Gabriel Sala

Electric and thermal model for non-uniformly illuminated concentration cells

Non-uniform illumination produces significant local heating in concentration solar cells. In addition, it produces ohmic drops higher than expected, mainly because the cell operates locally at higher irradiance. Thus, a slight reduction in the open-circuit voltage and a stronger one in the fill factor are produced. However, the darker and colder part of the cell, at the maximum power point, becomes almost inactive, and this is beneficial because it contains the poor-quality edge region. Therefore, the only cell region in operation is the active illuminated part of the device, and it has excellent performances, so the reduction of overall performance is less than it might have been expected.

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.

Some Results of the EUCLIDES Photovoltaic Concentrator Prototype

A photovoltaic concentration array prototype of 60·4 m2 of aperture is described. It uses reflecting linear optics kept in focus by means of horizontal single-axis tracking. All its cells are connected in series so as to avoid laborious field interconnection work. This prototype is being followed by a demonstration plant of 3479 m2 of aperture. The prototype performances are presented and fitted to a model that allows their prediction under conditions different from those of measurement. On the basis of this model the demonstration plant performances are anticipated. A cost analysis is presented based on our best estimates after the erection of the present prototype. It shows that the cost of the electricity, in medium or large size installation, should be strongly reduced with respect to that produced by flat modules.

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.

The EUCLIDES prototype: An efficient parabolic trough for PV concentration

The project EUCLIDES, subsidized by the European Union, had the aim of demonstrating the feasibility of cost reduction using reflective parabolic trough solar concentrators. The concentrator is conceived as one axis, horizontal tracking North/South oriented array, 72 meters long. The geometric concentration ratio is 32X. A prototype, 24 meters long, has been developed and installed in Madrid, Spain. The overall efficiencies of 14 series connected receiving modules is 15.0% at 25/spl deg/C. Such modules consist of 12 BP Solar SATURN concentrator solar cells, fully encapsulated. Costs analysis, after the prototype construction, shows that a total cost of 3.30

Luminescence inverse method For CPV optical characterization.

/Wp for a grid connected solar power plant is achievable at the 10 MW production level. Also parabolic troughs have proved their suitability as PV concentrators.

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

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).