Moisture-temperature degradation in module encapsulants: The general problem of moisture in photovoltaic encapsulants

A general research approach was outlined toward understanding water-module interactions and the influence of temperature involving the need to: quantify module performance loss versus level of accumulated degradation, establish the dependence of the degradation reaction rate on module moisture and temperature levels, and determine module moisture and temperature levels in field environments. These elements were illustrated with examples drawn from studies of the now relatively well understood module electrochemical degradation process. Research data presented include temperature and humidity-dependent equilibrium leakage current values for multiparameter module material and design configurations. The contributions of surface, volume, and interfacial conductivities was demonstrated. Research directions were suggested to more fully understand the contributions to overall module conductivity of surface, volume, and interfacial conductivities over ranges of temperature and relative humidity characteristic of field environments

Observations of solar-cell metallization corrosion

The Engineering Sciences Area of the Jet Propulsion Laboratory (JPL) Flat-Plate Solar Array Project is performing long term environmental tests on photovoltaic modules at Wyle Laboratories in Huntsville, Alabama. Some modules have been exposed to 85 C/85% RH and 40 C/93% RH for up to 280 days. Other modules undergoing temperature-only exposures ( 3% RH) at 85 C and 100 C have been tested for more than 180 days. At least two modules of each design type are exposed to each environment - one with, and the other without a 100-mA forward bias. Degradation is both visually observed and electrically monitored. Visual observations of changes in appearance are recorded at each inspection time. Significant visual observations relating to metallization corrosion (and/or metallization-induced corrosion) include discoloration (yellowing and browning) of grid lines, migration of grid line material into the encapsulation (blossoming), the appearance of rainbow-like diffraction patterns on the grid lines, and brown spots on collectors and grid lines. All of these observations were recorded for electrically biased modules in the 280-day tests with humidity

Electrochemical aging effects in photovoltaic modules

Leakage currents were experimentally measured in PV modules undergoing natural aging outdoors, and in PV modules undergoing accelerated aging in laboratory environmental chambers. The significant contributors to module leakage current were identified with a long range goal to develop techniques to reduce or stop module leakage currents. For outdoor aging in general, module leakage current is relatively insensitive to temperature fluctuations, but is very sensitive to moisture effects such as dew, precipitation, and fluctuations in relative humidity. Comparing ethylene vinyl acetate (EVA) and polyvinyl butyral (PVB), module leakage currents are much higher in PVB as compared to EVA for all environmental conditions investigated. Leakage currents proceed in series along two paths, bulk conduction followed by interfacial (surfaces) conduction

Interconnect fatigue design for terrestrial photovoltaic modules

The results of comprehensive investigation of interconnect fatigue that has led to the definition of useful reliability-design and life-prediction algorithms are presented. Experimental data indicate that the classical strain-cycle (fatigue) curve for the interconnect material is a good model of mean interconnect fatigue performance, but it fails to account for the broad statistical scatter, which is critical to reliability prediction. To fill this shortcoming the classical fatigue curve is combined with experimental cumulative interconnect failure rate data to yield statistical fatigue curves (having failure probability as a parameter) which enable (1) the prediction of cumulative interconnect failures during the design life of an array field, and (2) the unambiguous--ie., quantitative--interpretation of data from field-service qualification (accelerated thermal cycling) tests. Optimal interconnect cost-reliability design algorithms are derived based on minimizing the cost of energy over the design life of the array field

Oppositely-verging thrusting structures in the North Argentine Andes compared with the German Variscides

