D. Duncan Earl

Tracking Systems Evaluation for the “Hybrid Lighting System”

As part of the design and development effort for the “Hybrid Lighting System,” Oak Ridge National Laboratory (ORNL) scientists have evaluated two potential candidate-tracking systems for the solar collector. The first system, the WattSun Solar Tracker, built by Array Technologies, utilizes a patented, closed loop, optical sun sensor to sense the sun’s position and track it. The second tracking system, SolarTrak Controller, built by Enhancement Electronics, Inc., is a micro controller-based tracking system. The SolarTrak micro controller-based Tracker’s sun position is determined by computing the celestial bearing of the sun with respect to the earth using the local time, date, latitude, longitude and time zone rather than sensing the relative bearing of the sun with optical receptors. This system connects directly to the mechanical system hardware supplied by Array Technologies. Both the WattSun Solar Tracker and the SolarTrak Controller were mounted on the prototype “Hybrid Lighting” mechanical system (array) hardware. A simple switch allowed independent testing of each system. Upon completion of the evaluation of the two systems we found the WattSun Solar Tracker controller to be unacceptable for use with our prototype hybrid lighting system. The SolarTrak Controller has performed well to date and provides suitable tracking accuracy for use with our prototype “Hybrid Lighting System”. After a six-month evaluation period at ORNL, the first prototype “Hybrid Lighting System” was installed at Ohio University as part of an “Enhanced Practical Photosynthetic CO2 Mitigation.” This document will highlight the results of the tracker investigation and outline the remaining issues to be addressed, to provide a suitable tracking system for our “Hybrid Lighting” collector.© 2003 ASME

Luminaire development for hybrid solar lighting applications

Efficient hybrid luminaire development is an integral part of the Hybrid Solar Lighting Program at Oak Ridge National Laboratory. Hybrid luminaires are necessary to blend light from a fiber optic solar source with electric fluorescent lamps. The luminaire designs studied involve a commercially available fluorescent luminaire that has been modified to include optical elements for efficiently dispersing fiber optic solar light sources. Quantitative measurements of optical efficiency and spatial intensity distribution for two luminaire designs are compared.

Characterization of Transmission Properties of 3M LF120C Plastic Optical Light Guide

Transmission studies of 3M optical light guide, type LF120C with nominal 12.6 mm core diameter, were performed to characterize the material for use in hybrid solar lighting applications, in particular for the transport of sunlight from a collector to discrete lighting fixtures (luminaires). The light guide properties studied included: total transmission (in lumens) per unit length, transmission as a function of input angle and wavelength, transmission as a function of bend radius, and transmission through two bends. The preliminary value for total transmission is 96.6% per meter. Angular input begins to drop significantly at angles greater than 25 degrees. Wavelength transmission has significant minima at about 643 and 750 mm. Losses through bends are much greater for light input at large angles. In addition to the data compilations and detailed summaries of measurement findings, the measurement system and error sources are described.Copyright

Initial Results From an Experimental Hybrid Solar Lighting System in a Commercial Building and Overview of Related Value Propositions

This paper describes preliminary results from research on a new hybrid solar lighting (HSL) system being developed to reduce electric lighting in commercial office buildings. A physical description of HSL system components along with preliminary results from an experimental system deployed in a commercial building in Knoxville, TN are provided. Results from a systems-level, chromaticity model are compared with experimental data. A total lumen distribution efficiency of over 50% was recorded for the initial prototype having optical fibers an average of 6 m (19.5 ft) in length. The total electrical power displacement of the 1 m2 HSL proof-of-concept prototype is estimated to be between 522–2350 watts per 1000 W/m2 of incident solar radiation on the collector depending on the type of electric lights being used in conjunction with the solar lighting system. By adding the reductions in heat gain associated with reduced electric lamp use and predicted performance improvements achieved by a system redesign, the electrical power displaced in a commercial prototype could rise to between 702–3160 W (peak)/m2 of collected sunlight not including any additional electrical power that can be generated using the otherwise wasted IR energy. The color temperature of the distributed sunlight emerging from the optical fibers is approximately 5100°K and the chromaticity values in uniform color space (u′v′) are approximately (.2010, .4977). These values match well with modeled results and will vary slightly depending on the day, time, atmospheric conditions, and system configuration. The paper concludes with a discussion of new value propositions that HSL provides architects, energy providers, building owners, and occupants and briefly outlines anticipated disadvantages.Copyright

Spectral Transmission of a Solar Collector and Fiber Optic Distribution Hybrid Lighting System

Increased use of solar energy will reduce requirements for non-renewable energy sources such as fossil fuels and reduce associated greenhouse gas emissions. The benefits of replacing fossil-based energy with solar energy are often dependent on the application and operational or duty cycle for power demand. One particularly efficient use of solar energy is hybrid lighting. In hybrid lighting, solar light is concentrated into optical fibers and then coupled with supplemental electrical lighting to maintain a constant level of illumination. The system is able to offer reliable lighting with less energy consumption from the electrical grid (which is often driven by non-renewable sources). This technique offers energy efficiency benefits since the solar light is used directly and suffers no conversion losses. Furthermore, the solar spectrum provides an illumination that lighting engineers value for it’s quality; office inhabitants appreciate for its comfort; and retailers believe leads to increased sales. When available solar light is low, the hybrid system allows traditional light sources to reliably meet lighting demands. The success of the solar hybrid lighting system is dependent on the collection and transmission efficiency of the system. In this study, the spectral transmission of a hybrid lighting system is characterized. The system is composed of a 200-sun concentration reflective solar collector and a plastic fiber optic distribution network. The ultraviolet (UV), visible, and near-infrared (NIR) spectral transmission was characterized over a spectral range of 200 nm to 2400 nm. The UV and NIR performance of the system is critical since optical fiber damage can be caused by both UV and NIR light; thus, optimal system design maximizes the collection and transmission of visible light while minimizing the transmission of the UV and NIR light. Spectral transmission data for all components in the hybrid system are presented, and performance properties relative to solar applications are discussed.

