Two-stage solar concentrators based on parabolic troughs: asymmetric versus symmetric designs

Abstract

While nonimaging concentrators can approach the thermodynamic limit of concentration, they generally suffer from poor compactness when designed for small acceptance angles, e.g., to capture direct solar irradiation. Symmetric two-stage systems utilizing an image-forming primary parabolic concentrator in tandem with a nonimaging secondary concentrator partially overcome this compactness problem, but their achievable concentration ratio is ultimately limited by the central obstruction caused by the secondary. Significant improvements can be realized by two-stage systems having asymmetric cross-sections, particularly for 2D line-focus trough designs. We therefore present a detailed analysis of two-stage line-focus asymmetric concentrators for flat receiver geometries and compare them to their symmetric counterparts. Exemplary designs are examined in terms of the key optical performance metrics, namely, geometric concentration ratio, acceptance angle, concentration-acceptance product, aspect ratio, active area fraction, and average number of reflections. Notably, we show that asymmetric designs can achieve significantly higher overall concentrations and are always more compact than symmetric systems designed for the same concentration ratio. Using this analysis as a basis, we develop novel asymmetric designs, including two-wing and nested configurations, which surpass the optical performance of two-mirror aplanats and are comparable with the best reported 2D simultaneous multiple surface designs for both hollow and dielectric-filled secondaries.

Nonimaging High Concentrating Photovoltaic System Using Trough

“…Table 2 gives an overview of trough based CPV systems and their major improvements in terms of solar concentration, acceptance angle, and efficiency. Low concentrating systems had achieved geometric concentration of 9.93, 23.4, 50, 53, 68, and 74 [36,[48][49][50][51][52], respectively, while medium concentrating systems achieved geometric concentration of 220 and 285 [29,53], respectively. HCPV systems were analyzed, which had geometric concentration of 364 and 600 [54,55], respectively.…”

Diffuse Solar Micro‐Concentrators Using Dielectric Total Internal Reflection with Tunable Side and Top Profiles

“…These included compound parabolic concentrators (CPCs), dielectric tailored edge ray concentrators, dielectric-filled aplanatic optics, and DTIRCs. [24,[28][29][30][31][32][33][34][35][36][37][38][39] Conventional concentrators are designed only for normal-incidence radiation, and thus the power accepted by the solar cell drops sharply outside of a narrow acceptance angle of AE1°-2°from normal incidence. [40] CPCs and DTIRCs, in contrast, are able to maintain a power multiplication ratio that is close to the geometric concentration ratio of the design over a much wider angular range up to the specified acceptance angle, at which 50% of the concentration factor is maintained.…”