Conventional tracking solar concentrators track sunlight by rotating the concentrator optics to face the sun, which adds to the cost and bulk of the system. Beam-steering lens arrays, in contrast, allow solar tracking without bulk rotation of the optics. It consists of lens arrays stacked in an afocal configuration, and tracking is implemented by relative translation between these lens arrays. In this work, we present a phase-space methodology for analyzing and optimizing the performance of the beam-steering, and for revealing optical aberrations in the system. Using this methodology, we develop a beam-steering lens array with a simulated ≈70% efficiency across a two-axis ±40°tracking range, and a divergence of the outgoing beam of less than ±0.65°. We also present a functional small-scale prototype and demonstrate the feasibility of the concept for solar tracking. Beam-steering lens arrays can be placed in front of conventional concentrator optics and operated with little or no external tracking. This may enable low-cost robust concentrated solar power systems, and could also find other applications such as solar lighting and steerable illumination.
An essential part of a concentrated solar power system is the solar tracker. Tracking is usually implemented by rotating the entire optical system to follow the sun, adding to the bulk and complexity of the system. Beamsteering lens arrays, on the other hand, enable solar tracking using millimeter-scale relative translation between a set of lens arrays stacked in an afocal configuration. We present an approach for designing and comparing beam-steering lens arrays based on multi-objective optimization, where the objective is to maximize efficiency, minimize divergence, and minimize cost/complexity. We then use this approach to develop new configurations with improved performance compared to previously reported results. As an example of a design suitable for high-concentration applications, we present a system consisting of four single-sided lens arrays that can track the sun with a yearly average efficiency of 74.4% into an exit-cone with divergence half-angle less than ±1 •. We also present a simplified system consisting of three single-sided lens arrays, which can be implemented with less mechanical complexity and potentially lower cost. This simplified system achieves 74.6% efficiency and a divergence half-angle of less than ±2.2 • , and might be relevant for low or medium concentration applications. We believe that these results demonstrate the previously untapped potential of beam-steering lens arrays. If such designs are successfully manufactured, they may become an attractive alternative to conventional external solar trackers for a range of solar energy applications.
Beam-steering lens arrays enable solar tracking using millimeter-scale relative translation between a set of lens arrays. This may represent a promising alternative to the mechanical bulk of conventional solar trackers, but until now a thorough exploration of possible configurations has not been carried out. We present an approach for designing beam-steering lens arrays based on multi-objective optimization, quantifying the trade-off between beam divergence and optical efficiency. Using this approach, we screen and optimize a large number of beam-steering lens array configurations, and identify new and promising configurations. We present a design capable of redirecting sunlight into a <2°divergence half-angle, with 73.4% average yearly efficiency, as well as a simplified design achieving 75.4% efficiency with a <3.5°d ivergence half-angle. These designs indicate the potential of beam-steering lens arrays for enabling low-cost solar tracking for stationary solar concentrators.
Line-focus solar concentrators are commonly designed by extruding a two-dimensional concentrator in the third dimension. For concentration in air, these concentrators are, by the nature of their design, limited by the two-dimensional solar concentration limit of . This limit is orders of magnitude lower than the concentration limit for three-dimensional solar concentrators. Through the use of étendue squeezing, we conceptually show that it is possible to design line-focus solar concentrators beyond this 2D limit. This allows a concentrator to benefit from a line focus suitable for heat extraction through a tubular receiver, while reaching concentration ratios and acceptance angles previously unseen for line-focus concentrators. We show two design examples, achieving simulated concentration and concentration ratios, with a acceptance angle. For comparison, the 2D concentration limit is at this acceptance angle. Étendue-squeezing line-focus solar concentrators, combined with recent developments in tracking integration, may enable the development of a new class of concentrated solar power systems.
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