Nonimaging optics

Nonimaging optics (also called anidolic optics) is the branch of optics concerned with the optimal transfer of light radiation between a source and a target. Unlike traditional imaging optics, the techniques involved do not attempt to form an of the source; instead an optimized optical system for optimal radiative transfer from a source to a target is desired. The two design problems that nonimaging optics solves better than imaging optics are: solar energy concentration: maximizing the amount of energy applied to a receiver, typically a solar cell or a thermal receiver illumination: controlling the distribution of light, typically so it is "evenly" spread over some areas and completely blocked from other areas Typical variables to be optimized at the target include the total radiant flux, the angular distribution of optical radiation, and the spatial distribution of optical radiation. These variables on the target side of the optical system often must be optimized while simultaneously considering the collection efficiency of the optical system at the source. For a given concentration, nonimaging optics provide the widest possible acceptance angles and, therefore, are the most appropriate for use in solar concentration as, for example, in concentrated photovoltaics. When compared to "traditional" imaging optics (such as parabolic reflectors or fresnel lenses), the main advantages of nonimaging optics for concentrating solar energy are: wider acceptance angles resulting in higher tolerances (and therefore higher efficiencies) for: less precise tracking imperfectly manufactured optics imperfectly assembled components movements of the system due to wind finite stiffness of the supporting structure deformation due to aging capture of circumsolar radiation other imperfections in the system higher solar concentrations smaller solar cells (in concentrated photovoltaics) higher temperatures (in concentrated solar thermal) lower thermal losses (in concentrated solar thermal) widen the applications of concentrated solar power, for example to solar lasers possibility of a uniform illumination of the receiver improve reliability and efficiency of the solar cells (in concentrated photovoltaics) improve heat transfer (in concentrated solar thermal) design flexibility: different kinds of optics with different geometries can be tailored for different applications Also, for low concentrations, the very wide acceptance angles of nonimaging optics can avoid solar tracking altogether or limit it to a few positions a year.