This PDF file contains the front matter associated with SPIE Proceedings Volume 6652, including the Title Page, Copyright information, Table of Contents, Plenary Papers, and the Conference Committee listing.

Nanoantennas, coupled to rectifying nanodiodes ("rectennas"), could be used for converting broadband visible/near-infrared energy to direct current, and could serve as fast, high-Q infrared detectors at designed wavelengths. We study and model the efficiency of antennas coupled to metal-insulator-metal (MIM) and thermionic emission diodes, over a wide range of incident wavelengths. We find that tuning the antenna's reactance, so that the antenna acts as an inductor and resonantly cancels the diode capacitance, can enhance energy conversion efficiency by more than an order of magnitude above the broadband level, at the resonance frequency. We discuss maximizing the efficiency of a modern rectenna-based broadband energy conversion system, especially in the challenging visible regime, and recommend using nanodiodes with conduction via thermionic emission. We recommend further modeling of and experiments with nanoantennas, in order to calculate total efficiency of the nanorectenna's energy conversion.

The optical characterization of a CPC concentrator is typically performed by using a solar simulator producing a collimated light beam impinging on the input aperture and characterized by a solar divergence (± 0.27°). The optical efficiency is evaluated by measuring the flux collected at the exit aperture of the concentrator, as function of incidence angle of the beam with respect to the optical axis, from which the acceptance angle can be derived. In this paper we present an alternative approach, based on the inverse illumination of the concentrator. In accordance with this method, a Lambertian light source replaces the receiver at the exit aperture, and the light emerging backwards at the input aperture is analyzed in terms of radiant intensity as function of the angular orientation. The method has been applied by using a laser to illuminate a Lambertian diffuser and a CCD to record the irradiance map produced on a screen moved in front of the CPC. Optical simulations show that, when the entire surface of the diffuser is illuminated, the "inverse" method allows to derive, from a single irradiance map, the angle resolved efficiency curve, and the corresponding acceptance angle, at any azimuthal angle. Experimental characterizations performed on CPC-like concentrators confirm these results. It is also shown how the "inverse" method becomes a powerful tool of investigation of the optical properties of the concentrator, when the Lambertian source is spatially modulated inside the exit aperture area.

PV Optics is a user-friendly software package developed to design and analyze solar cells and modules. It is applicable to a variety of optical structures, including thin and thick cells with light-trapping structures and metal optics. Using a combination of wave and ray optics to include effects of coherence and interference, it can be used to design single-junction and multijunction solar cells and modules. This paper describes some basic applications of PV Optics for crystalline and amorphous Si solar cell design. We present examples to examine the effects on solar cell performance of wafer thickness, antireflection coating thickness, texture height, and metal loss.

In this paper we present a method of optical characterization of solar concentrators based on the use of a laser beam. The method, even though constrained by lengthy measurements, gives nevertheless interesting information on local mirror surface defects or manufacturing defects, like internal wall shape inaccuracies. It was applied to 3D-CPC-like concentrators and the measurements were supported by optical simulations with commercial codes. The method, simple to apply, requires just a laser to scan the CPC input aperture following a matrix-like path, at a controlled orientation of the beam. Maps of optical efficiency as function of the laser beam incidence angle are obtained by matching the CPC exit aperture with a photodetector with an efficient light trapping. The integration of each map gives the CPC efficiency resolved in angle of incidence, so curves of optical transmission (efficiency) as function of incidence angle can be drawn and the acceptance angle measured. The analysis of the single maps allows to obtain interesting information on light collection by the different regions of CPC input area. It reveals, moreover, how the efficiency of light collection depends on several factors like surface reflectivity, number of reflections of the single beam, local angle of incidence, local surface defects, and so on. By comparing the theoretical analysis with the experimental results, it is possible to emphasize the effects directly related to manufacturing defects.

Worldwide lack of comprehensive measured solar radiation resource data for solar system design is well known. Several simple clear sky solar radiation models for computing hourly direct, diffuse and global hemispherical solar radiation have been developed over the past 25 years. The simple model of Richard Bird, Iqbal's parameterization C, and Gueymard's REST model are popular for estimating maximum hourly solar resources. We describe a simple polynomial in cloud cover (octa) modifier for these models that produces realistic time series of hourly solar radiation data representative of naturally occurring solar radiation conditions under all sky conditions. Surface cloud cover observations (Integrated Surface Hourly Data) from the National Climatic Data Center are the only additional (hourly) input data to model total hemispherical solar radiation under all sky conditions. Performance was evaluated using three years of hourly solar radiation data from 31 sites in the 1961-1990 National Solar Radiation Data Base. Mean bias errors range from - 10% to -20%, and are clear sky model dependant. Root mean square error of about 40%, are also dependent upon the particular model used and the uncertainty in the specific clear sky model inputs and lack of information on cloud type and spatial distributions.

