Development and testing of high concentration flat-plate Fresnel lenses

Abstract

In the work, stages of designing, optimizing, manufacturing and testing the circular flat-plate Fresnel lenses (FLs) for photovoltaic modules with multi-junction solar cells (SCs) are presented. A mathematical model based on ray tracing has been developed for optimizing lenses design parameters and calculating their optical-power characteristics (OPCs). In searching the optimum combination of the lens aperture, its focal distance and refracting profile parameters, the optimization criterion was the maximum of the average sunlight concentration at high optical efficiency in the focal spot of minimum size. Analysis of OPCs of circular Fresnel lenses with conical (the generatrix of surface is a straight line) and curvilinear (the generatrix of surface is a curved line) refracting surfaces has been carried out. Fresnel lens specimens were fabricated and a control of their profile parameters has been done. Experimental lens OPCs have been obtained with use of newly developed optical test bench. A degree of the effect of the light flux and Fresnel lens geometrical imperfections on validity of the experimental data interpretation has been determined. To establish the lens optical efficiency values at standard irradiance conditions, the correction of the calculation model was done. Also, the effect of temperature on the lens optical efficiency is studied.

Improved Concentration Capabilities of Flat-Plate Fresnel Lenses

“…The results of the mathematical simulation of characteristics of circular FLs with flat operating facets show [16] that, to rise their power efficiency, it is necessary to decrease the profile tooth pitches, and, hence, to increase their number at a preset lens size. The positive effect is achieved, in this case, due to more precise approximation of the initial plane-convex lens surface by the great number of sections of the operating facet conical surfaces (facet generating lines are straight ones).…”

“…Investigation of the effect of the profile pitch on the average concentration ratio K av in the focal spot (interception coefficient K int =0.95) of FLs with straight and curved generating lines of operating facets have shown that FLs with curved generating lines of operating facets conserve a relatively high concentrating capability in the whole investigated range of the profile pitch variation [16]. The comparison was carried out for combined "silicon-on-glass" FL with the side dimension…”