Los Andes del Norte argentino y el Varíscico de Alemania, a pesar de sus diferentes edades y situación geológica, se consideran buenos ejemplos de orógenos conve rgentes con cabalgamientos con ve rgencia opuesta. Los retrocabalgamientos están relacionados con cabalgamientos ciegos profundos con los que componen sistemas conjugados que son signifi c a t ivos en el acortamiento de la corteza media y superior. Tanto en los Andes del Norte argentino como en los Variscides se detectaron sistemas profundos de fallas conjugadas, en los primeros mediante cart ografía geológica e investigaciones de conductividad eléctrica y en los segundos mediante sísmica de reflexión. En los Varíscides se pueden reconocer estructuras conjugadas a todas las escalas en la corteza superior y combinaciones giga ntescas en la corteza inferior. En los Andes las zonas de alta conductividad eléctrica, situadas en la corteza inferior, están ordenadas en sistemas conjugados que pueden representar grandes fallas corticales asociadas a la subducción de la placa de Nazca. Debajo del borde oriental de las Sierras Pampeanas y del tramo Sur de las Sierras Subandinas (Sistema de Santa Bárbara) que tienen vergencia hacia el Oeste, es probable que exista una combinación conjugada a escala cortical similar a las descriptas en los Varíscides. Los otros cinturones con ve rgencia hacia el Este y hacia el Oeste de los Andes del Norte argentino muestran dispositivos en abanico similares a los reconocidos en cinturones orogénicos como los Alpes y los Pirineos. La comparación con orógenos cuya estructura profunda está bien estudiada permite especular sobre la estructura profunda de los Andes del Norte argentino donde la información cortical es aún insuficiente. Los Varíscides y otros orógenos cuya estructura ha sido investigada con sísmica de reflexión profunda sugieren que los frentes retrove rgentes están sistemáticamente asociados con cabalgamientos corticales profundos. En el caso de los Andes esto implicaría que debajo de los frentes retrove rgentes de la Cordillera Oriental y de las Sierras Pampeanas pueden existir cabalgamientos litosféricos significativos.The Andes of north Argentina and the german Variscides, in spite of their different ages and geological settings, are considered good examples of conve rgent orogens displaying oppositely ve rgent thrusts. The back-thrusting is related to deep seated blind thrusts forming conjugate fault combinations which are significant in upper and mid-crustal shortening. Deep-seated conjugate fault systems in the Variscides were detected in reflection seismic profiles and in the Andes of north A rgentina by mapping and through electrical conductivity investigations. In the Variscides conjugate fault systems may be recognized at eve ry scale in the upper crust and they form giant combinations in the lower crust. In the Andes the enhanced conductivity zones within the lower crust are arranged in conjugate systems, that could represent crustal detachments associated with Nazca plate subduction. In the Andes crustal conjugate fault structures similar to those described in the Variscides, could be present under the west verging eastern border of the Pampean Ranges and beneath the southern Subandean Ranges (Santa Bárbara System). The other oppositely - vergent belts of the north Argentine Andes show fan arrangements similar to those recognized in other orogenic zones such as the Alps and the Pyrenees. The comparison with other well-studied orogens allows speculation about the deep structure of the north A rgentine Andes, where there is insufficient crustal information. The Variscides and other orogens whose deep structure has been investigated by deep seismic reflection profiles, suggest that in the oppositely ve rgent orogens the back-thrusting fronts are systematically associated with crustal - scale thrusting. In the case of the Andes this could imply that significant lithospheric thrusting may be present below the big back-thrusting fronts of the Eastern Cordillera and Pampean Ranges

Module voltage isolation and corrosion research

A summary of recent research at JPL on two topics related to achieving long term reliability of photovoltaic modules: voltage isolation and electrochemical corrosion is presented. Special emphasis is given to similarities and differences in performance between crystalline silicon modules and amorphous silicon modules

Topics in electrochemical degradation of photovoltaic modules

Electrochemical degradation of photovoltaic modules was examined. It is found that the extent of electrochemical damage is dependent on the integrated leakage current. The PV electrochemical degradation mechanisms in the two polarities are different: (1) degradation rates in the two polarities are of the same order of magnitude; (2) center tapped grounded arrays are a preferred system configuration to minimize electrochemical degradation. The use of thicker pottant layers and polymer substrate films to reduce equilibrium leakage current values is suggested. A metallized substrate layer, if used, should be isolated from the pottant and the frame by polyester layers, and EVA modules appear to be consistent with 30 year life allocation levels for electrochemical damage. Temperature acceleration factors are well behaved and moderately well understood; humidity acceleration factors vary radically with module construction and materials and require additional research

RDF/S)XML Linguistic Annotation of Semantic Web Pages

Although with the Semantic Web initiative much research on web pages semantic annotation has already done by AI researchers, linguistic text annotation, including the semantic one, was originally developed in Corpus Linguistics and its results have been somehow neglected by AI. ..

The gravity field of the Tucuman plain and its implications in structural geology

Le résultat de la prospection gravimétrique de la plaine de Tucuman montre une fosse ayant plus de 3000 mètres de sédiments. Cette fosse est intéressante pour la prospection des hydrocarbures et l'examen géothermique. (Résumé d'auteur