Common methods for ground-based measurement of direct normal and diffuse solar irradiance include the simultaneous use of two instruments, usually a pyrheliometer and pyranometer or two pyranometers one of which is fitted with a shading ring. This article describes a passive method of obtaining the direct and diffuse components using a single pyranometer and an innovative shading band containing regularly spaced perforations to allow for alternate shading and exposure of the instrument's sensor as the sun transits the sky. Under clear sky conditions a saw tooth curve is generated that may be reformed into two distinct curves, one each for global and diffuse irradiance. The unknown direct normal values are then readily calculated. The approach potentially offers a cost advantage over dual-instrument and rotating band systems and an accuracy advantage over the single-instrument approach. In conjunction with a reference pyrheliometer under clear sky conditions, the device can be used in shade-unshade calibrations of pyranometers without need of manual operations. Design of the shading band is described and preliminary experimental results are presented. Results show that good accuracy is obtainable, on the order of ± 40 Watts per square meter for global, diffuse and direct estimates, under clear sky conditions, when compared with independent reference data.

The IR loss in diffuse measurements made by thermopile pyranometers is examined. Diffuse measurements are used for the study of IR losses because diffuse irradiance is much smaller than the total irradiance and hence the IR effects can be more clearly seen. Specifically, diffuse measurements of an Eppley PSP pyranometer are compared to those made with a Schenk Star pyranometer. Pyranometers with black and white or star type junctions suffer minimal IR loss because the reference and receiving junctions of the thermopile are at the same thermal level. The difference between diffuse values can be attributed to calibration and cosine response errors as well as IR loss. This is a preliminary study over one month when pyrgeometer data are available. Examination of the differences at various times of the year and at more than one location is necessary to generalize the findings in this report. Several methods of correcting for IR loss are examined. First subtracting out the average nighttime offset during the day is tested. Next an extrapolation between early morning and late evening offsets is tested. This should help eliminate the IR offset in both the morning and evening hours, but underestimate the IR losses during the rest of the day. Next, correlations of IR losses calculated using pyrgeometer measurements with temperature, relative humidity, and irradiance are evaluated. Initial results show that it should be possible to use more commonly available measurements rather than prygeometer data to estimate IR loss for Eppley PSP pyranometers.

The measurement of the horizontal diffuse radiation, a priori a straightforward task, is fraught with difficulties. It is possible to measure the diffuse radiation by both direct and indirect methods. The most accurate method is probably the indirect one, which utilizes concurrent measurements of the horizontal global and the normal incidence beam radiation. The disadvantage of this method is the relatively expensive tracking system required for measuring the latter. The diffuse radiation can be measured directly with a pyranometer outfitted with either an occulting disk or shadow ring, which prevent the beam radiation from impinging on the pyranometer sensor. The former method can provide accurate measurements of the diffuse radiation but requires a relatively expensive sun tracking system in the east-west axis. The shadow ring is a stationary device with regard to the east-west axis and blocks the beam radiation component by creating a permanent shadow on the pyranometer sensor. The disadvantage of the shadow ring is that it also blocks a portion of the sky, which necessitates a geometrical correction factor. There is also a need to correct for anisotropic sky conditions. Four correction models have been applied to the data and the results evaluated and ranked.

Using the same SMARTS radiative code as for the development of improved reference spectra for PV rating, an analysis of the spectral sensitivity of specific PV technologies to varying air mass and other factors is presented. To the difference of previous studies, the approach taken here considers realistic atmospheric conditions, as measured at five North- American sites from widely different climatic zones. Two different PV applications (latitude-tilted flat-plates and vertical building-integrated modules) are showcased with seven possible materials, including a-Si, m-Si, and triple junctions. Considering the most frequent clear-sky conditions around the summer solstice at the selected sites, the Spectral Enhancement Factor (SEF) is calculated both for a fixed air mass (1.5) and daily-average spectral conditions. This analysis provides a preliminary assessment of how latitude, local climatic conditions, and PV geometry affect the relative merits of different technologies relatively to standard rating conditions. In particular, it is shown that, in summer, latitude-tilt PV modules experience bluer incident spectra than the reference spectrum, therefore favoring the a-Si modules (SEF > 1). For vertical-tilt PV systems, the SEF is generally lower than for latitude-tilt systems, with the notable exception of m- Si. When considering daily-average results, the effective SEF can become extremely low in the case of a-Si (down to 0.65) and moderately high for m-Si (up to 1.09). It is concluded that the effects of location, season, and PV material on the spectral effect needs to be investigated in detail, particularly for applications involving vertical building-integrated systems.

The optical design of a solar concentrator is based not on understanding and evaluating a point solution in time, but instead on the integrated performance over a band of time. Important additional factors are to evaluate different locations in the world and different seasons. Here we construct a software tool for modeling bands of time and use it to study different types of passive, low-concentration, CPC-profile solar collectors. Extruded trough geometry is shown to have superior performance to an annulus, and a cylindrically curved CPC profile had better pointing tolerance than the trough collector.

In this work we present the optical design of a solar concentrator for an High-Flux solar furnace of a solar laboratory, these concentrator is compound for an aspheric mirror surface sectioned in 121 hexagonal facets to simplify the construction process, its total diameter is 6.6 m and a focal length is 3.68 m, also was developed the corresponding algorithm to determine the correct position and orientation of each hexagonal section that compound the arrangement. We present the results of the focused energy of this configuration and we propose a modification on the original position of the mirrors for optimizing the focusing of energy by the sun furnace. These modifications produces an increment on the energy focused on a small area in a remarkable way similar to used a parabolic mirror. The algorithm before mentioned was programmed in MathCAD and it calculates the modification of the original position of each hexagonal mirror giving us a file that ZEMAX can read. This file contains the information of each 121 mirrors from the arrangement and also the correct form, position and direction, simplifying the traditional input process one by one.