CONCENTRATION LIMIT OF SOLAR FRESNEL LENSES

摘要

Fresnel optics decouple global and local shapes, which adds an additional degree of freedom in design. Tlus allows to tailor the global shape of a F'resnel lens to meet the Abbe-sine- condition. On the other hand, F'resnel optics may suffer in general from either losses or dilution because the etendues of incoming and outgoing radiation do not always match. We show that tailoring the lens to meet the Abbe-sine-condition leads to a spherical global shape centered in the absorber, and for this particular shape the etendues do meet. A practical approximation of such a lens can be designed with a continuous upper surface. The biggest technical issue are chromatic aberrations due to dispersion. Dispersion is minimized by minimum deviation design. Tlus conflicts with the Abbe-sine-condition. We show the performances of such lenses by ray-tracing