In this paper a method to characterize the anisotropy of diffuse illumination incident on photovoltaic systems is presented. PV systems are designed based on standard conditions in which only consider direct and isotropic diffuse illumination. Anisotropic illumination can cause the PV system output to step outside of the design specifications. A baffled multi-detector sensor system is described having a discrete set of azimuthal and declination angle combinations in order to constantly sample the irradiance and the incidence angle of the diffuse illumination in all zenith directions. The sensor was deployed in the Tucson Electric Power Solar Test Yard alongside with commercially available PV systems that are independently monitored. Constant and transient sources of anisotropic diffuse illumination, such as surface reflection and cloud edge effects respectively, are measured and modeled with ray tracing software. Results of the method are described for characterizing diffuse illumination at the TEP Solar Test Yard. Understanding the anisotropic diffuse illumination can potentially allow to more accurately predict PV system or to optimize energy harvesting of systems with non-standard mounting conditions as well as building integrated photovoltaic applications.
A model for the thermal properties of holographic planar concentrators on module performance is presented and verified with experimental data. The holographic planar concentrator modules consist of ribbons of volume holograms placed next to photovoltaic cells to achieve a low level concentration effect. The holographic ribbons increase the surface area required to produce a fixed amount of output power but reduce the cost of the module by eliminating approximately half of the photovoltaic cell material, in this case monocrystalline bifacial silicon cells. Due to the low concentration, the temperature reduction effect of the added surface area overcomes the added heat provided by the holograms. The theoretical point at which the added concentration by holograms overcomes the cooling effect provided by the extended region for varying theoretical holographic contributions is also presented.
We present the results of combining copper indium gallium (di)selenide (CIGS) photovoltaic cells with holographic planar concentrating film over a broad range of illumination levels. The film, originally designed for silicon bifacial solar applications worked well with the CIGS cells. The Voc, cell efficiency and fill factor reached full operating values at lower light levels; with a significant boost in performance being recorded. The holographic regions of the concentrator act as extended heat transfer surfaces, allowing the CIGS cells to operate at lower operational temperatures than they normally would in a traditional PV application.
KEYWORDS: Sun, Holography, Solar concentrators, Phase modulation, Temperature metrology, Holographic concentrators, Silicon, Solar cells, Glasses, Picture Archiving and Communication System
Dual aperture holographic planar concentrator (DA-HPC) technology consists of bifacial cells separated by strips of
holographic film that diffract the light from the spacing into the cells for direct incident, diffuse, roof-reflected and
albedo irradiance. The holographic film is angularly dependent of the seasonal sun angle. DA-HPC modules are
compared to single aperture conventional modules for clear and cloudy days as well as for a seasonal period of eight
months. Direct-current IV and alternating-current power curves are used to compare modules with comparable silicon
active area and cell efficiency.
We describe a technique to package 15-µm-diam single-mode fibers on a silicon substrate that can be incorporated into an endoscopic probe tip. The single-mode fibers in the array can be used in coherent imaging applications such as optical coherence tomography. Fiber-to-substrate and fiber-to-fiber coupling effects are studied using beam propagation techniques to determine the different design characteristics and the maximum length of the reduced diameter fiber that can be packaged in the probe tip. Single-mode fibers are etched to reduce the cladding diameter from 125 to 15 µm. A 2-µm-thick silica layer is grown in the silicon substrate to minimize the fiber-substrate coupling. Reduced diameter fibers are placed into a 5-mm by 150-µm trench etched in a silicon-silica substrate and fixed with UV curable cement. Active alignment is used to ensure the correct alignment of fibers. The fiber array is experimentally evaluated to test fiber placement accuracy, throughput, and cross talk. Optical coherence tomography images are also obtained with the array.
The good optical properties of PQ (phenanthrenequinone)-doped PMMA (poly methylmethacrylate) and its flexibility to
fabricate different substrate configurations make this material attractive for holographic recording. In previous work,
filters in PQ/PMMA for Wavelength Division Multiplexing (WDM) and Optical Code Division Multiple Access
(OCDMA) were demonstrated and shown to have a 0.03nm/°C thermal tuning range operating near 1550nm. In this
paper we investigate the effect of adding silicon dioxide nanoparticles to PQ/PMMA in order to measure the thermal
tuning range and investigate the performance of these filters.
Two types of solar concentrators for use with standard silicon photovoltaic cells are compared. The first is a spectral
shifting luminescent concentrator that absorbs light in one spectral band and re-emits light at longer wavelengths where
the absorption of standard silicon photovoltaic cells is more efficient. The second type is a holographic planar
concentrator that selects the most useful bands of the solar spectrum and concentrates them onto the surface of the
photovoltaic cell. Both types of concentrators take advantage of total internal reflected light, do not require tracking, and
can operate with both direct and diffuse sunlight. The holographic planar concentrator provides a simpler and more cost
effective solution with existing materials and construction methods.
Optical Coherence Tomography (OCT) shows great promise for low intrusive biomedical imaging applications. A
parallel OCT system is a novel technique that replaces mechanical transverse scanning with electronic scanning. This
will reduce the time required to acquire image data. In this system an array of small diameter fibers is required to obtain
an image in the transverse direction. Each fiber in the array is configured in an interferometer and is used to image one
pixel in the transverse direction. In this paper we describe a technique to package 15&mgr;m diameter fibers on a siliconsilica
substrate to be used in a 2mm endoscopic probe tip. Single mode fibers are etched to reduce the cladding
diameter from 125&mgr;m to 15&mgr;m. Etched fibers are placed into a 4mm by 150&mgr;m trench in a silicon-silica substrate and
secured with UV glue. Active alignment was used to simplify the lay out of the fibers and minimize unwanted
horizontal displacement of the fibers. A 10-channel fiber array was built, tested and later incorporated into a parallel
optical coherence system. This paper describes the packaging, testing, and operation of the array in a parallel OCT
system.
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