Edgar Martínez-Guerra

Mathematical Analysis of Nonimaging Fresnel Lenses Using Refractive and Total Internal Reflection Prisms for Sunlight Concentration

During the design of nonimaging Fresnel lenses, the reflectance losses at the refracting surfaces should be taken into account because, depending on the parameters of each prism, semiacceptance angle and output angle , these losses can decrease the total efficiency of the lens. On this subject, an analysis and comparison between a Fresnel lens composed only of refractive prisms and others with total internal reflection (TIR) prisms are presented and, using this information, a design method of hybrid Fresnel lenses composed of refractive and TIR prisms is proposed to reduce reflectance losses from the surface. The work presents the radiance profile and transmittance for a Fresnel lens of each type, to compare its advantages and disadvantages providing an alternative for the design and construction of nonimaging Fresnel lenses according to optical devices requirements.

Design of a segmented nonimaging Fresnel dome for nontracking solar collection

Abstract. The efficiency of sunlight collection systems is related to the optical element used as a collector. On this subject, the design of a nontracking solar collector that consists of a segmented nonimaging Fresnel dome is presented. It is formed by the conjunction of different zones for solar collection, where each one is a nonimaging Fresnel lens that collects a specific angular range (θin) of sunlight received in the northeast of Mexico, but the methodology presented can be easily extended to other geographic locations. The final design is a semistationary segmented collector with a 100-cm diameter and 50-cm focal length that needs a 180-deg rotation over the XY-plane in each equinox. The numerical simulations show that the nontracking segmented collector has a combined acceptance semiangle of θin=±105  deg with an average efficiency of over 67% from 9:00 to 18:00 h. The spatial and angular distributions of the sunlight collected are also included. This design has a collection area equal to that of a single nonimaging Fresnel lens with an acceptance semiangle of θin=±45  deg. These results are reproducible and provide valuable data for designing nontracking solar collectors based on nonimaging Fresnel lens.

Optimization design of nonimaging Fresnel lens using total internal reflection prisms for sunlight concentration

The efficiency in Fresnel lenses is affected by three principal sources: energy loss by absorption, chromatic dispersion and reflectance losses at refracting surfaces. On this subject, the design of nonimaging Fresnel lenses integrated by refractive and total internal reflection prisms is presented. This design method uses iterative calculations for design every prism and it selects the best option for avoid reflectance losses. A design and characterization of a Fresnel lens that takes chromatic aberration into account is shown, including a comparison with a nonimaging Fresnel lens composed only by refraction prisms is performed and with other integrated by only total internal reflection prisms. In addition, the study about how acceptance angle and the number of prisms affects the final transmittance of the lens is included.

Numerical analysis of lateral illumination lightpipes using elliptical grooves

Lightpipes are used for illumination in applications such as back-lighting or solar cell concentrators due to the high irradiance uniformity, but its optimal design requires several parameters. This work presents a procedure to design a square lightpipe to control the light-extraction on its lateral face using commercial LEDs placed symmetrically in the lightpipe frontal face. We propose the use of grooves using total internal reflection placed successively in the same face of extraction to control the area of emission. The LED area of emission is small compared with the illuminated area, and, as expected, the lateral face total power is attenuated. These grooves reduce the optical elements in the system and can control areas of illumination. A mathematical and numerical analysis are presented to determine the dependencies on the light-extraction.

Design of a segmented nonimaging Fresnel lens optimized for non-tracking solar collection

The success of solar systems, such as photovoltaic and sunlight illumination systems, is principally determined by the primary optical element used as collector. On this subject, the design of a segmented nonimaging Fresnel lens is presented; this collector is formed by the conjunction of different zones for solar collection, where every zone is made of a nonimaging Fresnel lens that collects a specific angular range of sunlight, according to the solar radiation of the northeast received in Mexico. Every collector section focus in a common area. The different zones are designed considering the apparent solar movement due to the daytime and the seasonal displacement over the year. The collector total performance is presented, including spatial and angular distribution. The collector presents an average performance over 80%, with an acceptance half-angle of 120°, and a collection area similar to that in a collector with 45° of acceptance half-angle.

Modeling of efficient light extraction in light-pipes through specular surfaces with elliptical and lineal front shapes

Extraction light in light-pipes with different specular surfaces was analyzed. In the analysis, the impact of the surface shape in all properties of the extracted light in order to obtain an efficient extraction and a uniform illumination using a LED as light source. Also, several parameters of the specular surface to obtain spatial uniformity inside the light-pipe are considered. In this case, the simulation was made for a rectangular lightpipe. One objective of this work is to compare how the front face shape of the specular surface can affect the extraction of light in the lateral face of the light-pipe, only straight and elliptical front faces were used in this work and the comparison between them at different tilts and lengths were made. The main purpose of the front face was extract the light uniformly at the lateral face and this was done by studying simulations on OpticStudio Zemax. The results show how the extraction length is lower in the elliptical front but its total power performs better than the line front.