The distance temperature map as method to analyze the optical properties of Fresnel lenses and their interaction with multi-junction solar cells

Abstract

The optical efficiency of Fresnel lens based solar concentrators varies with the temperature of the Fresnel lens. The dependency of any quantity of interest (e.g. optical efficiency) on Fresnel lens temperature can be visualized by 2d color plots that simultaneously show it as a function of the distance between solar cell and Fresnel lens and as a function of Fresnel lens temperature. This visualization, which is called DTmap, strongly facilitates the analysis of the thermal behavior of a Fresnel lens and the optimization of module height. Based on DTmaps we reveal and discuss serveral details of the thermal behavior of silicone on glass (SOG) Fresnel lenses. In addition, the DTmap is shown for the efficiency of a system consisting of a Fresnel lens and a lattice matched three-junction and a four-junction solar cell. The results demonstrate that the interaction of the concentrator optics and the solar cell is not trivial and may also be studied using DTmaps.

The role of draft facets in temperature effects in silicone-on-glass Fresnel lens applications

“…It can be seen that the strongest temperature dependence of loss mechanisms can be found in the change in projected, unusable draft area (Figure 2, c). In consequence, CPV systems may show their optimum behavior some degree Celsius above the curing temperature [2], if e.g. a secondary optics or the like is used to compensate the geometrical spillage in operational conditions.…”

“…For this, the findings in [2] are extended by the discussion of the optical loss caused by the draft area with respect to a change in operational temperature and geometrical Fresnel lens design parameters. This study is based on simulations.…”

“…In this study, Fresnel lenses (Grooves-Facing-Short-Conjugate lenses (GFSC), see [1] and Fig. 2) with constant prism heights are discussed, for which a critical temperature dependency is reported (see literature [1][2][3][4][5] in [2]), involving a change of focal length with change in temperature and a defocusing effect due to different CTEs of the involved materials silicone and glass. Experimental validation of the involved models can be found in [3].…”