Efficient Fresnel lens for solar concentration

The development effort in optical components for optimally concentrating solar energy has thus far emphasized reflecting elements, such as cylindrical and compound parabolic mirrors. In this paper we consider transmission elements, particularly a new design for an efficient linear Fresnel lens capable of high concentration for a given acceptance angle. The predicted performance of the lens is comparable to that of the “ideal” reflector, while providing greater reliability at a lower cost.     

Convex fresnel lens with large grooves

The concentration capability of linear Fresnel lenses is limited mainly by coma and chromatic aberrations and by the width of the individual grooves of the lenses. We consider new designs for these lenses in which the concentration is almost independent of the groove's size, and which are free of coma at the edge of the acceptance field. Specifically, a concentration factor as high as 34 is achieved for monochromatic radiation coming from an acceptance angle of ± 1°.     

Solar thermal engine systems using two stage concentrators

The overall efficiency of a system including a solar paraboloidal concentrator augmented by a new type of nonimaging second stage concentrator (shaped like the bell of a trumpet) and coupled to a heat engine is investigated. Typically, a relative increase of 10 per cent in system efficiency was found due to the second stage.     

Two stage linear Fresnel lenses

A new design of a second stage reflective element, which is closely related to the earlier trumpet configuration, is presented. The implementation for linear Fresnel lenses is derived, leading to high solar concentration with both convex and flat lenses.     

A fixed Fresnel lens with tracking collector

The application of a wide angle concentrating Fresnel lens to a linear solar energy system, in which the optical concentration is stationary while the absorber follows the locus of best foci, is investigated. The two substantial direction possibilities of the linear axis, east-west and polar, are compared to each other. It is shown that such a concentrator may operate about six hours a day throughout the year with an average effective concentration exceeding 10. Specifically, a polar installation, including a fixed lens and a fixed assembly of separate absorbers behind it, may enable sufficient concentration for residential heating and airconditioning without any moving parts.