High-temperature, point-focus, pressurised gas-phase solar receivers: a comprehensive review

Gas-phase solar receivers use atmospheric or pressurised gas as their heat transfer fluid (HTF). The ideal gas-phase receiver would provide high thermal efficiency and high HTF outlet temperature with low pressure drop and low capital cost. In practice, these four objectives are hard to achieve simultaneously since it is difficult to (cost-effectively) overcome the intrinsically poor heat transfer performance between the solid absorber and the gaseous HTF. Thus, this review provides an in-depth look at the recent progress towards solving this challenge of pressurised gas-phase receivers to identify the remaining knowledge/research gaps. In general, gas-phase receivers can be classified as direct or indirect solar absorbers and by the type of heat transfer enhancement (HTE) employed to address the poor absorber-to-HTF heat transfer rate. The present review suggests the receiver designs that show the most promise for further improvement from each of the active, passive and compound HTE methods. This study also finds that there is a need for more proof-of-concept tests for these receiver designs, since the number of studies which include real prototypes operating under real weather conditions is limited. Based on a review of successful prototyping research, this review suggests proper prototyping procedures for high-temperature receivers. Overall, the authors believe the present study presents an up-to-date, comprehensive review of the progress on gas-phase receivers, along with some meaningful, specific guidance on the necessary next steps in their development. This is significant because gas-phase receivers represent the best near-term solution for pushing solar systems to higher temperatures, enabling integration with advanced/combined cycles and solar thermochemical reactors with endothermic chemical reactions at high temperature (e.g. mineral processes and solar fuels).