Optimization of solar linear Fresnel reflector system with secondary concentrator for uniform flux distribution over absorber tube

Solar linear Fresnel reflectors (LFR) are attractive because of low cost and optimal utilization of land area. They provide high concentration ratio when used in conjunction with secondary concentrators. A pilot plant of LFR system with 154 m(2) of primary mirror field installed at Vallipuram, India has been considered for the present analysis. This type of collectors give rise to high variation of solar radiation flux in the circumferential direction of absorber for the cases with fixed aim line of primary mirrors. In the present work, the concept of variable aim lines for primary mirrors is introduced to defocus and spread the radiation flux in a more uniform manner over the absorber. In particular, both the tilt angles and the radii of curvature of the individual Fresnel mirrors are modified to obtain a better flux uniformity. In addition, a novel segmented parabolic secondary concentrator profile has also been developed, which in conjunction with the variable aim line concept leads to a high optical efficiency of 76.4% and a coefficient of flux variation value of 0.13. On the other hand, 74.9% and 70.9% of optical efficiencies along with 0.17 and 0.33 values of coefficient of variation are obtained with more commonly employed compound parabolic concentrator and trapezoidal concentrator profiles respectively. (C) 2017 Elsevier Ltd. All rights reserved.