the model proposed by Jeter determines an exergy factor of 0.96, while Spanner, Petela, Press and Badescu calculate a value of 0.93. Parrott's model obtains a value of 0.99, which is above the value for Carnot efficiency. The diluted exergy expressions were evaluated according to wavelength and temperature range, where the trend in each comparison was that the exergy calculated from Karlsson, Candau and Petela was always the lowest. This result is attributed to the fact that these expressions consider the spectral entropy of the medium the radiation passes through. Finally, some new approaches are analysed which consider empirical correlations based on meteorological variables to model the exergy of solar radiation. [ABSTRACT FROM AUTHOR]

Thermal energy storage (TES) systems can be used for recovering industrial waste heat and increasing energy efficiency, especially when coupled to batch thermal processes. Stratified water thermal storage tanks are the preferred technology for low-temperature applications, while molten salts are commonly used in medium and high-temperature applications with large storage capacities. No clear consensus exists on the appropriate TES technology for different industrial demands characteristics and their respective heat supply systems for medium and high-temperature applications. The present study analyzes several industrial sectors and their thermal processes, analyzing their temperature ranges, heat demands, and available TES technologies, which are classified by their operational conditions. The study presents two novel indicators for a preliminar compatibility assessment between TES and industrial sectors: a temperature compatibility indicator and exergy efficiency for TES and thermal processes. The results show that low and medium-temperature applications such as food, chemical, or textile industries exhibit high compatibilities with water (over 64%), high-temperature PCM (over 61%), and solid-state TES (100%), whereas molten salts and chemical looping demonstrate lower compatibility (below 24%). The exergy analysis for industrial cases shows that a lower temperature operating range for a TES induces low exergy efficiency. Regarding this scenario, high-temperature cPCM reaches efficiencies of over 44% for mid and high-temperature processes. Conversely, solid-state TES emerges as the most viable option for integration in high-temperature industries, exhibiting an efficiency of 62% with minimal exergy losses. The indicators defined in this study can be used for an early evaluation of TES integration in industrial applications, thus promoting emerging technologies selection through a quantitative comparison of the compatibility metrics. • Assessment of the potential for using TES in industrial heat supply systems. • Definition of compatibility metrics for TES based on temperature and exergy losses. • TES sizing and evaluation of compatibility indicators in industrial plant scenarios. • Applications below 300 °C exhibit several compatible TES, such as Water or PCM. • Solid-state TES shows the best results for high-temperature industrial heat demand. [ABSTRACT FROM AUTHOR]