Conventional parabolic trough solar concentrators have the benefit of only requiring 1-axis tracking and having a line-focus suitable for heat extraction using long receiver pipes. However, by being 1-axis concentrators, their fundamental limit of concentration is 212x, compared to the 45 000x limit for 2-axis concentrators. We propose to use two recent developments from nonimaging optics to develop practical high-concentration line-focus concentrators. The first is the use of beam-steering lens arrays to redirect sunlight, allowing a concentrator to benefit from 2-axis tracking without being aimed directly towards the sun. The second is the use of étendue squeezing to increase concentration across one axis, at the cost of reduced concentration across the second axis. We show how these two developments may be used to create line-focus concentrators not limited by the 212x concentration limit, and present our work towards designing a practical system implementing these concepts.
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. Beam-steering 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.
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 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.
Jan Torgersen, Aleksandr Ovsianikov, Vladimir Mironov, Niklas Pucher, Xiaohua Qin, Zhiquan Li, Klaus Cicha, Thomas Machacek, Robert Liska, Verena Jantsch, Jürgen Stampfl
Hydrogels are polymeric materials with water contents similar to that of soft tissues. Due to their biomimetic properties, they have been extensively used in various biomedical applications including cell encapsulation for tissue engineering. The utilization of photopolymers provides a possibility for the temporal and spatial controlling of hydrogel cross-links. We produced three-dimensional (3-D) hydrogel scaffolds by means of the two-photon polymerization (2PP) technique. Using a highly efficient water-soluble initiator, photopolymers with up to 80 wt.% water were processed with high precision and reproducibility at a writing speed of 10 mm/s . The biocompatibility of the applied materials was verified using Caenorhabditis elegans as living test organisms. Furthermore, these living organisms were successfully embedded within a 200×200×35 μm 3 hydrogel scaffold. As most biologic tissues exhibit a window of transparency at the wavelength of the applied femtosecond laser, it is suggested that 2PP is promising for an in situ approach. Our results demonstrate the feasibility of and potential for bio-fabricating 3-D tissue constructs in the micrometre-range via near-infrared lasers in direct contact with a living organism.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.