Simplified optical model, aiming strategy and partial defocusing strategy for solar Fresnel collectors

This paper presents the development of a simplified analytical optical model, an analysis of aiming strategies and a defocusing strategy for a Fresnel solar collector. The model aims to represent the main components of solar concentration on a Fresnel collector when considering independent rotation on each mirror in order compute the solar radiance flux on the absorber. The model is validated with data from a reference Ray-Tracing software and from experimental data. The model is then used to evaluate three aiming proposals with regards to solar radiance flux over the absorber. Data from the optical model and mirror inclinations proposed by the aiming strategies are used to implement a partial defocusing strategy for Fresnel collectors. The main purpose of this analysis is to assess the possible gains that individual manipulation of each collector mirror can bring to the process. It is shown that all the analyzed aiming methods present similar performances regrading the optical efficiency aspect. Thus, the use of the simplest solar aiming method presents itself as a very effective solution. Results also show the possibility to implement partial defocusing on Fresnel collectors, allowing the use of focus as a manipulated variable for control.