Ignacio Antón

Comparative analysis of different secondary optical elements for aspheric primary lenses.

The performance of different reflexive and refractive secondaries optimized for the same primary lens is studied by using ray-tracing simulation. Different solutions are approached according to materials and manufacturing processes currently available in the market, which can be potentially cost-effective for concentrator photovoltaic (CPV) modules. They are compared in terms of system optical efficiency and acceptance angle. In addition, irradiance distribution over the cell is also studied.

Solar simulator for concentrator photovoltaic systems

A solar simulator for measuring performance of large area concentrator photovoltaic (CPV) modules is presented. Its illumination system is based on a Xenon flash light and a large area collimator mirror, which simulates natural sun light. Quality requirements imposed by the CPV systems have been characterized: irradiance level and uniformity at the receiver, light collimation and spectral distribution. The simulator allows indoor fast and cost-effective performance characterization and classification of CPV systems at the production line as well as module rating carried out by laboratories.

Effects of Temperature on Hybrid Lens Performance

In hybrid Silicone‐on‐glass Fresnel lenses, an optical silicone is molded onto a glass substrate and forms the Fresnel structure. These lenses offer a cost effective solution as a primary optical element in point‐focus concentrator photovoltaic modules, as well as performance advantages. However, these lenses have a high performance variation with temperature due both to the change in index of refraction of silicone as well as to deformations in the facets caused by coefficient of thermal expansion (CTE) mismatch. In this study we perform measurements of the light flux at the focal plane of a family of SOG lenses, varying temperature and lens‐to‐receiver distances. The effect of varying silicone cure temperature and the depth of the silicone between the lens and the glass substrate on temperature dependence was investigated. A preliminary computer model of this behavior is presented.

Antireflective coatings for multijunction solar cells under wide-angle ray bundles

Two important aspects must be considered when optimizing antireflection coatings (ARCs) for multijunction solar cells to be used in concentrators: the angular light distribution over the cell created by the particular concentration system and the wide spectral bandwidth the solar cell is sensitive to. In this article, a numerical optimization procedure and its results are presented. The potential efficiency enhancement by means of ARC optimization is calculated for several concentrating PV systems. In addition, two methods for ARCs direct characterization are presented. The results of these show that real ARCs slightly underperform theoretical predictions.

Two-dimensional angular transmission characterization of CPV modules

This paper proposes a fast method to characterize the two-dimensional angular transmission function of a concentrator photovoltaic (CPV) system. The so-called inverse method, which has been used in the past for the characterization of small optical components, has been adapted to large-area CPV modules. In the inverse method, the receiver cell is forward biased to produce a Lambertian light emission, which reveals the reverse optical path of the optics. Using a large-area collimator mirror, the light beam exiting the optics is projected on a Lambertian screen to create a spatially resolved image of the angular transmission function. An image is then obtained using a CCD camera. To validate this method, the angular transmission functions of a real CPV module have been measured by both direct illumination (flash CPV simulator and sunlight) and the inverse method, and the comparison shows good agreement.

Luminescence inverse method For CPV optical characterization.

The luminescence inverse method may be used to optically characterize a concentrator photovoltaic module. With this method, the module angular transmission is obtained by evaluating the light emission of a forward biased module. The influence of the emission of the cell when measuring the angular transmission is evaluated, and the process of building a global angular transmission from the set of individual optics-cell unit functions is explained. A case study of a module composed by several optics-cell units is presented. In order to validate the proposed measurement, results for five different CPV technologies are compared for both direct methods (i.e., solar simulator) and indirect methods (i.e., Luminescence inverse method).

Design and modeling of a cost-effective achromatic Fresnel lens for concentrating photovoltaics

This paper presents a novel Fresnel lens capable of significantly reducing chromatic aberration in solar applications. The optical performance of this achromatic lens has been analyzed through ray-tracing simulations, showing a concentration factor three times higher than that attained by a classic silicone on glass (SOG) Fresnel lens while maintaining the same acceptance angle. This should avoid the need for a secondary optical element, reducing the cost associated with its manufacturing and assembly and increasing the module reliability. The achromatic lens is made of inexpensive plastic and elastomer which allows a highly scalable and cost-competitive manufacturing process similar to the one currently used for the fabrication of SOG Fresnel lenses.

Off-Axis Characteristics of CPV Modules Result From Lens-Cell Misalignment—Measurement and Monte Carlo Simulation

Concentrator photovoltaics (CPV) requires accuracy in optical alignment. Optical misalignment in the module was measured and analyzed. Such information was useful to identify assembly problems and improved module performance. A Monte Carlo simulation was developed to analyze the impact of alignment errors by assembly errors. The simulation result implied that the key statistical parameters for module performance were not averaged errors but the standard deviation and the worst value. “Cutting above certain level” was effective, including the introduction of jigs that keep misalignment at a certain level. The standard deviation of misalignment should be controlled to less than 20% of the designed acceptance half angle.

Spectral Characterization of Mini Concentrator Optics for its Use With MJ Cells

New concepts of concentrator modules have been proposed in the last years based on refractive optics and cost effective III-V devices at high concentration levels. The small size of the cells, the high concentration ratio and the compact aspect of the optics are some of the particular characteristics of these C-systems. In this paper we face out the optical characterization of these mini concentrator systems. A new method is proposed for indoor characterization of the spectrally dependent optical efficiency, which allows to obtain the integrated optical efficiency with any light spectrum and to calculate the electrical efficiency with multi-junction solar cells. Influence of the spectral transmittance of an optics on 2J cells current mismatch has been assessed

Understanding causes and effects of non-uniform light distributions on multi-junction solar cells: Procedures for estimating efficiency losses

This paper presents the mechanisms of efficiency losses that have to do with the non-uniformity of the irradiance over the multi-junction solar cells and different measurement techniques used to investigate them. To show the capabilities of the presented techniques, three different concentrators (that consist of an acrylic Fresnel lens, different SOEs and a lattice matched multi-junction cell) are evaluated. By employing these techniques is possible to answer some critical questions when designing concentrators as for example which degree of non-uniformity the cell can withstand, how critical the influence of series resistance is, or what kind of non-uniformity (spatial or spectral) causes more losses.