Fresnel lens solar energy

Internationally, researchers have developed large Fresnel lenses with the aim of using them in solar concentrator systems. Fresnel lenses are planarized concentrating optics that are lightweight and relatively inexpensive; they can be either spot-focused or line-focused. They are typically made from acrylic or other transparent plastics, though glass versions also exist, and are primarily employed in concentrated photovoltaic power-generation systems.

From the 1970s through the 1990s, China conducted research and development on Fresnel lenses for solar energy applications. Some researchers employed compression molding to produce large-area, flexible, transparent plastic Fresnel lenses, while others used composite-forming tools to fabricate 1.5-meter-diameter point-focusing Fresnel lenses; however, the results in both cases were less than satisfactory. More recently, compression molding has been used to manufacture linear glass Fresnel lenses, but the precision remains inadequate and further improvements are needed. In addition, two novel solar concentrators based on the principle of total internal reflection have been proposed; although they have not yet been put into practical use, they offer valuable insights. One is the optical-fiber concentrator, which consists of an optical-fiber lens connected to optical fibers. Sunlight is focused by the fiber lens and then transmitted via the fibers to the point of application. The other is the fluorescent concentrator, which is essentially a transparent plate—typically made of acrylic—doped with fluorescent pigments. This plate absorbs the portion of sunlight whose wavelengths match the fluorescence absorption band and subsequently emits fluorescence at longer wavelengths corresponding to the emission band. Due to the refractive-index difference between the plate and the surrounding medium, the emitted fluorescence undergoes total internal reflection within the plate and is guided toward the edge surface. The concentration ratio depends on the ratio of the plate’s area to its edge area and can readily reach 10 to 100. Moreover, such plates can absorb incident light from various directions as well as scattered light, eliminating the need for solar tracking.

Key words:

Fresnel lens,Solar energy