Effects of geometrical parameters of a dish concentrator on the optical performance of a cavity receiver in a solar dish-Stirling system

Abstract

Dish-Stirling concentrated solar power (DS-CSP) system is a complex system for solar energy-thermal-electric conversion. The dish concentrator and cavity receiver are optical devices for collecting the solar energy in DS-CSP system; to determine the geometric parameters of dish concentrator is one of the important steps for design and development of DS-CSP system, because it directly affects the optical performance of the cavity receiver. In this paper, the effects of the geometric parameters of a dish concentrator including aperture radius, focal length, unfilled radius, and fan-shaped unfilled angle on optical performance (ie, optical efficiency and flux distribution) of a cavity receiver were studied. Furthermore, the influence of the receiver-window radius of the cavity receiver and solar direct normal irradiance is also investigated. The cavity receiver is a novel structure that is equipped with a reflecting cone at bottom of the cavity to increases the optical efficiency of the cavity receiver. Moreover, a 2-dimensional ray-tracking program is developed to simulate the sunlight transmission path in DS-CSP system, for helping understanding the effects mechanism of above parameters on optical performance of the cavity receiver. The analysis indicates that the optical efficiency of the cavity receiver with and without the reflecting cone is 89.88% and 85.70%, respectively, and former significantly increased 4.18% for 38 kW XEM-Dish system. The uniformity factor of the flux distribution on the absorber surface decreases with the decreases of the rim angle of the dish concentrator, but the optical efficiency of the cavity receiver increases with the decreases of the rim angle and the increase amplitude becomes smaller and smaller when the rim angle range from 30° to 75°, So the optical efficiency and uniformity factor are conflicting performance index. Moreover, the unfilled radius has small effect on the optical efficiency, while the fan-shaped unfilled angle and direct normal irradiance both not affect the optical efficiency. In addition, reducing the receiver-window radius can improve the optical efficiency, but the effect is limited. This work could provide reference for design and optimization of the dish concentrator and establishing the foundation for further research on optical-to-thermal energy conversion.