The past two decades have seen a surge in applications of concentrated solar power (CSP) technology. The generation of solar-fuels, such as hydrogen, via CSP-thermal receiver/reactor technology has progressed from large scale demonstration to preliminary commercial venture. Solar receiver/reactors vary widely, and one of the distinguishing characteristics between reactors is the way in which reactants are introduced into the high-temperature reaction environment. Here, we focus on gravity-driven feeding of solid-particle reactants via hoppers and metering splines which can be employed for solar-thermochemical dissociation of metal oxides during continuous or batch processing. This relatively simple method can provide consistent and uniform reactant flow with high durability and low maintenance. We present experiments and analysis of gravity feeding of solid particles for CSP applications, focusing on the case study of 1-5 mu m ZnO powder at mass flow rates of 0-2 g/s. ZnO powder feeding is facilitated by adding vibration to the hopper followed by metering past a rotating spline, and delivered via gravity to an ultra-high temperature reaction cavity comprised of inclined alumina tile reaction surfaces. This paper will address hopper and spline design, feed rate characterization and modeling, particle residence time, and the effect of moisture and hopper vibration on the effective delivery of ZnO powder to the thermochemical reactor. (C) 2014 Elsevier B.V. All rights reserved.