Experimental evaluation of carbon-coated sand as solar-absorbing and thermal energy storage media for concentrated solar power applications

• Sand particles coated with graphite, carbon black and glucose were synthesised. • Original and fluidised (w/ and w/o radiation) coated samples were characterised. • Graphite samples showed the best homogeneity and coating stability up to 1000 °C. • Enhancements up to 45% were obtained for photothermal conversion efficiency. • Coating sand particles improves industrial-scale fluidised bed efficiency by 50% Innovative systems using solid particles for solar energy capture, heat transfer, and thermal energy storage are emerging in next-generation concentrating solar power plants. This study investigates silica sand enhancement using novel coatings of graphite, carbon black, and glucose, evaluating their thermal stability, optical properties and durability under operational conditions. The coated samples were subjected to fluidisation and radiation treatments to simulate real-world conditions. Thermogravimetric analysis, specific heat capacity measurements, optical absorptance evaluation, and photothermal conversion efficiency testing were performed. The results show that graphite-coated sand exhibits superior optical and thermal performance, achieving a 44.9 % increase in photothermal conversion efficiency compared to uncoated sand. While carbon black coatings displayed higher absorptance, their heterogeneity compromised long-term effectiveness. Glucose coatings degraded above 280 °C, rendering them unsuitable. An industrial-scale fluidised bed model was used to assess the impact of the observed enhanced particle absorptance on the resulting performance of these systems, revealing thermal efficiency improvements of 50 %. These findings confirm that graphite-coated sand is a viable solution for high-temperature concentrating solar power plants applications, offering stable performance, enhanced light-to-heat conversion and improved energy efficiency in large-scale implementations.