This PDF file contains the front matter associated with SPIE Proceedings Volume 7046, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

Solar global and diffuse radiation intensities are, in general, measured on horizontal surfaces, whereas stationary solar conversion systems (both flat plate solar collector and PV) are tilted towards the sun in order to maximize the amount of solar radiation incident on the collector surface. Consequently, the solar radiation incident on a surface tilted to the south (northern hemisphere) must be determined by converting the solar radiation intensities measured on a horizontal surface to that incident on the tilted surface of interest. There exist a large number of models designed to perform such a conversion. Eleven such models have been tested utilizing data measured in Beer Sheva, Israel. The data consist of hourly solar global and diffuse radiation on a horizontal surface, normal incidence beam and global radiation on a south-oriented surface tilted at 40°. The individual model performance is assessed by an inter-comparison between the calculated and measured solar global radiation on the south-oriented surface tilted at 40° using both graphical and statistical methods. The relative performance of the different models under different sky conditions, i.e., clear, partially cloudy and cloudy as defined by the hourly clearness index value, has been studied.

The series electrical nature of the multi-junction solar cell is both the source of its desirable overall efficiency and of its sensitivity to spectral balance. Owing to the series connection of the spectrally selective junctions, variations in the spectra of the solar input, optical transfer function, and cell quantum efficiency have significant impact on annual energy production despite being effectively indistinguishable in instantaneous power output. This paper will outline spectral filtering approaches for experimental characterization, and spectral simulation methods for estimating annual energy production. We will also present system level design to optimize for annual energy production.

Photovoltaic technology will have a substantial impact on the nation's wealth and economy in 21^st century. The main obstacle for widespread use of PV energy at present is the higher cost of PV energy generation equipment compared to that of fossil fuels. Improved in-line diagnostics can reduce the cost and increase the productivity by significantly improving the yield of the process. Here we present the first results of development of a high-throughput PV (Photovoltaic) characterization system, which can provide fast and accurate data on the spatial uniformity of thickness, refractive indices, and birefringence of the thin films comprising the solar cell in a single scan over the entire solar cell area. The unmatched throughput, the amount of retrieved information, and the unique capability of characterization of both plane and structured surfaces and interfaces of such a system will provide the opportunity to use this system and develop in-situ, real time process diagnostics/prognostics capabilities that would result in improved yield and reduced cost of solar cell manufacturing. Here we provide the modeling results, demonstrate applicability of the technique for characterization of organic solar cells and discussing the modifications of the system that would permit characterization of structured solar cell surfaces.

To improve the efficiency of solar thermal collectors, selective coatings need to be maximally transparent to sunlight (up to 2500 nm wavelength) and maximally reflective to heat radiation. One way to improve the transparency for sunlight without compromising the reflective properties at longer wavelengths is structuring thin metal films with holes. The purpose of this paper is to develop computer model capabilities to predict the optical properties of such structures by solving the Maxwell and materials equations using the finite element method in three dimensions. Coupling both sets of equations enables us to incorporate the full dispersion of metals, including their negative real part of permittivity. The finite element model is validated in two ways: firstly, by simulations of structured films using the FDTD method in the range of positive permittivity; and secondly, by the transmission and the ellipsometric measurement of homogeneous films. The simulations predict that holes with a diameter between 300 and 500 nm - and aligned in arrays with a mutual distance between 500 and 800 nm - significantly improve the performance of selective layers used for solar thermal collectors.

In this paper, a new process for the formation of hemispherical structures as an omni-directional anti-reflection (omni-AR) coating in solar cell is reported. We also demonstrated the simulation results of the angular and spectral dependences of the total reflectivity on various micro-structured surfaces. Close to zero reflection can be achieved in some micro-structured surfaces over an extended spectral region for large ranges of incident light angles. Daily generated current in such hemispherical solar cells hence enhanced to 1.5 times of bulk silicon solar cells. The impact of feature size, density, shape and refractive index has all been investigated. The experimental results agree reasonably well with the theoretical work. Such an omni-AR structure offers an attractive solution to current bulk crystalline silicon solar cells, as well as thin film, organic and future quantum based solar cells.

One promising application of semiconductor nanostructures in the field of photovoltaics might be quantum dot solar concentrators. Quantum dot containing nanocomposite thin films are synthesized at EPFL-LESO by a low cost sol-gel process. In order to study the potential of the novel planar photoluminescent concentrators, reliable computer simulations are needed. A computer code for ray tracing simulations of quantum dot solar concentrators has been developed at EPFL-LESO on the basis of Monte Carlo methods that are applied to polarization-dependent reflection/transmission at interfaces, photon absorption by the semiconductor nanocrystals and photoluminescent reemission. The software allows importing measured or theoretical absorption/reemission spectra describing the photoluminescent properties of the quantum dots. Hereby the properties of photoluminescent reemission are described by a set of emission spectra depending on the energy of the incoming photon, allowing to simulate the photoluminescent emission using the inverse function method. By our simulations, the importance of two main factors is revealed, an emission spectrum matched to the spectral efficiency curve of the photovoltaic cell, and a large Stokes shift, which is advantageous for the lateral energy transport. No significant energy losses are implied when the quantum dots are contained within a nanocomposite coating instead of being dispersed in the entire volume of the pane. Together with the knowledge on the optoelectronical properties of suitable photovoltaic cells, the simulations allow to predict the total efficiency of the envisaged concentrating PV systems, and to optimize photoluminescent emission frequencies, optical densities, and pane dimensions.

