On-site optical characterization of large-scale solar collectors through ray-tracing optimization

Abstract

[eng] In order to increase the trust and willingness to invest in concentrating solar collectors, an accurate labeling andcertification process is of utmost importance. Today's collector testing standards specify methods for assessingthe thermal performance of most types of fluid heating solar collectors. However, they do not provide an ap-plicable testing procedure for obtaining the incidence angle modifier of large-scale line-focusing collectors. Suchcollectors need to be tested directly in the field, where optical characterization by conventional methods, such asfactorization, fails. This study presents a new approach to obtain the incidence angle modifier by fitting ray-tracing curves to the measured optical efficiency data set. The new method has been tested on a fixed mirrorsolar concentrator with a mobile focus. Prior to this study, 49 experimental data points have been obtained forthe optical efficiency after measuring for four testing days according to the ISO 9806 rules. These experimentaldata points served as a basis for the fitting procedure to validate the ray-tracing model. Stable optimized so-lutions of the collector's optical parameters have been determined within a reasonable computation time scale.From a comparison of the optimized solution to a simplified ray-tracing simulation, it was seen that the weightedroot-mean-square error was improved by 27.7%. In conclusion, the proposed procedure overcomes practicalhurdles and has many advantages over conventional methods.