Abstract
An analytical method to calculate and optimize the performance of a multi-mirror combined solar dish collector is proposed in this work. It is based on the method of directly calculating the optical efficiency of a reflecting point, which can consider the influence of many factors. The distribution of the reflected solar intensity is obtained by the convolution of the actual solar intensity distribution and Gaussian distribution of the optical error. Then, the optical efficiency for a single mirror is calculated through integration over the total area of the mirror, and the method is validated by the SolTrace code. It is a rather quick method that reduces the amount of calculation and keeps high accuracy. The heat loss per unit area for the cavity receiver is assumed to be constant at a definite operation temperature for performance analysis and optimization. Taking a 62.25 m2 combined dish system with 249 square spherical mirrors as an example, the effects of system focal length, open radius of receiver, optical error, and focal length of the mirror on the system intercept factor and efficiency are studied. An optimization model is developed for maximizing the annual average net thermal efficiency. If the mirrors used have the same focal length for reducing the manufacture cost, when the optical error is 2 mrad, the net thermal efficiency and the intercept factor of the optimized system are 85.87% and 98.60%, respectively, while the concentration ratio is about 2000.
Highlights
Accepted: 26 January 2022Concentrated solar thermal systems are among the most cost-effective ways to replace fossil fuel
In the case of an optical error of 2 mrad, the net thermal efficiency of the system is reduced to 85.87%, with an optimal uniform mirror focal length of 8 m and a concentration ratio of about 2000
Each mirror is regarded as a heliostat; the present method for the combined solar dish system is rather similar to that of the solar tower system, but the receiver is a cavity with a circular opening, unlike the rectangular opening of the solar tower system
Summary
Accepted: 26 January 2022Concentrated solar thermal systems are among the most cost-effective ways to replace fossil fuel. The parabolic solar dish system is a highly valued concentrated solar thermal system because of its high concentration ratio and efficiency at high temperatures [1]. Both the thermal and the optical efficiency of parabolic dish collectors are the highest among all concentrators [2]. They use parabolic mirrors to concentrate solar rays on the focal point where their energy can be converted and transported by a receiver [3]. A combination of small mirrors is generally used, which means that a number of small mirrors are fixed on the structure to let their center form a large paraboloid
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