Environmentally responsible steel-slag-based solid particles for highly efficient and durable solar selective absorptance and thermal storage

Concentrated solar power (CSP) is a green energy technology that efficiently harnesses solar energy. Solid particles constitute the key medium for solar photothermal conversion and storage. However, drawbacks such as high thermal radiation loss and poor high-temperature stability limit their application. This paper proposes solid particles based on steel slag for highly efficient and durable selective sunlight absorptance and thermal storage. Raw pellets are obtained via a simple extrusion and rolling process, and sinter them to derive solid particles. These particles exhibit excellent selective solar absorption characteristics and have good potential for efficient heat storage. The average solar absorption of the solid particles sintered at 1310 °C reaches 93.20%, and the emissivity at 700 °C is 80.25%. Furthermore, the specific heat and the thermal conductivity of wafer-like materials are 1.09 J/(g·K) and 2.92 W/(m·K), respectively. In addition, the solid particles are arranged for exhaustive and harsh high-temperature durability tests, and they exhibit an ultra-stable solar weighted absorptance of 93.25 ± 0.09% (mean ± standard deviation), excellent resistance to thermal shock, and superior abrasion resistance. Moreover, the low cost and simplicity of the process greatly enhance the scalability of steel-slag-based solid particles. In summary, by innovatively addressing the challenges faced by solid particles, such as high radiative heat loss, poor heat storage capacity, and high-temperature instability, this study accumulates an advantage in the competition with phase-change and thermochemical materials, and greatly improves the feasibility of using solid particles in large-scale applications.