A New Two-Foci V-Trough Concentrator for Small-Scale Linear Fresnel Reflectors

Abstract

We present the design of an original secondary cavity for use in Small-Scale Fresnel Reflectors in photovoltaic applications. The cavity is similar to the classical V-trough, but the primary reflector system is configured so that there are two focal points on the aperture. The rays coming from each side of the primary system reach the opposite side of the cavity, producing a non-symmetrical distribution of the irradiance. This modifies the acceptance half-angle and allows us to break the maximum limit for the concentration ratio of ideal symmetric concentrators. Our study is analytic, and we provide formulas for any number of reflections. Numerical simulations with a ray-tracing program based on MATLAB are included. We provide a comparison of optical concentration ratio, height and cost parameter between our system and two classical designs with a single focal point: the V-trough and the Compound Parabolic concentrators. This way, we verify that our design yields better concentration ratios while keeping the ray acceptance rate at one. Our solution proves to be better than both the classical one-focus V-trough and the Compound Parabolic concentrator. Specifically, the proposed solution is significantly better than the classical one-focus V-trough in optical concentration ratio, with an increase between 15.02 and 35.95%. As regards the compound parabolic concentrator, the optical concentration ratio is always slightly better (around 4%). The height of the cavity, however, is notably less in this design (around 54.33%).

Sawtooth V-Trough Cavity for Low-Concentration Photovoltaic Systems Based on Small-Scale Linear Fresnel Reflectors: Optimal Design, Verification, and Construction

“…Oprea et al [42] indicated that the optical efficiency could be estimated by a function of two parameters: the ray acceptance rate and the average number of reflections, n. The role this average n plays when calculating the irradiance losses is briefly recalled: in general [37], the fraction of the radiation incident on the aperture that is transmitted to the absorber needs to be multiplied by ρ n m , where ρ m is the reflectivity of the mirror. Pardellas et al [27] indicated that slight errors in the calculation of n are almost irrelevant to the final value of ρ n m (this is also verified herein).…”

“…A standard V-cavity was used in the design of a daylighting system based on optical fiber bundles and a small-scale linear Fresnel reflector [26]. Concentrated photovoltaic systems based on a small-scale Fresnel reflector have also used the standard V-trough cavity [27]. All these studies used a standard V-trough cavity.…”