Solar Energy, Collected, Concentrated, Transported, and Distributed as Light With No Energy Conversion Via a Hybrid Solar Lighting System

Hybrid solar lighting (HSL) is a technology in which sunlight is collected and distributed via optical fibers into the interior of buildings. Analogous to hybrid electric vehicles that use both batteries and internal combustion engines to power cars, hybrid lighting employs roof-mounted collectors to concentrate sunlight into flexible optical fibers and carry it inside buildings to “hybrid” light fixtures that also contain electric lamps. As the two light sources work in tandem, control systems keep lighting levels constant by dimming the electric lights when sunlight is bright, and turning them up as the sky darkens with weather conditions or nightfall. Data indicate that on a bright, sunny day the power consumption for lighting can be reduced by 50% or more. Today, lighting in U.S. residential and commercial buildings consumes close to 5 quadrillion BTUs of primary energy and one-fifth of all electricity. In commercial buildings, one-quarter of all energy demand is for lighting. With a forecasted doubling of commercial floor space by the year 2020 comes an urgent and growing need to find more efficient ways of lighting our nation’s buildings. Typically, less than 25 percent of the electrical energy consumed for lighting actually produces light; the rest generates heat, which increases the need for air-conditioning. Unlike conventional electric lamps, the sunlight from HSL systems produces virtually no waste heat. A nationwide field trial program is under way to provide system performance data and user-feedback essential for the successful commercialization of HSL. Field trial installations include San Diego State University, San Diego, CA; Pacific Northwest National Laboratory, Richland, WA; Sacramento Municipal Utility District, Sacramento, CA; Wal-Mart, McKinney, TX; Aveda Corp., Minneapolis, MN; Staples, Long Island, NY; Braden’s Furniture, Knoxville, TN; Multipurpose Research Facility, Oak Ridge National Laboratory (ORNL), Oak Ridge, TN; University of Nevada-Las Vegas, Las Vegas, NV; Hybrid Lighting Laboratory, ORNL, Oak Ridge, TN. This paper describes the field trial program and summarizes the results to date from the field trial installations.

Alignment of an inexpensive paraboloidal concentrator for hybrid solar lighting applications

We describe a practical method for precisely aligning the optical components of a low-cost solar concentrator developed for fiber optic solar lighting applications. A two-stage alignment process, involving both mechanical and optical alignment techniques, is described which allows the tilt, centering, and focal alignment of a large parabolic primary reflector relative to a segmented planar secondary mirror to be accurately determined. The alignment strategy is well suited to optical systems utilizing large reflectors with non-referenced optical axes and non-precision surface characteristics, as is typical of many inexpensive reflectors.

First-generation hybrid solar lighting collector system development and operating experience

Research is underway at Oak Ridge National Laboratory (ORNL) that could lead to entirely new, highly energy-efficient ways of lighting buildings using the power of sunlight. In addition to providing light, the hybrid lighting system will convert sunlight to electricity much more efficiently than conventional solar technologies using thermo-photovoltaic cells. In commercial buildings today, lighting consumes more electric energy than any other building end-use. It accounts for more than a third of all electricity consumed for commercial use in the United States. Typically, less than 25% of that energy actually produces light; the rest generates heat that increases the need for air-conditioning. ORNL is developing a system to reduce the energy required for lighting and the air-conditioning loads associated with it, while generating power for other uses. The system uses roof-mounted concentrators to collect and separate the visible and infrared portions of sunlight. The visible portion is distributed through large-diameter optical fibers to hybrid luminaires. (Hybrid luminaires are lighting fixtures that contain both electric lamps and fiber optics for direct sunlight distribution.) When sunlight is plentiful, the fiber optics in the luminaries, provide all or most of the light needed in an area. Unlike conventional electric lamps, they produce little heat. During times of little or no sunlight, sensor-controlled electric lamps will operate to maintain the desired illumination level. A second use of the hybrid lighting collector system is to provide sunlight for enhanced practical photosynthesis carbon dioxide mitigation. In this project the hybrid lighting collector system is being used to provide sunlight to a lab-scale photobioreactor for growing algae that is being used for CO2 mitigation. The end goal of this project is to provide a photobioreactor that can be used to mitigate CO2 in fossil fuel fire power plants. This paper will discuss the development and operating experience to date of two hybrid lighting solar collectors installed at ORNL and at Ohio University. The first hybrid lighting collector system was tested at ORNL and then installed at Ohio University in June of 2002. A second collector of the same design was installed at ORNL in September of 2002. The Ohio University collector system has been running continually since its installation while the ORNL unit has been operated in a research mode on most sunny days. They have operated with very little human interaction and this paper will summarize the development, operating experience, collection efficiency, as well as providing information on additional data being collected as part of the system operation.

Beam profiler for single-photon applications based on compressive sampling techniques

We report the development of a low-cost beam characterization technique appropriate for extremely low light levels. The technique makes use of compressive sampling strategies that have been developed recently for imaging applications.

Beam Profiler for Single-Photon Applications based on Compressive Sampling Techniques

We report the development of a low-cost beam characterization technique appropriate for extremely low light levels. The technique makes use of compressive sampling strategies that have been developed recently for imaging applications.