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Thermal energy constitutes up to 90% of global energy budget, centering on heat conversion, transmission, and storage; therefore, the technology for harvesting solar energy worth to be developed. One of them is the concentrated solar power (CSP) solar towers where suntracking heliostats reflect solar radiation to the top of a tower where the receiver is located. The great advantage of CSP over other renewable energy sources is that energy storage is feasible, particularly when the heat transfer fluid (HTF) is also used as thermal energy storage (TES) material which is the case of solid particles. A lot of development efforts are under way for achieving commercial direct solar solid-particle systems. Solid particle systems for transferring high temperature thermal energy are purposed for increasing the efficiency of these systems when converting heat into electric power. This review recapitulates the concept of these systems taking into account the main receiver designs, particle conveyance, particle storage systems and components, the heat exchanger, and the main challenges that must be overcome to split this technology as a commercial one, especially from the materials availability point of view. This review summarizes the actual status of the use of solid particles for TES and as HTF for CSP Tower, and condenses all the available information and classifies them considering the main functional parts and remarking the current research in each part as well as the future challenging issues.

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Current concentrated solar power (CSP) plants that operate at the highest temperature use molten salts as both heat transfer fluid (HTF) and thermal energy storage (TES) medium. Molten salts can reach up to 565°C before becoming chemically unstable and highly corrosive. This is one of the higher weaknesses of the technology. Solid particles have been proposed to overcome current working temperature limits, since the particle media can be stable for temperatures close to 1000°C. This work presents a review of solid particles candidates to be used as HTF and TES in CSP plants in open receivers. In addition, the interactions between solid particles with major system components are described in this review, for example, with TES system or heat exchanger. The parameters and properties of solid particles are identified from the material science point of view explaining their nature and the relation to the power plant efficiency and lifetime durability. Finally, future development is proposed; such as material selection according to each specific design, materials characterization, or durability test.

The use of solid particles as heat transfer fluid (HTF) presents a great potential to overcome drawbacks addressed in commercial Concentrated Solar Power (CSP) plants. The solid particles thermal energy storage (TES) system allows achieving both high thermal performance at high temperature and low cost from the material perspective. The conversion efficiency of CSP solid particles-based systems at high temperatures strongly depends on the optical properties and thermophysical properties of materials used both as HTF and as storage medium. The present study is aimed to provide more experimental data and evidences of the potential in using particulate solids for CSP application. The solar absorptance and the specific heat capacity of silicon carbide (SiC), silica sand (SiO2), and hematite (Fe2O3) are studied after different aging times at 750ºC and 900ºC. The solar absorptance slightly increases over the aging process except for the silica sand, which decreases its absorptance in the first 100 hours, reaching a plateau. After the aging treatment, the specific heat capacity is increased for both SiC and silica sand. However, for the iron oxide the specific heat capacity is lower after aging. The black silicon carbide SiC is proven to be the best option to be used up to 900ºC as it shows the highest solar absorptance (96%) and the highest heat storage capacity.