Optimal focal length of primary mirrors in Fresnel linear collectors

Abstract

In a linear Fresnel plant adopting slightly curved primary mirrors (cylindrical or parabolic), a significant gain in the collected radiation can be achieved using primary mirrors with different focal lengths, dependent on the position of the mirror with respect to the receiver. This work introduces a universal function that provides the optimal focal length of a mirror, given only the mirror’s position relative to the receiver and the latitude, for a NS-oriented collector with a flat horizontal effective target. In a solar plant with the focal lengths defined by this function, the efficiency gain with respect to a solar field adopting identical mirrors is estimated in the range 1.5–6%, with the gain increasing if mirror imperfections or tracking errors are present: this means that the regulation of the focal lengths is especially useful in containing the loss of efficiency due to defects. The given rule is tolerant to errors in the focal length regulation (up to 10%). The function can be used as a reference for future projects, or as a starting point for more refined optimizations

Methodology for an Opto-Geometric Optimization of a Linear Fresnel Reflector for Direct Steam Generation

“…However, even ignoring the dimensions and specifications of the receiver, the geometry of a LFR is defined by numerous parameters, which can be changed independently, at least in principle: the width, the position, and the focal length of each mirror are all independent variables. Therefore, the geometry of the solar field depends on 3 N m degrees of freedom, where N m is the number of mirrors [8].…”

“…Considering some descriptions for different Fresnel reflectors designs; a similar configuration (a similar field is considered because a detailed description of the FRESDEMO field is not available (mainly the location of the mirrors)) of the FRESDEMO's field; located in the Plataforma Solar de Almería, Spain, is proposed; this LFR is shown in Figure 4. The field is composed of several modules each with 25 mirrors of 0.60 m width and 100 m length, distributed in a 21 m wide-field oriented in N-S direction [6][7][8]19,[23][24][25][26][27][28]. As a summary in Table 1, the parameters considered are shown.…”

“…This interest has led to different studies discussing the opto-geometric parameters to be determined and optimized. Abbas and Martínez-Val [6] analyzed the optical design of Fresnel Reflectors width and shifts of the mirrors, Boito and Grena [7,8] developed a model to find the optimal focal length of the primary mirrors and also an optical optimization relating the plant cost and the concentrated solar radiation. Qiu et al [9] presented a strategy to homogenize the heat flux in the receiver area employing multi-objective genetic algorithms and Monte Carlo ray-tracing.…”

Design, economic, and environmental assessments of linear Fresnel solar power plants

“…In this article, a sensitivity analysis is developed to optimize the performances of seven LFSTPP models for cost and efficiency. To decide the values of SM, FLH, and FFF, 50 MW STPPs based on LFR technology analyzed, using the System Advisor Model (SAM) software developed by the National Renewable Energy Laboratory (NREL) USA. Different plants have been proposed and simulated, to determine the optimum design and configuration of a STPP with minimum LCOE.…”