Solar concentrators for advanced solar-dynamic power systems in space

This report summarizes the results of a study performed by Hughes Danbury Optical Systems, HDOS, (formerly Perkin-Elmer) to design, fabricate, and test a lightweight (2 kg/sq M), self supporting, and highly reflective sub-scale concentrating mirror panel suitable for use in space. The HDOS panel design utilizes Corning's 'micro sheet' glass as the top layer of a composite honeycomb sandwich. This approach, whose manufacturability was previously demonstrated under an earlier NASA contract, provides a smooth (specular) reflective surface without the weight of a conventional glass panel. The primary result of this study is a point design and it's performance assessment

A preliminary assessment of small steam Rankine and Brayton point-focusing solar modules

A preliminary assessment of three conceptual point-focusing distributed solar modules is presented. The basic power conversion units consist of small Brayton or Rankine engines individually coupled to two-axis, tracking, point-focusing solar collectors. An array of such modules can be linked together, via electric transport, to form a small power station. Each module also can be utilized on a stand-alone basis, as an individual power source

Lightweight solar concentrator structures, phase 2

This report summarizes the results of the program conducted by Ultramet under SBIR Phase 2 Contract NAS3-25418. The objective of this program was to develop lightweight materials and processes for advanced high accuracy Space Solar Concentrators using rigidized foam for the substrate structure with an integral optical surface

Measurement, modeling, and adjustment of the 10.4-m-diameter Leighton telescopes

The design of the Leighton telescopes and the unique techniques used in their fabrication make these telescopes particularly amenable to precise modeling and measurement of their performance. The surface is essentially a continuous membrane supported at 99 uniformly distributed nodes by a pin joint triangular grid space frame. This structure can be accurately modeled and the surface can be adjusted using low- resolution maps. Holographic measurements of the surface figure of these telescopes at the Caltech Submillimeter Observatory (CSO) and the Owens Valley Radio Observatory (OVRO) have been made over several epochs with a repeatability of 5 - 10 micrometer over the zenith angle range from 15 to 75 degrees. The measurements are consistent with the calculated gravitational distortions. Several different surface setting strategies are evaluated and the 'second order deviation from homology,' Hd, is introduced as a measure of the gravitational degradation that can be expected for an optimally adjusted surface. Hd is defined as half of the RMS difference between the deviations from homology for the telescope pointed at the extremes of its intended sky coverage range. This parameter can be used to compare the expected performance of many different types of telescopes, including off-axis reflectors and slant-axis or polar mounts as well as standard alt-az designs. Subtle asymmetries in a telescope's structure are shown to dramatically affect its performance. The RMS surface error of the Leighton telescope is improved by more than a factor of two when optimized over the positive zenith angle quadrant compared to optimization over the negative quadrant. A global surface optimization algorithm is developed to take advantage of the long term stability and understanding of the Leighton telescopes. It significantly improves the operational performance of the telescope over that obtained using a simple 'rigging angle' adjustment. The surface errors for the CSO are now less than 22 micrometer RMS over most of the zenith angle range and the aperture efficiency at 810 GHz exceeds 33%. This illustrates the usefulness of the global surface optimization procedure

Concentrator enhanced solar arrays design study

The analysis and preliminary design of a 25 kW concentrator enhanced lightweight flexible solar array are presented. The study was organized into five major tasks: (1) assessment and specification of design requirements; (2) mechanical design; (3) electric design; (4) concentrator design; and (5) cost projection. The tasks were conducted in an iterative manner so as to best derive a baseline design selection. The objectives of the study are discussed and comparative configurations and mass data on the SEP (Solar Electric Propulsion) array design, concentrator design options and configuration/mass data on the selected concentrator enhanced solar array baseline design are presented. Design requirements supporting design analysis and detailed baseline design data are discussed. The results of the cost projection analysis and new technology are also discussed