We present a cheaper and environmentally friendly method to fabricate efficient spectrally selective solar absorber materials. The sol-gel technique was used to fabricate carbon-silica (C-SiO₂) and carbon-nickel oxide (C-NiO) composite films on aluminium substrates. UV-Vis and FTIR spectrophotometers were used to determine the solar absorptance and thermal emittance of the coatings. C-NiO coatings gave the best spectral characteristics. We show that it is possible to achieve a solar absorptance of 0.94 and a thermal emittance of 0.12. So far, to our knowledge, no commercial spectral solar absorber has these spectral responses.

Selective solar absorber coatings of carbon dispersed in SiO₂, ZnO and NiO matrices on aluminium substrates have been fabricated by a sol-gel technique. Spectrophotometry was used to measure the near-normal reflectance of the composite coatings. Calculations of absorbed and emitted power, power retention, solar absorptance and thermal emittance were performed from the reflectance curves. The root-mean-square (rms) deviations of the reflectance curves from the ideal case were computed to determine the sample with the best performance characteristics. The thermal emittances of the samples were 30% for the SiO₂, 15% for the ZnO and 10% for the NiO matrix materials. The solar absorptances were 90%, 89% and 93% for SiO₂, ZnO and NiO samples, respectively. Based on the results, NiO matrix samples had the best solar selective behaviour, followed by ZnO and last were the SiO₂ based samples.

Increasing momentum around several different types of concentrating flat panel designs provides challenges with respect to modeling energy harvest. While there have been several simulation models created for standard flat panel PV modules, simulating low concentrating PV modules is more complex and less readily available. Specifically, since the optical characteristics of each low concentrating module is different, the energy prediction model must incorporate an optical model specific to the concentrator design. A PV module energy production model is created using a solar irradiance model (combining HDKR, NREL data and Meteonorm) and optical models for different panel types. Resulting energy production values are then correlated with actual measurements to verify the model and methodology. The simulation model is exercised across various geographic latitudes to illustrate how different module types can be most useful in specific locations. The results show an illustrative guideline for predicting module production and therefore selection. The model is specific to energy production and is useful to compare different module technologies under various conditions. Key findings include the following: optics engineers should consider application related issues when modeling various concentrating flat panel designs; computer scientists working on energy harvest software (e.g., PV Watts) need to include optics issues related to each concentrating flat panel; aberrations in climate databases can cause significant biases in energy harvest output; and system installers should follow manufacturer guidelines when installing concentrating flat panels.

The Solar Resource Enhancement Factor (SREF) method is proposed here to help solar system designers optimize their installations and decrease their risk. The method is based on solar radiation data from 239 sites in the United States to evaluate the variance in collected irradiation when using flat-plate and concentrating solar collectors (thermal or PV) mounted on fixed or tracking structures of various geometries. SREF can be predicted from readily available solar resource indicators and latitude for winter, summer or annual usage. An estimate of the year-to-year variability of the annual collected energy is also provided. The method should be accurate enough for use in most areas of the world.

A method has been developed to estimate IR radiative losses using solar radiation and meteorological data without the need for pyrgeometer data. The modeled IR radiative losses are not as accurate as that obtained using pyrgeometer information, but 95% of the modeled IR radiative losses are with a few W/m² of the actual IR radiative losses. Currently this method is limited to having a least some period when pyrgeometers measurements are available. More testing and evaluations are needed at a number of locations to test the general applicability of the model developed.

Solar irradiation data is scarcely available in regions suitable for solar energy applications. For the design of solar power plants, accurate but affordable measurements are indispensable. Accurate sensors are little appropriate for remote stations due to soiling, high power consumption and elevated costs. Rotating shadowband devices represent a prospective alternative. This paper describes new corrections for the systematic deviations of a Rotating Shadowband Pyranometer (RSP) with an integrated temperature probe. The correctional functions were developed on data from 23 different RSPs over an entire year. An average reduction of the root mean square deviation of direct normal irradiation from above 6.5% to below 2.5% was achieved.

Flashing artificial light sources are used extensively in photovoltaic module performance testing and plant production lines. There are several means of attempting to measure the spectral distribution of a flash of light; however, many of these approaches generally capture the entire pulse energy. We report here on the design and performance of a system to capture the waveform of flash at individual wavelengths of light. Any period within the flash duration can be selected, over which to integrate the flux intensity at each wavelength. The resulting spectral distribution is compared with the reference spectrum, resulting in a solar simulator classification.

In the solar tower thermal power generation system, the precision of the slope angle of the heliostat is the major factor, which influences the efficiency of the system, consequently, this angle should be tested accurately. In this paper, the methods based on laser deflectometry are proposed to measure the shape error of the mirror facet and the connected error of the facets; such apparatus and corresponding software packages are developed. With the help of these two apparatus, the heliostat of 100², consisting of 55 mirror facets of 1.8182 m²; (hexagon), for the 1MWe solar tower power plant in Beijing are measured and connected successfully.

Usually photovoltaic modules are characterized under standard testing conditions by subjecting them to an irradiation of 1000 W/m² with an AM 1.5 spectrum and a cell temperature of 25°C. However, not all modules perform the same under real conditions since their efficiency is strongly affected by environmental fluctuations. To get real operation data, expensive outdoor test are performed. However, for most of the new thin film technologies, these data are not available yet. The experiments were conducted in an indoor solar simulator, which fulfills the requirements of irradiation level and solar spectrum within a homogeneous area of 2 by 2.5 meters. In this contribution we compare different PV modules, including first generation, thin films and emerging technologies, in order to understand their behavior under various conditions. The modules were tested as a function of incident angle and diffused versus direct irradiation. Another aspect that is also taken under consideration is the influence of temperature on the module performance. These measurements are necessary in order to make a correct assessment of energy yield in several geographical locations for residential, commercial and utility applications.