Challenge and Research Trends of Solar Concentrators

Primary and secondary solar concentrators are of vital importance for advanced solar energy and solar laser researches. Some of the most recent developments in primary and secondary solar concentrators were firstly presented. A novel three-dimensional elliptical-shaped Fresnel lens analytical model was put forward to maximize the solar concentration ratio of Fresnel-lens-based solar concentrators. By combining a Fresnel lens with a modified parabolic mirror, significant improvement in solar laser efficiency was numerically calculated. A fixed fiber light guide system using concave outlet concentrators was proposed. The absence of a solar tracking structure highlights this research. By shaping a luminescent solar concentrators in the form of an elliptic array, its emission losses was drastically reduced. Simple conical secondary concentrator was effective for thermal applications. New progresses in solar-pumped lasers by NOVA University of Lisbon were presented. By adopting a rectangular fused silica light guide, 40 W maximum solar laser power was emitted from a single Ce:Nd:YAG rod. An aspheric fused silica secondary concentrator and a small diameter Ce:Nd:YAG rod were essential for attaining 4.5 % record solar-to-laser power conversion efficiency. A novel solar concentrator design for the efficient production of doughnut-shaped and top-hat solar laser beams were also reported. More importantly, a novel solar concentrator approach for the emission of 5 kW-class TEM00 mode solar laser beams from one megawatt solar furnace was put forward at the end of this book, revealing promising future for solar-pumped lasers

Useful strategy in the design of energy-efficient buildings using innovative daylighting systems

This research work has been carried out to utilize daylight more effectively for indoor illumination in an energy efficient building without any compromise on indoor environmental quality; especially the visual comfort on task plane. Two different daylighting systems have been designed and constructed, and a series of tests have been performed to assess their photometric characteristics as well as their performance. A typical system considered has an optic concentrator capable of tracking the sun and making high density fluxes of solar rays. It consists of either dish or funnel shaped concentrators followed by optical fiber cables and diffusers at the end. The design of a dish concentrator (diameter less than 30 cm) is prepared by rotating a simple parabolic profile in compliance with the major physical requirements. This geometrical simplicity has also been applied for the design of a funnel shaped concentrator created by combining two parabolas. When the sunlight is highly focused, it is then redirected and undergoes a number of reflections to enter a light guide for its final transmission to the terminal device. The light reaching the terminal device finally gets consumed by the interior of a building for indoor illumination. The active daylighting system considered in this study offers substantial advantages over conventional solar designs in its fabrication, installation, operation, and utilization of the sun's energy. The proposed daylighting system is durable and suited to economical operation for different schemes of indoor illumination of buildings. Each component of the system could be made from off-the-shelf technology, thus making the generic unit inexpensive to manufacture. Depending on spatial demand or characteristics, the amount of daylight introduced could be controlled without undue difficulties. To assess the photometric characteristics of a daylighting system, goniophtometer and spectrometemr easurementsa re made,w hich provided its luminous intensity distribution and spectral radiance. The spatial distribution of light emerging from the optical cable is examined by monitoring the workplane illuminances for the mock-up spaces in Nottingham (UK) and Jeju (Korea). Six different types of terminal devices (optical lenses, light rod) are also examined experimentally to elicit the most optimal design for use with a daylighting system. Of those tested, the circular shape acrylic rod spreads out the light most widely followed by semi-concave lens whereas the semi-convex lens has shown the smallest light spreading ability. The test results have revealed some distinctive features of the present dishdaylighting system in bringing natural daylight to non-daylit areas or interior spaces too deep for conventional daylighting apertures. Especially, it proved the effectiveness of the system when applied for individualized lighting allowing individual control over the amount of light in space and to suit individual preferences for lighting conditions. Experimental data from measurements are further extended to develop the numerical models with RADIANCE and ECOTECT for theoretical predictions under different situations. The image of luminance ratio maps generated by RADIANCE and the fish-eye photographs of the sky were conducive to realistic assessment of possible glare reduction and uniformity improvement not just for the task plane but also for its surroundings. There were some appreciable changes made in the indoor luminance distribution thanks to our daylighting system. It has clearly demonstrated its functional reliability and usefulness to control brightness and thus promote indoor visual environment